best telefunken to pcb ?

i wanted to make a pre amp to combo with an la-2

ergo UA la-610

i thought doing a V72 telefunken pcb.


but i know their are other variations of pre's that telefunken
has made ,

any one have any prefrances on telefunken pre's.

and are the parts all availabe to mankind.

i was considering purchasing one this week so i could dissect it.

i know in doing the pcb of the la-2 it was a life saver to have a
real one available to a/b and refer to .

so ill probably do the same , a good price for one ?


any comments or ideas much appreciated

I do believe that CJ has done a lot of work on the Telefunken 72S and the 76
http://www.groupdiy.com/index.php?topic=8247&highlight=v72
http://www.groupdiy.com/index.php?topic=7853&highlight=v72
http://www.groupdiy.com/index.php?topic=6360&highlight=v72
http://www.groupdiy.com/index.php?topic=6272&highlight=v72
http://www.groupdiy.com/index.php?topic=2680&highlight=v72
http://www.groupdiy.com/index.php?topic=322&highlight=v72

Watching with interest!!

The 72 would be a ton easier, and sounds just as good if not better than the complicated 76.
I think Telefunken used kind of a PC board, maybe more like a turret setup, but I remember seeing resistors on a brown piece of Permali in one of Tommypiper's V modules.

The parts count in the 72 is low, so a PC board should be real easy.

Does the V72 need an input xformer like 1:15 or 1:20? I can't remember where I read this, if I did. How about the aoutput does it use anything exotic? I always though these telefunkin thingies used hard to find iron.

Kiira

Yeah I miss that fella. Double :sam: :sam: to him.

i've been thinking about this a bit also. the v72 would be easier for sure, but it does have a 1:20 input transformer, a 180+ H choke, and a high ratio output transformer, something more like 10:1 or 9:1. also, there is no provision for changing the gain.

i don't see any of these things being a total deal breaker (and it only gets worse with the v76) but you'd need to source the choke and output transformer as custom units to do a faithful copy.

the lundahl LL1636 could possibly work for the input transformer. and then a simple attenuator after the second tube, with no output transformer going straight into the la-2 sans input transformer. dunno if you could get away without the choke.

another thing to consider is that the la-2 has a lot of gain to begin with if you use a high ratio input transformer.

ed

I have a Thordarson 20A01 which is 600:240000. I think that is 1:20.

Wouldn't any 10:1 output xformer do? a wsm is $9.

Kiira

I believe WOB said you could use the Cinemag CMMI-10C for V72 input. That's what I plan on doing. Sowter makes the big inductor (support our host!). Not sure what to say about the output iron. I bought a custom wound one from WOB. Maybe CJ has some ideas.

A P

couldn't we just ask Oliver to make some for us ? his V78m, which is based on V72s if i'm not mistaken, uses in/out trannies that he made himself, using original telefunken winding machine :roll:

I never really understood why the V72 is so revered as a mic pre. It sounds good as hell but Ive never been able to get tons of use out of them as mic pre's because they are so low gain. 34dB or something like that. They sound awesome, but you have to have a really hot mic or a really loud source. How many people fiending to build them have actually used them on a session? It would be a lot of work to build one of those and have it be usable in such a small amount of circumstances. I sold all my v72s cause I could never use them when I wanted to. I still have v77's though, they dont sound identical but they still sound very very good and have more than twice the available gain so you can actually use them whenever you want with whatever mic you want. If I was building one of them for practical use in a recording situation as a mic pre, I would investigate a v77 or something with higher gain before getting too excited about a v72. If you have lots of high output tube mics, then they are awesome, but with the average mic they really leave a lot to be desired. V76's are expensive for a reason, I think the V77 might be the better compromise. I dont think a v77 woudl be more expensive or more time consuming to build than a v72. Just a thought.

dave

The S model has 40 db gain with the voltage divider getting rid of 1/3 the neg feedback.

The output iron is not that special, just a sec-pri-sec-pri-sec structure on some M6 with no real tricks.

The choke is available from many people also. It goes together pretty quick due to the lack of bells and whistles. If you have all the parts and the chassis drilled, 2 days max to complete. As opposed to the years I spent on the V76, but there was a lot of emails to Ollie on that one. And the 300 dollar input trans took a while to buy.

Yes, the 72 was designed for a condenser mic, or a 57 in front of a Marshall.

[quote author="buttachunk"][quote author="CJ"]And the 300 dollar input trans took a while to buy.[/quote]

Sheesh... Aren't real V72s around that same price ?[/quote]

300$ no way. On ebay they seem to be $800+ each. For a 34 decibel pre? seems like a lotta money for something with limited use. :? :roll:

Kiira

Well, the iron on all those old modules is suspect becuase of the lead breakout. The lead sleeves were silk, and they just evaporate when you touch them, exposing the bare magnet wire to the can, chassis, etc.

It is a very nice sounding mic pre. And if you are in to that retro Beatles thing, it's a lot of fun.

The 300 dollar input was for the V76, not the 72.
The mu metal was 100 of that 300.
The 1:30 Ollie iron with cage is just as quiet as the 1:10 Jensen.

Yes, the 40 dB gain of the V72 was always too low for me (doing acoustic music). I never understood its mystique either. I borrowed a racked pair from Oliver once and they were a bit noisy, but that could have been my ground loop or some other problem or my fault. CJ, is your V72 only up to 40dB gain? I thought it had more gain, like your V76?

I like Dave's idea of the V77. Here is straight off Oliver's website moments ago:

"The V77 was a Siemens made supercharged V72 with a maximum gain of 80 dB. It produced sound like a V72 but with the gain and plus of the V76; with an external switch (W77) the gain could be adjusted from 0 to 80 dB. Tube set-up, choke and output x-former are identical; the input x-former is wound the same way but with a 1 to 40 ratio, because in order to get the required S/N ratio the V77 needed a different power x-former with two separate filament windings."

That sounds like something worth building if the parts can be sourced. A 1:40 ratio! 80 dB!

I like Uberjam's idea of asking Oliver about a small group order for any custom iron we'd need. CJ can teach us all how to make the chokes. We could have a choke winding party...

they definitely sound different. V72's definitely sound awesome but v77s sound great and are just usable. When I owned v72's I was always pissed with them because I could never use them on the sources I wanted to use them on. They are best used IMO as line amps in the role they were designed for. The 77 at leats has the available gain to deal with the whole purpose of plugging in a mic pre- ampliflying a low level mic to line level. If it was me and building a 76 was out of the question, a 77 would be next on a list that wouldnt include a V72 at all. Think of all the other really great tube pre's out there that have good gain for mics that would come in before a v72. Of course if you want the v72 sound, you gotta build one, and there's definitely a place in any studio for a v72, I just posted this because its just one of those things that everyone talks about and I think a lot of folks who have never used them dont realize exactly the deal with them. they sound great, so people deal with them, but you just cant use them on everything or many things for that matter. If you have lots of high output tube mics, then its a different story, but for thhe average condenser or dynamic they present unusable scenarios more than usable ones.

dave

If the V72 doesn't give you enough gain, put two in series

I have heard of people putting faders behind V72 preamps for an extra 10dB or so, getting excellent results!

quick question: do the V72 and V72s have different trannies?

from Ollie :
The actual x-former is the same, it is the way the coils are hooked up, V72>v72S and V76>V76S is identical how this was done.
In order to change the set up, you have to take the x-former apart, place the coils in the right order and hook them up to S specs...Do not try this at home...

and this is the link to Ollie's comments regarding V72 gain issues :
http://recforums.prosoundweb.com/index.php/m/37994/0#msg_37994

I used to have a pair of V72, I was frustrated because I couldn't find any usable application of them due to lack of gain. I tried various mics & sources, but they're simply to noisy and it's hard for me to judge whether they sound goor or not 'cause the noise was to obvious.
I once put two V72 in series too, in order to get more gain, but then I heard some nasty input distortions from the second unit . I tracked a bass player once with a Demeter Tube DI in front of V72, although I also heard input distortion on my V72 , but the bass player seemed to like it. That's the first & only time I could make any use of my V72.
I read somewhere that those V72 were made to compensate gain loss after a line signal passes a passive EQ, like Eckmillers, which caused gain loss of exactly 34dB

I sold my V72 & get a bunch of various Vx76 modules instead.

Ü

The comments about the V72 being fixed at 40dB gain inspired me to start this new thread over on the Drawing Board:

I have no problem using v72 preamps with guitar cabs and tube mics(higher gain) for vocals running to a joe meek comp then to AD converter.

for drums I need to pad these down alot or use for overheads. Also Joe of JLM fame says that its best to have a variable pad in front of these unlike the badly setup boutique audio setup that wires an attenuator after the preamp.

I would like to know more about the correct setup for these as far as getting gain like the v78. seems you needd to change the inut impedance as you change the negative feedback loop.

If it's feasible, I'd be interested to have a closer look at doing a V77. Same output transformer and choke is helpful. The question will be sourcing an input transformer and the special AC transfomer that Oliver mentions on his site... intriguing project. CJ, whaddya think?