AC30 layout and mods for build
Hi,
I want to build an AC30 from scratch. I have a lot of previous experience building all types of pedals and even very complex guitar wiring. I can read schematics but prefer working off layouts when soldering as I get lost when reading a schematic! However, I am still in the process of learning electronics theory so there some things that I don’t understand.
What is a reliable source for an AC30 schematic and layout?
How would I go about integrating an active effects loop?
What are the most popular mods to this circuit?
22uf
Hi,
I want to build an AC30 from scratch. I have a lot of previous experience building all types of pedals and even very complex guitar wiring. I can read schematics but prefer working off layouts when soldering as I get lost when reading a schematic! However, I am still in the process of learning electronics theory so there some things that I don’t understand.
What is a reliable source for an AC30 schematic and layout?
How would I go about integrating an active effects loop?
What are the most popular mods to this circuit?
22uf
Last edited:
I'm not sure if it's the right one, but they have a 61 here:
Vox Vintage Circuit Diagrams
I also like the voxshowroom page:
The VOX Showroom - Vox AC30C2 Amplifier - A Look Under the Hood
There are some layouts around the internet, but I haven't built one yet.
Vox Vintage Circuit Diagrams
I also like the voxshowroom page:
The VOX Showroom - Vox AC30C2 Amplifier - A Look Under the Hood
There are some layouts around the internet, but I haven't built one yet.
But they are the schematics aren’t they. I’ve looked at thevoxac30guide.com and that book looks promising, but I don’t think that the layouts in this book will include an active fx loop.
I know, this is why I thought would be great to get a 60’s circuit and build an effects loop into it.
Sorry but waste of time and effort, in exchange of nothing.
The AC30 gets its chimey yet creamy distortion from power tubes overdrive, way too late for any effects loop of any kind.
To say it more precisely, the basic idea behind Loops is to put "clean" effects (phase, chorus, etc.) *after* distortion, so they are not smeared by it.
Impossible here (same as in a true Plexi or Twin or most any Classic amp) because because no matter where you put it, it will still be *PRE*-distortion.
2 options:
a) tried and true "add the effects in the mix" .... or drive an attenuator, go through effects and reamp.
b) use pedals up front, the way they (and AC30) were designed to.
Leave effects loops to amps who get all their distortion at the preamp (Mesa Muddy 😉 ) or .... SS ones (Valvestate and 1000 others).
Ah right yeah, I totally agree with that. Is there any way to run effects in between the amp output and the speaker, say through different pedal design? The thing is, is that I only like power amp clipping, but want delay and chorus etc to remain clean.
Make an AC-4 and take the output of that into your pedals.
An externally hosted image should be here but it was not working when we last tested it.
So you mean the output of the AC30 goes into the input of the ac4, then the out of the ac4 goes the input of the pedals, then the output of the pedals go into the speaker? How would that do anything?
No, if you want the sound of a Vox, use a little one (AC-4) and distort it, send the output to your pedals, then into whatever you are using now.
So if pedals can go in between amp and cab on the ac4, why can’t they go in between on the AC30? The reason I’m asking is because an ac4 wouldn’t be loud enough for gigging.
No, the pedal can not go between an amp and cab. You want the sound of output tub distorting but you want it to happen before your pedals. The way to get that is to overdrive the amp and then attenuate the signal so it is low enough to go into your pedals. Once through your pedals it has to be amplified again and then sent to your speakers. The reason I suggested going through the AC-4 is because it would make little sense lugging around a 30W amp if all you are going to do is throw away all that power and just use it as an effect box. In that case it makes more sense to use a smaller Vox amp up front. There is no way you can funnel 30W through a pedal, 1W for that matter. Can you drive a speaker with your pedals now? There are Class D amps that fit on a pedal board making that kind of power but I doubt that is what you had in mind.
Couldn't he drive a pentode between the preamp and the PI of the AC30, to have the clean AC30 as the power amp and tube distortion in the preamp?
If he is going to attenuate there will be no speaker distortion, maybe just the OT frequency cut-off. Wouldn't it be easier to have an Ef86 before the PI?
It would be interesting to measure the frequency response of the desired amp and achieve that by other means, for example a single pentode, or in case the PP sound is too characteristic to emulate with a single pentode use a PP configuration driving an interstage transformer.
In case you don't want the big amp anyway a class-D amp would make it pretty portable.
If he is going to attenuate there will be no speaker distortion, maybe just the OT frequency cut-off. Wouldn't it be easier to have an Ef86 before the PI?
It would be interesting to measure the frequency response of the desired amp and achieve that by other means, for example a single pentode, or in case the PP sound is too characteristic to emulate with a single pentode use a PP configuration driving an interstage transformer.
In case you don't want the big amp anyway a class-D amp would make it pretty portable.
Good Luck with your journey. Pay attention not only to the part value but also the material. Makes a huge difference.
I have made a 3W version of a 5E3 Deluxe with pentode output tubes. There is no reason it can not be used as an effects box and fed into another amp. Some things are possible, some are unpractical. The trick is to find a solution that is practical and sounds the way you want. It helps in doing this by knowing what you can achieve out of electronics.
Yes I suppose it is a bit much at the moment. Are there any books that you recommend to get me more up to scratch on these things?
i am the least reliable guy from this section, seldom ignored, but if you follow my advice, there will be great results:
AC-30 / el84 based:
1- don't use cathode bypass caps for either ecc83 in preamp and el84 in power
2- yet on cathodes... use 820r 2w metal film resistor for the early preamp cathodes, 1k for the later ones
3- phase inverter/ long tail pair: cathodes unbypassed aswell... use 890r 2w metal film resistor on both cathodes in parallel as aways... total: about 1.7k... for the second resistor that follows the cathode resistor, go for 33k 2w metal film
4- for power tubes / el84 go for 250r 10w wirewound resistors, remember: NO CATHODE BYPASS CAPS
5- lower the presence/ post phase inverter bright control cap from 4.7nf to 2.2nf
6- start with all 12ax7 plate resistors @ 82k. if after all you enjoy my idea and lust for more feel/dynamics, then the first triode plate RP goes for 68k
this mods will not make your amp sound better or worse, but they will enable your amplifier to show more of your playing dynamics and will unlock more nuances from your instrument's natural tone
AC-30 / el84 based:
1- don't use cathode bypass caps for either ecc83 in preamp and el84 in power
2- yet on cathodes... use 820r 2w metal film resistor for the early preamp cathodes, 1k for the later ones
3- phase inverter/ long tail pair: cathodes unbypassed aswell... use 890r 2w metal film resistor on both cathodes in parallel as aways... total: about 1.7k... for the second resistor that follows the cathode resistor, go for 33k 2w metal film
4- for power tubes / el84 go for 250r 10w wirewound resistors, remember: NO CATHODE BYPASS CAPS
5- lower the presence/ post phase inverter bright control cap from 4.7nf to 2.2nf
6- start with all 12ax7 plate resistors @ 82k. if after all you enjoy my idea and lust for more feel/dynamics, then the first triode plate RP goes for 68k
this mods will not make your amp sound better or worse, but they will enable your amplifier to show more of your playing dynamics and will unlock more nuances from your instrument's natural tone
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