The Amp Garage

Using mixing resistors will weaken the voltage of each signal 50% from the voltage division. (This is less then a 50% reduction in "volume.") Injecting each preamp in to opposite sides of a LTPI preserves the full strengths. Look at an 18watt Marshall on how to do it. If using pre PI MVs, it won't ...

Yes one board has the actual relay switch, and associated components, and the other board rectifies the 6.3VAC to DC, and regulates it at 12V IIRC which is what actually triggers the switching in the relay. So you need both. Is there something wrong with your current power transformer? So the amp w...

Yes but I think that's an unpopulated board. Granger sells good ones and even better, forum member Colossal sells finished boards and power supplies, and provides excellent customer service, and downright help on installs. He'll be along shortly I bet, but here's his stuff : http://www.colossalamps...

Thank you guys.

And if I wanted to go the Foot switch route I assume $15 spent here would
take care of it - http://www.mojotone.com/amp-parts/Relay-Switching-Kits

Sorry for all the dumb questions and not having this to present before asking.

Does this look OK?

Thanks Smoke.

I don't need to lose the NFB, I just need to get both circuits in the way they are.
It sounds like going to a single input, through a switch is what I need to look at. The whole ABY idea is were I got off track.

Check out Steve's comment. You have 4 gain stages with the 36 and 3 with the Xpress, as the signals will be out of phase with one another when blended, and will sound like ass. Audio signals are flipped 180 when they go through a tube's amplification process(Cathode followers do not). If you absolu...

Do you have a rough schematic of what you have? Mixers will work to blend, but you will be cutting each amp's signal in half, essentially. I would put them on a switch before the cap feeding the PI, and then you don't have to compromise each channel as much, of you course then you have the compromi...

Phil_S wrote:Well, then, go back to my first suggestion. Insert one channel at the top and the other at the bottom. Lose the feedback. You have options here!

I'll try feeding the top and bottom and see where that gets me. Thanks for all the help.

Look at the AB763 schematic. It shows a pair of 220K mix resistors, taking the feed from the vibrato and normal channels, and going into a coupling cap that feeds the upper half of the PI. You'll see. I understand this, but my problem is the JCM channel is feeding the Coupling cap off of a MV. It e...

Take note! If one preamp circuit has more gain stages then the other then they can not be blended/ used at the same time as they are out of phase with each other, that is unless you want the out of phase sound of a Strat with its 3 blade switch in the middle position all the time! This is one of th...

sluckey wrote:I would leave the NFB alone. Connect the two preamp outputs together thru two 220K mixing resistors and feed that into one PI input (just like Fender does).

So would those just need to be in series with each preamps coupling cap?

Thanks Phil.

Yeah, I'm trusting my software more than chrome.

So my question then is - do I just remove the 100r to ground and replace the the 10k with a 100k and go to my 4ohm speaker? Or do I just take the 10k to ground?

Hello All. I recently was given an old Silverface bassman 100 and figured it to be the perfect starting point for me to start modding an amp. I build guitars and pedals regularly and had been fighting the urge to git into an amp as long as I could, but the fender was too much to resist. So I started...

Very nice.