DIY Retro-176's "Interstage" + "Symmetry" mods

[Thee_Aldeen]

hey guys,

today i am working on figuring out Retro's take on the 176.  I stumbled upon: http://jbb.ru/176/ when i was looking for a clean layout for the redd47, just so happens my boss has been begging for me to build a vacuum tube limiter &/or compressor, running into jbb's build of the 176 had me doing Google searches to see others & i stumbled upon RETRO's take on it & discovering their nifty additions of the Asymmetry & Interstage mods. Asymmetry chooses whether the (+) peaks of the input fire the compressors sedition or the (-) or (both) summed together & the Interstage mod allows the user to add addition iron forcing the signal through a different chain into an interstage transformer.  (THIS IS WHAT I UNDERSTOOD FROM READING OTHER'S POSTS & BRIEFLY SCANNING A S.O.S. SOUND ON SOUND ARTICLE — I COULD BE WRONG OR MISSING DETAILS).

My question is how would i implement the Asymmetry option myself?
*If we have time we can go over how to implement the Interstage as well :")

Thanx fellow DIY'ers!

PS. job surely couldn't have made it easier!  Amazing work re-drawing the schematics to taste & the layouts look AMAZING -- beautifully easy on the eyes & all-around a great help -- THANK YOU KIND SIR! :"D 


jbb-176 schematic: http://jbb.ru/schematics/176-shem.htm
Retro-176 pic: http://lghttp.17114.nexcesscdn.net/808784/vking/media/catalog/product/r/e/retro_176_1.jpg

 

[abbey road d enfer]

My question is how would i implement the Asymmetry option myself?

You could start by pulling off C6 (negative peaks) or C7 (positive peaks) and judge if it's really worth it.

 

[Thee_Aldeen]

My question is how would i implement the Asymmetry option myself?

You could start by pulling off C6 (negative peaks) or C7 (positive peaks) and judge if it's really worth it.

im guessing this would be damn-hard to hear or tell the difference...i LOVE mods, but i like my mods to actually be noticeable, i do mods fora handful of reasons but my fav is being able to use the same preamp on either the same or different source, but being able to flip a switch and being able to receive a new colour-pallette of tones that can then be summed up and sit real nicely in the mix together (i.e. don't sound exactly thee same).

anyone wanna throw out some ideas for some new mods?  Sounds like for the Asymmetry mod all one needs to do is have C6+C7 on a DPTT, middle=both, left-C6, right C7 (or disconnects when throw, haven't figured out what gets same action.

 

[abbey road d enfer]

My question is how would i implement the Asymmetry option myself?

You could start by pulling off C6 (negative peaks) or C7 (positive peaks) and judge if it's really worth it.

im guessing this would be damn-hard to hear or tell the difference...

Many musical waveforms (violin, bass, guitar, oboe, trumpet...) are asymmetrical, so you would hear a noticeable difference, but nothing that wouldn't be corrected by adjusting the threshold.

 

[pH]

I've been wondering about the interstage switch on the Retro myself.

Looking at the CCD-LA1D limiter as a comparison:  http://gyraf.dk/schematics/CCA_LA1D_Limiter.gif

-they simply couple the stages with capacitors instead of a transformer as with the UA176. Is it really as simple as that?

Paul

 

[abbey road d enfer]

I've been wondering about the interstage switch on the Retro myself.

Looking at the CCD-LA1D limiter as a comparison:  http://gyraf.dk/schematics/CCA_LA1D_Limiter.gif

-they simply couple the stages with capacitors instead of a transformer as with the UA176. Is it really as simple as that?

Paul

Probably. Although there are possibilities to improve the transient behaviour even without a coupling transformer, by reducing the common-mode gain of the second stage, which involves turning V2 in an LTP by adding a resistor between junction R10/11 and ground.
There are three basic options there:
- CR coupling - with or without the sub-option of doctoring the CM gain
-transformer coupling, which offers the best thump rejection
- common-mode clamp inductor: that's a center-tap inductor, which provides CM rejection by cancelling thumps coming from each side in the magnetic core; this is a good second best in terms of thump rejection.
If I had to have a switch, I would make it between the first and the third options, because it would only take a DPDT. That's probably what they have done. Switching between CR coupling and xfmr coupling would take a 4PDT.
Now I wonder what's the point of having a switch that actually degrades performance. Seems to me like having disconnectable power-steering on a Corvette.
I can understand why, in the first place, a manufacturer would opt not putting the inductor (bulk, cost), but having it on board and switchable seems just plain weird to me. Just one more knob for the mktg dept, probably...