It's (sort of) ALIVE!

[Dmoney]

Depends on the amp I guess. I guess its pretty invasive as you need to punch an extra octal socket or two in for the rectifier valves.

I could do something similar in this amp but I wanted to get kind of a modern sound while using a valve rectifier.
If I wanted to try a diode rectifier i guess i could try a weber copper cap, or at least carry one as a spare rectifier that isn't made of glass etc. I'm not sure if i'd have to rewire my amp to use of of those things though.

[hunter]

good thinking, but it has one already. I might be partially that the highs will come out more when it's cranked up a bit.
The controls are (left to right) Gain, Bass, Mid, Treble, MV, Pres, Res.

Increasing the presence at lower volumes is usually what I find I end up doing on amps similar to this. That high end missing from the speakers when they aren't being driven so much can be compensated for using that. To a degree. It's not what I'd call 'ideal' but for jamming at home who cares.

I'd like to get a little more crunch into it too. I need some more time to test it out. I already found the resonance control is scratchy. I know exactly why that is the case though and it's not a bad thing really.

I also need to draw out some correct schematics for what I have at this stage. eek!

You can always add a label to the pot like ZVEX, "Crackle Ok" :)

[Dmoney]

hahah! yes I could!

I just need to add a capacitor to fix that problem. but at the moment there are other tweaks to do first.
at some point I also want to try some other crazy things. plan plan plan.

Im already thinking about what to build next!

[viking]

:drink: Wow! Congrats !I hope it 'll sound as good as it looks  :headphones1: Well done !

i hope so too... though if it sounds good right away it'll be pretty lucky.
I might try some 6550 output valves in it. The bias circuit has a pretty big range so it should work in that respect.
i'll try and make a clip or something somehow

  Man,that would be GREAT !If you could make a vid or a clip,before & after all your tweaking etc..at every stage,that would be real interesting !But,i guess you have enough work to do already... :?

[Dmoney]

Tweaking this thing is tiring!

Resonance control is gone
presence control is gone.
replaced by something similar to a vox cut control.

Preamp is getting brighter.

debating whether to try changing the preamp to something like a sovtek mig.
I've never played that kind of preamp before. kind of like splawns and kranks too.

[hunter]

I think it's time for some clips!  8)

By the way, for that kind of design, if you could get schematics from Budda Superdrives, I would go for that, they are great amps!

[Dmoney]

I agree!

I've tried doing some quickly just now.
I've just done 1 that i'll upload to my soundcloud account.

Its not done very loud. and its only recorded on my macbooks built in mic.
you get the idea about the cleans, then a bit where you get the dynamic of soft picking into hard strumming when using a bit more gain, then a kind of compressed and then open distortions with the gain maxed out.

I tried to keep the level fairly constant by my mac starts to phase and compress and doing weird stuff in the heavier parts.
First really heavy distortion part has a slightly different feel to second one. the second (in the room at least) sounds more aggressive.

i think for all of this I had bass 3 oclock, mids 11 oclock, treble 12:30 oclock.
kind of where i'd usually run them if using a marshall.

so... gibson LPC with nailbombs
no boost or any pedal
3 12ax7's in the typical JCM800 config. (cathode follower driven tone stack)
EL34 powered, GZ34 rectified.

playing is terrible.
im also walking around while playing & fiddling with the amp... one thing you can hear is the strap creaking on my guitar! maybe i should changes the strap locks i use!

http://soundcloud.com/user8302510 - here you go!

[hunter]

Sounds great! Not sure it needs anything else? A good booster in front maybe?

[Dmoney]

its pretty close to being done i think now. I've chopped some stuff out and changed some values here and there.
I'd play it without a boost, but it would be cool to hear it with one. my friend is coming over to try it soon. he usually uses a old two channel dual rec, but he's been getting into boosted jcm800 tones, so it will be cool to see what he thinks of this...

what i need to do now, is get rid of some faint kid of blatty solid state sounding break up in the highs that happens with lower gain settings as the cleans break up. maybe it needs a grid stop or treble bleed/attenuation in there somewhere.
I also want to try running it on 6550's. I just want to work out what output power I should be expecting from it.

I need to order more parts since I have used some spares to get to this point. I'll get it correct and make it all neat again.

today i thought it had broken! it was making intermittent ruffling and popping sounds, but it turned out the V1 12AX7 had gone a bit bad. swapped it and all that noise went away.

[jpfamps]

The "blatty" break up is, in my experience, usually due to one stage getting clattered and hard clipping the signal, usually as a result of grid conduction.

You can often hear it when a note or chord decays, but at high gain settings it is usually obscured by the other stages distorting.

Can be a pain to track down, but it is usally cured by addition of grid stoppers and or paying attention to the gain structure of the amp.

Power can be measured with a suitable dummy load, a signal generator and a multimeter (preferably a true RMS one). This will allow you to measure maximu clipped output power, however a 'scope would be needed if you want to measure power output at the onset of clipping.

[Dmoney]

You can often hear it when a note or chord decays, but at high gain settings it is usually obscured by the other stages distorting.

Can be a pain to track down, but it is usally cured by addition of grid stoppers and or paying attention to the gain structure of the amp.

thats sounds like it. as a note decays you can hear it. the grid to the cathode follower and the grid to its driver have no grid stop.

Apart from that, I'm done.
I'll update the schematics tomorrow. I changed quite a lot.

[Dmoney]

right!

I think I'm even closer to finished!

I went away from the direction I was heading, back towards a more normal JCM800 circuit, but it went too fuzzy for me.
so I went back to my favourite point, disconnected some bypass caps and got back to a sound I liked.

Put a grid stop in on the 3rd stage driving the CF.

realised I had some high frequency oscillation at high volumes. so I went back and used some 500pf's across the first 2 plate resistors, and i remembered HTH's recommendation for a 10pf across the plate/cathode pin on the first 12AX7. I did all that, then got left with some fizzzzzzzz. So i increased the 47pf cap across the PI plates to 250pf.

Now it sounds fine. and that horrible noise is gone. (the one mentioned before) and no oscillation that i can hear! and my valves haven't spontaneous red-plated so I'm hoping there is no parasitic oscillation either...

waiting on some bits... then I'll tidy up the chassis.
woo!


I haven't been able to crank this sucker without using an attenuator yet though... so that might be a bad sign.