It's (sort of) ALIVE!

[Dmoney]

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...





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!

[viking]

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

[Dmoney]

: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

[Mr. Air]

I know absolutely nothing about amps, but really cool idea to build your own. I hope it turns out great.

[sgmypod]

mmm pretty, Frank is a real nice guy and very helpful too

[Andrew W]

Very impressed with that.  Great job.

[gordiji]

it looks like the mad inventors workshop! very well done, hope it sounds as good as it looks.

[shobet]

Looks tidy, will be interesting what it sounds like.

[hunter]

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!

[dave_mc]

sweet :D

[blue]

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?...

[Dmoney]

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.

[hunter]

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?

[Dmoney]

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!

[blue]

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