i just finished my AC4

[pietro_moog]

hi guys.
i finished my AC4 with tremolo, and this thing sounds great. i'm in love with it, i play it like all the time. the thing is this amp has much less output volume than my 5F2a.
and it doesn't break up. at max volume it bites a tad bit but it's really not like my tweed.
is this normal?
and it has electrical noise. a much higher noise floor than the tweed.
(but maybe that comes from my bad build-it's really messy inside with long wires.
i'm gonna rehouse it in the future)
is that normal too?
the tremolo is sweet, i only wish it has more depth.

[frankeg]

Can we get a look at the schematic you built from and some pics of your wiring?

[pietro_moog]

i'm sorry,i don't have a camera now. i used the schematics from the vox site.
i found out that my power voltage is low, so the low volume comes from that.
i used some shielded wire for the signal and the noise floor is lower now. in the future i'll rehouse it and do better wiring.
it's the break up thing that i don't get. isn't supposed to break?
what should i do?

thanks guys

[pietro_moog]

so, the schematics i used are these. on come from the the vox site and the other from somewhere on the web
my ac4 still doesn't saturate. i does some small crunch at 90% of gain
voltages are like the schematics ones, about 5v more.
[IMG]http://www.blueguitar.org/new/schem/vox/ac_4.gif
[/IMG]http://www.blueguitar.org/new/schem/vox/ac_4.jpg

[frankeg]

I'm NOT an AC4 expert but from the schematics you provided it looks like the grid input is wired as a voltage divider. Not sure why unless they were purposely limiting the input. You could rewire so that the 100k grid resistors follow the 1meg ground resistor. This was exactly how the first Epiphone Valve Jr's input was wired (as a voltage divider) and one of the main reasons people started modding it. BTW, I'd definitely clean up any lead dress issues and long wires. If you have noise now with lower gain, it will only get worse with more gain....Good luck

[pietro_moog]

you mean the resistors at the input? i built it as you told.
i don't know, i just think this amp was designed to be clean. maybe the ef86 doesn't have as much gain as a 12ax7..
it does crunch a tad at high volume but i was expecting more.. maybe i just need to push it with a booster.
i'm happy. i have a 5f2a that makes a beautiful overdrive, now a clean amp could be fun.
maybe i'll try to copy the ef86 implementation of the ac10

[frankeg]

The EF86 has plenty of gain and drive capability and I agree with you that the design your working from is limiting the tube (less drive). The EF86 "was" known to be very sensitive to circuit designs and vibration. I do mean the resistors at the input of your design. Look at schematics of most other amps and you'll see the difference I'm talking about. Specifically the 1meg to ground and 100k input grid resistors. If you are seeking more drive from your guitar you could rewire your input as I suggested above...

[Meddon]

Hi pietro_moog, did you get more drive from your AC4?
I'm curious since I've just finished an AC4 myself and find it to be good sounding but relatively clean (compared to anything tweedy anyway). I'd like to get more drive from the amp, but haven't started to mess with the circuit yet.

Also, are you happy with the tremolo in the amp? Mine is quite limited when it comes to speed, the tremolo speed only goes from meduim fast to very fast. Slow speeds aren't possible.

[pietro_moog]

hi.
yeah, i did some mods. this thing is awesome. however i decided to dismantle it and build a ac10 in the next future, since i have already a 5f2a.
yeah, the tremolo isn't capable of slow speeds but i think it's nice. for my ac10 i'll search something more articulate.
my amp is breaking up a bit now, i think i was designed to be a fairly clean amp (for some headroom) with tons of bass because of the small speaker.
look at these files:
4shared - My 4shared - shared folder - free file sharing and storage

i made a "voice" mod to the output cap using dc30 preamp schematics with this
Tube-Town Online-Store - Alpha Stufendrehschalter 2 * 6 xsw19
banzai seems to have it 2€ cheaper
it filters out some bass and add sparkle.
for a nice gain try to use ac10 values (except the depth pot and the output caps network)
mine it's still loud and clean, but breaks up at nice levels in a nice way

ac4 is really nice, i wish it has a depth pot and slower settings..

[pietro_moog]

take a look to some threads about the ef86 and how to prevent microphonics, that could be helpful

[pietro_moog]

i compared the vibrochamp tremolo and the ac4 one, they are the same.
if you want a more usable tremolo try to copy the fender one.
i didn't try yet, just saying

[Meddon]

Good idea, I'm gonna look into the Vibrochamp trem circuit and see if I can tweak the AC4s trem to be more usable.

[pietro_moog]

i found out that the ac4 tremolo is a crippled version of the 5e9a tremolux tremolo.
all you need is a 2M speed pot and a 250k depth wired in parallel to the 100k resistor.
take a look at that schematics.
i bet it's gonna sound veeery good.
i wish i have the money now to rebuild my ac4 with a proper cabinet..

[Meddon]

pietro_moog, I replaced the 5.6 Mohm resistor with 1 Mohm (like in most ef86 preamps) and was rewarded with much more gain. Now the amp breaks up nicely when turned up.