[i45one]

Ok guys, don't go flaming before I explain what I am doing here.

I want to replace the line muting transistors with relays, preferably
without having to build a timer circuit to control them. And I MIGHT
want to experiment with other opamps, resistor types in the audio
path, and checking the stability of the PS and cleaning it up if
needed. (That will come later)

My question is if I can trigger a 5v reed type relay from the points
at Q203 and Q501 that I have circled in red on the following image.
And would this type of modification require 2 or 4 SPST relays to
replace Q101, Q102 and Q201,Q202

The schematic image can be found he

http://img521.imageshack.us/img521/4843/7esmodsqb4.png

Any assistance with this would be greatly appreciated.

J

[Richard Crowley]

"i45one" wrote ...
Ok guys, don't go flaming before I explain what I am doing here.

I want to replace the line muting transistors with relays, preferably
without having to build a timer circuit to control them. And I MIGHT
want to experiment with other opamps, resistor types in the audio
path, and checking the stability of the PS and cleaning it up if
needed. (That will come later)

My question is if I can trigger a 5v reed type relay from the points
at Q203 and Q501 that I have circled in red on the following image.
And would this type of modification require 2 or 4 SPST relays to
replace Q101, Q102 and Q201,Q202

The schematic image can be found he

http://img521.imageshack.us/img521/4843/7esmodsqb4.png

Any assistance with this would be greatly appreciated.

Seems odd that there appears to be a stereo muting
function (Q103 driving Q101 & Q201) AND separate
muting functions for L and R channels. If you wanted
to retain the full functionality, you would need 4 separate
relays (or maybe use a DP relay for Q101 & Q201?)

Without seeing the missing parts of the schematic, maybe
Q103-Q101-Q201 is the power-on mute, and the other two
are some kind of operational mutes?

It should be easy enough to look up the gain and
collector current ratings of the driver transistors and
compare to the coil specs on your proposed relays.
Don't forget to put diodes across the coils to snub
any kickback EMF.

[i45one]

Thanks for the input RC


Without seeing the missing parts of the schematic, maybe
Q103-Q101-Q201 is the power-on mute, and the other two
are some kind of operational mutes?

Agreed... I don't have the unit yet, I will have it on Friday. I will
be able to actually pinpoint what controls what and under what
conditions. I got a good deal on this thing and got it mainly for a
tinker box.


It should be easy enough to look up the gain and
collector current ratings of the driver transistors and
compare to the coil specs on your proposed relays.
Don't forget to put diodes across the coils to snub
any kickback EMF.

Both of the driver transistors have a IC rating of -100mA and min hfe
of 50. As for the relays, I will have to find some that are suitable.
I think you are correct in recommending DP relays on the main output.

If you are interested at all in seeing the rest of the schematic, let
me know and I can post it.

Thanks again,

J

[i45one]

On the relays, I found some SPDT relays with 200 ohm coils which I
think would be a draw of 25ma @ 5v. I'm no technician, but an avid
hobbiest so correct me if I am incorrect in my assumptions. Thats why
I do these things, to learn :-)

[Richard Crowley]

"i45one" wrote ...
On the relays, I found some SPDT relays with 200 ohm coils which I
think would be a draw of 25ma @ 5v. I'm no technician, but an avid
hobbiest so correct me if I am incorrect in my assumptions. Thats why
I do these things, to learn :-)

Georg Ohm would agree with your calculation.

Is there a voltage rating on the relay coils?
Are they 5V relays?

[i45one]

On May 10, 11:57 pm, "Richard Crowley" wrote:
"i45one" wrote ...

On the relays, I found some SPDT relays with 200 ohm coils which I
think would be a draw of 25ma @ 5v. I'm no technician, but an avid
hobbiest so correct me if I am incorrect in my assumptions. Thats why
I do these things, to learn :-)

Georg Ohm would agree with your calculation.

Is there a voltage rating on the relay coils?
Are they 5V relays?

Yes, the coils are rated at 5V. I found some other relays rated at 6V
with the same coil impedance. And to correct myself, I was speaking of
DPST relays. There is one thing that has me a bit perplexed. One of
the trigger transistors shows a switched voltage of -11.3. I am surely
going to have to do some actual measurements of the circuit to see
what transistors are controlling what and when. I also need to see
what voltage states are produced during muted and unmuted operation.

I will have the unit on Monday, so I will know for sure why there are
multiple muting circuits.