Cabsims... and even more cabsims

Stompboxes circuits published in magazines, books or on DIY electronics websites.
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caspercody
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Post by caspercody »

Thanks BMXGUITARSBMX.

Something like this:
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temol
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Post by temol »

caspercody wrote: Did your KMG V30 cab sim have a issue of being below unity volume? My build is slightly lower then unity volume, and I would love to get it up (volume that is). I tried increasing the voltage to 18vdc and 32vdc, but this had no improvements on volume.
Sorry, cannot help you with this. I've breadborded V30 cabsim, but I focused on the sound only, not the volume levels. There was a difference in the signal levels between the cabsims. But I only adjusted input level of the audio interface to compensate for this.
Also, when I breadboard the circiut, I usually do not use any bypass switch.

T.

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caspercody
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Post by caspercody »

Thanks Temol

In your opinion, which cab sim was the best sounding, or more cab like to you?

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temol
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Post by temol »

Heh.. tough question. I'd list three or four cabsims I liked most. LS14, Lart (the one from my second batch of cabsims, not the simple cabsim), 4x12 Celestion Vintage 30 (TrueVAL), I also like multicab speaker sim by DSM (because of possible adjustments).
Someone on the Russian forum mentioned about oscillation problems with Lart's cabsim (the one I have mentioned I like). I have not had any problems with the circuit on a breadboard. But now, when built on a pcb, it squeals sometimes, mainly when powered on.

T.

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Post by caspercody »

Thanks!!

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temol
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Post by temol »

I'm back with six new circuits.
Setup same as previously.

Let's go



http://www.jackrabbit.pl/foto/upload/20 ... e58fc6.jpg
20180423213211-04e58fc6.jpg
20180423213211-04e58fc6.jpg (35.23 KiB) Viewed 7490 times
sample #1 - no cabsim

sample #2 - LS10 by Lionsound.

http://www.jackrabbit.pl/foto/upload/20 ... 0d8e85.jpg
20180423182037-b10d8e85.jpg
sample #3 - 4x12 cabinet simulator by TrueVAL (ver 7.0.2012). One knob - Low boost.

http://www.jackrabbit.pl/foto/upload/20 ... db0abd.jpg
20180423182034-80db0abd.jpg

sample #4 and #5 - speakersim from MARcus NRG 2400 v3.0. Two graphs, one is from a "normal" cabsim, second graph - there is another filter (opamp) that cuts around 600kHz.

http://www.jackrabbit.pl/foto/upload/20 ... 6ec402.jpg
20180423182037-356ec402.jpg
sample #6 and #7 - BAJA CV30M1960A Speaker Simulator pedal. Quote from the author "speaker cabinet simulator based on the response characteristics of the Marshall 1960A quad box loaded with Celestion vintage 30 loudspeakers. In addition I have included the response characteristic of a typical tube output stage, output transformer reactive loading stage with the cabinet response - this can be switched in or out for comparison"

http://www.jackrabbit.pl/foto/upload/20 ... daafd3.jpg
20180423182035-e1daafd3.jpg
sample #8 and #9 - Blackstar HT5 Speaker emulated out (posted by J0K3RX). It's possible to switch between 1x12 and 4x12 cab.

http://www.jackrabbit.pl/foto/upload/20 ... d1b25c.jpg
20180423182036-edd1b25c.jpg
sample # 10, #11 and #12 - dr Caligari by TrueVAL. . Three knobs - Hi sweep, Low sweep, Damping. #10 - all knobs @ min, #11 all knobs @ max, #12 mixed positions. For dr Caligari I have recorded few more samples. You can hear how the sweep control works.



#1 - Hi sweep
#2 - Low sweep
#3 - Damping sweep
#4 - Low @ max, Damping sweep
#5 - Damping @ max, low sweep
#6 - Hi & Damping @ max, Low sweep

http://www.jackrabbit.pl/foto/upload/20 ... 567125.jpg
20180423182036-63567125.jpg
T.

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temol
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Post by temol »

Here's another cabsim - different version of dr Caligari, with 16 opamps. Slightly different frequency response.

Image

This is the only new cabsim I have now, so I took three previously tested cabsims, just for comparison.

Image



#1 - no cab
#2 to #7 - dr Caligari with different settings of Hi and Low sweep potentiometers.
#8 - 4x12 Celestion Vintage 30
#9 - LS14
#10 - Lart 2.

T.

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temol
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Post by temol »

Here's the updated frequency response for dr Caligari cabsim. It turned out that I had to rebuild the breadboard (problem with HF filters)

Image

T.

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J0K3RX
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Post by J0K3RX »

The Dr. Caligari sounds good to me, has a good range of EQ shaping possibilities that all sound usable.

Check out this link, has allot of very useful information and acoustic simulation tools like floor & wall reflection simulators, room simulator, speaker directivity simulators etc... Could be useful is adding options to these cab sims like on/off axis mic, open/closed back cab, cab size etc..
http://www.tonestack.net/index.html#

This link has some really interesting/good information also.
https://troygrady.com/2014/02/04/hail-t ... 2-cabinet/

For me I like a 4x12 cab loaded with 2 - Celestion V30 or G12M Greenbacks and 2 - G12H-75 Creambacks in a diagonal configuration.

I like 2x12 cab loaded with the same as above but with only one of each, obviously..

To my ears it's just a wider sound with allot of harmonic presence...

Maybe BAJA's Celestion Blue and his CV30M with a mix/blend pot.. :hmmm:

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temol
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Post by temol »

This time only four circuits, although much more samples.
Setup as usual.


Image

sample #1 - no cabsim

sample #2 - Marshall LXH. I have two schematics for this cabsim. One from Hexeguitar website, the other one - from original LXH website (website is down, but there is always Wayback Machine). Schematics differ slightly. Not sure which one is "correct". I've recorded only one version (Hexeguitar), although I attach two frequency response plots.

Image


sample #3 to #5 - dr Caligari 4x4 (16 opamps). I re-recorded this one because of the issues with previous layout. #3 - low & hi set to min, #4 - low & hi set to max and #5 - mixed settings, and backed off damping knob a little bit.

Image
Image


sample #6 to #13 - ADA Varicab. Three switches - two for the cab size and one for dark/bright. It supposedly emulates 2x10, 1x12, 2x12, 4x12 cabs.

Image
Image
Image
Image
Image


sample #14 - Hyperbolic cabinet simulator. This one has some issues with interfering delay lines. It's not easy to find setting of the "dimension" knobs that does not produce a whistle in the background

Image

Only four cabsims but loads of troubleshooting the breadboard layouts... very easy to make a mistake or a short circuit but not easy to spot it. Marshall - I've completly rebuilt the circuit three times, caligari - two times.
Here you can see two simulators. Upper half - dr Caligari, lower half - Marshall.
IMG_8864.JPG
T.

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george giblet
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Post by george giblet »

I stumbled on this cool old thread the other day. When the thread was running I never managed to find a schematic for the "MARcus NRG 2400 v3.0" sim temol used. Apparently there's two versions.

Does anyone have a link to the schematic?

Thanks!
by temol » 23 Apr 2018, 22:03
I'm back with six new circuits.
Setup same as previously.

Let's go

File on a Soundcloud.

sample #1 - no cabsim

sample #2 - LS10 by Lionsound.

sample #3 - 4x12 cabinet simulator by TrueVAL (ver 7.0.2012). One knob - Low boost.

sample #4 and #5 - speakersim from MARcus NRG 2400 v3.0. Two graphs, one is from a "normal" cabsim, second graph - there is another filter (opamp) that cuts around 600kHz.

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temol
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Intripped
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Post by Intripped »

Reposted here for future reference
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george giblet
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Post by george giblet »

Awesome guys, thanks a lot.

Having the sound samples in this thread is fantastic.

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temol
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Post by temol »

Some time ago I've build MARCus NGC2410 cabsim which is a NGC2400 with additional, third, gyrator notch fiter (around 560 Hz). It's just a copy of the first gyrator, but with 33n istead of 4n7. It's all 0805 smd, powered by 9V single supply, vref taken from a voltage divider (usual configuration). It starts to oscillate like mad on a power on, and it's this new gyrator squealing. I can stop the oscillation by touching non inverting input of the "new" opamp. (sometimes multiple times before it stops). I can restart the oscillation in the same way - just by touching the input or C/R connected directly to the opamp input. The oscillation frequency is around 510 Hz - according to the oscilloscope, and the amplitude is quite high - 7V p-p. Any ideas how to troubleshoot it? What might be the issue here? Poor pcb design? General circuit instabillity?

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Post by ppluis0 »

temol wrote: 12 Feb 2021, 17:20 What might be the issue here?
H temol,
What technology of op amps are you using ?
I had trouble sometimes with Jfet input operationals (TL0xx) and were corrected when replacing with bipolar ones (RC4558, NE5532, LM833 and the like)

Hope this help 8)

Cheers,
Jose

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temol
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Post by temol »

I've put TL074 and TL072 there. I'm not sure if I have any smd quad other than TL074.

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george giblet
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Post by george giblet »

The oscillation frequency is around 510 Hz - according to the oscilloscope, and the amplitude is quite high - 7V p-p. Any ideas how to troubleshoot it? What might be the issue here? Poor pcb design? General circuit instabillity?
The fact the oscillation occurs near the gyrator frequency points to a stability problem with the gyrator.

The problem is likely to be the high-Q resonant circuits combined with the large 470k gyrator resistors. The high impedance feed circuit
3k6 and 10k doesn't help but we need that.

You can try these mods, any one of the three. No guarantee but from why I can see they should help.

The aim of all mods is to improve the gain margin of the gyrator opamp on the third band to reduce the risk of oscillations.
--------------------------------------------------------------
MARCus NGC2410 - Band 3 mod
--------------------------------------------------------------
Mod 1: Reduce the 470k on the gyrator to 220k.
Then adjust 33n gyrator cap to keep the same frequency.

The reduction of the gyrator resistor helps stability.

Currently have gyrator inductance,
L = 33n * 510 * 470k = 7.910H

Want,
L = C * 510 * 220k = 7.910H

Need, C = 70.5nF
Use C= 68nF
--------------------------------------------------------------
or Mod 2: Combine the two 510 ohms into a single 1k at the gyrator.

The gyrator looks like an inductor in series with 510 ohm (the one one opamp).
Then we add another series 510 ohm resistor (the top one).

We can combine the two series resistances and move those to the gyrator,
then remove the top series resistor.

This should help stability.


Currently have gyrator inductance,
L = 33nF * 510 * 470k = 7.910H

Want to combine the two 510 ohm resistors into a 1k resistor
as part of the gyrator,

L = C * 1k * 470k = 7.910H

Need, C = 16.8nF
Use C = 15n in parallel with 1n8

Summary of changes is,
- short top 510ohm,
- replace the 510ohm the opamp with 1k
- replace the 33nF cap with 16.8nF = 15nF parallel with 1n8
--------------------------------------------------------------
or Mod 1 and Mod 2 combined

Do both ideas.


Currently have gyrator inductance,
L = 33nF * 510 * 470k = 7.910H

Want,
L = C * 1k * 220k = 7.910H

Need,
C = 36.0nF
Use C = 33n in parallel with 3n3

Tweak: use a 240k resistor so we don't need to parallel the caps,

Want,
L = C * 1k * 240k = 7.910H

Need,
C = 33n

(Could use 200k and 39nF as well).
--------------------------------------------------------------

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george giblet
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Post by george giblet »

I found a reference which said something along the lines that a circuit appeared to oscillate at the resonator frequency by in reality it was oscillating at a much higher frequency then that oscillation was going off and on at the resonator frequency. With this in mind a much less intrusive mod would be to put say a 1nF cap across the 10k to ground which follows the 3.6k resistor (after the first opamp).

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Post by temol »

george,

thank you for all this explanation.
I've just implemented the mods you've prosposed. Not 100% success but there's some progress.
1n across 10k does not change anything. With or without gyrator mods.
Changed 510R to 1k, replaced 470k with 249k. Now, the oscillation apperars on power-on and fades out after 2 or 3 seconds (most of the times :) ).
Maybe I should try the same mod for the next gyrator - lower the 470k value to 220k and increase 4n7 to 10n.
I have this circuit in lstpice now. From what I can see modification of he gyrator values takes around 1dB from the notch.

I took some screenshots from the oscilloscope FFT measurements.
DS1Z_QuickPrint2.png
DS1Z_QuickPrint3.png

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