6p6s power amp

[Tony]

Decided I'd get started on something new now that I've almost finished the documentation for the previous project.

Based around the ax84 push pull power amp. I'll tweak the values as I go as I think this will have too much low end as it is.

Going to use 6p6s valves (6v6 Russian equivalent)

Got the basic layout done but I'm going to be adding more features as I go such as low end shape & feel toggles and a vintage /modern mode.

Should push about 20w or 30-35w with 6l6 hoping to cram it into a 1u rack

[Adam]

Very cool!

[Mike]

I actually love 6V6s, very cool.

[Alan]

6V6's are pretty slick! This should be great.

[Tony]

Boards arrived today. Can't wait to get on with this.

Decided to try the whole balanced PI thing from the hifi world. If it sounds like crap it's literally just changing one resistor from 100k to 82k.

Decided on the presence I'm going to have 3 way toggle to go from jtm45/plexi/jcm800

And on the depth have what I hope will be different tightness/feel options and probably a nfb defeat option.

Marker for scale.

[Überschall]

Nice!!!

[Mike]

I look forward to hearing the results.

[beneharris]

That's awesome. Clean design.

Where else do you post this kind of stuff? I've got a couple of pedal forums I'm on, but would like to get into some more high end audio stuff like this.

[Tony]

That's awesome. Clean design.

Where else do you post this kind of stuff? I've got a couple of pedal forums I'm on, but would like to get into some more high end audio stuff like this.

I pretty much only post on here and sloclone ridiculous amount of knowledge on that forum but it's slowed right down the last year or two of you aren't talking about cloning various Friedman amps etc.

What I do design wise is pretty much work how a turret board would be laid out but without stuff going off at angles etc.

It's a good way to ensure you meet the spacing/creep age requirements for high voltages as it pretty much forces you to. 2.5mn between bare surfaces and 0.5mm between coated.

A good experiment /practice for you would be to take something like a jcm800 and grab the ceriatone layout or something and work through drawing that out and then change bits as needed.

If you grab easyeda (it's free) I can share some of my layouts with you to muck around with as well as my footprint library for common parts used in amps. The latter will save you a load of time as it can be a pain creating them.

Also if you want to read up on the why /how check out Merlin Blemcowes website. He also has good books around designing guitar preamps and poweramps.

http://www.valvewizard.co.uk/

[beneharris]

Thanks for the tips. I've got tons of experience with Eagle and getting pedal boards designed and layed out, etc.

But yeah, stuff like component spacing isn't really an issue at 9v, so that is the sort of stuff I need to learn. I've looked at buying those books before, might be time I do that.

[Tony]

Thanks for the tips. I've got tons of experience with Eagle and getting pedal boards designed and layed out, etc.

But yeah, stuff like component spacing isn't really an issue at 9v, so that is the sort of stuff I need to learn. I've looked at buying those books before, might be time I do that.

The preamp one has a design of his own for a 'super high gain preamp'.

That is apparently very good. I should get around to trying it.

He has a lot of useful tips for minimising noise like doing away with the tradition of a 68k input grid stopper that actually generates more hiss than the valve itself.

[Mahler]

A new challenger has appeared! Joining in on the fun on this one, it's gonna be sweet

[Tony]

A new challenger has appeared! Joining in on the fun on this one, it's gonna be sweet

You will probably finish this before I even order the rest of the parts to start. So feel free to take the stage.

[Tony]

Custom power transformer arrived today. Seems to be made from uranium or something as it weighs as just or ever more than most 50-100w ei core transformers I've used.

[7 Dying Trees]

all looks very nice cant wait to see if the balanced pi sound good

[Tony]

all looks very nice cant wait to see if the balanced pi sound good

Easy enough to try in any amp. Just change the common 82k for 100k in the PI. Obviously you will need a gain matched valve too.

I aren't expecting the heavens to open and the gods of tone to shine upon me but if you don't try these things you never know!

The uberschall AFAIK by default has the symmetry pot set to balance the PI but that obviously goes out of the window as soon as someone changes the valve without adjusting it.

[Tony]

Some small updates on this.

I populated the board as the output transformer is on the way. My caps of choice were out of stock so I searched by footprint/value/voltage.

You would think this would work out fine. I ended up with these neat looking Rifa caps.



However after installing them i noticed it said 100n+220r on the top so i dug further into the datasheets and it turns out they are RC snubber caps and have a parallel 220ohm resistor in them which wouldn't really be ideal for the coupling caps so out they came and in went some JB poly caps that i got a great deal on. 50 for £5. Having used their polypropylene caps before in the krankish test build i'm confident of the quality. They do look way less cool though.



And for bonus points I finally got around to testing my effects loop boards.

[Tony]

The output transformer finally arrived.

Tiny but heavy! Going to be a tight squeeze getting it into 1u as its ended up slightly thicker than the datasheet claims.



Also because I can't be bothered making a separate topic for it. Finished testing the new Goliath Preamp pcb the other day. Excuse the abysmal playing and the guitar going out of tune.

[desertdweller]

The output transformer finally arrived.

Tiny but heavy! Going to be a tight squeeze getting it into 1u as its ended up slightly thicker than the datasheet claims.



Also because I can't be bothered making a separate topic for it. Finished testing the new Goliath Preamp pcb the other day. Excuse the abysmal playing and the guitar going out of tune.

That sounds AWESOME! I love it.

[Tony]

Right I finished wiring this in the most awkward way ever. Built it inside an old SLO chassis with two valves inside two out but it made me have to lay things out stupidly.

I don't think I'm going to fit this OT into a 1u enclosure at all the secondaries are stupidly stiff and come out at the top. Add that to the transformer being thicker than the datasheet claims and its going to end up having to go into 2u (at which point I should have done 50w!)

However it sounds fantastic. I need to do a bit of tweaking to the NFB as the presence and depth essentially function as on /off switches.

It's also ungodly loud. With the master on 0.1 (just tap the pot) it's louder than my SLO clone 50w on 2 was.

[Tony]

Done a little tweaking. Tried the modern presence setup that doesn't have a scratchy pot and it lost a fair bit of range and the ability to fully bypass at 0 so back to the traditional scratchy pots. Not a big deal and I'd rather have the whole range of the knob be useful rather than the first 30% or so.

Should hopefully get the bite /feel switches wired in tomorrow now that I've found my switches.

Impressed with it so far super clean and tight which is what I was aiming for and it sounds huge depending how you dial the presence /depth.

[Tony]

Installed the bite & feel/character toggles. They change the presence & depth arrangements.

Video is shit quality and i just ramble on but it gives you somewhat of an idea. Think i'll keep them so I can get on with preparing to transplant it into a rack chassis.

Bite & Feel Toggles - YouTube

[Tony]

Just done a little more tinkering. Tried the scale control from Merlin Blencowes book.

It works super well to drive the power amp a bit harder increasing sustain, breaking up the power section a bit and lowers the volume quite significantly.

At first I didn't like it as it seemed to neuter the presence /depth and voicing toggles but I just had to turn the master up a bit more.

Having it in a pot feels a bit redundant as there's only three spots where it's useful so I think I'll throw a couple on a toggle.

Been speaking with a friend who used to work at orange and found that's what he did for the bedroom/headroom toggle on the rocker line.

I'd post up a video but it's useless as my phone seems to normalise everything.

[Coop]

Just catching up on this thread. Everything about this is awesome. Sounds fanfuckingtastic!

[Tony]

Just catching up on this thread. Everything about this is awesome. Sounds fanfuckingtastic!

Thanks. It's taken a lot of tweaking but I finally think I'm happy with where it is. Just undecided on the scale control so I'm going to play with that for a few days and see how I feel before I start drilling holes in a rack chassis