PRR Vari-mu

« **Reply #20 on:** December 23, 2004, 05:26:29 PM »

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...

« **Reply #21 on:** December 23, 2004, 05:50:11 PM »

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?

« **Reply #22 on:** December 23, 2004, 05:54:35 PM »

> 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.

« **Reply #23 on:** December 23, 2004, 06:00:54 PM »

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.

« **Reply #24 on:** December 23, 2004, 06:36:52 PM »

is there a link somewhere to this line amp? i can't seem to find it in any of the metas or by searching?? :?:

« **Reply #25 on:** December 24, 2004, 12:12:18 AM »

i swear that wasn't there!

too many :guinness: :guinness: :guinness: i think.. sorry!

« **Reply #26 on:** December 28, 2004, 01:22:49 PM »

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?

« **Reply #27 on:** December 28, 2004, 04:49:04 PM »

> 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

« **Reply #28 on:** December 28, 2004, 05:26:12 PM »

Thanks PRR, now that you said that it's as clear as day.. this cold medicine is making me confused!

« **Reply #29 on:** January 05, 2005, 07:58:15 AM »

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:

« **Reply #30 on:** January 05, 2005, 08:11:47 AM »

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.

« **Reply #31 on:** January 05, 2005, 09:53:51 AM »

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

« **Reply #32 on:** January 05, 2005, 09:56:57 AM »

The LTR110's should do fine here. Monacor also has a ground isolator transformer named fga40

Jakob E.

« **Reply #33 on:** January 05, 2005, 10:01:45 AM »

ok - but i aint gonna get far without a psu :roll:

« **Reply #34 on:** January 05, 2005, 10:04:44 AM »

Yes - you could do a similar setup to the Pultec supply..

Jakob E.

« **Reply #35 on:** January 05, 2005, 11:36:23 AM »

like so?:

ta

« **Reply #36 on:** January 05, 2005, 02:01:40 PM »

That looks right..

« **Reply #37 on:** January 06, 2005, 07:56:17 PM »

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?:

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

Best,

D

« **Reply #38 on:** January 07, 2005, 10:28:41 AM »

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!

« **Reply #39 on:** January 07, 2005, 02:20:07 PM »

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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