BAJA Marshall 1960A driven by tube amp simulation  [documentation]

Original effects with schematics, layouts and instructions, freely contributed by members or found in publications. Cannot be used for commercial purposes without the consent of the owners of the copyright.
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bajaman
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Post by bajaman »

Here's another circuit snippet for those who want an analog Marshall 1960A quad box loaded with G12M Celestion "Greenback" speakers driven by a high output impedance tube amplifier simulator.
The design was modeled after simplified impulse response curves for a Marshall 1960A cabinet driven from a solid state amplifier and impulse responses for the G12M Greenback speaker driven from a high output impedance tube amplifier.
On the schematic below the output of the tube amp driven section is the junction of C6 and R6 - C16 is the input coupling capacitor for the Marshall 1960A cabinet response simulator.
The first graph shows the frequency response of the Quad box driven from a typical low impedance flat transistor power amplifier.
The second graph shows the frequency response of the tube amplifier driven raw celestion G12M speaker (red line) and the combined response characteristic for a tube amp driven Marshall 1960A cabinet loaded with Celestion G12M Greenbacks (grey line).
enjoy :D
bajaman
Baja Celestion G12M Greenbacks in Marshall 1960A quad box driven from high impedance tube amplifier source schematic.jpg
Baja Celestion G12M Greenbacks in Marshall 1960A quad box driven from low impedance source.jpg
Baja Celestion G12M Greenbacks in Marshall 1960A quad box driven from high impedance tube amplifier source.jpg
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Post by bajaman »

Here is the first revision and the reason for it :wink: Hopefully it will be the last :wink:
I realised after i posted here that the tube amplifier driven response characteristic applied to a Celestion G12M Greenback in free space - NOT in an actual speaker cabinet :slap:
In free space the Greenback has a natural low end resonance around 75Hz - in the Marshall 1960A sealed cabinet, this resonance is typically raised to around 130Hz due to the enclosed volume of air in the cabinet - the impedance is also raised to a slight degree but this is not as important as the raised frequency when designing a suitable simulation filter.
So, I have modified the tube driven response characteristic to more accurately emulate this raised frequency of resonance - only involved changing two capacitor values in the schematic (C4 and C7)
These are reduced to 220n and 2.2n respectively - all other values remain the same.
enjoy :D
bajaman
Baja Celestion G12M Greenbacks in Marshall 1960A quad box driven from high impedance tube amplifier source schematic revision 1.jpg
Baja Celestion G12M Greenbacks in Marshall 1960A quad box driven from high impedance tube amplifier source revision 1.jpg
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Post by FuzzMonkey »

Thank you very much for your hard work and time spent on designing this. I'd love to see a version based on the Celestion Vintage 30. :thumbsup

Keep up the excellent work!

~ Fuzz.

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Post by bajaman »

I'd love to see a version based on the Celestion Vintage 30
I would suspect that it would not be that much different as a basic simulation in a Marshall 1960A box :wink:
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Post by FuzzMonkey »

bajaman wrote:
I'd love to see a version based on the Celestion Vintage 30
I would suspect that it would not be that much different as a basic simulation in a Marshall 1960A box :wink:
I'm guessing the odd parts value changes etc? But I look forward to trying this one out.

~ Fuzz.

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Post by bajaman »

I'm guessing the odd parts value changes etc? But I look forward to trying this one out.
I'm looking forward to hearing your thoughts and observations when you have built it too! :wink:
cheers
bajaman
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Post by bajaman »

Change R19 from 18k to 27k and change C4 from 220n to 270n for a more Celestion Vintage 30 speaker type response characteristic (resonance slightly lower in frequency) :wink:
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Post by J0K3RX »

Waiting... rcustoms where are you? :twisted: I need to try this! I love the sound of greenbacks!

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Post by FuzzMonkey »

bajaman wrote:Change R19 from 18k to 27k and change C4 from 220n to 270n for a more Celestion Vintage 30 speaker type response characteristic (resonance slightly lower in frequency) :wink:
:applause:

Many thanks. Picked up the few bits needed to breadboard this up today so I should up and running in the next few days. Fingers crossed.

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Post by atreidesheir »

This is the curve as I see it for ReaEQ, for mixing or playing in the box. If you have not tried Reaper's vst set, it is awesome and free, and that makes it more awesome. They are all excellent tools for anyone recording music, and if you have not tried Reaper and you record music, its demo is generous and it is $60 for a lifetime license. But you can download the effects set for free to use in any daw.

Image
Here are the specifics.

----------------------frequency ----------------gain ------------------bandwidth (octave)
band 1(high pass) -------134.3--------------------+7.00 --------------------------------------0.08

band 2 ---------------128. -----------------------+ 6.6 --- ----------------------------------- 4.00

band 3 -----------------402.6 --------------------+5.7------------------------------------------4.00

band 4 ------------------466.5 ------------------(-)14.4 -------------------------------------- 3.78

band 5 -----------------4476.6----------------------+7.2 ----------------------------------------2.49

band 6 ---------------16600 --------------------(-)3.9 --------------------------------------- 2.57

band 7 ----------------13809.9 ------------------(-)29.5 ---------------------------------------0.65
High Shelf
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Post by rcustoms »

Something like this?
celestion machine enclosure.pdf
(21.56 KiB) Downloaded 371 times
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Post by FuzzMonkey »

rcustoms wrote:Something like this?
celestion machine enclosure.pdf
:applause:

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Post by rcustoms »

another puzzle solved
enjoy
CELEST MACH marshall enclosure.jpg
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Post by FuzzMonkey »

A quick question; is it possible to use this at the tail end of a overdrive circuit to simulate the a Greenback loaded 4x12 or am I barking up the wrong tree on this one? :?

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Post by bajaman »

sorry Rafael - you were too quick for me. :lol:
It seemed a shame to have one half op amp doing nothing when it could easily provide a nice stable low impedance bias reference.
It also allows the use of larger biasing resistors which further reduces the current draw :wink:
This circuit can either be realised with three dual op amps or one quad and one dual.
many thanks for Rafael's excellent PCB layout - very much appreciated :thumbsup
cheers
bajaman
Baja Celestion G12M Greenbacks or Vintage 30s in Marshall 1960A quad box driven from high impedance tube amplifier source.jpg
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Post by bajaman »

A quick question; is it possible to use this at the tail end of a overdrive circuit to simulate the a Greenback loaded 4x12 or am I barking up the wrong tree on this one?
a perfectly good question and yes it can be, BUT the simulator does not include preamplifier and tone control shaping of an actual tube amplifier, merely the interaction of the tube output stage and speaker cabinet responses. :wink:
Please feel free to share your thoughts here when and if you decide to build it :thumbsup
cheers
bajaman
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Post by rcustoms »

bajaman wrote:
A quick question; is it possible to use this at the tail end of a overdrive circuit to simulate the a Greenback loaded 4x12 or am I barking up the wrong tree on this one?
a perfectly good question and yes it can be, BUT the simulator does not include preamplifier and tone control shaping of an actual tube amplifier, merely the interaction of the tube output stage and speaker cabinet responses. :wink:
Please feel free to share your thoughts here when and if you decide to build it :thumbsup
cheers
bajaman
hi steve nice work ,the pcb based on your design is almost ready.
another question ,if we put your cab emulator between a tube pre amp and solid stage power amp ,can simulate the cabin responce?
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Post by The G »

bajaman wrote:
A quick question; is it possible to use this at the tail end of a overdrive circuit to simulate the a Greenback loaded 4x12 or am I barking up the wrong tree on this one?
a perfectly good question and yes it can be, BUT the simulator does not include preamplifier and tone control shaping of an actual tube amplifier, merely the interaction of the tube output stage and speaker cabinet responses. :wink:
Please feel free to share your thoughts here when and if you decide to build it :thumbsup
cheers
bajaman
As I see it, the perfect place for this would be just before a solid-state power amp. My actual test power amp is TDA7294 based and it has a stripped down Boss GE-7 just before the power amp. My initial idea was to be able to dial in a nice-to-my-ears tone from a Hi-Fi loudspeaker. I realize now that the equalization curve matches somewhat the one of Baja's filter. I'm building a practice amp for a friend and I'll compare Baja's filter with the stripped down GE-7. Seeing the way my things progress, though, it may take a while.

I think a good way to use Baja's filter is: amp simulator > cabsim > Baja's filter > solid-state power amp.

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Post by rcustoms »

ggedamed wrote:
bajaman wrote:
A quick question; is it possible to use this at the tail end of a overdrive circuit to simulate the a Greenback loaded 4x12 or am I barking up the wrong tree on this one?
a perfectly good question and yes it can be, BUT the simulator does not include preamplifier and tone control shaping of an actual tube amplifier, merely the interaction of the tube output stage and speaker cabinet responses. :wink:
Please feel free to share your thoughts here when and if you decide to build it :thumbsup
cheers
bajaman
As I see it, the perfect place for this would be just before a solid-state power amp. My actual test power amp is TDA7294 based and it has a stripped down Boss GE-7 just before the power amp. My initial idea was to be able to dial in a nice-to-my-ears tone from a Hi-Fi loudspeaker. I realize now that the equalization curve matches somewhat the one of Baja's filter. I'm building a practice amp for a friend and I'll compare Baja's filter with the stripped down GE-7. Seeing the way my things progress, though, it may take a while.

I think a good way to use Baja's filter is: amp simulator > cabsim > Baja's filter > solid-state power amp.
hi ggedamed ,i think that in this case,the cabsim and baja filter are only one thing? right steve?
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Post by rcustoms »

REV.1
Please extra eyes.
CELEST MACH marshall enclosure REV.1.jpg
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