PRR Vari-mu

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Wasn't there talk a while back of modding this to drive well enough for +4 operation? Does anyone recall the topic? Or am I imagining things...
 
there was a topic but it just suggested using another opamp gain stage, I'm going to work on this when i get a chance. I need(would like) +4 because all my interfaces are +4. any suggestions from Herr Professor? I was thinking another stage with a simple opa2604 or something with a pot in front of it..?

Edit: Since I am ignorant of tube design, what happens if the 100vdc is higher or lower than dead-on 100vdc?
 
> what happens if the 100vdc is higher or lower than dead-on 100vdc?

The threshold level changes. That's why there is a trimmer for that.
 
I've been thinking of breadboarding NYD's line amp, but haven't really decided what I would use it for. Perhaps as an amp to this? Thoughts/Guidance/"you're an idiot" comments always appreciated.
 
forgive my ignorance but I am unlcear as to the reason for the 1k trimmer on the output.. is that for impedence or for output attentuation?
 
> I am unlcear as to the reason for the 1k trimmer on the output.. is that for impedence or for output attentuation?

Adjusts threshold by trimming the level into the sidechain.

http://headfonz.rutgers.edu/comp5/Comp5.html
 
Hey...

Just been going through the mainline site for a misc order of parts and came across a cpl of v cheap transformers which I'm wondering if could be used in this project:

http://www.mainlinegroup.co.uk/mless/main.php?act=Card&id_element=2645

http://www.mainlinegroup.co.uk/mless/main.php?act=Card&id_element=1335

No idea if they're suitable - but this diy lark is a funny game, and u (or i rather) just never know ;)

All the best

:thumb:
 
It's impossible to say from those (missing) specs.

I don't think they'd be useable - but there may be a small chance anyway..

But at the low price of "ground isolation" transformers for car-fi, there should be no reason to try unknown transformers..

Jakob E.
 
Cheers jakob...

Have u a specifc part # to hand that I can find in the UK, there's alot of types for those "ground isolation" transformers it seems and I aint to sure...or, I have some monacor LTR110's (4 in all) so I guess I could just use them...?

Also, I'm wondering what to do for a psu - the one PRR has on the page he put up is for 120V US mains...could I make somthing similar to the psu you done for the pultec clone but make some alterations - So, (TX1) 220V:12V > (TX2)12V:120V (then use the same ckt PRR done from that point onwards). Then for the +/- 16V and 12V heater supply just use another 12-0-12V TX...or just take the 2 12VAC lines from between tx1 and tx2 and feed of from there?

Cheers
 
like so?:

prr-vari-psu.JPG


ta
 
soz to bother again, but i've redrawn another psu ckt based around a dif tx setup as i've a pair of the ones shown to-hand and would like to use them if poss instead of gettin another 2...so, as they are dual type with 15V secondaries (instead of the 12V like before) - would this work?:

prr-vari-psu2.JPG


Is the 12V output for the heaters ok? I'm guessing I can reduce R10 a lil smidge?

Best,

D
 
bump...

so...i guess i'll just build the above and turn on from a distance with a snooker cue or summin...lemme see those fingers!
 
Hi Dearry

For the 100v supply, why not adapt the G9 HT supply & recalculate the resistors to give you 100v regulated.

I've had problems with Zener regulated supplies like this, getting the current right, etc. A pass transistor would help a lot in this situation.

Have a look at this for an example of a zener + pass transistor design.
http://www.welbornelabs.com/pdf.htm

Corrected link :

http://www.welbornelabs.com/ps3.pdf

Regards
Peter
 

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