THE ENGINEER'S THUMB... At last, a better compressor!  [documentation]

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teleK
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Post by teleK »

The rest of FSB history shall be merlin and mictester battling to see who can build the better compressor. Both saying things that almost make sense to me and seem reasonable. The winner will be the person who takes the colorsound supasustain and turns it into a rack unit with five thousand parts.
That being said, could we build the thing that kills the dynacomp? cause i am so down for that. And the whole "10 ms" thing should be dropped. You've both basically concurred it makes no difference in the scope (of guitars) that we are talking about. But yeah. I am loving this discussion :popcorn:

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Post by merlinb »

mictester wrote:If "Merlin" can be civil, I'll happily listen to him. If he has something that can contribute to my fund of knowledge, I'll gratefully accept it. I would hope that he has a similarly open-minded attitude, we can find some common ground, and make some advances in this rather bizarre mixture of electronics and art, theory and myth!
I think I have been very civil, considering. After all, it is not easy to be civil to someone who once attempted to steal one of my circuits and defame me in the process, and someone who seems to make grand claims about his own work without having shown any evidence of having built anything ever, one who promises things he never delivers, and who has a great deal to criticise about my work without even bothering to read its description!

Not cool "Chris". Not cool at all.

BTW, if you do try out my circuit, please post a photograph to prove you really have built it. It will be a first.

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mictester
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Post by mictester »

merlinb wrote: BTW, if you do try out my circuit, please post a photograph to prove you really have built it. It will be a first.
I will, but I'm a little too busy at the moment doing some work for real money. This is what's on the bench right now, being aligned for installation at a "Special Event" (RSL) radio station shortly:
50W_Stereo_Rig.png
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Post by tube-exorcist »

mictester wrote:
merlinb wrote: BTW, if you do try out my circuit, please post a photograph to prove you really have built it. It will be a first.
I will, but I'm a little too busy at the moment doing some work for real money. This is what's on the bench right now, being aligned for installation at a "Special Event" (RSL) radio station shortly:
The attachment 50W_Stereo_Rig.png is no longer available
Cool.... is this a Ramsey or a Veronica Kit ?

BTW, I can´t see a limiter inside - here is the schematic of a pirate-radio-feed-foward-limiter-with-ota-in-the-feedback-loop from 1982:
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Post by mictester »

tube-exorcist wrote: Cool.... is this a Ramsey or a Veronica Kit ?
Certainly not. The boards are designed by me and etched by a company in west London, the PICs are programmed by me, the exciter design is based on an application note for the Minicircuits POS150 VCO block and the rest is fairly standard RF design practice. The PSU is a module made by Coutant, the transformer comes from ILP, and the heatsinks are Redpoint. It incorporates a 16X oversampled stereo coder, an RDS coder, telemetry outputs (so that the temperatures and voltages can be remotely monitored) a VSWR monitor and auto cutout (in the event of a bad match it won't fry the output stage). The specifications are pretty good - the frequency stability is +/- 100 Hz, the harmonic outputs are never worse than -68 dB ref carrier and in-band spurs are better than -90 dB ref carrier. The unit is completely frequency agile, but you need a key to the programming keyswitch to change the settings. Power output is continuously adjustable from 5 Watts to 30 Watts (actually quite a bit more, but that's all I'll admit to)....
tube-exorcist wrote: BTW, I can´t see a limiter inside - here is the schematic of a pirate-radio-feed-foward-limiter from 1982:
I wonder where you found that - and where the little quotation on the diagram came from.... :roll:

There is a limiter, but it's external to the rig. It's a delay-line type and incorporates the pre-emphasis circuit as well. It's external to the main transmitter to prevent the risk of getting RF into the more sensitive parts of the audio processing. This is rather more sophisticated than some of the "pirate" gear I used to see!
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tube-exorcist
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Post by tube-exorcist »

And will you put these inside or outside ?
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Post by jstbrowsin »

whats all the bitchin about?? I mean REALLY cant we all just get along! :evil:

If its been done before. . . oh well. :roll:

Why don't you guys put your heads together and work on improving it rather than banging heads trying to 1 up each other sheeesh.

I for one am supportive of ANYONE who improves upon someone else's design. Well done Merlin :thumbsup
But I'm not supportive of people who wants to tear down someones efforts. Shame on you Mic :thumbsdown and to think I stuck up for you in that whole GlassBlower debacle! [smilie=a_whyohwhy.gif]

I thought this forum was to help each other not whats happening here. [smilie=puppydogeyes.gif]

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Post by Syder »

+1

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Post by HEAD »

Hmm, by all means this compressor doesn't work or sound good on a guitar i.m.h.o. I built it and tried it and didn't like. Everyone is free to make his own decision...

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Post by mictester »

tube-exorcist wrote:And will you put these inside or outside ?
Lovely!

I've got a TY5/125 here somewhere - now THAT'S a bottle!
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mictester
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Post by mictester »

HEAD wrote:Hmm, by all means this compressor doesn't work or sound good on a guitar i.m.h.o. I built it and tried it and didn't like. Everyone is free to make his own decision...

OK. I can see where Merlin's coming from - he's going in the right direction (sort of). However, the feedforward method has been widely tried and widely rejected because it's significantly less stable than the conventional approach. The VCA he's used is similar to the approach I used to use - it was done to overcome the sonic limitations of the OTA in my case. I put the variable gain amplifier in the negative feedback loop of a good quality op-amp, so that increasing its gain reduced the audio coming out of the op-amp. This mitigated the less than stellar performance of the 3080, 3094, 5517 or 13700. I always use the linearising diodes in the 13700 to further reduce the distortion....

I'm going back to other ways of doing gain reduction. One method I've used lately is to put a 4066 gate to short the audio path to ground, and switch the gate at ultrasonic frequency using a variable mark / space ratio oscillator. It's easy to get multiple attenuators (for stereo) to have exactly the same gain reduction, and the switching discontinuities are entirely removed by the lowpass filters after the switching element. I've just got to get a really accurate DC envelope to M/S input transfer function, and still manage to keep the current consumption down (people still insist on battery power). I'm using CMOS as far as possible. This looks like it really might be a better mousetrap!
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Post by tube-exorcist »

mictester wrote: One method I've used lately is to put a 4066 gate to short the audio path to ground, and switch the gate at ultrasonic frequency using a variable mark / space ratio oscillator.
You mean like in the Fostex 3070 Compressor/Limiter or in the BSS FDS-320 ?
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Post by mictester »

tube-exorcist wrote:
mictester wrote: One method I've used lately is to put a 4066 gate to short the audio path to ground, and switch the gate at ultrasonic frequency using a variable mark / space ratio oscillator.
You mean like in the Fostex 3070 Compressor/Limiter or in the BSS FDS-320 ?
I haven't seen the circuit of either of these - I'd be interested to see how they overcame the transfer function issues. My approach came out of a circuit sketch I found in a notebook for an experimental audio mixer that allowed cross-fading from one input to another using variable M / S switching of a pair of FETs. I thought of trying the idea with 4066s as the switching elements, and the range of control is excellent, but that conversion from envelope to squarewave ratio is a real problem for me.
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Post by juanro »

At risk of (totally and finally) derailing Merlin's post, I'd like to mention the MXR Envelope Filter (built succesfully) and some "found on the web" 4066-switching based phasers (couldn't made them to work realiably enough), as two more examples of variable duty cycle switching to get variable resistances. Also, if you can read spanish you can see an early attemp of mine: http://foro.cuartitodiyer.com/viewtopic ... t=digitrem for a 4066 based tremolo.


Now, back on compressing.

Juanro
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Post by mictester »

Juanro

Just looked at your "digitrem" - a great approach. Please start another thread here for that!

I'll have some time to work on compression after the weekend - I'm spending a week away, but will have laboratory facilities available to me.

Merlin

I WILL try your design out, and will give it a fair hearing. If I'm wrong (and I frequently am) then I'll give you all due complements for a good design. If, however, it overshoots and sounds as peculiar as I suspect it will, I'll report back and possibly suggest some improvements - I offer this in the spirit of collaborative development and in the hope that we can all get on in future!
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Post by bajaman »

................................................ sounds good to me :wink: :applause:
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Post by HEAD »

mictester wrote:Juanro

Just looked at your "digitrem" - a great approach. Please start another thread here for that!

I'll have some time to work on compression after the weekend - I'm spending a week away, but will have laboratory facilities available to me.

Merlin

I WILL try your design out, and will give it a fair hearing. If I'm wrong (and I frequently am) then I'll give you all due complements for a good design. If, however, it overshoots and sounds as peculiar as I suspect it will, I'll report back and possibly suggest some improvements - I offer this in the spirit of collaborative development and in the hope that we can all get on in future!
:thumbsup
Meanwhile I tried the elector tda7025 based compressor and I must say that I realy like it at the moment. It's also a fairly easy build - though the tda ic is a bit pricier.

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Post by uncleboko »

juanro wrote:At risk of (totally and finally) derailing Merlin's post, I'd like to mention the MXR Envelope Filter (built succesfully) and some "found on the web" 4066-switching based phasers (couldn't made them to work realiably enough), as two more examples of variable duty cycle switching to get variable resistances. Also, if you can read spanish you can see an early attemp of mine: http://foro.cuartitodiyer.com/viewtopic ... t=digitrem for a 4066 based tremolo.


Now, back on compressing.

Juanro
Cannot download this schematic - has Cristina nationalised circuit diagrams as well??

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Post by uncleboko »

uncleboko wrote:
juanro wrote:At risk of (totally and finally) derailing Merlin's post, I'd like to mention the MXR Envelope Filter (built succesfully) and some "found on the web" 4066-switching based phasers (couldn't made them to work realiably enough), as two more examples of variable duty cycle switching to get variable resistances. Also, if you can read spanish you can see an early attemp of mine: http://foro.cuartitodiyer.com/viewtopic ... t=digitrem for a 4066 based tremolo.


Now, back on compressing.

Juanro
Cannot download this schematic - has Cristina nationalised circuit diagrams as well??
Ah ha, took some dulce de leche and downlowded it - looks as good as "El Palacio de la Papa Frita" in Lavalle!!

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Post by merlinb »

HEAD wrote:...'cause you've posted it days before in another forum. :secret:
Ah. makes sense.
mictester wrote: I'm going back to other ways of doing gain reduction. One method I've used lately is to put a 4066 gate to short the audio path to ground, and switch the gate at ultrasonic frequency using a variable mark / space ratio oscillator.
Almost a nice idea, but unfortunately there's rather a lot of "prior art":
Image

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