trinityamps.com

I did the bypass on mine and the amp works perfectly at all volume levels. It sounds rally good.

I've done the bypass as well and noticed a big difference.

Something else I've noticed is that I seem to get more range from the gain and master volume when in 'tude mode.

What I mean is that I can dial things down a lot more than I can when in tweed mode.

I'm off to review the schematics on that...

That's normal.

In tude mode you have a lot more gain (read volume) on tap. It's easier to dial down because there is more to dial down, if that made sense.

_________________
http://pdfelectronics.com

I removed the jumper and I'm back to sputtering sound when the volume and master volume aren't close to maxed

OK, so we now know that both amps are working fine, but something's wrong in the VRMs of both amps...


In Tweed mode you have negative feedback, like in a regular Tweed Champ or Princeton, which makes the amp less dynamic in terms of highs and lows.

_________________
Great tones come in small glass jars!

What would be the next suggestions for troubleshooting the VRM?

Check how the voltage at the second filter cap changes between when the VRM is shorted out and when it's in circuit (VRM up full). Next check how the voltage on the wiper of the VRM's pot changes as you turn it slowly. Does it increase and decrease smoothly, or does it jump at some points? Next also check how the voltage at the 2nd filter cap changes while you slowly turn the VRM pot. Again it should change smoothly and evenly. Carefully check all solder joints in the VRM section (with the filter caps fully discharged).

_________________
Great tones come in small glass jars!

No big difference with or without the short when the VRM is at max - both scenarios measured 402V.

Dialing the VRM and measuring across pins 1 and 2 of the VRM is interesting:

VRM dial indicator - measured V
Idle - 0 V (or pretty darned close to 0)
4 - 15V
5 - around 30V
6 - around 45V
7 - around 60V
8 - around 85V
9 - just over 200V
10 - just over 330V
Max - 362V

I see a big jump just after 8 - which is where things start to function - and you indicated we should be looking for that. I see the MOSFET and the zener diode in that part of the circuit..

I'll double check the resistors again.

Yep. That makes sense and that's what I expected, but the difference is HUGE.

I should have been clearer in adding that in tweed mode, anything less than around 6 on both gain and master volume and I may as well unplug... and that's with the VRM maxed.

Edit: and I say it that way to help characterize what I'm hearing - not to be whining..

Check that R16 is 22k and not the 220k R5. Both are on the Tweed/'tude switch. Ensure you don't have them switched around.

_________________
Fantasy Noise is what my shop of dreams is called and was the only way to beat my addiction, like many here I suffer from G.A.S.


Tele's make the best noise

Checked and double checked.

They're good and in the correct places..

Just tried a 6L6 because the output tube is the only thing I haven't swapped yet.

Love the tone.

Still have the same issue - I expected as much, but thought it worth a try anyway.

I must say though, once things get warmed up and as long as I keep the VRM above 8, I can get some amazing tones out of this thing.

For example, Gain at max, Master volume at about 7, and VRM just a hair above 8 sounds like I've got a fuzz pedal hooked up. Awesome.

Is youir VRM control the solid shaft version or the split shaft version? It could be coming down to the VRM control. Odd.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

It has the solid shaft.

Yes, that really looks odd. What about the voltage readings at the wiper of the VRM's pot?

_________________
Great tones come in small glass jars!

I've been calling the Power Level pot "VRM"

I measured those voltages across pins 1 and 2 of the pot. Pin 2 being the wiper.

The VRM is the whole she-bang with the FET, pot, resistors and zener. However, it does look like something funny is happening at the pot.

_________________
Great tones come in small glass jars!

Yeah, I realized that I was using the wrong term along the way, but everyone was playing along. So, I didn't want to mess up the conversation by changing things mid-stream.

I de-soldered two of the leads from the pot so that I could measure the resistance out of circuit (just to be 100% certain). There's definitely a problem there. Big jump when we get to the 9 setting and there it looks more like something you'd expect from a 5 to 5.5 setting - close to half and half.

So, where can I pick up another? I see a1 has one listed on their site, but I'm not sure if it's the same in terms of physical size...

Is it a linear pot or an "audio" one? I forget exactly what kind we specified. If it's an audio pot, then the change in resistance won't be linear. You can compare with the gain and volume pots which are also "audio" (ie logarithmic). However, the jump you described seemed a little too abrupt to me. It would have also been useful, if before you had removed the pot yo could have checked the whole VRM's output voltage as you moved the pot. It should track the voltage on the pot's wiper to within a few volts.

_________________
Great tones come in small glass jars!

I'm pretty sure it's an audio pot.
But yeah it's still not looking right. Right?

I can put the pot back in circuit tomorrow and check the voltages
You're talking about the variance of B+ right?