Has anyone ever done a PCB or build for V72 or V78?

[kepeb]

ya, i'm in when this happens too
i was looking all over the place for a version which wont require a mortgage.
found some docs in German only. the solid state and tube version but iirc all the transistors on the v72(T) were well old and its beyond what i could conceive to bring it up to date.

one of the brainiacs here could tho

 

[abechap024]

I think we should think about things to make this '76 more DIY'able.

Up for consideration....Removing the variable High-pass filter

Also installing a separate rotary PAD switch for the first 4 spots on the gain switch. That was we don't need to try and source a 4 pole 12 position switch. 

Anyone who ever had the opportunity to routinely use one find a certain range of gain settings most used? Would it be practical to throw out the whole padded input section in lue of one -20 db ish pad switch??

-Abe

 

[kazper]

Just build a V76M it has the filters removed etc..

The EF86 tube change makes sense and that is fairy standard in the 72 repro's. Those fancy switches could be stocked or boughten from a couple places, not overly expensive but not cheap. I know a couple types that are off the shelf from a UK supplier and can be brought in via backdoor through a US distr. Elma makes a excellent switch and is fairly cheap in numbers. Worst case I think you would want to probably add more positions to the gain settings and make it more precise.

Sower has a nice V76 schematic and sells a set of transformers for it.

 

[abechap024]

A work in progress....
a V76 with no filters. The v76M is slightly different circuit....maybe switch over to that.
Based around EF86 tubes...

Idea mentioned earlier why don't we just make a pcd for the 76 but make it an easy optoin to turn it into a stereo 72 preamp.

Or make 72 boards and then people can put 2 back to back to get a 76....options!

 

[grantlack]

giving the hpf the chop seems prudent, nothing that can't be handled after the fact.  sure, hpf at mix won't be IDENTICAL to if it had been recorded as such, but all things being considered it's something that most just set and forget anyway.  eyes peeled!

 

[edanderson]

speaking of NY , maybe
Ed anderson is up for it ?
He's certainly proven capable of producing
the goods so far , guess that depends on his time
and or interest , mignt have to do a prebuy

since my name was mentioned, thought i would throw in my two cents.

the iron is not trivial.  the input, as CJ showed in his dissection of the v76 input, is VERY special, and the materials alone to make the transformer to the original spec would be correspondingly very expensive.  oliver archut at TAB funkenwerk has done a nice job re-creating the transformers faithfully for his own units, and would probably be the best bet for a DIY version w/ original type transformers.  no doubt the sowters are very good transformers also, but i doubt that the designs have much to do with the originals.

the input is a very high ratio, 1:30, which is very uncommon for a mic input, so there are few off the shelf substitutes.  same thing with the choke, a specialized part, not easy to find elsewhere in that level of quality. the output is no cakewalk either.

there's nothing stopping someone from making a "simplified" version of the v72 or v76, with ef86 and different transformers, maybe no plate choke.  the v76 is actually a reasonably complicated circuit, not easy to troubleshoot if you've never looked at it before, but with some care it should be possible.  i would recommend an adjustable pad on the output.

ed

 

[mad.ax]

A few observations...

-I have worked on original V72 and V76, and remember that I always thought how nice would it be to just gut the damn crowded up thing down, and rewire the iron and tubes in a nice brand new rack!

-The 'mojo' is a) in the iron, and b) the EF804S. Both are unobtainium.

-Tab Funkenwerk makes what is probably the best new/pimped up recreation. And for the price they're selling it, I pretty much doubt one can DIY it. AFAIK, Oliver doesn't sell those specific transformers.

-the EF804s (and all substitute you can think of) are highly microphonic. They are shockproof mounted for a reason.

-speaking of substitute, 804 are not pin to pin compatible with 86. There are other interesting options that doesn't even share the same sockets. EF12 (F8) or EF40 (Rimlock) for instance.

So my advice would be to design a pcb more like a turret board, with everything on the pcb, but the tube socket, that could be wired from there. Or at least, having just a big hole to mount tube socket on the board. This would allow from some kind of elastic mount, noval or rimlock socket, and ability to wire different pinouts.

Axel

 

[Davo]

Making a single 72 board... and wiring em in series for a 76, seems like a good idea... more modular at that point.

In my experience, trying to find good low noise ef86's has been a nightmare... the 804s is a better tube (just in terms of noise), although as Axel points out, definitely unobtainium...
I like the idea of the hole+ rimlock socket that can be shockmounted

The iron is the interesting part of this equation

cheers
dave

 

[kazper]

Just do separate a PCB for the V72. Combining them is silly for the cost of PCB's. Both projects would be fine. In essence you could fairly easy modify a project like the Orange86 as a V72, since it''s based on the Redd 47 which is based on a V72.

I have a Drip V72 build, sounds fantastic using EF86 tubes. Never compared real to my clone, but never the less the clone sounds great.

As Ed had discussed, the more I looked into this last night the more specialized the transformers are shown. As Tab-Funkwerk put it the device's could not be made with the original attention to details and materials for a price point anyone would pay in todays economy.

Using the 50/90 rule an DIY version would get you close, but bot real or Tab close. Thats 90% desired "sound" for 50% of the cost.



If your doing your layout look up Orange 86 and check out how he did the PCB mounts.


Here is some info and why I recommended the V76M:
V76/80 - with switchable lowcut at 80Hz and 300Hz. Fixed input filter 40Hz and 15kHz.
V76/120 - with switchable lowcut at 120Hz and 300Hz.Fixed input filter 40Hz and 15kHz.
V76m - special version without switchable low/highcut and without fixed input filters; linear frequency response from 20Hz to 20kH

Source: http://gwagner.50webs.com/v76.htm

V76M Link

 

[abechap024]

Sowter has the input and choke iron.

Anyone see any reason why we couldn't change the 4uf  caps to 4.7uf caps? Also change the 2uf caps to 2.2uf?
Only reason would be easier part sourcing.

Cheers,
Abe

 

[guavatone]

You would definitely need to cut some tracks of the Orange 86.  V72 uses a pentode for V2, whereas the redd/Orange
uses a dual triode in parallel.  Also the Feedback is a bit different, with a positive FB from V2 cathode to V1.  But
it is not impossible.  Most of the HT is probably similar, yet my eyes hurt seeing HT come from below.

The V78 is basically a V72 with a variable gain on V1 and different I/P xfmr wiring.  I was thinking about tackling a
poor mans V76, but I want to finish a couple of vari-mu limiters first.

 

[guavatone]

Actually. It's not that hard. I only see one trace to cut so far.  A few jumpers here and there.  I mapped out a possibility so far without gain switch or V2 HT with Inductor.  i can't remember what value resistor to sub for inductor tough.  I'll post a photo soon.

 

[kazper]

Maybe you could just do a slight PCB change and have the Orange72. I'd buy 2.

Drip used the Sowter 9375 PCB mounted Plate Choke.

If I can link them together V76 style or use them separated as 2X V72 might buy 8 V76 units worth..

 

[abechap024]

That would be cool if you changed the Orange circuit.

I've been kicking this circuit around for a bit. I've decided I want a pair of '76 preamps.

Schematic (you probably want to download and view - its quite large.

Its actually the V76 with the filters omitted (not V76m)

It would use the 1:30 input and 9:1 output iron from sowter. I'm still looking on the inductors but sowter does stock one. (probably want to replace with resistors for now if possible)

Right now the PCB is 2 layer but I'm going to try and fit it one layer so people can etch if they want. --->

PCB
PCB No Holes
Res_Def


(these images are 4x)

 

[kazper]

I actual contacted Sowter this morning about more info on there plate choke and the other couple inductors, still waiting for a response.

It's going to be a good $500-600 for the iron per... And no that the not close iron price.

 

[abechap024]

It's going to be a good $500-600 for the iron per... And no that the not close iron price.

Crazy! I at the moment would not want to invest that much.
A little more than 100$ for the input transformer...and then figure about the same for output. I say we omit the chokes if possible. I know we would need to replace them with a resistor. Though I don't know how awful this would be to the sound. Or if it won't really be noticeable...
Surely there has to be other options for input transformer. Even if its not *Exactly* It might get us well enough in the ballpark

 

[Biasrocks]

It's going to be a good $500-600 for the iron per... And no that the not close iron price.

I say we omit the chokes if possible. I know we would need to replace them with a resistor. Though I don't know how awful this would be to the sound. Or if it won't really be noticeable...
Surely there has to be other options for input transformer. Even if its not *Exactly* It might get us well enough in the ballpark

You're not building a V72/76 any more. Which is fine, just don't expect it to sound like one.

At the price of the Sowter iron, you're pretty close to buying a raw V72 module.

Mark

 

[abechap024]

You're not building a V72/76 any more. Which is fine, just don't expect it to sound like one.

At the price of the Sowter iron, you're pretty close to buying a raw V72 module.

Mark

Haha yea thats a good point. Well seems like one of those projects that if your just going to go half way there, you might as well go a different easier/cheaper way to get to the same spot.

 

[guavatone]

Has anyone compared A-B'd the drip V72 to the original?
I recall greg saying they were pretty close.  I wonder why he no longer has them.
I may just have to make one

 

[desol]

the iron is not trivial.  the input, as CJ showed in his dissection of the v76 input, is VERY special, and the materials alone to make the transformer to the original spec would be correspondingly very expensive.  oliver archut at TAB funkenwerk has done a nice job re-creating the transformers faithfully for his own units, and would probably be the best bet for a DIY version w/ original type transformers.