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Messages - stratitis

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


Gain for dual FET stage:

Gain for single FET stage:

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: )

"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] ( ).

That's what I've found:
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):

Power amplifier uPC1188H:

Q1,2,8,9,10,11 (amplifier stages):
2SK184, N channel J-FET

Q3,6,7,13,14, 19(?) (signal switches, tone stack output impedance converter):
2SK246, N channel J-FET

Q15,16 (tone stack driver):
2SK363, N channel J-FET

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...
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!  :tu:
Found another interesting pot in the 5150-III 50W tone stack of CH3:
You can read 1M 5%-A-taper or 1.5M A-taper...
Schematics and Layouts / What does 1M10A pot mean?
April 12, 2020, 01:06:46 PM
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...
Problem solved:
This link helped via wayback machine:
Direct link:
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?
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?