the new V72 (pre order closed)

A have a pair laying around for some time now...


Did anyone build this unit successfully? I mean could anybody comment on these before I order the transformers?


Zander

I have also a pair here.
The transformer costs are huge if you buy them from Sowter. Does anyone know of (cheap) replacement for the Sowter's for In/Out transformers? Maybe anything from Edcor may fit?

Andy

Anyone got a schematic for this build? The dropbox links are all dead.

Cheers

Ian

Haven't had time to start my build, but managed to grab those files when they were still up...

here goes:

Parts....

part list...

Front...

this is a working link from reply #70

https://www.dropbox.com/sh/ff410b83ua3hhnh/AAAWEg-l6N11fy8g41Xz1IwIa?dl=0

Martin pm'd me and said, there will be news in February !

Hey guys, good news. Everything is back to normal here and i found something in the mailbox today.



I wonder what we could do with them I wanna try a few things and see what options we can get on transformers, cases, frontplates, etc. I will soon start a thread where you can follow the progress.

Sounds awesome!

Hi.

This has taken me a while to complete.
It sounds really good.


Thanks Martin.

Looks great! I need to get my pair finished. What transformers did you use?

duantro said:

Looks great! I need to get my pair finished. What transformers did you use?

Click to expand...

Hi duantro,

I used the ....
Sowter 1960 Telefunken V72 input trx
Sowter 1275e V72 output trx
Sowter 9375 V72 choke
The power trx was the torroidal supplied by Martin

This is a single channel.

aomahana said:

Hi duantro,

I used the ....
Sowter 1960 Telefunken V72 input trx
Sowter 1275e V72 output trx
Sowter 9375 V72 choke
The power trx was the torroidal supplied by Martin

This is a single channel.

Click to expand...

Great! I just bought a pair of Sowter transformer sets. I'm designing my front panel now. Can anyone tell what the mode switch VB stands for on the switch pcb? Variable Gain?

duantro said:

Great! I just bought a pair of Sowter transformer sets. I'm designing my front panel now. Can anyone tell what the mode switch VB stands for on the switch pcb? Variable Gain?

Click to expand...

Yes, this switches between the original fixed gain and the variable gain.
I bypassed this switch, and only used variable gain.
So I didn't install the middle switch, and linked ....
A to pin 2
B to pin 6
C to pin 10 (top pin)

aomahana said:

Yes, this switches between the original fixed gain and the variable gain.
I bypassed this switch, and only used variable gain.
So I didn't install the middle switch, and linked ....
A to pin 2
B to pin 6
C to pin 10 (top pin)

Click to expand...

Thanks, that makes sense. I hate spending a lot of money on a nice front panel and getting things incorrect, or labeled that doesn't make sense.
Is the gain switch first position 25db really 10 jump (35db), and all of the rest are 5 db jumps?

duantro said:

Is the gain switch first position 25db really 10 jump (35db), and all of the rest are 5 db jumps?

Click to expand...

I haven't actually measured the gain, but for my uses the values work fine.

I finally got assembled. Going to burn tubes in tomorrow and hopefully try it out. Still need to do phantom power board, but excited to hear it.

I used the v72 today in the studio, and it sounds reeeaally good! I'm having a little buzzing on the right channel, only when in variable gain mode, and boost is up high. Maybe it is from AC wiring of Left board that is near the output transformer? I'll have to investigate. The other issue- The input pad steps are much too drastic. Like 30db steps. I'll need to try to decipher how this pad is done, and try to change this. Any input would be appreciated. I'm very happy with the sound.

Left channel ( from overhead picture view) is dead quiet. Right channel has a slight 60 cycle (and harmonics) hum, even with input unplugged. The lorlin switch wires are there because no matter how much I try to measure pcb's when I get my front panel made, the holes are always a little off. That would be a nice addition for people who make the pcb's to share these exact dimensions. Perhaps my power switch is too close to the extender wires on the far right lorlin? The veroboard on center back is phantom slow start board. Mains transformer is outside of case on the back, 48v transformer is on back right side by power inlet.
[list type=decimal]
[*]I've swapped output wiring to the other clean output transformer > phase flip switch> xlr, and hum is still present.
[*]I've disconnected the switch board's star ground wiring and buzzed to check for another ground present causing a loop, and nothing.
[*]I've re-flowed solder to any suspect cold solder joints, checked other grounds, and nothing.
[*]I've routed power wiring for left board as far to the rear of right output transformer, no difference.
[*]I've disconnected power to the left board completely, and no difference.
[*]I've disconnected the 6vac to the indicator lamp, no difference.
[*]I've pivoted right choke, no difference
[/list] 
Anyone have any thoughts on what else to search?