# Thermionic Deluxe gain issue



## PKRPedals (Jun 20, 2019)

I just got done building the thermionic deluxe and am a little disappointed with the gain. It doesn’t seem to have near the gain of the actual be-od pedal. The tight pot acts like a volume almost. Any ideas? The trimmers are all the way up also


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## Chuck D. Bones (Jun 20, 2019)

Post a hi-res pic so we can verify all the parts.  I built a Brown Betty (basically a single channel version of the TD) and it has plenty of gain.  Some trimmers have their rotation reversed, did you try turning the trimmers the other direction?  Unless you are playing a bass guitar thru this pedal, the Tight control is not going to behave like a volume control.  Verify that C3A & C3B are 10nF.  Both channels behave the same way?


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## PKRPedals (Jun 21, 2019)

I have been through it and checked caps and such. I turned the trimmers both ways and it is at it's highest gain setting. It is not getting the distortion that it should. It is both channels are very low gain


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## chongmagic (Jun 21, 2019)

My build had lots of gain on both channels, perhaps one of your TL072 ICs is wonky?


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## PKRPedals (Jun 21, 2019)

I would agree with you but it would have to be at least 2 IC's because both channels are affected. When I turn down the trimmers, almost all the volume goes away. When I turned up the tight pot, the volume goes away. It's crazy


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## chongmagic (Jun 21, 2019)

I had a bad ic on channel B and it would cause the volume to increase as I turned the volume knob counterclockwise.


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## Chuck D. Bones (Jun 21, 2019)

And you're sure all the resistor values are correct?  You can verify most of them in-circuit with an ohmmeter, at least see if they are in the ballpark.  R8, R10, R12 & the GAIN pot are the most critical for setting the gain & distortion.  If TIGHT is not working right & C3 is correct, then I suspect R25 is way too low.


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## PKRPedals (Jun 21, 2019)

I can go back through again and check and get back


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## Chuck D. Bones (Jun 21, 2019)

Posting a hi-res photo would be helpful.


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## PKRPedals (Jun 21, 2019)

I'll see if I can do that.


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## PKRPedals (Jun 21, 2019)

I noticed that the LED’s on the gain side don’t light up when playing. The other LED’s in the middle do light up. The ones on the side blink when I hook up power though


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## chongmagic (Jun 21, 2019)

Did you double check the LED orientation?


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## PKRPedals (Jun 21, 2019)

I hope this picture helps. It is as good as I could get. The others were too large to attach


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## PKRPedals (Jun 21, 2019)

I did check the orientation of the LED's and they are correct. I checked the voltages on my TL072's and they are all the same. I checked my pots and they are good. I checked a bunch of resistors and caps and they are all pretty close to what they should be. Channel B has more gain than channel A but it's not pleasant to the ear at all. Kind of sounds like a bad fuzz. Are the LED's on the left side supposed to light up when played? Mine don't, they only flicker when hooking up power.


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## PKRPedals (Jun 22, 2019)

Went through and checked all the resistors and they appear to be correct. Will try and check caps a little later. Whatever it is, it is the same for both channels. So if I made a mistake, I made it twice. This is a little perplexing to say the least.


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## Chuck D. Bones (Jun 22, 2019)

LED1 & LED2 do no light up in normal operation because there is so little current running in them.  LED3 & LED4 will light up if the Gain, trimmer and Presence are set high enough.  Max brightness will be governed by the Presence pot.  They will not be as bright as the front panel LEDs.  
It's possible that the colors did not all come across correct in the photo, but here's what I see that doesn't look right: 
R3A is 1K, s/b 10K
R5A is 3.9K, s/b 39K
R8A is 2.2K, s/b 22K
R9A is 2.2K, s/b 22K
As best I can tell, everything else on the board looks OK.
I can't read R32-R37 because they are in the shadow.  Verify that IC1-1 and IC1-7 are both close to +4.5V.  If those are good, then check pins 1 & 7 on all of the other opamps.  Should be between +4V and +5V.
Can't tell if the switch wiring is correct because the wires disappear out of view.  I see an extra wire on the A/B switch, I assume you're doing something clever like a 2-color LED.
I see you are using a Mammoth C10K pot.  I bought one from them that was very noisy, so there may be a lot quality problem.  Try checking the resistance between pins 1 & 3 in-circuit, should go all the way down to zero when Presence is dimed.
If you get this far and haven't found the problem, then we have to suspect bad parts.  The resistors I mentioned yesterday, measure them.  It's rare, but resistors do get mismarked sometimes.  
Finally, I never trust stamped-pin sockets.  If you have an IC that's not working properly, it's more likely that the socket is bad than the IC is bad.
Good luck!


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## PKRPedals (Jun 22, 2019)

Thanks 
I will dig in later when I get home. I hope this will solve it else I just start over
Thanks again


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## Robert (Jun 22, 2019)

I notice some of your pots don't have dust covers.   Is it possible some of the pots on the bottom row are touching the back of the PCB?


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## PKRPedals (Jun 22, 2019)

The pots on the bottom row all have dust covers. I only used the ones without covers because I knew they wouldn’t be touching anything. I’m thinking I may have put in a wrong cap. I went over all the resistors and they all measure as they are supposed to. I will go back over them again just to be sure though. I got to get it out of the box so I can access the back of the components and go from there. Thanks for all the replies and help. I hope this thing will be singing soon.


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## PKRPedals (Jun 22, 2019)

Problem solved! I have to stop working on these late at night. I ended up putting 47n caps where the 47p caps were supposed to go. Got that straightened out and it sounds great now. Thanks to everyone that took an interest.


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