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#1
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1st try kt88 amp
please see the schematic in alt.binaries.schematics.electronic
under "1st try kt88 amp" it is a Mullard 5-10, Pat Turner, and www.diytube.com inspired mash-up. -Don |
#2
Posted to rec.audio.tubes
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1st try kt88 amp
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#3
Posted to rec.audio.tubes
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1st try kt88 amp
"Don" please see the schematic in alt.binaries.schematics.electronic under "1st try kt88 amp" it is a Mullard 5-10, Pat Turner, and www.diytube.com inspired mash- up. And tell us your comments and suggestions! ** Very few people can see that group as most news servers have blocked all " alt.binaries". ..... Phil |
#4
Posted to rec.audio.tubes
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1st try kt88 amp
On Sep 3, 1:29*pm, "Phil Allison" wrote:
"Don" please see the schematic in alt.binaries.schematics.electronic under "1st try kt88 amp" it is a Mullard 5-10, Pat Turner, andwww.diytube.cominspired mash- up. And tell us your comments and suggestions! ** Very few people can see that group as most news servers have blocked all " alt.binaries". .... *Phil Someone associated my name with a circuit schematic somewhere with a KT88 but I can't see the schematic and it is most unlikely to be a "comispired mash-up" I designed. I don't follow all the posts on the web relating to me because there are so many. There is 100MB downloaded from my site each day, this is neither good or bad, and could be just bots searching the site; I don't much care about it. But a Mullard 5-10 would not have a KT88 used in it and I don't have a Mullard 5-10 schematic at my site, mainly because there are better ways to build an amp than following Mullard's lead of the parsimonious bean counter dominated 1950s. One man's mash up is another man's dog's breakfast. And a dingo's breakfast is just a **** and a lookaround, whatever. Patrick Turner.i |
#5
Posted to rec.audio.tubes
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1st try kt88 amp
On Sep 2, 8:03*pm, Don wrote:
please see the schematic in alt.binaries.schematics.electronic under "1st try kt88 amp" it is a Mullard 5-10, Pat Turner, andwww.diytube.cominspired mash-up. -Don Can't see it... could you post it somewhere else that is universally accessible? That said, and from memory, the 5-10 (I built two back in the day and I'm still a "5-10 fan") used EL84 (6BQ5) o/p tubes driven directly from a 12AX7 LTP phase splitter for 11 to 14 watts maximum output depending on OPT connections (ultralinear or simple pentode, respectively.) Your KT88's could give over twice that output power but will likely need more drive than the LTP can provide - hence the extra driver stage in the Williamson design. BTW, there was a Mullard 5-20 (20 watts) using EL34 o/p tubes around the same time, also with a direct LTP phase splitter drive, but I don't know if that was pushing the LTP drive limit. If I had two KT88's (I wish!) I'd build the Williamson design, but stabilize it with the "low frequency shelf" discussed here at length a short while ago. Cheers, Roger |
#6
Posted to rec.audio.tubes
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1st try kt88 amp
In article 2edeb104-6024-43e8-9749-
, says... On Sep 2, 8:03*pm, Don wrote: please see the schematic in alt.binaries.schematics.electronic under "1st try kt88 amp" it is a Mullard 5-10, Pat Turner, andwww.diytube.cominspired mash- up. -Don Can't see it... could you post it somewhere else that is universally accessible? try http://mysite.verizon.net/vze11z1rm/ |
#7
Posted to rec.audio.tubes
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1st try kt88 amp
On Sat, 03 Sep 2011 11:21:52 -0400, Don
wrote: In article 2edeb104-6024-43e8-9749- , says... On Sep 2, 8:03*pm, Don wrote: please see the schematic in alt.binaries.schematics.electronic under "1st try kt88 amp" it is a Mullard 5-10, Pat Turner, andwww.diytube.cominspired mash- up. -Don Can't see it... could you post it somewhere else that is universally accessible? try http://mysite.verizon.net/vze11z1rm/ You won't be hearing much until you sort out the connections to that output transformer. d |
#8
Posted to rec.audio.tubes
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1st try kt88 amp
If I had two KT88's (I wish!) I'd build the Williamson design, but stabilize it with the "low frequency shelf" discussed here at length a short while ago. Cheers, Roger Regarding the "low frequency shelf" and high frequency roll-off filters: why are they usually after the voltage amp? Why not a band-pass filter before the V1 tube? o-----||---/\/\/\/\--------------------o | | === | | | | | | o---------------------------------------o -Don |
#10
Posted to rec.audio.tubes
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1st try kt88 amp
On Sun, 04 Sep 2011 00:16:25 -0400, Don
wrote: If I had two KT88's (I wish!) I'd build the Williamson design, but stabilize it with the "low frequency shelf" discussed here at length a short while ago. Cheers, Roger Regarding the "low frequency shelf" and high frequency roll-off filters: why are they usually after the voltage amp? Why not a band-pass filter before the V1 tube? o-----||---/\/\/\/\--------------------o | | === | | | | | | o---------------------------------------o -Don I think it is a sort of masochism - a craving for low and high frequency instability. Large phase shifting mechanisms within a loop are never a great idea. There should be ideally a single pole that doesn't let up until beyond the unity gain frequency. d |
#11
Posted to rec.audio.tubes
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1st try kt88 amp
"Don Pearce" wrote in message ... On Sat, 03 Sep 2011 11:21:52 -0400, Don wrote: In article 2edeb104-6024-43e8-9749- , says... On Sep 2, 8:03 pm, Don wrote: please see the schematic in alt.binaries.schematics.electronic under "1st try kt88 amp" it is a Mullard 5-10, Pat Turner, andwww.diytube.cominspired mash- up. -Don Can't see it... could you post it somewhere else that is universally accessible? try http://mysite.verizon.net/vze11z1rm/ You won't be hearing much until you sort out the connections to that output transformer. Looks to me like there are two separate identical output transformers, which has the disadvantage of not cancelling out the partial saturating effect of the output tube's quescient current, and not maximizing the cancellation of even order harmonics. |
#12
Posted to rec.audio.tubes
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1st try kt88 amp
On Sun, 4 Sep 2011 05:01:12 -0400, "Arny Krueger"
wrote: "Don Pearce" wrote in message ... On Sat, 03 Sep 2011 11:21:52 -0400, Don wrote: In article 2edeb104-6024-43e8-9749- , says... On Sep 2, 8:03 pm, Don wrote: please see the schematic in alt.binaries.schematics.electronic under "1st try kt88 amp" it is a Mullard 5-10, Pat Turner, andwww.diytube.cominspired mash- up. -Don Can't see it... could you post it somewhere else that is universally accessible? try http://mysite.verizon.net/vze11z1rm/ You won't be hearing much until you sort out the connections to that output transformer. Looks to me like there are two separate identical output transformers, which has the disadvantage of not cancelling out the partial saturating effect of the output tube's quescient current, and not maximizing the cancellation of even order harmonics. It looks like the schematic is from a Spice simulation, which won't model a tapped transformer without special fiddling. Even so, those two closest secondary taps should be connected to each other. d |
#13
Posted to rec.audio.tubes
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1st try kt88 amp
"Arny Krueger" wrote in message ... "Don Pearce" wrote in message ... On Sat, 03 Sep 2011 11:21:52 -0400, Don wrote: In article 2edeb104-6024-43e8-9749- , says... On Sep 2, 8:03 pm, Don wrote: please see the schematic in alt.binaries.schematics.electronic under "1st try kt88 amp" it is a Mullard 5-10, Pat Turner, andwww.diytube.cominspired mash- up. -Don Can't see it... could you post it somewhere else that is universally accessible? try http://mysite.verizon.net/vze11z1rm/ You won't be hearing much until you sort out the connections to that output transformer. Looks to me like there are two separate identical output transformers, which has the disadvantage of not cancelling out the partial saturating effect of the output tube's quescient current, and not maximizing the cancellation of even order harmonics. Whoops! I didn't notice that the secondary of one output transformer is basically connected to the air. That basically negates the existance of the one half of the output stage! Hopefully, this is all a consequence of a overly-simplistic modelling program, as others have pointed out. |
#14
Posted to rec.audio.tubes
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1st try kt88 amp
On Sep 4, 12:16*am, Don wrote:
If I had two KT88's (I wish!) I'd build the Williamson design, but stabilize it with the "low frequency shelf" discussed here at length a short while ago. Cheers, Roger Regarding the "low frequency shelf" and high frequency *roll-off filters: why are they usually after the voltage amp? Why not a band-pass filter before the V1 tube? o-----||---/\/\/\/\--------------------o * * * * * * * * * * * * *| * * * * | * * * * * * * * * * * * === * * * * * * * * * * * * * * * * *| * * * * * * * * * * * * * * * * *| * * * * * * * * * * * * * * * * *| * * * * | * * * * * * * * * * * * *| * * * * | o---------------------------------------o -Don They have to be inside the NFB loop. They are there to stabilize the loop gain in the face of three phase leads (up to 90 deg each) at VLF from the two RC couplings and one OPT. Cheers, Roger |
#15
Posted to rec.audio.tubes
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1st try kt88 amp
In article ,
(Don Pearce) wrote: On Sun, 04 Sep 2011 00:16:25 -0400, Don wrote: If I had two KT88's (I wish!) I'd build the Williamson design, but stabilize it with the "low frequency shelf" discussed here at length a short while ago. Cheers, Roger Regarding the "low frequency shelf" and high frequency roll-off filters: why are they usually after the voltage amp? Why not a band-pass filter before the V1 tube? o-----||---/\/\/\/\--------------------o | | === | | | | | | o---------------------------------------o -Don I think it is a sort of masochism - a craving for low and high frequency instability. Large phase shifting mechanisms within a loop are never a great idea. There should be ideally a single pole that doesn't let up until beyond the unity gain frequency. The use of a dominant pole to stabilize the feedback loop is transistor thinking, not always practical in tube circuits. -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
#16
Posted to rec.audio.tubes
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1st try kt88 amp
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#17
Posted to rec.audio.tubes
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1st try kt88 amp
In article ,
says... "Don Pearce" wrote in message ... On Sat, 03 Sep 2011 11:21:52 -0400, Don wrote: In article 2edeb104-6024-43e8-9749- , says... On Sep 2, 8:03 pm, Don wrote: please see the schematic in alt.binaries.schematics.electronic under "1st try kt88 amp" it is a Mullard 5-10, Pat Turner, andwww.diytube.cominspired mash- up. -Don Can't see it... could you post it somewhere else that is universally accessible? try http://mysite.verizon.net/vze11z1rm/ You won't be hearing much until you sort out the connections to that output transformer. Looks to me like there are two separate identical output transformers, which has the disadvantage of not cancelling out the partial saturating effect of the output tube's quescient current, and not maximizing the cancellation of even order harmonics. Flipper is correct- I didn't have a symbol for a ultralinear OPT. Pretend that there is one UL transformer on the schematic. -Don |
#18
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1st try kt88 amp
On Sun, 04 Sep 2011 11:24:20 -0500, John Byrns
wrote: In article , (Don Pearce) wrote: On Sun, 04 Sep 2011 00:16:25 -0400, Don wrote: If I had two KT88's (I wish!) I'd build the Williamson design, but stabilize it with the "low frequency shelf" discussed here at length a short while ago. Cheers, Roger Regarding the "low frequency shelf" and high frequency roll-off filters: why are they usually after the voltage amp? Why not a band-pass filter before the V1 tube? o-----||---/\/\/\/\--------------------o | | === | | | | | | o---------------------------------------o -Don I think it is a sort of masochism - a craving for low and high frequency instability. Large phase shifting mechanisms within a loop are never a great idea. There should be ideally a single pole that doesn't let up until beyond the unity gain frequency. The use of a dominant pole to stabilize the feedback loop is transistor thinking, not always practical in tube circuits. Just good engineering practice and pretty much standard in op amps. And the first op amps were valve, not transistor. d |
#19
Posted to rec.audio.tubes
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1st try kt88 amp
In article ,
(Don Pearce) wrote: On Sun, 04 Sep 2011 11:24:20 -0500, John Byrns wrote: In article , (Don Pearce) wrote: On Sun, 04 Sep 2011 00:16:25 -0400, Don wrote: If I had two KT88's (I wish!) I'd build the Williamson design, but stabilize it with the "low frequency shelf" discussed here at length a short while ago. Cheers, Roger Regarding the "low frequency shelf" and high frequency roll-off filters: why are they usually after the voltage amp? Why not a band-pass filter before the V1 tube? o-----||---/\/\/\/\--------------------o | | === | | | | | | o---------------------------------------o -Don I think it is a sort of masochism - a craving for low and high frequency instability. Large phase shifting mechanisms within a loop are never a great idea. There should be ideally a single pole that doesn't let up until beyond the unity gain frequency. The use of a dominant pole to stabilize the feedback loop is transistor thinking, not always practical in tube circuits. Just good engineering practice and pretty much standard in op amps. And the first op amps were valve, not transistor. That's all pretty much true, however we aren't talking op amps in this thread, were talking valve audio amps, and more specifically the particular design Don posted. Can you give us a worked example of how you would use a dominant pole to stabilize Don's amplifier design, specifying all relevant time constants in the amplifier. I would be especially interested in how you would do the low frequency stabilization were a number of irritating tradeoffs often come into play, and any assumptions about the effect of the OPT on phase shift are likely to be more accurate than at high frequencies. The object is for the amplifier to remain stable with a speaker load, no load, and any other load it might be likely to encounter during its lifetime. -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
#20
Posted to rec.audio.tubes
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1st try kt88 amp
On Sun, 04 Sep 2011 12:20:16 -0500, John Byrns
wrote: In article , (Don Pearce) wrote: On Sun, 04 Sep 2011 11:24:20 -0500, John Byrns wrote: In article , (Don Pearce) wrote: On Sun, 04 Sep 2011 00:16:25 -0400, Don wrote: If I had two KT88's (I wish!) I'd build the Williamson design, but stabilize it with the "low frequency shelf" discussed here at length a short while ago. Cheers, Roger Regarding the "low frequency shelf" and high frequency roll-off filters: why are they usually after the voltage amp? Why not a band-pass filter before the V1 tube? o-----||---/\/\/\/\--------------------o | | === | | | | | | o---------------------------------------o -Don I think it is a sort of masochism - a craving for low and high frequency instability. Large phase shifting mechanisms within a loop are never a great idea. There should be ideally a single pole that doesn't let up until beyond the unity gain frequency. The use of a dominant pole to stabilize the feedback loop is transistor thinking, not always practical in tube circuits. Just good engineering practice and pretty much standard in op amps. And the first op amps were valve, not transistor. That's all pretty much true, however we aren't talking op amps in this thread, were talking valve audio amps, and more specifically the particular design Don posted. Can you give us a worked example of how you would use a dominant pole to stabilize Don's amplifier design, specifying all relevant time constants in the amplifier. I would be especially interested in how you would do the low frequency stabilization were a number of irritating tradeoffs often come into play, and any assumptions about the effect of the OPT on phase shift are likely to be more accurate than at high frequencies. The object is for the amplifier to remain stable with a speaker load, no load, and any other load it might be likely to encounter during its lifetime. Short answer - no, it isn't possible with this design. Capacitive and transformer AC coupling combine to demand low frequency compensation to get anything reasonably stable. Motor boating has always been a plague to this kind if amp. As for high frequencies, there are too many uncontrolled sources of phase shift for that to work. And of course the severe limitation in open loop gain puts the cherry on the top. Dominant pole is what you use when you have everything under control. As for different loads, if the amp had decently low output impedance (which demands high OL gain and feedback), there would be issues with stability into odd loads. The design is a compromise, but that is fine - it is clearly an experiment with something a little historic. d |
#21
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The drive requirements of the OP stage are not as critical as mentioned in earlier posts. The KT88, EL34 & 6550 all have G about double that found in the original Mullard circuits where we find 6L6, 5881, Etc.
A single dominant pole is a safe way to go in this cct. There are a couple of worked samples in RDH4 worth looking at. Also strongly recommended by none other then Norman Crowhurst. You can read about how to implement all in a couple of his articles. I like the cct proposed by Alex Pogossov recently. The attachment shows how it is connected in an SE Amp. The frequency selective network is in the cathode of the first stage rather than between stages. My opinion, anyway, having done it. Cheers, John Stewart PS- The bicycle went more than 1000 KM in August (622 miles). Pedalling again today. Hey Patrick, hows it going in OZ? J |
#22
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1st try kt88 amp
On Sun, 4 Sep 2011 22:05:12 +0000, John L Stewart
wrote: The drive requirements of the OP stage are not as critical as mentioned in earlier posts. The KT88, EL34 & 6550 all have G about double that found in the original Mullard circuits where we find 6L6, 5881, Etc. A single dominant pole is a safe way to go in this cct. There are a couple of worked samples in RDH4 worth looking at. Also strongly recommended by none other then Norman Crowhurst. You can read about how to implement all in a couple of his articles. I like the cct proposed by Alex Pogossov recently. The attachment shows how it is connected in an SE Amp. The frequency selective network is in the cathode of the first stage rather than between stages. My opinion, anyway, having done it. Cheers, John Stewart PS- The bicycle went more than 1000 KM in August (622 miles). Pedalling again today. Hey Patrick, hows it going in OZ? J +-------------------------------------------------------------------+ |Filename: Alex Pogossovs Solution.jpg | |Download: http://www.audiobanter.com/attachment.php?attachmentid=245| +-------------------------------------------------------------------+ Why would you want a circuit that drops the gain by about 16dB at 100Hz? What is its actual purpose? d |
#23
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Quote:
The cct posted is given only as an example of the concept posted earlier by Alex P. You can select any RC combination to yield the frequency that fits your requirement. Also pick the R to determine the depth of the step. You can also control the max phase shift. Very useful. Rather than using attenuation between stages this cct uses degeneration to get the required LF step. Probably don't need either in most 2-stage FB amplifiers. But I had to use a between stages step network in a FB pair UL amp using a 6LU8 I built a few years back to get rid of an LF hump. It showed up in an AudioXpress publication. Cheers, John |
#24
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1st try kt88 amp
On Sep 5, 1:46*am, (Don Pearce) wrote:
On Sun, 4 Sep 2011 22:05:12 +0000, John L Stewart wrote: The drive requirements of the OP stage are not as critical as mentioned in earlier posts. The KT88, EL34 & 6550 all have G about double that found in the original Mullard circuits where we find 6L6, 5881, Etc. A single dominant pole is a safe way to go in this cct. There are a couple of worked samples in RDH4 worth looking at. Also strongly recommended by none other then Norman Crowhurst. You can read about how to implement all in a couple of his articles. I like the cct proposed by Alex Pogossov recently. The attachment shows how it is connected in an SE Amp. The frequency selective network is in the cathode of the first stage rather than between stages. My opinion, anyway, having done it. Cheers, John Stewart PS- The bicycle went more than 1000 KM in August (622 miles). Pedalling again today. Hey Patrick, hows it going in OZ? * * * * * * * *J +-------------------------------------------------------------------+ |Filename: Alex Pogossovs Solution.jpg * * * * * * * * * * * * * * *| |Download:http://www.audiobanter.com/attachment.php?attachmentid=245| +-------------------------------------------------------------------+ Why would you want a circuit that drops the gain by about 16dB at 100Hz? What is its actual purpose? d Ans: To get the loop gain (forward gain times NFB gain) well below unity at the low frequency where the phase lead becomes 180 degrees (due to two RC couplings and one OPT.) Very low frequency oscillation in the range 0.5 to 2 Hz can result if there in no low-frequency shelf inside the loop. Cheers, Roger |
#25
Posted to rec.audio.tubes
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1st try kt88 amp
On Tue, 6 Sep 2011 09:03:54 -0700 (PDT), Engineer
wrote: On Sep 5, 1:46*am, (Don Pearce) wrote: On Sun, 4 Sep 2011 22:05:12 +0000, John L Stewart wrote: The drive requirements of the OP stage are not as critical as mentioned in earlier posts. The KT88, EL34 & 6550 all have G about double that found in the original Mullard circuits where we find 6L6, 5881, Etc. A single dominant pole is a safe way to go in this cct. There are a couple of worked samples in RDH4 worth looking at. Also strongly recommended by none other then Norman Crowhurst. You can read about how to implement all in a couple of his articles. I like the cct proposed by Alex Pogossov recently. The attachment shows how it is connected in an SE Amp. The frequency selective network is in the cathode of the first stage rather than between stages. My opinion, anyway, having done it. Cheers, John Stewart PS- The bicycle went more than 1000 KM in August (622 miles). Pedalling again today. Hey Patrick, hows it going in OZ? * * * * * * * *J +-------------------------------------------------------------------+ |Filename: Alex Pogossovs Solution.jpg * * * * * * * * * * * * * * *| |Download:http://www.audiobanter.com/attachment.php?attachmentid=245| +-------------------------------------------------------------------+ Why would you want a circuit that drops the gain by about 16dB at 100Hz? What is its actual purpose? d Ans: To get the loop gain (forward gain times NFB gain) well below unity at the low frequency where the phase lead becomes 180 degrees (due to two RC couplings and one OPT.) Very low frequency oscillation in the range 0.5 to 2 Hz can result if there in no low-frequency shelf inside the loop. Cheers, Roger So it is a horribly bodged solution to a problem that has no business being there in the first place? The idea of implementing negative feedback and then defeating it by killing the open loop gain it mediates is beyond ludicrous. d |
#26
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1st try kt88 amp
On Sep 6, 12:37*pm, (Don Pearce) wrote:
On Tue, 6 Sep 2011 09:03:54 -0700 (PDT), Engineer wrote: On Sep 5, 1:46*am, (Don Pearce) wrote: On Sun, 4 Sep 2011 22:05:12 +0000, John L Stewart wrote: The drive requirements of the OP stage are not as critical as mentioned in earlier posts. The KT88, EL34 & 6550 all have G about double that found in the original Mullard circuits where we find 6L6, 5881, Etc. A single dominant pole is a safe way to go in this cct. There are a couple of worked samples in RDH4 worth looking at. Also strongly recommended by none other then Norman Crowhurst. You can read about how to implement all in a couple of his articles. I like the cct proposed by Alex Pogossov recently. The attachment shows how it is connected in an SE Amp. The frequency selective network is in the cathode of the first stage rather than between stages. My opinion, anyway, having done it. Cheers, John Stewart PS- The bicycle went more than 1000 KM in August (622 miles). Pedalling again today. Hey Patrick, hows it going in OZ? * * * * * * * *J +-------------------------------------------------------------------+ |Filename: Alex Pogossovs Solution.jpg * * * * * * * * * * * * * * *| |Download:http://www.audiobanter.com/attachment.php?attachmentid=245| +-------------------------------------------------------------------+ Why would you want a circuit that drops the gain by about 16dB at 100Hz? What is its actual purpose? d Ans: To get the loop gain (forward gain times NFB gain) well below unity at the low frequency where the phase lead becomes 180 degrees (due to two RC couplings and one OPT.) *Very low frequency oscillation in the range 0.5 to 2 Hz can result if there in no low-frequency shelf inside the loop. Cheers, Roger So it is a horribly bodged solution to a problem that has no business being there in the first place? The idea of implementing negative feedback and then defeating it by killing the open loop gain it mediates is beyond ludicrous. d Not a bodge... steering the Nyquist plot around the "minus 1" point for all frequencies is established practice in feedback control systems. It's also perfectly acceptable here. BTW, the higher break point (of the two) for the VLF shelf is well below 100 Hz... around 15 to 20 Hz is typical to stop a 1 Hz or so VLF oscillation. I'll agree that the removal of one of the RC couplings in the forward path would be good, but hard to do when you have a separate driver stage after the phase splitter. There are direct-coupled DC-amplifier designs, but they are far more difficult to implement than a VLF shelf and, anyway, not needed. Also, a massively larger primary inductance in the OPT primary would be next to godliness... but most of us (in NA, at least) cannot afford that so we use the best Hammond iron we can afford or find a decently large OPT from a recycled high grade amplifier! Cheers, Roger |
#27
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1st try kt88 amp
On Wed, 7 Sep 2011 15:58:48 -0700 (PDT), Engineer
wrote: So it is a horribly bodged solution to a problem that has no business being there in the first place? The idea of implementing negative feedback and then defeating it by killing the open loop gain it mediates is beyond ludicrous. d Not a bodge... steering the Nyquist plot around the "minus 1" point for all frequencies is established practice in feedback control systems. It's also perfectly acceptable here. BTW, the higher break point (of the two) for the VLF shelf is well below 100 Hz... around 15 to 20 Hz is typical to stop a 1 Hz or so VLF oscillation. I'll agree that the removal of one of the RC couplings in the forward path would be good, but hard to do when you have a separate driver stage after the phase splitter. There are direct-coupled DC-amplifier designs, but they are far more difficult to implement than a VLF shelf and, anyway, not needed. Also, a massively larger primary inductance in the OPT primary would be next to godliness... but most of us (in NA, at least) cannot afford that so we use the best Hammond iron we can afford or find a decently large OPT from a recycled high grade amplifier! Cheers, Roger Don't know where you got those numbers. It does this: http://www.soundthoughts.co.uk/look/shelf.png d |
#28
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1st try kt88 amp
In article ,
(Don Pearce) wrote: On Tue, 6 Sep 2011 09:03:54 -0700 (PDT), Engineer wrote: On Sep 5, 1:46*am, (Don Pearce) wrote: On Sun, 4 Sep 2011 22:05:12 +0000, John L Stewart wrote: The drive requirements of the OP stage are not as critical as mentioned in earlier posts. The KT88, EL34 & 6550 all have G about double that found in the original Mullard circuits where we find 6L6, 5881, Etc. A single dominant pole is a safe way to go in this cct. There are a couple of worked samples in RDH4 worth looking at. Also strongly recommended by none other then Norman Crowhurst. You can read about how to implement all in a couple of his articles. I like the cct proposed by Alex Pogossov recently. The attachment shows how it is connected in an SE Amp. The frequency selective network is in the cathode of the first stage rather than between stages. My opinion, anyway, having done it. Cheers, John Stewart PS- The bicycle went more than 1000 KM in August (622 miles). Pedalling again today. Hey Patrick, hows it going in OZ? * * * * * * * *J Why would you want a circuit that drops the gain by about 16dB at 100Hz? What is its actual purpose? Ans: To get the loop gain (forward gain times NFB gain) well below unity at the low frequency where the phase lead becomes 180 degrees (due to two RC couplings and one OPT.) Very low frequency oscillation in the range 0.5 to 2 Hz can result if there in no low-frequency shelf inside the loop. Cheers, Roger So it is a horribly bodged solution to a problem that has no business being there in the first place? The idea of implementing negative feedback and then defeating it by killing the open loop gain it mediates is beyond ludicrous. On Sunday you suggested "a single pole that doesn't let up until beyond the unity gain frequency", isn't that equally ludicrous as it also "kills the open loop gain"? -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
#29
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1st try kt88 amp
On Thu, 08 Sep 2011 09:31:41 -0500, John Byrns
wrote: In article , (Don Pearce) wrote: On Tue, 6 Sep 2011 09:03:54 -0700 (PDT), Engineer wrote: On Sep 5, 1:46*am, (Don Pearce) wrote: On Sun, 4 Sep 2011 22:05:12 +0000, John L Stewart wrote: The drive requirements of the OP stage are not as critical as mentioned in earlier posts. The KT88, EL34 & 6550 all have G about double that found in the original Mullard circuits where we find 6L6, 5881, Etc. A single dominant pole is a safe way to go in this cct. There are a couple of worked samples in RDH4 worth looking at. Also strongly recommended by none other then Norman Crowhurst. You can read about how to implement all in a couple of his articles. I like the cct proposed by Alex Pogossov recently. The attachment shows how it is connected in an SE Amp. The frequency selective network is in the cathode of the first stage rather than between stages. My opinion, anyway, having done it. Cheers, John Stewart PS- The bicycle went more than 1000 KM in August (622 miles). Pedalling again today. Hey Patrick, hows it going in OZ? * * * * * * * *J Why would you want a circuit that drops the gain by about 16dB at 100Hz? What is its actual purpose? Ans: To get the loop gain (forward gain times NFB gain) well below unity at the low frequency where the phase lead becomes 180 degrees (due to two RC couplings and one OPT.) Very low frequency oscillation in the range 0.5 to 2 Hz can result if there in no low-frequency shelf inside the loop. Cheers, Roger So it is a horribly bodged solution to a problem that has no business being there in the first place? The idea of implementing negative feedback and then defeating it by killing the open loop gain it mediates is beyond ludicrous. On Sunday you suggested "a single pole that doesn't let up until beyond the unity gain frequency", isn't that equally ludicrous as it also "kills the open loop gain"? Not at all. It operates as a local feedback loop within the overall loop. At lower frequencies, where it really matters to have particularly the output stage included, the loop stretches from beginning to end. As the frequency rises the loop transfers steadily to just the voltage amplifier. This does result in a slight rise in harmonic distortion above about 10kHz, but frankly by then who cares? And this pole is going to have to be present in some or other form anyway because high frequency instability needs to be tamed - so why not make it simple, predictable and controllable? d |
#30
Posted to rec.audio.tubes
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1st try kt88 amp
In article ,
(Don Pearce) wrote: On Thu, 08 Sep 2011 09:31:41 -0500, John Byrns wrote: In article , (Don Pearce) wrote: On Tue, 6 Sep 2011 09:03:54 -0700 (PDT), Engineer wrote: On Sep 5, 1:46*am, (Don Pearce) wrote: On Sun, 4 Sep 2011 22:05:12 +0000, John L Stewart wrote: The drive requirements of the OP stage are not as critical as mentioned in earlier posts. The KT88, EL34 & 6550 all have G about double that found in the original Mullard circuits where we find 6L6, 5881, Etc. A single dominant pole is a safe way to go in this cct. There are a couple of worked samples in RDH4 worth looking at. Also strongly recommended by none other then Norman Crowhurst. You can read about how to implement all in a couple of his articles. I like the cct proposed by Alex Pogossov recently. The attachment shows how it is connected in an SE Amp. The frequency selective network is in the cathode of the first stage rather than between stages. My opinion, anyway, having done it. Cheers, John Stewart PS- The bicycle went more than 1000 KM in August (622 miles). Pedalling again today. Hey Patrick, hows it going in OZ? * * * * * * * *J Why would you want a circuit that drops the gain by about 16dB at 100Hz? What is its actual purpose? Ans: To get the loop gain (forward gain times NFB gain) well below unity at the low frequency where the phase lead becomes 180 degrees (due to two RC couplings and one OPT.) Very low frequency oscillation in the range 0.5 to 2 Hz can result if there in no low-frequency shelf inside the loop. Cheers, Roger So it is a horribly bodged solution to a problem that has no business being there in the first place? The idea of implementing negative feedback and then defeating it by killing the open loop gain it mediates is beyond ludicrous. On Sunday you suggested "a single pole that doesn't let up until beyond the unity gain frequency", isn't that equally ludicrous as it also "kills the open loop gain"? Not at all. It operates as a local feedback loop within the overall loop. At lower frequencies, where it really matters to have particularly the output stage included, the loop stretches from beginning to end. As the frequency rises the loop transfers steadily to just the voltage amplifier. This does result in a slight rise in harmonic distortion above about 10kHz, but frankly by then who cares? And this pole is going to have to be present in some or other form anyway because high frequency instability needs to be tamed - so why not make it simple, predictable and controllable? So if I follow you, you are not talking about a single overall negative feedback loop containing a dominant pole within, but instead you are talking about nested feedback loops where the dominant pole within the overall feedback loop is created by a second shorter internal feedback loop that rolls off the high frequencies? -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
#31
Posted to rec.audio.tubes
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1st try kt88 amp
On Tue, 13 Sep 2011 11:41:11 -0500, John Byrns
wrote: In article , (Don Pearce) wrote: On Thu, 08 Sep 2011 09:31:41 -0500, John Byrns wrote: In article , (Don Pearce) wrote: On Tue, 6 Sep 2011 09:03:54 -0700 (PDT), Engineer wrote: On Sep 5, 1:46*am, (Don Pearce) wrote: On Sun, 4 Sep 2011 22:05:12 +0000, John L Stewart wrote: The drive requirements of the OP stage are not as critical as mentioned in earlier posts. The KT88, EL34 & 6550 all have G about double that found in the original Mullard circuits where we find 6L6, 5881, Etc. A single dominant pole is a safe way to go in this cct. There are a couple of worked samples in RDH4 worth looking at. Also strongly recommended by none other then Norman Crowhurst. You can read about how to implement all in a couple of his articles. I like the cct proposed by Alex Pogossov recently. The attachment shows how it is connected in an SE Amp. The frequency selective network is in the cathode of the first stage rather than between stages. My opinion, anyway, having done it. Cheers, John Stewart PS- The bicycle went more than 1000 KM in August (622 miles). Pedalling again today. Hey Patrick, hows it going in OZ? * * * * * * * *J Why would you want a circuit that drops the gain by about 16dB at 100Hz? What is its actual purpose? Ans: To get the loop gain (forward gain times NFB gain) well below unity at the low frequency where the phase lead becomes 180 degrees (due to two RC couplings and one OPT.) Very low frequency oscillation in the range 0.5 to 2 Hz can result if there in no low-frequency shelf inside the loop. Cheers, Roger So it is a horribly bodged solution to a problem that has no business being there in the first place? The idea of implementing negative feedback and then defeating it by killing the open loop gain it mediates is beyond ludicrous. On Sunday you suggested "a single pole that doesn't let up until beyond the unity gain frequency", isn't that equally ludicrous as it also "kills the open loop gain"? Not at all. It operates as a local feedback loop within the overall loop. At lower frequencies, where it really matters to have particularly the output stage included, the loop stretches from beginning to end. As the frequency rises the loop transfers steadily to just the voltage amplifier. This does result in a slight rise in harmonic distortion above about 10kHz, but frankly by then who cares? And this pole is going to have to be present in some or other form anyway because high frequency instability needs to be tamed - so why not make it simple, predictable and controllable? So if I follow you, you are not talking about a single overall negative feedback loop containing a dominant pole within, but instead you are talking about nested feedback loops where the dominant pole within the overall feedback loop is created by a second shorter internal feedback loop that rolls off the high frequencies? That is exactly what a dominant pole is - a nested feedback system in which the voltage amplifier is controlled by a single capacitive feedback element. The overall feedback which surrounds it is flat, and composed of two resistors, the ratio of which sets the gain of the amplifier. d |
#32
Posted to rec.audio.tubes
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1st try kt88 amp
In article ,
(Don Pearce) wrote: On Tue, 13 Sep 2011 11:41:11 -0500, John Byrns wrote: In article , (Don Pearce) wrote: On Thu, 08 Sep 2011 09:31:41 -0500, John Byrns wrote: In article , (Don Pearce) wrote: On Tue, 6 Sep 2011 09:03:54 -0700 (PDT), Engineer wrote: On Sep 5, 1:46*am, (Don Pearce) wrote: On Sun, 4 Sep 2011 22:05:12 +0000, John L Stewart wrote: The drive requirements of the OP stage are not as critical as mentioned in earlier posts. The KT88, EL34 & 6550 all have G about double that found in the original Mullard circuits where we find 6L6, 5881, Etc. A single dominant pole is a safe way to go in this cct. There are a couple of worked samples in RDH4 worth looking at. Also strongly recommended by none other then Norman Crowhurst. You can read about how to implement all in a couple of his articles. I like the cct proposed by Alex Pogossov recently. The attachment shows how it is connected in an SE Amp. The frequency selective network is in the cathode of the first stage rather than between stages. My opinion, anyway, having done it. Cheers, John Stewart PS- The bicycle went more than 1000 KM in August (622 miles). Pedalling again today. Hey Patrick, hows it going in OZ? * * * * * * * *J Why would you want a circuit that drops the gain by about 16dB at 100Hz? What is its actual purpose? Ans: To get the loop gain (forward gain times NFB gain) well below unity at the low frequency where the phase lead becomes 180 degrees (due to two RC couplings and one OPT.) Very low frequency oscillation in the range 0.5 to 2 Hz can result if there in no low-frequency shelf inside the loop. Cheers, Roger So it is a horribly bodged solution to a problem that has no business being there in the first place? The idea of implementing negative feedback and then defeating it by killing the open loop gain it mediates is beyond ludicrous. On Sunday you suggested "a single pole that doesn't let up until beyond the unity gain frequency", isn't that equally ludicrous as it also "kills the open loop gain"? Not at all. It operates as a local feedback loop within the overall loop. At lower frequencies, where it really matters to have particularly the output stage included, the loop stretches from beginning to end. As the frequency rises the loop transfers steadily to just the voltage amplifier. This does result in a slight rise in harmonic distortion above about 10kHz, but frankly by then who cares? And this pole is going to have to be present in some or other form anyway because high frequency instability needs to be tamed - so why not make it simple, predictable and controllable? So if I follow you, you are not talking about a single overall negative feedback loop containing a dominant pole within, but instead you are talking about nested feedback loops where the dominant pole within the overall feedback loop is created by a second shorter internal feedback loop that rolls off the high frequencies? That is exactly what a dominant pole is - a nested feedback system in which the voltage amplifier is controlled by a single capacitive feedback element. The overall feedback which surrounds it is flat, and composed of two resistors, the ratio of which sets the gain of the amplifier. I beg to differ, a "dominant pole" does not require nested feedback loops, it can also be a simple pole within a single overall feedback loop controlled by the same two resistors you describe. -- Regards, John Byrns Surf my web pages at, http://fmamradios.com/ |
#33
Posted to rec.audio.tubes
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1st try kt88 amp
On Tue, 13 Sep 2011 12:08:14 -0500, John Byrns
wrote: So if I follow you, you are not talking about a single overall negative feedback loop containing a dominant pole within, but instead you are talking about nested feedback loops where the dominant pole within the overall feedback loop is created by a second shorter internal feedback loop that rolls off the high frequencies? That is exactly what a dominant pole is - a nested feedback system in which the voltage amplifier is controlled by a single capacitive feedback element. The overall feedback which surrounds it is flat, and composed of two resistors, the ratio of which sets the gain of the amplifier. I beg to differ, a "dominant pole" does not require nested feedback loops, it can also be a simple pole within a single overall feedback loop controlled by the same two resistors you describe. Oh jeez. OK. But the way it is done 99%, no, 100% of the time is by putting the pole around the voltage amplifier. That way the dominant pole reduces the voltage amplifier distortion at high frequencies. If you just stick in a pole it can't. Why would anyone compromise their HF open loop gain for nothing? d |
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