PRR Vari-mu

« **on:** June 05, 2004, 08:41:23 AM »

I have just found 2 transformers from OEP to 20?.
I was wondering if they where suitable for the PRR Vari-mu compressor.

Kent's Vari-mu page:
http://www.conditionedresponse.com/DIY/C5/index.html

moan or DIY :grin:

Mikkel Meyer

INFO:
Specifically designed for direct printed circuit board mounting on a 0.1 inch grid.

A foil screen is provided between the primary and secondary windings and the transformers
are rated at 100mW at 300 Hz and 1mW at 30 Hz (less than 1% T.H.D.)

« **Reply #1 on:** June 05, 2004, 08:46:24 AM »

They should work..

Use the 150-Ohms type as input transformer and the 600-ohms type as output transformer.

Connect both primary and secondary windings in series to acheive maximum inductance (to retain low-end)

Be sure to connect internal interwinding shield to 0V/gnd. This to ensure correct CMRR/output balance

Jakob E.

« **Reply #2 on:** June 05, 2004, 08:52:58 AM »

that is 2.4kΩ at the output if I put them in series.
isn't that too much?

The speed of reply is the same as in the old forum.
Superb!

« **Reply #3 on:** June 05, 2004, 09:06:57 AM »

No, 2K4 nominal impedance on the transformer is fine.

The actual output impedance is related to the source impedance - the tube driving the transformer, not the transformer itself (other than the ratio).

The ECC82's output impedance is in the region of 2K4 anyway - maybe you should wire the output transformer as 2:1, 2400:600R

« **Reply #4 on:** June 05, 2004, 07:49:03 PM »

Thanks!
The Link is already included in Kents page.

Has anybody else than Kent build one of these?
How is the sound?

« **Reply #5 on:** June 06, 2004, 06:07:23 AM »

Yes, maybe a simple 2m2 Log attenuator between the A/R circuit and the two 3k3 resistors. But it would be wise to have another hi-Z buffer here, not to disturb the release timing by introducing a shunt to gnd wia the ratio pot.

Jakob E.

« **Reply #6 on:** June 06, 2004, 07:34:22 AM »

Actually, you won't need all the components around that opamp buffer.

Go directly into the NON-inverting input. Mind you, TL074 is very high impedance, no problem here.

And then just connect input to output, in a standard 1x/non-inverting-buffer circuit. That is, unless you find that you need extra gain here - you might for high ratios. In that case use e.g. 100K feedback/10K from inv-in to gnd to get ~10x gain . No compensation caps needed at this high gain - it has a slewrate of something like two weeks.

Third, make the ratio pot lower resistance - for fast action you may need some drive current here. Say 10K or 2K2 (log).

Jakob E.

(EDITED)

« **Reply #7 on:** June 07, 2004, 06:58:19 PM »

> suitable for the PRR Vari-mu

Should be. A key goal of the design is NO fancy transformer specs.

> Be sure to connect internal interwinding shield to 0V/gnd. This to ensure correct CMRR/output balance

If you have one, do that. But it should work "OK" without such frills.

> that is 2.4k? at the output... isn't that too much?

No. The one transformer feeds grids (and the 6.6K balancing resistors), the other feeds the input of an op-amp. The transformers "see" a low source Z and a high load Z, so their exact nominal impedance isn't very important. (This is "wasteful" of audio signal power, but no big deal.)

> add a ratio pot/switch

It is low ratio and variable ratio. It isn't precise enough to have a "Ratio". If you don't need precision limiting, and have good ears, a "sloppy" limiter like this gives gentler less-obvious compression. You can squash peaks from less than 2:1 to over 4:1 depending how hard you drive it. If you want much less than 2:1, maybe you don't want a limiter at all. If you want more than 5:1, you want something a little more complicated than a plain rectifier and tube limiter. I think a "Ratio" control would just be confusing. Crank-up the source until you get enough squash, and don't think in terms of numbers.

« **Reply #8 on:** June 07, 2004, 07:44:07 PM »

I'd really lke to get the PCB's made and build one of these.

Haven't done it before....so far, I've got this:

http://music-club.rutgers.edu/headfonz/comp5/Comp5.html

then I'm thinking I'd need the exact dimensions that the boards should be

and send the info to something like http://www.pcbexpress.com/

is the more to it than that?

Please let me know. I want to learn the steps in doing this.

thanks,

ChrisA

« **Reply #9 on:** June 07, 2004, 08:15:56 PM »

Quote from: "ChrisA"

I'd really lke to get the PCB's made and build one of these.

Haven't done it before....so far, I've got this:

http://music-club.rutgers.edu/headfonz/comp5/Comp5.html

then I'm thinking I'd need the exact dimensions that the boards should be

and send the info to something like http://www.pcbexpress.com/

is the more to it than that?

Please let me know. I want to learn the steps in doing this.

thanks,

ChrisA

Sending a fab house a schematic and the form factor dimensions of a PCB won't do it, (unless you are hiring a PCB Designer from the fab house). You need the PCB layed out on a CAD tool, then send the output in the form of gerber files, a fab drawing and NC Drill files to the fab house in order for them to make you boards. For a one time project you would be better off etching one yourself, there are pointers to the Group DIY site with instruction on how to do that.
Kelley

« **Reply #10 on:** June 07, 2004, 08:50:31 PM »

hmmm...I don't think I have the time to get into all of that right now, but would really like to make one of these..

I guess my next questions would be then:

1- does anyone have the ability to make some PCBs for this that I could buy from them

or

2- does anyone have the gerber files, the fab drawing and NC Drill files that they would be willing to make available?

thanks,

Chris

« **Reply #11 on:** June 08, 2004, 07:00:12 AM »

Kent has made the layout already: http://www.conditionedresponse.com/DIY/C5/index.html
You can download a pdf file from his page.

« **Reply #12 on:** June 08, 2004, 11:20:22 AM »

I tried to make my layout WAY EASY for the beginner. Huge traces and lots of space. You can go to Radio Shack and get one of those etching kits and do it (I'll never hear the end of it now). Even if you're dead set against an etch there are few components so you could make it on perfboard without too much hassle.

cheers,
kent

« **Reply #13 on:** December 23, 2004, 10:21:47 AM »

is there a parts list for this? I can just figure it out but I thought i would ask first.. :green: actually all i really need are sizes, I believe that some R's need to be 1/2w or greater but it's not really specified..

« **Reply #14 on:** December 23, 2004, 01:26:01 PM »

ah nevermind, i figured it out the old fashioned way! :cool:

« **Reply #15 on:** December 23, 2004, 01:46:06 PM »

So, did you end up with a prts list that could help others looking to build one of those?

« **Reply #16 on:** December 23, 2004, 02:01:04 PM »

sure did, I ordered everything through digikey. i had some of the values already so it is missing a few values of resistors, but everything else is easy to find. I'll compile the list and post it. :thumb:

« **Reply #17 on:** December 23, 2004, 02:24:03 PM »

here's what i ordered. some values are a few % off since I desired metal film and some of the values weren't availiable. I also ordered some of the resistors a little larger than needed because they were either more availiable or cheaper, some I fudged and bought a little more expensive parts. All R's are metal film, caps should be 105deg, films are polypro.

transformer pc mount 237-1078-ND 16.22
3.3k 3.32KXBK-ND 0.10
1k 1.00KXBK-ND 0.10
2.21k 2.21KXBK-ND 0.10
50k 49.9KXBK-ND 0.10
22R 22.1XBK-ND 0.10
1k 2w 1.0KW-2-ND 0.168
16R 2w 16W-2-ND 0.168
1k 1w BC1.0KW-1CT-ND 0.16
22k 1w BC22KW-1CT-ND 0.16
100R pot 3306F-101-ND 0.57
1uf polypro cap BC2116-ND 1.26
1000uf 25v 493-1558-ND 0.81
5000uf 25v 493-1574-ND 2.22
100uf 250v 493-1419-ND 1.95
24v 1w zener 1N4749ADICT-ND 0.24
400v 4A bridge(2a wasn't availiable) KBL04-ND 2.07

total was about 50$ add a few more dollars for the resistors that I didn't order. I got tubes from the tube store for around 12$ each. going to get the RS trafos tonight and etch my board tommorrow. i have tube sockets and everything else already.

good luck! :thumb:

« **Reply #18 on:** December 23, 2004, 02:37:27 PM »

> some values are a few % off

I design like 20% resistors are standard (they used to be!). I don't think there is anything here that can't be 10% off from what I sketched. However I have not built it and nobody has really "perfected" it, so my advice would have been to build it with common (5% carbon film) resistors, thrash, tweek, and then rebuild with magic resistors.

« **Reply #19 on:** December 23, 2004, 04:02:28 PM »

oh there will be plenty of parts changing, thrashing and magic to be sure! I just wanted to explain why the parts i ordered were different than the schemo so that people would know beforehand so there is no confusion.

Subject / Started by	Replies	Last post
PRR Vari-mu bias supply voltage criticality? Started by fazeka The Lab	8 Replies 2462 Views	November 09, 2007, 05:10:30 AM by fazeka
PRR Vari-Mu help thread Started by MrZpliff « 1 2 3 » The Lab	46 Replies 13977 Views	November 03, 2020, 09:13:06 AM by bernatvm
PCC85 in PRR Vari-Mu Started by living sounds Drawing Board	8 Replies 2856 Views	October 30, 2010, 11:00:30 AM by living sounds
spaghetti bowl PRR Vari Mu!! Started by mac « 1 2 » Dynamic Processors	21 Replies 5142 Views	April 06, 2011, 11:50:42 PM by PRR

Related Topics