PRR Vari-mu
« Reply #40 on: January 07, 2005, 02:38:07 PM »
link dead here...


PRR Vari-mu
« Reply #41 on: January 07, 2005, 02:59:48 PM »
Hey Peter...

I was more curious if the tx hookup was okay (with left open windings on the 2nd one), as for the 100V supply I assumed it'd be coo as it's what PRR originally drew and what Kent went with on the box he put together...didn't mention any probs with it on his page (http://www.conditionedresponse.com/DIY/C5/index.html)...



PRR Vari-mu
« Reply #42 on: January 07, 2005, 04:37:09 PM »

I thought you had designed yourself. If it aint broken, dont fix it!


Here's the corrected link :


If opportunity doesn't knock, build a door.


PRR Vari-mu
« Reply #43 on: January 07, 2005, 10:06:01 PM »
There are much simpler methods for implementing a pass transistor in a zener regulator.  I showed a simple way in the slow ramp phantom project.

Just look at the components surrounding Q1 for this.  You need to adjust R1.  I'll have to dig up the formula... and if you want to limit the inrush current, insert a 1 or 2W resistor in series with the collector of Q1.

"The sow would rather have her ear than a purse." - PRR


PRR Vari-mu
« Reply #44 on: January 08, 2005, 12:27:38 AM »
> I've had problems with Zener regulated supplies like this, getting the current right

If the input-output voltage is small, the current will be all over the place for small changes in input voltage. Shunt regulators need a BIG I/O difference to be happy. Here I've aimed at 160V raw, 100V regulated, and it should be pretty un-fussy for reasonable supply change. Also the total load is not so huge, so I let it be wasteful.

> simpler methods for implementing a pass transistor in a zener regulator.

And for that matter: I drew a regulated supply only because I am anal about levels. I would adjust for 2.8V peak output in heavy limiting, with ANY reasonable wall-power voltage. Around here that can be 104V to 124V. The threshold shifts with supply voltage, so "2.8V" could be 2.4V or 2.9V, a 1.6dB shift. If you set-up each day and generally trim by ear, +/-1dB variations are insignificant. And if you limit some things light and some things heavy, the peak output can land anywhere in a 5dB range. (My goal was no limiting up to -10dB, soft limiting above that, and gross surprises almost-never exceeding 2.8Vpk, my reference level.)


PRR Vari-mu
« Reply #45 on: January 08, 2005, 01:15:01 AM »
Quote from: "PRR"
And for that matter:
Uhh, PRR, my apologies if you thought that I meant "your method".

I was referring to the circuit shown at the link on the WelLabs website...

And I would probably not dare dabble into your design unless I saw a gross mistake, which would be really uncharacteristic for yourself, sir.

"The sow would rather have her ear than a purse." - PRR


PRR Vari-mu
« Reply #46 on: January 08, 2005, 01:33:30 AM »
> my apologies

No apology from you. My apology for over-designing the thing.

And I knew you could not be commenting on my pass-element because I didn't post one for this design. I over-design, but not over-over-design (usually). I'm lazy and cheap, and will work hard to avoid one extra part to order and solder.

I think my Zener-hack will generally work. I also think most folks would be just as happy if they left out the Zeners altogether. The rise and variation of limiting level is smaller than most studio practice cares about.

If someone wants to nail the supply voltage to 100.000V, or even 97V-103V, it's their box and their fun. But I don't think it is warranted unless you have a nut like me sticking an audio voltmeter up the output socket, while working in rooms wired for candles. (Nearly true: the Music Building did have electric lights when new, but that was sorta high-tech. But there were no electric typewriters, and all phonographs were wind-up.)


PRR Vari-mu
« Reply #47 on: January 08, 2005, 01:07:35 PM »
> can I pull phantom out of the center of those zeners?

Yes. But note that this isn't a mike-amp, unless you only use it with hot mikes on very loud sources. You need another gain of up to 100 to use it for general-purpose mike work. While you could pull gain of 10 with a 1:10 input transformer, you also want gain adjustment to set the amount of overdrive and depth of limiting. And that's a bad place to put a pot. So you really need some form of preamp.

I've thought a lot about using it as a mike input. With some modifications, it might be usable in specific situations. The 3V-6V overload level matches the hottest mikes in the loudest music. The noise level is high but at these whopping input levels that may not matter. For AKG414 on string quartet, just lightly trimming the loudest note of the piece (limiting for safety, not for effect), you could switch transformer ratio to maybe 1:4 (really 1:2+2). A 1:5+5 tranny could bring up a slightly softer act, or a loud act on dynamic mikes. But you can't wind a good tranny to much higher impedance than 1:10 from 150Ω, so it won't work for soft acts on dynamics, or limit for effect even with loud acts on dynamic. And tapping a wide range of ratios, 1:1 to 1:10, on one tranny, with the highest ratios giving very high (for a good transformer) impedance, is not easy.

But you could use a 1:10 mike transformer, a 12AU7 or 12AY7 volt-amp, a gain-pot, a cathode follower, and a 10K:10KCT transformer into the limiter grids.


PRR Vari-mu
« Reply #48 on: March 12, 2005, 04:11:21 PM »
please.need help.i build this project but dont work well.i need fix error in the schematic.or i dont now.the tl074 work bad.12au7 and 5532 work fine.


PRR Vari-mu
« Reply #49 on: March 13, 2005, 07:56:02 AM »
Hey Supermagoo,
What's the problem? :?:


PRR Vari-mu
« Reply #50 on: March 13, 2005, 10:07:21 AM »
hi gert. have you built this project? i think that there must be a new schematic with fixed errors because i built it all correctly  but doesen´t work properly.  :sad:  :?:


PRR Vari-mu
« Reply #51 on: March 14, 2005, 12:18:27 PM »
Whay do you mean by "not working properly"? Don't expect large gain reduction, because there isn't.What trannies did you use?


PRR Vari-mu
« Reply #52 on: March 14, 2005, 08:28:18 PM »
hey, I built this unit some time ago with no problems whatsoever.  what problems are you having?
Welcome to the GroupDIY leper colony! when something falls off, we just replace it with a tube!
occupation: General Electron Mayhem

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PRR Vari-mu
« Reply #53 on: March 15, 2005, 11:28:23 AM »
first of all my english is bad.try to understand me.trannies=transformers?.
the audio path works fine but has loss bass. 12au7 and 5532 work fine. attack and release control work fine.the voltage of psu works fine (all) .i think the problem is in the tl074 .in the output of tl074 i conected to other circuit to chek and soud distorted .and the 12au7 never compress, only goes by.the 12au7 only compress when i connect negative input of tl074 with a resistence to ground.that  is why i think something is missing in the schematic or is bad.
pd:the transformer is not of a good quality.and i checked all in my lab with headphones, not in my control room with my krk monitors.
thanks for your help :green: .cristian of argentina.


PRR Vari-mu
« Reply #54 on: March 15, 2005, 01:30:00 PM »
Note that there is two pages about PRR varimu in the web.


This is the original, but there is also a page by Kent that I cannot find now, with diferent schems, but mostly just attack/release control provisions, as well as VU meter...

Couldn´t find the link. Try the meta!


PRR Vari-mu
« Reply #55 on: March 15, 2005, 01:34:30 PM »
> attack and release control work fine. ...the 12au7 never compress,

If it never compresses, what are the attack and release controls doing? They only affect compression, which you say you are not getting.

Output of the TL074 is not supposed to be listenable audio. In fact each TL074 output pin should make "clean audio" plus a DC voltage (which may be upsetting the amp you use to check it). The junction to the left of the two diodes should be very-very distorted audio.

What DC voltages are on all the pins of the TL074?


PRR Vari-mu
« Reply #56 on: March 15, 2005, 01:38:11 PM »
Just for the notes, I´ve found it...


Also check the first link in the compressor meta for a mod for variable ratio control.


PRR Vari-mu
« Reply #57 on: March 15, 2005, 01:44:58 PM »
> check the first link in the compressor meta for a mod for variable ratio control.

That is in fact THIS thread.

There is no variable-ratio mod in this thread- probably the Meta editor was thinking of another limiter project.

And of course if it doesn't work, vari-ratio is pointless. Get it working before you gimmick it up.

Michael Krusch

PRR Vari-mu
« Reply #58 on: March 15, 2005, 05:22:07 PM »
Quote from: "kubi"
Is there a chance to add a ratio pot/switch or does it simply make no sense for that vari-µ limiter?
A variable/switchable resitor near the junction of the two 3.3k resistors?


Quote from: "gyraf"
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.

But the thread has grown and grown, so I throw that ratio part out of the meta.


PRR Vari-mu
« Reply #59 on: March 16, 2005, 12:35:34 PM »
Hey guys,
When I take a look at schematic(by now you all know witch one)isn't the releasetime  affected by the attacksettings of the pot?Or am I  mistaking?


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