TH Customs Supreaux Deux Help!

[playpunk]

Hello Everybody:

I have populated a Th Customs Supreaux Deux and I'm getting 18v on tp2 (which is, I believe, connected to the j201 transistor.) That voltage reading didn't change at all based on where the trimmer was set. Also, the circuit has very little gain/volume and no clipping right now. Things just aren't right.

Does this mean that my j201 is bad or fried, or could it mean that the trimmer isn't good? I am going to replace the trimmer as the first step, but I'm not sure how to diagnose it if the trimmer isn't the problem.

I was able to bias the other transisters (which are smd on the SOT adaptor boards) just fine, and I have smd j201's available, but have a thru-hole part in there right now.

[midwayfair]

Use a continuity checker to see if your trimpot's lugs are shorted together.

You shouldn't get any sound if your transistor's drain is slammed against the 9V rail, though. The signal would all get dumped and the transistor probably wouldn't operate much above 17V. So something else weird seems to be happening.

[playpunk]

I piulled the trimpot out and replaced it, but couldn't retest. A quick poke with the multimeter gave me 0.0 v with the new trimmer, so there's that


Sent from my iPhone using Tapatalk

[playpunk]

Ok I had a minute with this... There are some weird things going on. I get signal and the two 2n5457 and jfets bias correctly at 12v. The j201 won't go lower than 16.7v and will go up to 18 v.

I reflows everything. I get 9.3 v off of the two top legs of my 7660 charge pump and 12v on both of the electros for the 2n5457 and 18v in the j201.

The output is very splatty and has no sustain.

I am kinda stumped here... On my phone so pictures are a pain


Sent from my iPhone using Tapatalk

[playpunk]

Sent from my iPhone using Tapatalk

[playpunk]

Sent from my iPhone using Tapatalk

[playpunk]

Just to be clear, this is a th customs supreaux deux.


Sent from my iPad using Tapatalk

[playpunk]

Ok, I pulled the JFET and replaced it with an SMD j201. Now it biases up right right about 12v. I get signal at output, but it is weak. It doesn't sound splatty and gated like it did with the thru hole j201, but it is not right. I have tried to follow the signal and can get through the schematic up to l3 of the volume control, but kind of lose it after that.

I would appreciate some advice on what to do next - which other voltages to check, etc.

I have checked and rechecked everything. Please help!

[midwayfair]

Ok, I pulled the JFET and replaced it with an SMD j201. Now it biases up right right about 12v. I get signal at output, but it is weak. It doesn't sound splatty and gated like it did with the thru hole j201, but it is not right. I have tried to follow the signal and can get through the schematic up to l3 of the volume control, but kind of lose it after that.

I would appreciate some advice on what to do next - which other voltages to check, etc.

I have checked and rechecked everything. Please help!

Post voltages on all pins of all transistors, not just the drains.

You want to audio probe the gates and drains of each transistor to narrow down where the problem occurs.

Also, measure the source resistor on Q3.

[playpunk]

Ok, I pulled the JFET and replaced it with an SMD j201. Now it biases up right right about 12v. I get signal at output, but it is weak. It doesn't sound splatty and gated like it did with the thru hole j201, but it is not right. I have tried to follow the signal and can get through the schematic up to l3 of the volume control, but kind of lose it after that.

I would appreciate some advice on what to do next - which other voltages to check, etc.

I have checked and rechecked everything. Please help!

Post voltages on all pins of all transistors, not just the drains.

You want to audio probe the gates and drains of each transistor to narrow down where the problem occurs.

Also, measure the source resistor on Q3.

Should I pull the part and measure it to make sure it's right or just measure the voltage on that resistor?

[playpunk]

On t3 I am getting 0.0 at G, 12.6 (ish) at S and .4 at drain

on t2 I am getting 13.4 at G, 12.5 (ish) at both S and D

on t1 I am getting 11.6 at Source, 0.0 at G and .45 at D

So I'm guessing r5 & r6 are screwed up somehow?

[playpunk]

So the other one I built at the same time works perfectly and sounds great




Sent from my iPhone using Tapatalk

[midwayfair]

Transistor 2's gate connection is somehow getting positive voltage, and your source is somehow sitting at 12V when it should be at a couple volts max. Whatever your problem is, it's connected to one of those two spots. Start with the gate.

And you have the pins mixed up on your measurements. Look up the datasheets and compare with the schematic.

[playpunk]

Jon thanks so much for your help. I have been looking at
The schematic and layout lead me to believe that there is something wrong with the board, as I can't see any issues with the components. I wouldn't be as confident if the other board I built wasn't working perfectly.

Is there anything else I can do to check? Should I check for continuity between the legs of the transistor? 


Sent from my iPhone using Tapatalk

[midwayfair]

Jon thanks so much for your help. I have been looking at
The schematic and layout lead me to believe that there is something wrong with the board, as I can't see any issues with the components. I wouldn't be as confident if the other board I built wasn't working perfectly.

Is there anything else I can do to check? Should I check for continuity between the legs of the transistor? 


Sent from my iPhone using Tapatalk

Since your eyes can't see an electronic connection, you can use the continuity reading to see if everything's connected where it should be and nothing's not connected where it shouldn't be. You have to check every component connected to Q2.