The Amp Garage

So you have both clean and OD now, meaning the back panel or foot switch noticeably changes the tone, and the OD trim, ratio, and level controls all work in OD? But in either mode the volume pot does nothing? You should be able to silence the amp with the volume pot in clean or OD mode, and all tha...

What about this jumper? That has continuity - from the red wire through both points. Also this is the clean/OD relay no? I have OD. I would think it was before it gets out of V1?? Here's the schematic I'm referring to so we're on the same page. V1 is actually flipped on Nik's. See pic So, pin8 = pi...

Swapped out the socket to be sure. Volume or switches still don't do anything... crap! Not sure where to go from here. You need to start at the input jacks and sweep right across the front panel, checking ALL wiring and grounds , jumpers etc to all sockets, jacks,, switches and pots. When you have ...

Looks like the relay coils are non-polarized, and the diodes are oriented correctly. I would hope so, since these boards were pre-assembled in the kit! However, the relay PCB's are not the same as the boards shown in the layout drawing. I can't see where the contact traces connect in the photos abo...

martin manning wrote:

MusicMaker wrote:It goes from zero to 868 ohms. (0-10 respectively).

Seems low... maybe it's 868k ohms (almost 1Meg)?

Yeah, forgot the "K"

Going to be out of town this weekend. Revisit on Monday...

Swapped out the socket to be sure.

Volume or switches still don't do anything... crap!

Not sure where to go from here.

You can only see the static current when setting idle bias, and being within a few mA is close enough. I would swap V4 and V7 to get the total current on each side a little closer to matching, set the average current to ~37 mA and call it good. You have the ability to adjust the dynamic balance wit...

Good to know. Also, is it possible that when it was an full blown oscillator it could have damaged a component in the ckt? Might explain why no PAB...?

Update on bias voltages. Swapped out the 1k2 on the bias board for a 1k7 and my readings for bias are V4: 35 mV V5: 36.5 mV V6: 36.7 mV V7: 38.6 mV Will 38.6 be too hot? Should I lower V7 to keep it around 35 mV? Everything else drops as well if I do. Is there a sweet spot I'm shooting for? If these...

JazzGuitarGimp wrote:

MusicMaker wrote:I've been a little preoccupied with another project of mine... I'll get to the wiring soon.

Now we're talkin.... Nice! I'd love to have the skill set to do that.

I'd love to have the skill set to build amps like Martin does and the rest of you folks!!!


I'm just a hack!

I was thinking it wasn't the overdrive as that sounds great.

Probably to the PAB relay? There's no difference hitting the boost and all that preamp stuff is in the area.

I've been a little preoccupied with another project of mine... I'll get to the wiring soon.

Here are the voltages. I measured the bias and the "max" I can get now is 28mV idle current. That's with the pot all the way up. These voltages look good except for the V1 and V2 grids, which should be very nearly zero (like V1 pin 2, e.g.). Maybe your meter is auto-ranging to mV? To increase the b...

Don't know why Nik's diagram shows the blue wire going to V4. Could be he uses a different OT??

Here are the voltages.

I measured the bias and the "max" I can get now is 28mV idle current. That's with the pot all the way up.

SUCCESS! It works! I thought I was fairly careful wiring it. The 'problem' was following Nik's layout - the color of the OT wires were a swapped vs the TAG schematic. (I wonder why he did that?? Hmmm). I think it would make the PI oscillate improperly. Might it even be additive to the signal theref...

norburybrook wrote:if the OT primaries are the wrong way round you'll know immediately when you plug in and switch on .....trust me I've got it the wrong way 100% of the time on my last 3 builds ......the noise will certainly make you jump



Marcus

And yes, it's quite the noise indeed!