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AC30 sound. What should I build?

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11/13/1997 12:27 AM

AC30 sound. What should I build?

How do I get sound versatility from my guitar amp?

I use a Marshall JMP-1 with a 50W Class AB1 EL34 amp which I built. Sounds good but not the sort of sparklyness which you can obtain from an AC30 for example. However, the JMP-1 enables me to change the sound quickly via MIDI to crunchy sounds etc. so I want to keep that versatility.

If I build a ClassA AC30 type power amp will this bring back the sparkle to the clean sounds? And should I build it from 2 EL34s or 4 EL84s?

I would be glad of your sonic opinions.
Thanks
Colin

11/13/1997 4:42 AM

Hi Colin,

Is that AC30 sparkle you are hearing coming from the Top Boost channel ? If so you may not get it by connecting the JMP-1 to an AC30 output stage. The Top Boost pre-amp has a lot of bass cut and a "bright" cap across the vol pot. Try the JMP-1 into the AC30 Normal channel which has a flat frequency response. If you can get the sparkle with that set up then build the AC30 output stages.

Still working on those OTs I see. Express Transformers made me an AC30 OT for 25 pounds UK but I just use it as a paper weight. If I ever get any spare time I will try it out.

Dave

12/2/1997 9:36 AM
simon	Hi Dave Are Express Transformers a UK company? If so could you post their address as Ł25 UK for an AC30 OT sounds like a snip to me. Cheers Simon

12/2/1997 10:41 AM
Dave Harris	Simon, Express make power transformers. They don’t make or sell OTs. They made me a one off special for fun but I have not had time to try it out yet. The 25 pounds was probably just the material cost not a realistic selling price. Dave

11/18/1997 7:26 AM

Hi Colin,, Just thought I'd chime
in here as it had been so long
since I played through an AC30
class A amp for extended periods
I'd forgotten the nice things
4 el84 tubes in class A config
can do to a guitars tone. Sounds
like it might be the tone you
are looking for. I built a DIY
AC30 with 3 different preamps
and all of them sound great. So
I know for sure most of the
dynamics and responsiveness is
from the power section. Hard
to explain with words but the
tone is crystal clear, even
harmonic based, and very touch
sensitive. The way it should be.
When driven with any preamp
pedal and a Boss GX700 (I think)
I've tried it does wonderfull
things to an otherwise sterile
tone IMO. So its not just the
raunchy, smokey blues tones that
sound sooo good, but also in
clean mode a strat or a LP
can cut any gig. Period...
And since the harmonics are
even, when overdriven for hard
rock distorted tones, IMO there
is no better sounding crunch
machine...'nough said...
I havn't tried el34's in class
A yet but you might want to
check out a Matchless Chieftan
I think it is, but all I've
heard from said they prefer the
el84 class A tone to the el34
tone but your milage may vary...
Do it, you won't be sorry...
Steve K

11/19/1997 3:15 AM

OK Thanks.

I have just obtained a suitably sized box to build it in but I have been hanging on to decide what sort of amp to put in it.

You've convinced me to go ahead with the EL84 Class A design anyway. It's very interesting to see that you've tried it with different preamps, something which most people never do so it's usually hard to come to a conclusion on which part of the
circuit it making the difference.

OT design will now have to be changed for the CLassA design. Thats the first job.

Cheers

Colin

11/19/1997 3:46 AM
Steve Ahola	Colin: Once you get your Class A amp up and running, can you post your schematic somewhere? Other than the Vox schematics in the Pittman book, I really haven't seen many Class A circuits around. . Steve Ahola

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