Layout Help

[mikeboone]

I built a mutt of an amp that sounds pretty darn good but nothing is ever good enough until I break something...

The amp is simply a Plexi-ish 50W 2xEL34 output and PI with the Volume/Tone controls from a typical 18W amp. It sounds good when cranked or with an OD pedal but kind of plain at tolerable volume levels.

Now the fun part. I really like my Orange Tiny Terror. I want to hang that preamp/gain stage in front instead of the plain Jane Volume/Tone control that is there now. I have attached what is believed to be the TT schematic and my hand drawn layout of the preamp/gain section that I think may represent what will work. I need some input/critical review.

I have the input jack done and everything from the PI to the out done already. I just need to know if anyone sees anything inherently wrong with what I have drawn.

Thanks...

[loudthud]

What you have done will probably work. (I give it 75% chance of success.) The most important thing you sort of glossed over is the ground. How all those ground symbols are connected together could cause problems like hum pickup, gain controls that let signal bleed through when all the way down, or worst case, oscillation. I would not put both cathode resistors next to each other but I can't say that the way you have done it absolutely will cause a problem. How far away is the "D" node filter cap? Where is it grounded? It would be better to locate it between the two gain stages.

[tubeswell]

Can't really see anything 'wrong', but if it were me I'd design the board so that the 470k and the 220k that are shown attached to the pots' input lugs on your layout sketch, are actually on the board instead (for mechanical stability and ease of interchanging parts). And what's more, you could lay the board out so that you had those grounds, (and the pot grounds) and the cathode resistor grounds for V1A and v1B all grounding at the same point as the ground return for the filter cap at 'D', (which means that the 'D' cap would be better off being on the board in the same locality) and all connecting to the input jack ground/sleeve contact.

(edit - oops I see loudthud has gazzumped me with a simu-post)

[mikeboone]

Thanks guys... I will put your ideas into practice in some bread board protos before commiting to a final build. Attached is a pic of the amp that was modified to make it what it is today. As pictured it is the normal channel of a blackface AB763-ish 40W circuit. I originally had a single cathode bypass RC shared for both triodes but that was a disaster. I added a cath bypass directly off the tube socket to a lug on th chassis (not pictured). The D cap is the one all the way to the right. I decoupled that stage based on reading from this forum and the amp is quiet. I am going to make another board like this with the new toys when i get all this figured out.

As for the grounding, I have a ground point next to the board and one where the filter cap and the input coax lead is grounded. I was just thinking of putting those resistors across the pots to the grounded pole to make the build a little easier.

[NorCalTuna]

+++ Tubeswell~ Have you read merlin's grounding scheme? It would be really easy to adapt ideas from that into your build!