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Author Topic: Solid State version of a VOX AC-30 Guitar Amp  (Read 2507 times)

J M Fahey

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Re: Solid State version of a VOX AC-30 Guitar Amp
« Reply #15 on: January 26, 2017, 04:02:30 PM »











hope you can see them; if not I´ll try something else :)

joecool85

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Re: Solid State version of a VOX AC-30 Guitar Amp
« Reply #16 on: January 26, 2017, 04:21:00 PM »
Sorry, not loading here.

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Life is what you make it.
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blackcorvo

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Re: Solid State version of a VOX AC-30 Guitar Amp
« Reply #17 on: April 21, 2017, 01:57:57 PM »
Sorry, not loading here.

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Here, try this: http://imgur.com/a/1dfRh

GB

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Re: Solid State version of a VOX AC-30 Guitar Amp
« Reply #18 on: March 17, 2018, 10:48:07 AM »
Hi people... been absent for a while... won't bore you with the details.
I have (mostly) read the comments since my last post... some good thoughts in there. Thanks.
I have got a little more active I the last month or so and being doing some more development... aided by a supply of Toshiba FET's that I have been able to secure... 2SK117, 170, 369, 30's... etc.
This has been very helpful as they are:-
a) Graded at manufacture (BL, V, G, etc. versions) albeit that I still INDIVIDUALLY test and select them, and,
b) Especially made for audio applications
Importantly they have helped me refine the design process of biasing in "triode" mode as per the article I referred to some time back
(Google "Dimitri-Danyuk FET Triode Emulator")
I have developed an XL sheet making it easy to get all the components values I need by simply specifying Vgs, Idss, and the supply voltage.
BTW - There are also some "wider" considerations (not mentioned in the above) that need to be considered.
While I could go in to detail... this process seems to work... I have looked at numerous FFT spectrums on my scope... and, much more importantly, had the critical (positive) evaluation of several (good) musicians... unlike myself! :-(
I have also refined the output stage further with (again) a good supply of 2SK1058 and 2SK2221 (audio) power MOSFETs...
I could continue... but perhaps I'll wait for any feedback / questions about specific items before continuing...

Cheers
GJB

GB

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Re: Solid State version of a VOX AC-30 Guitar Amp
« Reply #19 on: March 17, 2018, 10:53:22 AM »
Hi... the Schematic posted above is not the latest design... gotta keep some secrets! :-)
But shows the general layout... and is (obviously) the preamp only.
GB

GB

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Re: Solid State version of a VOX AC-30 Guitar Amp
« Reply #20 on: April 27, 2018, 12:40:32 AM »
Hi guys... been of the grid for a bit... but there have been some developments.
Most notably I have "sold" (albeit only covering component costs) a couple of units and the feedback (forgive the pun) has been very encouraging.
One customer is a pro muso and also a guitar teacher - so quite critical of sound.
To address a couple of the point raised by others:-
1) The gate clipping of FETs will be different - and hard to accurately duplicate. It is what it is.
2) Nonetheless the FETs (PROPERLY set up) can do a good job of emulating a triode (12AX7). I have tested this using a DSO with FFT analysis.
3) The schematic of the output stage which is posted in this thread is mine - but a simplified view. Actual ccts need a bit more added.
4) Re the 1+1:1 transformer. That is one option. They can be salvaged from old PA amps but difficult (impossible) to buy new ones off the shelf.
5) I have used PA Line transformers. These have been applied to valve guitar amps - mainly using a (high) 100 volt version of same. I have used a (low) 25 volt version which, approximately, has a 3+3:1 primary / secondary ratio. A long and detailed story for another day - but with correct MOSFETs, and setting up currents and voltages correctly they work! - including the saturation effects mentioned by Katopan and Bulldozed in this thread.

Bottom line... I am now thinking about rolling all of this accumulated knowledge in to a kit and/or publishing details.
Would be most interested in any comments / interest on this possibility.

Cheers,
GJB

PS - there seems to be two threads going on here. Search "GB" for the other.

HamSandwich

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Re: Solid State version of a VOX AC-30 Guitar Amp
« Reply #21 on: April 28, 2018, 02:32:16 AM »
I’d buy a kit/pcb, but id also be interested to see and learn from the schematic!

GB

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Re: Solid State version of a VOX AC-30 Guitar Amp
« Reply #22 on: April 28, 2018, 06:29:55 AM »
Hi HS... thanks for that! Just working on the updated version now. Will keep you posted.
Cheers,
GB

 

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