Vox AC30 Top Boost clone finished

AC4, AC10, AC10 Twin, AC10 Reverb Twin, AC15, AC15 Twin, AC30 Twin, AC30 Super Twin, Top-Boost, Non-Top-Boost, AC50, AC100, 710, 760, 7120

Re: Vox AC30 Top Boost clone finished

Postby bobster on Wed May 24, 2017 10:11 pm

thats a fantastic job , well done i bet it sounds wonderful !
:thumbsup: :jam: :cheers:
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Re: Vox AC30 Top Boost clone finished

Postby pdf64 on Sat May 27, 2017 6:02 pm

autvox wrote:...At very high output you hear ah little bit of noise (same frequency as the input signal) out of the output transformer. At first i thougt it is a tube but it´s the OT. I think that´s normal at such a power level because the iron is in saturation and the windings also vibrate a bit...?!

Yes, it's perfectly normal at high signal levels for anything loose component in the OT EM circuit to vibrate in sympathy with the signal, as a result of imperfect potting. Nothing to be concerned about.
The distortion displayed on the scope is most likely due to the power tube control grids being driven positive (WRT the cathode) and clipping the signal from the LTP phase splitter, ie the standard point which defines max power output for regular AB1 amps.
If you've got a dual trace scope, you'll be able to see the 2 things happen is unison (ie g1 and output clipping), as signal level rises.

When used in the guitar bandwidth, I think that the OT in an AC30 is unlikely to saturate its magnetic circuit; I guess that it may have been specified for full power down to the standard 50 or 60 Hz.
That's not to say that it won't 'colour' the signal with low order harmonics, just that it won't crap out and hobble the power output, unless pushed hard <50Hz.

Assuming an 8 ohm load (and that your scope system isn't too far out of wack) it looks like your amp will manage 25 watts at the onset of clipping, which IME is standard vintage AC30s.
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Re: Vox AC30 Top Boost clone finished

Postby autvox on Thu Jun 01, 2017 10:02 pm

Many thanks! Yes the amp sounds very nice. :D

I´m glad that i don´t have to worry about it. It took a while that i really understood, technically, what´s behind your post. Nice to learn something new! :)
The picture of the scope isn´t very good but i measured the voltage across the load resistor (16ohm) at the largest sine wave (about 400Hz) i could get without clipping and it was 20,4VAC (nearly the same in every channel). So if i´m right i get exactly 26Watt without clipping, which is just right. Actually the scope shows the same voltage but the system is not really precise and very old. I usually only use it to see when the signal starts clipping and if everything is symmetrical and looks fine. You can also see the vibrato/tremolo work and check all the functions of the amp. Only after all that is checked i plug it into the speaker cabinet. The risk of blowing them up is just too high.

About the OT: Yes i thougt the same. Somewhere i read that the OT of the old AC30s gets into saturation because the core is not as large as in other amps (in relation to the output wattage). But i think the influence of the saturation on the sound is not as much as some expect. Another thing to mention is the way the OT windings are made and in what sequence, which is typical for the woden transformer and its sound/popularity. All of the little details in the amp, the PT, OT, choke and not to forget the whole circuit and layout, make the sound of an ac30. So i think, if you want to get a true ac30 sound it has to be built in the same way.
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Re: Vox AC30 Top Boost clone finished

Postby The Pup on Mon Jun 05, 2017 3:36 am

Nice work.
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Re: Vox AC30 Top Boost clone finished

Postby Blind Lemon Chitlin on Mon Jun 05, 2017 2:54 pm

Wow !!! You have done a great job with this build !!!! :cheers:
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Re: Vox AC30 Top Boost clone finished

Postby autvox on Tue Jun 06, 2017 7:13 pm

Thanks!!! :cheers:
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Re: Vox AC30 Top Boost clone finished

Postby LuciMan on Tue Jun 27, 2017 10:45 am

@autovox:

Very nice job! I like the accuracy in your work & how it's done! :thumbsup:

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Vox (Clones): AC3 TB (ex-SuperTwin '81- Rose Morris); AC10; AC15; AC30/4; AC30/6 TB (rear); AC30/6 TB Reverb
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Re: Vox AC30 Top Boost clone finished

Postby gusfinley on Wed Jun 28, 2017 6:18 am

Next time, try a large conical set screw to flare your turrets, that is what I use for my homebuilt turret press. It should keep them from splitting.

Are you sure you aren't making the new Vox AC30 60th anniversary amps? (notice the tagstrips they are using)

Image

Right click and select "view image" or "show image" to show the whole thing.
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Re: Vox AC30 Top Boost clone finished

Postby DougH on Wed Aug 16, 2017 2:48 pm

I wish I could see the pictures. :(
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Re: Vox AC30 Top Boost clone finished

Postby autvox on Thu Sep 14, 2017 9:24 pm

So...after a long time....now the photos are updated...and you can see them again :urawk:
i didn´t expect that this would happen...

That´s a nice idea with the turrets, i didn´t really think of it jet. I will try it in the next build...

Wow these new amps are really nice... i have never seen pictures of them before...but it´s interesting that the result is nearly the same...
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Re: Vox AC30 Top Boost clone finished

Postby gusfinley on Sun Sep 17, 2017 2:29 am

autvox wrote:
Wow these new amps are really nice... i have never seen pictures of them before...


Yes, but are they $3,000USD (AC15) and $4,000 (AC30) nice?
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