WOW! Very Impressive stuff here!!

[KMG]

Do you have any output readings from the transistors and from the output on the amp so I can check please?

Output of my preamp, CH1 - preamp out, CH2 - sim out

If you need to increase preamp output volume simply increase R46 value.

[Yazoo]

Thank you very much for taking the trouble to do this. I'll post how I get on.

[KMG]

Prototype head (JCM800 preamp + 5W PA):



Sample
Mix

[bancika]

Looks super clean, congrats!
The only remark is, I'm not a fan of mounting half a kilo worth of transformer directly to the PCB, it's asking for trouble.

[KMG]

I'm not a fan of mounting half a kilo worth of transformer directly to the PCB, it's asking for trouble.

These trafos has self-tapping screws mounting holes at bottom side.

Sample, same controls setting except master volume turned to MAX position
Mini Head Full Power

[KMG]

Additional samples
Mini head, gain at 2 hours, presence 2 hours, Depth & TS at middle positions
Mini head, gain at full position, Depth, presence & TS at middle positions

[Jdansti]

Awesome build and sound, KMG!

[stephanovitch]

Unbelievable KMG!

I work on a Mesa rectifier version of your LND150 stage to design preamp.
I have buy this little mosfet  5 years ago to emulate tube sound but I have never find enough time to achieve stage simulation.
I'm not an electronician ingeneer but I really like work to mod or repair or build stompboxes or amps!

Thanks for yours topics!

Have you made your output transformer yourself?

[KMG]

All the transformers for my fet power amplifiers (except micro PA) are made by my hands.
For 5W amp now I'm ordering transformers in a company specializing in the manufacture of transformers.
I gave them detailed specification of how to wind transformers.
One of these transformers used in prototype head.

[KMG]

The planned mini-head design
Budget version


Custom version


Another several samples
High input, gain at 3.5, TS, presence & depth at middle
High input, crunch
Low input, gain at 8, TS, presence & depth at middle
Low input
Low input + reverb in loop

[KMG]

Test of Prototype.

With SS & Tube preamps.

Because they have the same board connectors pinouts, swapping was very easy.
Controls settings are the same for different preamps while recording.
Fet_vs_Tube
Archive contains mix & only guitar tracks.
Legend:
SX_Y
X - track number
Y - preamp number
SX_YG - only guitar without mix.
Try to estimate who is who.

[KMG]

First "production" item of SS JCM800+5W

[rousejeremy]

Sounds great!

[KMG]

FET JCM800+5W video test by Konstantin Dolotov

http://www.youtube.com/watch?v=cB5XaE_vEJk

[KMG]

FET JCM800+5W (Clean, input Low) video test by Konstantin Dolotov, MD421 mic.

http://www.youtube.com/watch?v=1PUBfrtLzK0
Camera mic

http://www.youtube.com/watch?v=VTPZJFrwnPQ

[Yazoo]

Hi KMG I built the Engl pre-amp last year but I could never get the correct volume out of it, even after I used your suggestion and adjusted the output. One thing I was unsure about was the diodes D2, D4, D6 and D8. On the schematic, it says 4x1N60. I connected 4 1N60s in series in each of the 4 diode positions. Is that correct?

[KMG]

I connected 4 1N60s in series in each of the 4 diode positions. Is that correct?

Yes

[Pojo]

Hi KMG I built the Engl pre-amp last year but I could never get the correct volume out of it, even after I used your suggestion and adjusted the output. One thing I was unsure about was the diodes D2, D4, D6 and D8. On the schematic, it says 4x1N60. I connected 4 1N60s in series in each of the 4 diode positions. Is that correct?

Not sure if this is related to your issue, but there are 2 types of 1N60's out there. 1 is the germanium version, and the others are shottky with turn-on voltages of around .2V. I believe the germanium versions have a bit higher turn-on voltage.

The schematic is wayyy over my head so I have no idea if using one or the other would make a difference in output level, but might be worth considering.

[Yazoo]

Dear Pojo, thanks I'll check this out.  I can build them but I don't understand them.

[pappasmurfsharem]

Is the site down? Can't access it from my phone internet or my home network?