PRR Vari-mu
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Matthew Jacobs
Well-known member
Jazzboms said:
If I where you, I'd point-to-point and vero-board it. The tubes, transformers and pots on P2P and the sidechain and output on vero-board
helterbelter
Well-known member
Jazzboms said:
As Matthew says, it'd be easily done on Veroboard and P2P, but I think Dinesh has got a few boards left. http://www.groupdiy.com/index.php?topic=28107.msg437657#msg437657
Send him an email or PM.
> gain reduction of course reduces the output and if I'm using heavy reduction the gain loss has to be made up somewhere else. Input attenuation is not really necessary though it might be a good addition.
No no no. You are mixed up.
Leave the threshold mid-point. It will output up to 2V, which is Reference in some studios and fully digestable in +4dBu studios.
This assumes a fairly short <30mS or <30K attack. If you are doing long attacks it is all about how the un-limited transients upset later stages.
SLAM the INput to get your desired moosh. Slam lightly to take the peaks off an untrained singer, slam HARD to steam-roller and cross-modulate your grungy heavy thrash band.
A PC or iPod won't give heavy input slam.
Any source rated to cruise at +4dBu can peak over 6V which ought to be pretty damm slammed.
I expected this to go between a main console and a recorder. (Yes I still own a recorder.) The console can output -10dBu for light trim, +10dBu for moosh.
If you have various sources, you may want 10dB-20dB gain to bring a weak source up to heavy slam. And of course a gain control so strong sources aren't sonically damaged(?) before they hit the tube.
No no no. You are mixed up.
Leave the threshold mid-point. It will output up to 2V, which is Reference in some studios and fully digestable in +4dBu studios.
This assumes a fairly short <30mS or <30K attack. If you are doing long attacks it is all about how the un-limited transients upset later stages.
SLAM the INput to get your desired moosh. Slam lightly to take the peaks off an untrained singer, slam HARD to steam-roller and cross-modulate your grungy heavy thrash band.
A PC or iPod won't give heavy input slam.
Any source rated to cruise at +4dBu can peak over 6V which ought to be pretty damm slammed.
I expected this to go between a main console and a recorder. (Yes I still own a recorder.) The console can output -10dBu for light trim, +10dBu for moosh.
If you have various sources, you may want 10dB-20dB gain to bring a weak source up to heavy slam. And of course a gain control so strong sources aren't sonically damaged(?) before they hit the tube.
surfkat
Well-known member
Re-opening an old topic here. it seems that the links for the layout of this project have are no longer working. I would appreciate anyone posting a copy or pointing me to a working link of the layout. Many thanks in advance.
bernatvm
Well-known member
Just finished my compressor and, though it passes audio and compresses it, i have a band pass filter problem. My transformers are car isolators ones, with center tap. I tried feeding the sidechain in the center tap and I get the same result as I would with the 3k3 r4 and r33 resistors. I attach a screenshot of the frequency response. Note pink is the compressor (Left channel) and blue is the transformer alone using aligator clips from my interface and back to it.
I imagine there's some kind of impedance problem with my transformers but i don't know where to start looking. Thanks!
I imagine there's some kind of impedance problem with my transformers but i don't know where to start looking. Thanks!
Attachments
Is there perhaps overloading going on - i.e. is the curve the same at 20dB lower levels?
bernatvm
Well-known member
Yes, it is the same curve. Does it mean just not good enough transformers?
I had a similar-looking curve several years ago with too cheap transformers., including automotive ones.
Problem was solved with halfway decent ones. In keeping with the spirit of the project for lowest cost I used Edcors.
Problem was solved with halfway decent ones. In keeping with the spirit of the project for lowest cost I used Edcors.
bernatvm
Well-known member
It makes sense, but why do I get flat response when I messure the transformers with aligator clips? They don't respond the same way while inserted in this circuit...
..because source impedances are higher in circuit then..
bernatvm
Well-known member
bernatvm
Well-known member
I decided trying to swap the 5532. The only dual opamp I had laying arroud was a tl072. Whit the swap, the frequency response is now flat in the top end, no more LPF. Is this a bad 5532? Can the differences in this two chips (suposing they both good) have this impact in the frecuency response?
I'm buying some OEP transformers anyway, because the ones I'm using now don't go lower than 125Hz, but I would like to know what's the problem here. Thanks!
EDIT: It was a bad 5532. I build a buffer circuit for it in a protoboard and one of the two opamps in the packet shows this LPF behaviour.
I'm buying some OEP transformers anyway, because the ones I'm using now don't go lower than 125Hz, but I would like to know what's the problem here. Thanks!
EDIT: It was a bad 5532. I build a buffer circuit for it in a protoboard and one of the two opamps in the packet shows this LPF behaviour.
Aah, that's a freak accident then.. Rare, fortunately, but can be really hard to spot in experiments and prototypes..
/Jakob E.
/Jakob E.
bernatvm
Well-known member
gyraf said:
The datasheet of the 150R one says "N.B. Do not pass DC through windings". Doesn't DC from sidechaing go into the windings of the transformer? http://www.farnell.com/datasheets/1872255.pdf here's the datasheet
voltage, yes, current no. You apply the same voltage to both sides of the transformer, no current flows 
/Jakob E.
/Jakob E.
bernatvm
Well-known member
Just installed the OEPs and the frequency response is now more than acceptable, giving me -3db at 31Hz, which could be reffered as "rounded low end".
I'm trying to implement some mods, just for the sake of experimenting and learning some easy circuits with opamps. I have a board with switchable Active MS output matrix (and passive one with the input transformers). I also balanced the output using 5532 (i've read about the tascam problem but, as I said, i wanted to experiment with the 5532 designing my own circuits).
The problem is that whenever I power this routing/balancing board, the +-V suplies lower to +-8V or so and the output saturates because the opamps try to amplify past that region. They are fed from the original psu, but with a 1,5A (30VA) power transformer there should be more than enough power to drive 4 extra opamps and 4 relays, right?
Also my original idea was to fed the relays from the heater suply but, when they are active the GR meter slams to the right I should probably not use that rail, but why?
I'm trying to implement some mods, just for the sake of experimenting and learning some easy circuits with opamps. I have a board with switchable Active MS output matrix (and passive one with the input transformers). I also balanced the output using 5532 (i've read about the tascam problem but, as I said, i wanted to experiment with the 5532 designing my own circuits).
The problem is that whenever I power this routing/balancing board, the +-V suplies lower to +-8V or so and the output saturates because the opamps try to amplify past that region. They are fed from the original psu, but with a 1,5A (30VA) power transformer there should be more than enough power to drive 4 extra opamps and 4 relays, right?
Also my original idea was to fed the relays from the heater suply but, when they are active the GR meter slams to the right I should probably not use that rail, but why?
SIXTYNINER
Well-known member
...Some day ago while doing some tidying up and cleaning of the diy "corner"...
found a bag with inside pcbs named "PRR Vari Mu" ,
(...PRR Vari Mu ????? what is it? 8-I )
after done the cleaning , checked here around about ,
and found this thread ,
WOW so old project .. , from first years of this forurm ... ,
... but it seems to be cool , and worthy of spending at least some time on it ,
so apart this thread seems that the only docs-info about are on this link :
DIY 12AU7 compl
called "12au7 compressor" ,
but pcbs are the same as the PRR Vari Mu ,
found here also V2 and V4 of the PRR Vari Mu , also called "176" ,
(.... also some post i left , ...I didn't remember... )
but pcbs i found seems to be about the "V1" ,
so a question about is : there are more docs available about here or somewhere ,
like Bom , bullding info , issues and their solutions ,
internal wiring (pots , vu meter , other ) etc.. ?
attached the pdf of pcbs ,
thanks in advance for any help about !
cheers
found a bag with inside pcbs named "PRR Vari Mu" ,
(...PRR Vari Mu ????? what is it? 8-I )
after done the cleaning , checked here around about ,
and found this thread ,
WOW so old project .. , from first years of this forurm ... ,
... but it seems to be cool , and worthy of spending at least some time on it ,
so apart this thread seems that the only docs-info about are on this link :
DIY 12AU7 compl
called "12au7 compressor" ,
but pcbs are the same as the PRR Vari Mu ,
found here also V2 and V4 of the PRR Vari Mu , also called "176" ,
(.... also some post i left , ...I didn't remember... )
but pcbs i found seems to be about the "V1" ,
so a question about is : there are more docs available about here or somewhere ,
like Bom , bullding info , issues and their solutions ,
internal wiring (pots , vu meter , other ) etc.. ?
attached the pdf of pcbs ,
thanks in advance for any help about !
cheers
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