prr varimu compressor

Just found this project, was looking at some of the threads...lots of back and forth on it.
Anything i should know right off or advice if i consider doing this project, such as...
link- do these mods. Use this layout ect...

ummm....The man's handle is "prr"...not "ppr" ;D

prr...my mistake.- fixed it.
Handle...i never thought of a user name as a handle much....guess i should have as much as i love those old burt reynolds movies!  8)

mrphotodude said:

Just found this project, was looking at some of the threads...lots of back and forth on it.
Anything i should know right off or advice if i consider doing this project, such as...

Click to expand...

..yes..try the inexpensive groundloop transformers from the autostore that PRR suggests before you go buy something much more expensive...PRR really knows his stuff and designed this one to not need fancy spec. transformers...I'm really happy with mine the way He designed it..no mods needed..

j

I don't think Radio shack offers the transformer anymore. It's more of a assembly...

Anyone found the same thing to be true...

> I don't think Radio shack offers the transformer anymore.

http://www.radioshack.com/product/index.jsp?productId=2062214
Ground Loop Isolator $16.99 Catalog #: 270-054
Online:  In stock
Available at most stores, find it near you.....

SEATTLE-THIRD  206-682-7980 FISCHER STUDIO BLDG 1523 3RD AVE SEATTLE, WA 98101
SEATTLE-MERCER  206-283-4502 115 WEST MERCER SEATTLE, WA 98119 
SEATTLE-CALIF  206-935-0900 4505 CALIFORNIA AVE SW SEATTLE, WA 98116
SEATTLE-UNIV  206-632-4720 4223 UNIVERSITY WAY NE SEATTLE, WA 98105
SEATTLE-UNIVERSITY VLGE  206-523-0534 UNIVERSITY VILLAGE 4610 25TH AVE NE SEATTLE, WA 98105
SEATTLE-MARKET  206-784-8986 2032 N W MARKET ST SEATTLE, WA 98107
SEATTLE WESTWOOD TOWN CTR  206-937-8040 WESTWOOD TOWN CTR 2600 SW BARTON STE B-11 SEATTLE, WA 98126
SEATTLE-RAINIER AVE  206-725-5000 3820 RAINIER AVE S STE F SEATTLE, WA 98118
BELLEVUE-BELL WAY  425-454-4949 100 SE BELLEVUE WAY BELLEVUE, WA 98004
SEATTLE-15TH AVE NW  206-706-0541 8701 15TH AVE NW SEATTLE, WA 98117

> It's more of a assembly...

You need a knife to slit the label, then it comes apart.

i wonder if i used a quadfilar transformer...since i dont need center taps on the primaries or secondaries.
i have some jt-123 dbx jensens laying around as well as some old military stock 600:600 transformers i thought about using.
Maybe i can use one side of one tranny to do one input, the other half to do the other input...and use another transformer to do the same thing on the output?
I could just use one tranny for each if that is better...just curious about the quadfilar transformers since they are two seperate primaries and secondaries correct?
I know i have plenty of power transformers lying about, i will probally use one for the tube b+ and another for the lower voltages(i think i have a trannie with 110 and 12vac ct secondaries as well).
I have a bunch of parts laying around that i can make work for the project...just wanted to get some insides first. I can burn a board and probally have this project together in two part day sessions(if i am not distracted  )
are the 6bq7's the way to go with these or 12au7's?

thank you for the replies so far.
i just finished my s800 and tweaked it slightly and now need a decent mastering limiter for some outboard mastering gear(to avoid using software constantly).
I am just a hobbyist so its all fun.

PRR said:

> I don't think Radio shack offers the transformer anymore.

http://www.radioshack.com/product/index.jsp?productId=2062214
Ground Loop Isolator $16.99 Catalog #: 270-054
Online:  In stock
Available at most stores, find it near you.....

SEATTLE-THIRD   206-682-7980 FISCHER STUDIO BLDG 1523 3RD AVE SEATTLE, WA 98101
SEATTLE-MERCER   206-283-4502 115 WEST MERCER SEATTLE, WA 98119   
SEATTLE-CALIF   206-935-0900 4505 CALIFORNIA AVE SW SEATTLE, WA 98116
SEATTLE-UNIV  206-632-4720 4223 UNIVERSITY WAY NE SEATTLE, WA 98105
SEATTLE-UNIVERSITY VLGE   206-523-0534 UNIVERSITY VILLAGE 4610 25TH AVE NE SEATTLE, WA 98105
SEATTLE-MARKET   206-784-8986 2032 N W MARKET ST SEATTLE, WA 98107
SEATTLE WESTWOOD TOWN CTR   206-937-8040 WESTWOOD TOWN CTR 2600 SW BARTON STE B-11 SEATTLE, WA 98126
SEATTLE-RAINIER AVE   206-725-5000 3820 RAINIER AVE S STE F SEATTLE, WA 98118
BELLEVUE-BELL WAY   425-454-4949 100 SE BELLEVUE WAY BELLEVUE, WA 98004
SEATTLE-15TH AVE NW   206-706-0541 8701 15TH AVE NW SEATTLE, WA 98117

> It's more of a assembly...

You need a knife to slit the label, then it comes apart.

Click to expand...

Thanks, PRR

I have a self etch version I got from the black market. I had looked at the Radioshack part, and figured there was a transformer in side, but didn't want to blow $18 on something to destroy and it's passive or not the same as it was in design..

i wonder if one of these in 600:600 is okay...
i actually have one lying about...maybe i will give it a test when i put a unit together.
http://elexp.com/cmp_5008.htm

I would check the specs on that cheapie.  One of them on the list is 0dB 300-400 Hz?  Maybe the supplier has more info, and you can't go wrong with the price.  Thanks for the link.
The RS isolator is the same board with two trannies inside, but they went with a smaller size a few years back.  Still has good freq. response for auto and hi-fi use.
This was sonically the same as the RS part, for less than 1/2 price: http://www.antonline.com/p_Raptor--GL15--Metra-Ground-Loop-_242892.htm.  I use these in smart classroom systems and they "sound great".
Mike

here is a q for ya PRR....
why only 100 b+?
Doesnt the lower B+ cause a tube to distort easier? Generally i see 200 or more before the plate resistors.

Also, a tl074 has a higher slew rate then say the mc33079, but the 33079 has a higher bandwidth and lower thd. Would that be better?

I know it is probally a pain that you put all this work into a design then people want to change it before trying it..
I am more interested in learning why you did such and such then changing it so much...plus seeing if i can get a good result on stuff i already have around.

mrphotodude said:

here is a q for ya PRR....
why only 100 b+?
Doesnt the lower B+ cause a tube to distort easier? Generally i see 200 or more before the plate resistors.

Also, a tl074 has a higher slew rate then say the mc33079, but the 33079 has a higher bandwidth and lower thd. Would that be better?

Click to expand...

I'm not PRR, but I think I can answer..

the relatively low B+...to put the mu-action in reach of an opamp driven sidechain.
distortion wont be a problem since the output is rectified and sent back to the grids, to reduce the gain..bigger signal=less gain, that's the whole idea, right?..

why TL074?...the sidechain gain is low and minimum attack time limited to 1mS (on my schematic at least, if I didnt mess up the math). ..unless you want significantly shorter attack, why spend more money than you have too, on a chip you dont listen to....I guess a chip with better drive capacity than TL074 could make a differance, but I don't think you'd ever need it..(if I remember correct from the datasheet, the TL07x series has a built in 128ohm resistor in series with its output..)

...I'm sure if I'm wrong, PRR will correct me..

johan

okay, i got my unit together and after tweaking the psu to get the right voltages and having only one side built for testing...
i have a bunch of different transformers and ratios lying about and no matter what i try...it seems the unit is lacking bass.
not quite a "missing a riaa preamp" type of sound...but definatly lacking. I have my recording card putting a signal into the varimu....and coming out into my HP4(monitor controller) and if i a/b between one speaker and the other(one side has the compressor in the chain, the other is from pc to hp4 to monitor).... it seems a tad weak and missing bass....

now, this unit should work fine like such yes?
i don't need a line driver on the output of it or any such business?

Hi, check out bluebirds mod thread... it's somewhere in here...
i'm still experimenting with mine, (although I've gone pretty far afield from the straight project. I'm pushing mine to be a lot more like a UA 175...) but yes the interstage transformer has an effect on the bass.  I'm liking a higher impedence up against the tubes... but than again I'm using different tubes as well.
Kelly

what ratios are you using for the transformers?
i have seen some of the bluebird info..
i have a small batch of 6bq7's lying about i was thinking about trying after i got this thing going..
was thinking about trying 10k to 600's...but am trying to get this thing working basic before i hack and mod...

Hi Photodude- I did use a 10k to 600 and that worked very well. 
I'm pretty much thinking that's going to be the final setup.
I added a 5k trimpot in place of the gainset resistor in the 5532 opamp just after the interstage transformer.  This allows me to push the feedback gain up or down a touch which helps to deal with the stepdown and any tube imbalances (beyond just attenuating it, which is what the 1k pots AFTER this opamp do)
This is going to be in my mastering chain and it's the furthest I've strayed from a tried and true design, I've been visiting it intermittantly for more than a year now. : Someone asked me the other day, what is that thing? are you ever going to be done with it. It's a bit embarrassing...
Kelly

what i came up with today was putting long leads with alligator clips so i can swap a bunch of trannies...
ended up finding a setup that i had a pair of for each channel that sounded very good and gain is only slightly higher on the output then then input...
some old 1:1 military transformers i ripped out of a communications set made by atlantic for the input....and for the interstage...4:1 that came out of a reel to reel, sony i think.
that setup sounded better then the better grade and namebrand stuff i have lying about.
have to do some more testing and tweaking....have a stash of 6bq7's to try out.

okay...
this thing is killing me! Please...i really need help here!
It passes audio fine, but its not compressing! Unless the compression is so subtle that cranking all the knobs any one way or the other is completely useless.
i used the schematic and etch trace found here:
http://www.diyfactory.com/projects/diy12au7comp/diy12au7comp.htm

I have a 1:1 input and interstage at the moment, all of my parts match the schematic..
only one side is built right now for testing and i have it ghetto rigged into a box that i can take back and forth from my bedroom(studio) and workshop...
here is a overall pic:
http://img15.imageshack.us/img15/786/mu1om1.jpg
and a closeup of the mainboard:
http://img10.imageshack.us/img10/5452/mu2bj1.jpg

i have gone over and over this thing and the traces are fine, parts are fine...
When i am listening through it...the pots do nothing, have hooked them up a few ways...
no meter attached right now...
If i pull out the tl074 during listening...it does not change anything! When i shove it back in, there is a brief delay then it passes audio again. I have tried several opamps, all seem to be fine but do the same thing!

voltages from the psu are: 12.6,15.6,1.56,0,-15.4, 100

5532:
pin1= -14.6
pin2= -1.3
pin3= 0
pin4= -15.3
pin5= 15.5
pin6 3mv
pin7 and 8 are about 0

tl074:

pin1= 1.5
pin2= 1.5
pin3= 1.5
pin4 = 15.5
pin5= 1.5
pin6= 1.5
pin7= 1.5
pin8= 1.5
pin9= 1.5
pin10=1.5
pin11=  -15.3
pin12= 1.5
pin13= 1.5
pin14 = 1.5
pin15.....just seeing if you are listening...

i cannot figure out what is going on here!
hammer in hand  ???

dont know if this is an issue...
i am using an unbalanced input to the unit.

that tube look suspicious to me, with its clear top...is it functioning proparly?...is it a 12au7 or is it something else?...if something else, it might not work as intended..

when feeding a strong signal through the input, you should get a negative voltage on the junction of the attack and release pots..is that hapening?

..hang in there...you'll get it working soon...

j

the tube is fine, its an rca cleartop that has the triodes balanced...have swapped tubes around(have dozens of au7's).
i found what i think is PRR's original design last night, with a 470fixed for release and 1 ohm for attack via this schematic:
http://headfonz.rutgers.edu/comp5/Comp5.html

redid the one side for that and it does work, but very subtle...
was hoping this would be a throw together done project....but such is DIY 

what are the hanging "R"'s in the schematic supposed to represent? the ones going to nothing.