Bare Knuckle Pickups Forum
Forum Ringside => Guitars, Amps and Effects => Topic started by: Dmoney on September 16, 2010, 01:25:53 AM
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I've been a touch quiet, as I've been working on a little project.
After doing some reading and selling my only low to lowish gain capable amp, I decided a build project was in order.
This is the result...
(http://img.photobucket.com/albums/v174/xtattybobx/IMAG0133-1.jpg?t=1284596115)
(http://img.photobucket.com/albums/v174/xtattybobx/IMAG0134-1.jpg?t=1284596136)
Its a JCM800 sort of thing. Not a clone. It's running using a GZ34 rectifier, EL34's, and JJ 12AX7's.
Transformers are Hammond.
Inside you can see evidence of star grounding, metal film resistors and orange drop caps. F&T filters.
External bias measurement and adjust.
should be about 50watts.
I switched this on for the first time about 30mins ago but couldn't krank it. Tomorrow this thing will get a good going over. I borrowed some ideas from books and other amps. So I need to see if its all fit together but it will probably need a good tweaking to get the best out of it.
I have to say a MASSIVE thanks to Frank at JPF amplification. He helped me a lot with parts and advice. Check out the amps he is building for the JPF range. Real nice!
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:drink: Wow! Congrats !I hope it 'll sound as good as it looks :headphones1: Well done !
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: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
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I know absolutely nothing about amps, but really cool idea to build your own. I hope it turns out great.
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mmm pretty, Frank is a real nice guy and very helpful too
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Very impressed with that. Great job.
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it looks like the mad inventors workshop! very well done, hope it sounds as good as it looks.
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Looks tidy, will be interesting what it sounds like.
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Respect man, I was thinking about getting into the whole modding thing, but I lacked the confidence and perseverance. I do have kind of an idea though on how much it takes to do something like that. And as it didn't explode on firing up, you must have done pretty well!
Good on you and keep it up, I wanna hear clips soon!
And don't worry if it don't sound perfect from scratch, usually it takes tweaks and tweaks to get things right, so if this would work right away, you'd be either VERY smart or VERY lucky :)
Again, big tap on the back!
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sweet :D
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certainly looks excellent, well done our fella :)
valve rectifier in a jcm800 is an interesting idea too, i like it. i wonder can a "duel rectifier" type of circuit be retro-fitted to an old Marshall?...
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certainly looks excellent, well done our fella :)
valve rectifier in a jcm800 is an interesting idea too, i like it. i wonder can a "duel rectifier" type of circuit be retro-fitted to an old Marshall?...
if by dual recto circuit you mean the diode/valve rectifier switch, then yes, it's pretty easy. I think Mesa has a patent on it even though they probably didn't come up with it. I debated doing it in this.
sgmypod, Frank is indeed a great guy!
To answers Hunters question, it does need some tweaks.
Positives are it is TOTALLY silent. Even with the gain right up, and playing at a moderate volume, there is no (or only an extremely low level of) gain hiss.
The standby switching and power switching is mega safe in this amp, and it works!
It works and it sounds ok. can do really clean and get pretty heavy when the gain is pushed right up, but it doesn't get too crazy. crazy enough... which I like...
It has a pretty big low end, and I need to balance that out by getting more highs into the output, or maybe cutting lows earlier in the preamp.
At the moment it looks neat, but give it a month or two of tweaking and it will probably look like a rats nest, but then I guess that kind of acceptable in 'boutique' amps. lolzzz
EDIT: you can see smoke in the top picture... thats not the amp, that was me using my helping-hands to burn incense sticks... it adds to the tone of the finished amp... obviously.
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It has a pretty big low end, and I need to balance that out by getting more highs into the output, or maybe cutting lows earlier in the preamp.
Maybe if you add a resonance control, that would help tame the low end?
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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!
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certainly looks excellent, well done our fella :)
valve rectifier in a jcm800 is an interesting idea too, i like it. i wonder can a "duel rectifier" type of circuit be retro-fitted to an old Marshall?...
if by dual recto circuit you mean the diode/valve rectifier switch, then yes, it's pretty easy. I think Mesa has a patent on it even though they probably didn't come up with it. I debated doing it in this.
yep, that's exactly what i meant. don't know if it would really be worth getting it done on an existing amp, but it's certainly an interesting thought
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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.
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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" :)
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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!
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: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... :?
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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.
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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!
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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!
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Sounds great! Not sure it needs anything else? A good booster in front maybe?
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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.
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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.
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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.
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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.