Simulcast (latest version) semi working

innerlight

Active member
Hey all
just finished the new version of the simulcast. When engaged all knobs affect the sound, however the sound is weak in all three modes, a tiny bit of drive, not much increase in volume.
When I first plug it in to the power it sounds how it is meant to for two seconds then it fades back to that quiet/ weak state. if I really dig into the strings it sputters here and there like a gated fuzz.
I’ve built a duo cast in the past and it worked great.
Im pretty confident the problem lies with the ge transistor. I have an OC 71 in it right now. If I wiggle it about it has splutters here and there. I know the transistor works because it was in a functional duocast and it worked fine (a little weak but pretty good).
I have a bunch of MP20 transistors coming so I’ll try them when they arrive. Does anyone have any advice in the mean time? Many thanks.
 
How might I ensure contact on the transistor?
Performing a reliable continuity test with your multimeter. Following schematics, according to the transistor's pinout :
index.png page-29-pinout-of-oc71-transistor.jpg

Exemple: The arrow being the Emitter (1 on schematics), it should have continuity with R7 and C5.
So, if the soldering is good, if you touch the emitter leg, multimeter will ring continuously with one side of R7, and one side of C5.

When you wonder how to install a transistor, or how to take readings on it, you can just google it as follow : "OC71 pinout", or "OC71 datasheet".

You can also post voltage readings, always useful to see if the transistor, or other suspicious components, are operating correctly in the circuit.
 
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I'm pretty sure the transformer is ambidextrous, or whatever the proper term is for "orientation doesn't matter."
I believe the proper term nowadays is "gender neutral", but it may have already reverted back to "they" and "them" (though sometimes used in conjunction with).

Whatever you do, don't use "androgynous".
 
Performing a reliable continuity test with your multimeter. Following schematics, according to the transistor's pinout :
View attachment 41411View attachment 41412

Exemple: The arrow being the Emitter (1 on schematics), it should have continuity with R7 and C5.
So, if the soldering is good, if you touch the emitter leg, multimeter will ring continuously with one side of R7, and one side of C5.

When you wonder how to install a transistor, or how to take readings on it, you can just google it as follow : "OC71 pinout", or "OC71 datasheet".

You can also post voltage readings, always useful to see if the transistor, or other suspicious components, are operating correctly in the circuit.
Hey, those thingies look like octopi...
 
Performing a reliable continuity test with your multimeter. Following schematics, according to the transistor's pinout :
View attachment 41411View attachment 41412

Exemple: The arrow being the Emitter (1 on schematics), it should have continuity with R7 and C5.
So, if the soldering is good, if you touch the emitter leg, multimeter will ring continuously with one side of R7, and one side of C5.

When you wonder how to install a transistor, or how to take readings on it, you can just google it as follow : "OC71 pinout", or "OC71 datasheet".

You can also post voltage readings, always useful to see if the transistor, or other suspicious components, are operating correctly in the circuit.
Excellent! Massive thank you. I’ll look into this soon as I get a break from work (Saturday I’d say)
 
Hey all
just finished the new version of the simulcast. When engaged all knobs affect the sound, however the sound is weak in all three modes, a tiny bit of drive, not much increase in volume.
When I first plug it in to the power it sounds how it is meant to for two seconds then it fades back to that quiet/ weak state. if I really dig into the strings it sputters here and there like a gated fuzz.
I’ve built a duo cast in the past and it worked great.
Im pretty confident the problem lies with the ge transistor. I have an OC 71 in it right now. If I wiggle it about it has splutters here and there. I know the transistor works because it was in a functional duocast and it worked fine (a little weak but pretty good).
I have a bunch of MP20 transistors coming so I’ll try them when they arrive. Does anyone have any advice in the mean time? Many thanks.
When you wiggle the OC71, are you holding it by the can with your fingers?

Maybe try crimping the legs and resocketing to see if you get a consistent connection. I find it’s good practice to let a Ge transistor sit in place for a few minutes after handling it before drawing conclusions.
 
This won’t really tell you anything because you’ll be touching the leads to take the measurement. The issue could be that as it is seated in the socket, it is not making consistent contact.
I am not sure i understand what you meant.

I suggested Innerlight to do a continuity test on each transistor's leg, with one probe on the leg, and the other probe on the following component on schematics.

Isn't it a safe way to make sure that the transistor is correctly seated in its sockets, as well as confirming that the sockets are correctly connected to the circuit ?

I didn't suggest to probe the socket only, so I don't understand how the issue you described could escape our attention in such test ?

Quite the opposite, this test is meant to check if the transistor is correctly connected both to the socket and to the circuit ?
 
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When you wiggle the OC71, are you holding it by the can with your fingers?

Maybe try crimping the legs and resocketing to see if you get a consistent connection. I find it’s good practice to let a Ge transistor sit in place for a few minutes after handling it before drawing conclusions.
I’ll investigate this method too. I was wiggling the can with my fingers yes.
 
Would the transistor being the wrong HFE cause this sort of behavior? I have a tester on the way. Others have mentioned around 80 as optimal, can others confirm this?
 
I am not sure i understand what you meant.

I suggested Innerlight to do a continuity test on each legs, with one probe on the transistor's leg, and the other probe on the following component on schematics.

Isn't it a safe way to make sure that the transistor is correctly seated in its sockets, as well as confirming that the sockets are correctly connected to the circuit ?

I didn't suggest to probe the socket only, so I don't understand how the issue you described could escape our attention in such test ?

Quite the opposite, this test is meant to check if the transistor is correctly connected both to the socket and to the circuit ?
If you touch the transistor legs with a test probe while they are in the socket, you will apply pressure to the leg which will change it from its resting state. Because of that, you won't be measuring how it is without the probe touching the leg. With sockets, you could be applying pressure that makes a good connection that otherwise isn't there (i.e., the lead is not secure/making consistent contact in the socket).
 
Would the transistor being the wrong HFE cause this sort of behavior? I have a tester on the way. Others have mentioned around 80 as optimal, can others confirm this?
hmmmm
looks like a Sziklai pair from the schematic. It’ll be interesting to see what’s shaking once you get a tester on that ge transistor. Are you sure Q1 is good? Do you have any other low/medium-ish gain pnp transistors with the right pin out that you try in Q2?
 
OK so I checked continuity from both the empty sockets and each leg of (collector and emitter) of Q2 when it was socketed to their corresponding resistors, both worked so I think we are all good there. Im thinking next step is maybe trying other Transistors in there (when they arrive). If anyone has any other ideas please let me know!
 
Hi, I've got same issue with no gain and low output.
I'tried different GE PNP from 80 to 150 hFe with no luck. Different transistor and charge pump. I have pin 1 and dot down right, continuity to R10 and R11 are fine. Other pins to ground and to pot are fine.
Any clues how to make this work right?
I get about 17v+ on both transistors.
 
Hi, I've got same issue with no gain and low output.
I'tried different GE PNP from 80 to 150 hFe with no luck. Different transistor and charge pump. I have pin 1 and dot down right, continuity to R10 and R11 are fine. Other pins to ground and to pot are fine.
Any clues how to make this work right?
I get about 17v+ on both transistors.
Start a new thread, post pictures, etc.
 
I just spent a hour troubleshooting a Sushi Box Tube pedal. turned out that even though I was SUPER diligent with everything, reflowing all the solder points fixed the issue. Which is like 99% of the issue 99% of the time.

Here's mine, but it looks just like yours.

The transformer is rotated by 180º from yours but I think it's been determined elsewhere that it doesn't matter in this circuit. (don't quote me on that)
Ignore the jumpers on the pots, i had an issue with the high end and hacked a filter.

IMG_7277.jpg
 
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