Quote from: phatt on January 29, 2011, 02:25:19 AM

Just quitely, ar-hum.
That efx loop is about the fastest way to stuff up an other wise good system.
Never insert EFX loops at that point in the circuit as it will give Trouble down the track :trouble

I'd hate to see such good work go to waste. 8|
Phil.

I do not understand what is wrong with the effects loop?
Buffered output of a guitar-level (see the preamp section) is passed through a passive loop in the PA, which also has a  guitar-level sensitivity.

I'm not a good guitarist to record samples. Wait untill my friend will come to visit me.

For use with single or dual supply & additional possibility to use "-" or "+" of power supply as reference ground with single polarity supplying.
Construction allows you to add it to existing design simply by drilling hole for the output jack.

Frequency response

Dark blue - original С6 = 100 nF, red С6 = 47 nF, light blue С6 = 33 nF
Schematics

PCB (ready to tranfer)

Upper side assembly

Bottom side assembly

QuoteI can't tell by looking, but is this a master volume amp or straight forward plexi? If it isn't master volume, can it be easily modded to be? Also wondering if it has an effects loop?

Yes it`s mod of standard Plexi, added master volume after tone stack & passive (because preamp has low output impedance due to source follower at output) loop.

Preamp section:



Volume controls & tonestack has standard values like in original tube prototype MARSHALL 1959SLP.

For PA is used "Fet power amplifier with transformer output" 40W version.

Answer to question:

Quote from: crane on January 19, 2011, 04:56:22 PMI was also wondering if KMG would be so nice and post some more info about winding those nice output trafos for his FET power amps...

Number of turns in transformer windings on page "Fet power amplifier with transformer output" is given only for reference, because I think that you could not find exactly the same core (cross section & Bmax). So you need to calculate windings for your core parameters. Calculations are exactly the same as for the tube PP transformer. If you have calculator for tube PP transformer you can use it for calculation. Calculations based on primary coil impedance Ra-a (given on my page for each PA), desired lowest frequency (i calculate for 50Hz), core geometry & core material Bmax. Unfortunately i have articles about trnsformer calculations only in Russian.

QuoteLooks like at such high voltage these projects could cost close to real tube versions...

But the sound is also close to tube prototypes, especially while live playing. The main advantage of fet versions is their reliability & long time sound stability (no effect of emission loss).
During the "blind" tests guitarists usually say "I can`t tell what is the specific amplifier, but certainly, tube one".

Project files





Controls

Reamping samples.
Tone controls at preamp in middle position, "Presence" and "Depth" at PA also in middle position.
Digits after channel name represents "Gain" setting.
http://milas.spb.ru/~kmg/files/projects/Engl530/fet/reamp/5W4x12/
Recording path: E-MU Tracker Pre->Fet Engl->Fet PA 5W->Bull 412V+L(4x12)->Sennheiser e906->E-MU Tracker Pre
Reamping samples through Speaker simulator V30 preamp output.
Tone controls at preamp in middle position.
Digits after channel name represents "Gain" setting.
http://milas.spb.ru/~kmg/files/projects/Engl530/fet/reamp/SIM_V30/
Recording path:
For files without "R" in name:
E-MU Tracker Pre->Fet Engl->Speaker simulator V30->E-MU Tracker Pre
For files with "R" in name additionally through Digital reverb engine AL3201 with dry/wet mix 50/50:
E-MU Tracker Pre->Fet Engl->Speaker simulator V30->Digital reverb engine AL3201->E-MU Tracker Pre

Examples of two power supplies. Both has 12VAC input from wall adapter.
Simple transformer
http://milas.spb.ru/~kmg/files/projects/sharp/fet/Ps.pdf
DC/DC
http://milas.spb.ru/~kmg/files/projects/200vdcdc/200dcdcSch.pdf

Schematics (pdf)

Stage by stage frequency response in comparison with the original tube version (stage2 with different gain positions)

Ready to transfer PCB (pdf)

Upper side assembly (pdf)

Bottom side assembly (pdf)

Assembled board

Controls and input jacks (pdf)

Project page (with some samples)
http://milas.spb.ru/~kmg/jcm800fet_en.html

QuoteNot bad as a concept, but the waveforms he shows are SS type , not tube type, so the main object of getting so complex and expensive (just ask for a quotation on his output transformers) is not achieved.Just build a tried and true chip amp, from 5 to 150W; *or* a real tube one; again from 5W to 100W, and experiment with the preamp, stomp boxes, etc.
Good luck.

Several notes about differences between commonly used ss poweramps and tube ones.
Simple chip poweramps usually use very deep negative feedback. This leads to in first to very hard signal clipping & in second to very low PA output impedance.
Maybe first is not so important for modern sound styles which doesn`t use PA overdrive, but for vintage sound it maybe one of the first in creating sound. For example Marshall superlead plexi doesn`t have master volume, so PA begins to overdrive far from preamp overdrive.
Low output PA impedance lead to hard speaker dumping, that doesn`t allow cabinet to "breathe".
Look at frequency response of transformer output fet PA loaded on active load and cabinet (voltage on PA output).