Quote from: Loudthud on April 30, 2020, 11:03:59 PM
Not exactly a cascode circuit because the gates are connected together.

Completely different, I would say:



Yes, I wanted to know the name of the Roland Blues Cube gain stage circuit, if there is one, to google for it.

Quote from: Loudthud on April 30, 2020, 11:03:59 PM
A quick experiment on the curve tracer shows that it knocks Idss down to about 60% of the single JFET value. Gain is also lower. The curves look slightly more linear.

I've simulated the circuit in LTspice.
I used generic JFET model from LTspice. Input source: 100mVp, Ri=10kohm

Results:


Gain for dual FET stage:
270/160=1.7

Gain for single FET stage:
600/160=2.75

Dual FET output signal is slightly more distorted than single FET.

What's the benefit of dual FET?

What is the point or trick of those serialized/cascaded J-FETs (Q1, Q2)?



Can anybody name or explain this technology, please?

Obviously there are DSP (about 2014) and non-DSP versions (about 1996)

I'm interested in the non-DSP.
(user manual BC-30: https://static.roland.com/assets/media/pdf/BC-30_30-210_OM.pdf )

"This Vox-inspired special edition of Roland's analogue modelling amp is equally impressive at home, on stage or in the studio." [edit: this is a DSP version] ( https://www.soundonsound.com/reviews/roland-blues-cube-hot-british-el84-modified ).

That's what I've found:
https://www.vguitarforums.com/smf/index.php?topic=11865.0
There's a schematic of the Blues Cube 30 (no DSP, no reverb, no USB, no power control switch):


Better quality service manual (including schematics):
http://www.synfo.nl/servicemanuals/Roland/BC-30_BC-60_SERVICE_NOTES.pdf

Power amplifier uPC1188H:

http://www.electronica.ro/audio/uPC1188H.shtml
https://translate.google.com/translate?hl=de&sl=ru&tl=en&u=http%3A%2F%2Fradiostorage.net%2F3404-mikroskhema-upc1188h-usilitel-nizkoj-chastoty-18watt-pri-22v.html

Q1,2,8,9,10,11 (amplifier stages):
2SK184, N channel J-FET
https://alltransistors.com/pdfdatasheet_toshiba/2sk184.pdf

Q3,6,7,13,14, 19(?) (signal switches, tone stack output impedance converter):
2SK246, N channel J-FET
https://alltransistors.com/pdfdatasheet_toshiba/2sk246.pdf

Q15,16 (tone stack driver):
2SK363, N channel J-FET
https://alltransistors.com/pdfdatasheet_toshiba/2sk363.pdf

I want to analyze the schematics to understand the Roland "Tube Logic" technology.
I randomly found an used equipment offer of that amp (i never heard of it before) but the reviews I found were not too bad...
https://www.soundonsound.com/reviews/roland-blues-cube-hot-british-el84-modified
https://translate.google.de/translate?hl=de&tab=wT&sl=auto&tl=en&u=https%3A%2F%2Fwww.bonedo.de%2Fartikel%2Feinzelansicht%2Froland-blues-cube-hot-test.html

Can somebody help me finding "Roland Blues Cube Hot" schematic?

(PS: Sorry for the confusion and my extensive editing my postings. I did not know the "Hot" is a DSP modeling amp, I'm looking for the old all-analog - non-DSP version)

Thank you! 
Found another interesting pot in the 5150-III 50W tone stack of CH3:
1M5A.
You can read 1M 5%-A-taper or 1.5M A-taper...

What does 1M10A pot mean? There are other pots called 1M20A...
1.10 MOhms, analog taper (log)? And 1.20 MOhms, analog taper (log)?

Wanted: EVH 5150 III 100S Stealth Head schematics
Can anybody help?   
I found 5150 III 50 schematics but the 100W head has separate EQ and resonance control for each channel...
PS:
Problem solved:
This link helped via wayback machine:
https://music-electronics-forum.com/showthread.php?t=19518&page=2&p=440260&viewfull=1#post440260
Direct link:
http://web.archive.org/web/20161115042749/http://www.evhgear.com/support/

Thanks for your detailed reply.
Still a lot of work to do.  I try to extract a simplified schematic (one channel) as you did, to build a prototype for testing.

Sorry, still found 5150 III schematics (Fender). 
Which one did you refer to?
Did you build all 3 channels or just one?

Do you know if they sound different?
I thought they are nearly the same, maybe I'm wrong.
How did you "adjust" the single stages?

Unfortunately I could not find schematics of the 5150 III (=5153 ?).
All I found is the attached ones:

Quote from: Katoda on March 25, 2020, 04:55:18 PM
I used a TDA2030 power amp, I think I had the tube amp at the band rehersal place.

That's great, so I could use one of my cheap practice amps as final amp for testing.
To supply about +300V I could use 2 mains transformers back to back (for example: 230VAC -> 30VAC -> 30VAC -> 230VAC -> rectifier -> ~320VDC)
Could you post your schematics, please?

Hi Katoda,
thanks for your explanation!
May we discuss at your 5150-III thread?
https://www.ssguitar.com/index.php?topic=3931.msg30925#msg30925

Quote from: joecool85 on March 24, 2020, 12:56:47 PM
I see the biggest advantages of nutube vs low voltage regular tubes being: less weight, less space, less cost (sometimes anyway).  Also longer life span @ 30,000 hours of use!  Most regular tubes are rated at 5,000 - 10,000 hours from what I've read.  Mechanically nutubes should take a beating better as well (being dropped, banged around etc).
Sound wise, verdict is out, but many folks seem to feel that it cuts the mustard.

Maybe I should test one of the nutube amps or pedals.
But I really want to build an amp or preamp in the style KMG did.
Is KMG still active at this forum?