Question for TedF - What compressor..

[clintrubber]

[quote author="TedF"]Haaah!
I managed to upload a sketch.... it's at:
http://groupdiy.twin-x.com/displayimage.php?album=lastup&cat=0&pos=0
(or if it's not exactly there, look in my 'TedF jottings' album.)
[/quote]
File gone ? Searched, but...

Regards,

Peter

 

[12afael]

I have it . but I have troubles with http://www.twin-x.com/groupdiy/?album=lastup&cat=0&pos=0 so I can´t upload it. if someone can do it for me, pm me and I will send the file.

 

[12afael]

Thanx to Jeffry now I can upload files.

http://twin-x.com/groupdiy/displayimage.php?pos=-284

I`m simuling this circuit on swcad ltspice but I can`t find a led/ldr module. someone have a led/ldr spice model?

 

[clintrubber]

[quote author="12afael"]Thanx to Jeffry now I can upload files.

http://twin-x.com/groupdiy/displayimage.php?pos=-284

I`m simuling this circuit on swcad ltspice but I can`t find a led/ldr module. someone have a led/ldr spice model?[/quote]
Thanks !

Hmm, also interesting discrete circuit. Q3 & Q4 do a CFP together but some more thinking required about the fun of Q1 & Q2 there... some current thingy arrangement but haven't seen it like that before with a CFP.

Bye,

Peter

 

[Sorr]

Anyone have a link to Protech?

 

[mfdu]

fascinating.

i've already built a pair of fabio's What comps, and now got a pair of "forssell" boards on their way from gustav, so i'll have both kinds of DIY opto up an running.

groovy.

chris.

 

[Guest]

[quote author="clintrubber"][quote author="12afael"]Thanx to Jeffry now I can upload files.

http://twin-x.com/groupdiy/displayimage.php?pos=-284

I`m simuling this circuit on swcad ltspice but I can`t find a led/ldr module. someone have a led/ldr spice model?[/quote]
Thanks !

Hmm, also interesting discrete circuit. Q3 & Q4 do a CFP together but some more thinking required about the fun of Q1 & Q2 there... some current thingy arrangement but haven't seen it like that before with a CFP.

Bye,

Peter[/quote]

22K resistor will give nearly the same results that the CCS Q1 & Q2, IMHO...

Usage of a differential amp is interesting, but what if total gain in the VCA chain happens to be less than 22/32 on some lever of input signal?

 

[clintrubber]

[quote author="Wavebourn"]22K resistor will give nearly the same results that the CCS Q1 & Q2, IMHO...[/quote]
The current source instead of the 'more usual' resistor at that spot will there be for a reason otherwise Ted wouldn't have spent the extra parts.
And I'm curious to the reason :wink:
Building, listening & testing for THD, then swapping & again listening & measuring will need to be done I figure.

Ted, what were your thoughts behind using the current source there ?

Regards,

Peter

 

[TedF]

Hi Peter,
I'm afraid the answer's lost in the mists of time..... I used that arrangement when building a low noise class A amp in an equaliser some time ago.... I needed more open-loop gain than I could get with just a resistor as a collector load, otherwise it would have been a noise/gain compromise.
I probably stuck the current source in on the compressor to give me the advantage of stable distortion performance; stability can be a problem with this sort of circuitry.... it's a sort of bridge arrangement with dissimilar arms, and just as the compression ratio can be magnified by the bridge, so can performance problems!
But I don't think anyone should be hung up on the detail of that amp; any decent amp will do the job, in that particular design I was keen to exploit the 2nd order distortion that's natural to the 2-transistor arrangement.
The original thinking in the design is the bridge arrangement, where simply, the compressed leg acts against a polarity reversed uncompressed leg.
:guinness: Ted

 

[clintrubber]

Thanks Ted for adding that :thumb:

OK, I was wondering if you had stumbled on a nice variation or
a special trick here for that CFP-circuit.
But it doesn't seem to hurt to add it either.

in that particular design I was keen to exploit the 2nd order distortion that's natural to the 2-transistor arrangement.

The DSelf-page on CFPs shows that this arrangement is surprisingly low-THD so I'm wondering whether we would be able to enjoy the nice nature of distortion here ?
http://www.dself.dsl.pipex.com/ampins/discrete/cfp.htm

Next time I need a CFP I will build it up in steps & measure THD. If we want to spend more parts we could also add another CCS 'below' the circuit and make the 2k DC-less, as for instance here:

Note that DSelf says this topology with gain can not as easily benefit from a CCS-stuff but the ESP-circuit shows a way to do it (using AC-coupling) - whether it really benefits is another thing.


But as you said, let's not overdo things here - it'll all sound fine :guinness:


Regards,

Peter