Majestic12
Well-known member
I wonder if anybody has ever tried to reconstruct the 670 schematic with transistors and opamps instead of tubes and transformers.....
Fairchild 670 Solid State Concept
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Hank Dussen
Well-known member
Something like this: http://www.anamodaudio.com/am670.html?
I'm thinking in sometime make one with original signal path but solid state sidechain...
The varimu response have to come frome a tube, the rest of the circuit could be solid state, (input and output transformers from varimu tube should be there to kill common mode thumb from compression...
JS
The varimu response have to come frome a tube, the rest of the circuit could be solid state, (input and output transformers from varimu tube should be there to kill common mode thumb from compression...
JS
bockaudio
Well-known member
I have done it with a SS sidechain. Everything else stock.
Didn't Anamod do fully SS version?
Didn't Anamod do fully SS version?
Andy Peters
Well-known member
bockaudio said:
Yes, the Anamod is solid state.
-a
So what do they use as SS vari-mu elements? FET's?Andy Peters said:
The anamod principle - as I understood it from talking to Greg Gualtieri a couple of years ago - is about analoguely simulating a digital simulation of the analogue - i.e. back-translating dsp-functions into analogue domain.
Which means that it's probably a standard VCA or multiplier (that is, if anamod principle applies here)
Their tape simulations are quite extraordinary..
Jakob E.
Which means that it's probably a standard VCA or multiplier (that is, if anamod principle applies here)
Their tape simulations are quite extraordinary..
Jakob E.
That's a smokescreen (with a capital B and a capital S). Emulating a piece of analog equipment in the digital domain involves convolution. It's impossibly complicated to do a convolution in analog. They use analog building blocks that they tweak to do a fac simile of other analog building blocks.gyraf said:
They might, but I would tend to think that an FET or a transconductance amp would have a natural charcteristic that's closer to a 6386. Just guessing...
To me, tape simulation is to recording what putting cards to the spokes of a bicycle is to motocycling. ;D
It may be a technical feat, but it has zero practical value to me. I've spent 25 years of my life fighting with the limitations of tape; I'm glad it's over.
;D Just had a coffee-through-the-nose-laughing experience here. Thanks.
living sounds
Well-known member
I was once suggested that mosfets could be used instead of tubes. From what (little) I understand the sidechain needs high currents for fast attack times, so these could provide that.
living sounds
Well-known member
http://milas.spb.ru/~kmg/tubeemulation_en.html
A SS PM670 would be great. 8)
A SS PM670 would be great. 8)
Take a look at the EAR 660 - a multi tube vari gm arrangement with solid state, high current sidechain.
Quite popular too.
Also the Fairman tube limiter part in their channel strip unit uses a solid state side chain, but the vari gm part has only a pair of tubes kind of like the prr 175 limiter here.
Pretty much the closest I've seen to what you are describing. There has been some discussion of this in the past here.
Some searching on vari mu or fairchild and related terms would turn up lots of useful info.
Cheers
Quite popular too.
Also the Fairman tube limiter part in their channel strip unit uses a solid state side chain, but the vari gm part has only a pair of tubes kind of like the prr 175 limiter here.
Pretty much the closest I've seen to what you are describing. There has been some discussion of this in the past here.
Some searching on vari mu or fairchild and related terms would turn up lots of useful info.
Cheers
Making a SS side-chain is probably relatively easy; after all, the VT side-chain of the 660 is inferior in almost every respect (frequency response, THD, output impedance) to a benign SS.
The difficult part is the variMu stage. An FET is probably the closest natural substitute; current, voltage and impedance scaling is not trivial, though. I reckon no currently produced FET has been designed for this application, like the 6386 had been.
The difficult part is the variMu stage. An FET is probably the closest natural substitute; current, voltage and impedance scaling is not trivial, though. I reckon no currently produced FET has been designed for this application, like the 6386 had been.
The essence here is the recreation of tube amplifier distortion. In the Peavey patent, they address the cumulative distortion resulting from cascading several stages. In the russian paper, they address the effects of grid current.living sounds said:
None of this is relevant to a variMu compressor, because there is only one stage of gain cell and it is never allowed to run in grid-current mode, not forgetting the fact it is driven by a very low impedance.
Interesting read, though.
Kingston
Well-known member
It's been my long term interest to implement a vari-mu compressor sidechain using some common chip amp. The way I see it, they should win a tube power amp in just about every spec and consume less than 1/10 of the watts. There should be no effect on sound since sidechain is only there to charge the time constant network. Or perhaps a positive effect from perfectly linear amplification.
Majestic12
Well-known member
Hm, sounds like an interesting project to me... but I don't really know where to start. Replacing the 8386 tubes with some sort of FET circuit seems to be quite complicated...
Andy Peters
Well-known member
abbey road d enfer said:
Greg and Dave wouldn't say that it's "analoguely simulating a digital simulation."
Basically, it's the same principle as an analog computer (which is what op-amps were first invented to implement). A continuous-time mathematical model of the device in question is developed, and this model is implemented entirely in analog electronics.
-a
ruairioflaherty
Well-known member
bockaudio said:
David,
Did you discover that the solid state side chain worked just as well? Or was it missing any imperfections that added to the sound or behavior of the original?
The solid state sidechain in the EAR certainly works brilliantly, tweaky units but wonderful sound.
Cheers,
Ruairi
We run solid-state sidechain in our vari-mu comps (G10, G20) - so does Fairman, Tubetec etc.
Works very well indeed.
Jakob E.
Works very well indeed.
Jakob E.
I built one successfully with a tube/transformer audio path and a sold state sidechain. Works very well, you just need a power amp driving the time constant network and I found out that the transformer in front of the tc network is also needed for a specific reason.
