Menu

Show posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Show posts Menu

Messages - stratitis

#1
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?
#2
What is the point or trick of those serialized/cascaded J-FETs (Q1, Q2)?



Can anybody name or explain this technology, please?
#3
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

#4
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
#5
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)
#6
Thank you!  :tu:
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...
#7
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)?
#8
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/
#9
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.
#10
Sorry, still found 5150 III schematics (Fender).  ;)
Which one did you refer to?
Did you build all 3 channels or just one?
#11
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?
#12
Unfortunately I could not find schematics of the 5150 III (=5153 ?).
All I found is the attached ones:
#13
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?
#14
Hi Katoda,
thanks for your explanation!
May we discuss at your 5150-III thread?
https://www.ssguitar.com/index.php?topic=3931.msg30925#msg30925
#15
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?