Quote from: g1 on March 04, 2023, 06:35:33 PM

Quote from: Luthier Vandros on March 04, 2023, 12:31:48 PMonce the new silicon is in, I'll try to align voltages between green and red, along with biasing these little jerks.

On another forum J202 fet was working as a drop-in replacement for the 2N5485/TIS58 with no adjustment required.

TY, G1. I found a broken trace under the board. The 3819's are passing signal, but cery attenuated compared to the green channel. I imagine I'll have to tweak the drain resistors. Is there a rule of thumb? I have a solid 24v on the source rail (thanks to a 24v zener. More on that below.

Btw the schematic posted must be of a more recent model. My circuit board has several variances, such as no 24v zener off the E supply. Instead that tap is supplying 34v. Both the cap and dropping resistor have been replaced, so as a test, I tacked in a 24v zener. 

Cheers

I know this is an old thread, but just got a Tramp that has the exact same issues as the OP.  Wondering if there was ever a solution to the channel switching problem.  I have tried all the various one and two button foot switches I own-none make a difference. I've touched up the main PC board with solder and it generally works well except for low frequency oscillation on the gain channel if reverb is turned up (new tank installed).
Thanks.

Welcome, you sound like our kind of people!

My experience is that higher voltages give you more clean headroom.  It doesn't seem to affect tone at all.

I do not think it would matter, I think most signals going through the Op-Amps are in the Milli Volt range up to a few volts maximum.

There are some circuits that rely on the Op-Amp reaching the voltage supplied to start breaking upthe signal and making distortion however, but this is on purpose to give the tone some growl.

There are exceptions though and I hope someone who knows better will jump in and give their opinion.
Cheers
Mick

I recently bought a Signal Tracer/Injector Pen V6.3 from https://www.diyguitarpedals.com.au/shop/index.php?main_page=product_info&cPath=1&products_id=728.
I haven't tried it yet but I believe it is a signal injector and an audio amp all in one. It injects a signal on one probe and then picks it up and makes it audible on the other probe, should be easy to see where you loose the signal.
Depending on where you are you can also buy one from TH Customs who makes them.
 https://diy.thcustom.com/shop/signal-tracer-injector-pen-v6-2/
There is a Utube video of how to assemble and use it
Or just make something similar yourself.

Have you made sure that you have power going to the PCB in the amp ?
Do you have -9V on pin 4 and +9v on pin 8 of the 4558 OpAmps ?
Measure each one to ground, it should be 19v between pin 4 and pin 8.
Please check that you have the correct voltages on the PCB board.
Do any resistors look burnt ? , any capacitors swollen up ?
Remove the PCB and look at the copper tracks underneath, check all solder joints with a magnifying glass to see if they look bad, dull, etc.

I would start with a quick check of voltages followed by poking the components with a plastic pen or chopstick while strumming the strings, this might find a bad connection or solder joint even if you can't see it with the naked eye.
Remember to use something plastic to tap the components with and be very careful with any wires connected to the mains voltage.Fuse, main switch and transformer are deadly to touch, but like I was told when I was an electrical apprentice "It Only Hurts Until You Pass Out Or Die".
Cheers
Michael

thanks again guys
I tried running both preamp out to an old working Crate 15 combo and it was silent.
I am in this for the long haul so I am working on making a signal input like 1 khz connected to a guitar cable for testing.
then for trying to track the signal I might make an audible guitar cable plus capacitor to amp type signal tracer or maybe a cheap scope.

 thanks for the help

I was just idly thinking about the effect of op amp voltage on tone. Most op amp preamps typically use ±15V rails as that's the limit of the TL072 op amp commonly used, but is it an anachronism to be limited by this when there are modern op amps capable of higher rail voltages? Something like the OPA552PA is capable of ±30V, but all other things considered would it sound any different than if it was capped at ±15?

Quote from: Tassieviking on March 19, 2023, 11:01:15 PMThis might be the schematic for it

Yes that is the correct schematic, this is just the combo version but electronics are same.

Yes all 1k5 and 100R grid resistors charred and destroyed.
I've seen 100Rs before but not both.