[BUILD] NU VARIMU 436 build & help thread

[JMan]

Where did you get this nice faceplate/case for 436?

You might also want to reach out to @HerbertR directly. I know he has been kind enough to share some of his panel design files in the past, and the one he has for this project is really cool, so it's worth trying your luck!

 

[petermontg]

Hi all,

To them who built one. What kind of levels do you get? Where is your "unity" gain position with your input gain? Mine works fine, but I need to crank it up pretty hot to get to the level which I send into it. I almost never need to use the output pad for anything. I just wanted to get the same level when you bypass and unbybass the unit (when you don't compress of course).
Sounds fine in low levels, it's just low. I expected a much hotter output. But there is nowhere a calibrating manual for this unit, aside from the balancing tube voltag trimmers. That is fine on mine.
But I miss the thing that tells you what level you should send a testone in what input and threshold positions to get a specific output level..

Yea finding unity is a bit annoying alright. I find mine somewhere between 7/8 on the input and -5 on the output. If at 7 I am a little below if at 8 I am a little above so I guess it's half way or so between those positions.

 

[MaxSquare]

PCB available now !!!!!

https://groupdiy.com/index.php?topic=53011.msg676707#msg676707
ERRATA:
1) pcb version 1.0 had a minor error in powering the relays, which has been corrected on all boards. The silkscreen numbering for two resistors was the other way round. This has been corrected as well.

2) The heater wiring of the 12AT7 tube as indicated in the schematic and on the pcb is wrong. I’ll describe an easy fix later.

You don’t need to do anything at all. These minor errors have been corrected already.




Update 15.12.2018: prototype works fine.. PCBs will be released!! Limited first run!!



————————————————————————————————————————-

Boards arrived!! Time to order some Parts


Mainboard and control pcb



PSU

Could you please share the frontpanel drill template again? Thank you in advance!

 

[MaxSquare]

universal frontpanel design. Don´t change the drilling holes, adapt meter cutout to your choice of amperemeter (1mA)

Could you please share it again, it errors out now!

 

[scott2000]

Could you please share it again, it errors out now!

saving as .fpd seems to work...
Not sure if people can upload fpd files here so maybe that's why....

 

[MaxSquare]

Sorry for my ignorance please. I did not know about .fpd format and Front Panel Designer, a noob me! I thought it was corrupted .pdf. Thank you all for the help, all good now!

 

[Potato Cakes]

I grabbed a couple sets of the V1.1 PCB sets while they were still available. I'm going to try to get one of them built later this year. Regarding the V1.1 boards, do any of the PCB fixes from the 1.0 boards still need to be made (jumping the heater voltages, etc.)?

Thanks!

Paul

 

[zayance]

I grabbed a couple sets of the V1.1 PCB sets while they were still available. I'm going to try to get one of them built later this year. Regarding the V1.1 boards, do any of the PCB fixes from the 1.0 boards still need to be made (jumping the heater voltages, etc.)?

Thanks!

Paul

Hi There,

Heater should be hardwired V1.0 or V1.1, V1.1 corrects the Relay Circuit, that's all.

 

[Ralf]

Does anybody know of a higher quality alternative to the Lorlin rotary switches that will fit the same footprint? I took a look at ELMA but neither type 01 nor type 04 will work.

 

[Potato Cakes]

Why won't they work? I am curious because I was looking at using Elma type 04 for this project.

Thanks!

Paul

 

[PatchDog]

Could any of you that have built this lovely looking Nu Mu perhaps give a description of it's sound and what you use it on?

Is it comparable to the Manley at all?

Can it be pushed to get some subtle saturation?

Much appreciate anyone who can shed some experience/light. Thanks

 

[MaxSquare]

It sounds fantastic! Thank you very much to the author and everyone here!
Another question though - do you know attack and release time values of those corresponding switches?

 

[MaxSquare]

Dear DIY'rs, anyone, do you know release and attack times on NU VARIMU 436?

 

[HerbertR]

I have not measured them, but they work pretty well, as expected.

An other thing:
I'm interested to know if anyone has compared the advantages of the Bernbrue/Zayance Nu Varimu 436 circuit and the RS124.

-The circuits are basically nearly identical, the only difference being that the input attenuator is a variable stepped pad in the Nu Varimu 436 in - front - of the input transformer, and the load on the Mu input double triode is fixed at 39K Ohm with resistors, as far as I understand.

-In contrast, in the RS124 circuit, the input signal is applied to the Mu input double triode - after - the input transformer by a variable dual 50K Ohm potentiometer, across with a 3K9 Ohm resistor strapped.

The advantages or disadvantages are not entirely clear to me. I would be interested to know how you would rate the two designs, Saturation of the In-TX, better driving because of a fixed load on the Mu Tube???

Basically, the Nu Varimu is a very noble beast when used with a correspondingly high level of excellent transformers and tubes. But what if the Nu Varimu was enhanced with an additional variable/stepped Dual 50K potentiometer after the Input Tx like the RS124? The better RS124, Altec 436 and better Varimu 436?

 

[thelivingroom]

For those who have built this, how often do you find the need to re-zero the meters? I’m finalizing my front panel design and haven’t decided if I’m adding the zeroing holes on it or not. I prefer the look without them, but don’t want to regret it later if I have to pull it out all the time to zero the meters. Thanks!

 

[HerbertR]

For those who have built this, how often do you find the need to re-zero the meters? I’m finalizing my front panel design and haven’t decided if I’m adding the zeroing holes on it or not. I prefer the look without them, but don’t want to regret it later if I have to pull it out all the time to zero the meters. Thanks!

Hi, I never reset the meters to zero. After a few minutes of warming up the meters go to 0. But it was clear to me that I wanted direct access from the front panel, imo

Btw You absolutely must use matched tubes. Otherwise you won't get a usable "matched" stereo compressor for bus or mastering. For the 6BZ7 Mu Tube I would really recommend getting a pair of RCAs!! As for the 12AT7s I went with matched Telefunken ECC801s. The RCAs work phenomenally compared to Philips, Magnadyene..., no thank you. I think I spent 15 hours trying to find the best combination and fine tuning. If you can't balance them properly during the calibration procedure or tubes don't behave as you would expect from a compressor, e.g. only a little compression behavior, or you get too much harmonics at higher compression then get other Mu tubes like -> RCA Mu's.
My experience was that the two channels are in sync by about 0.1-0.2dB across the entire gain/attenuation range at classical line level usage. You can compensated a few tenth dB by using R144a or R144b with changing a "few" ohm load on the secondary TX output.

A compressor of this great quality needs really good tubes besides the Lundahls and Sowters... otherwise I think won't get the magic out... My mojo moment was the RCA tubes I heard in the unit. Regards from the pretty warm Austrian Alps

 

[thelivingroom]

Hi, I never reset the meters to zero. After a few minutes of warming up the meters go to 0. But it was clear to me that I wanted direct access from the front panel, imo

Btw You absolutely must use matched tubes. Otherwise you won't get a usable "matched" stereo compressor for bus or mastering. For the 6BZ7 Mu Tube I would really recommend getting a pair of RCAs!! As for the 12AT7s I went with matched Telefunken ECC801s. The RCAs work phenomenally compared to Philips, Magnadyene..., no thank you. I think I spent 15 hours trying to find the best combination and fine tuning. If you can't balance them properly during the calibration procedure or tubes don't behave as you would expect from a compressor, e.g. only a little compression behavior, or you get too much harmonics at higher compression then get other Mu tubes like -> RCA Mu's.
My experience was that the two channels are in sync by about 0.1-0.2dB across the entire gain/attenuation range at classical line level usage. You can compensated a few tenth dB by using R144a or R144b with changing a "few" ohm load on the secondary TX output.

A compressor of this great quality needs really good tubes besides the Lundahls and Sowters... otherwise I think won't get the magic out... My mojo moment was the RCA tubes I heard in the unit. Regards from the pretty warm Austrian Alps

Thanks @HerbertR! I have the trimmers for front panel access arriving tomorrow. I think I’m gonna go ahead and swap them out.

As far as tubes, I bought matched pairs (supposedly) of NOS Brimar 12AT7 and GE 5-Star 6201, Sylvania and GE 6AL5, and 1958 CBS and 1962 RCA 6BQ7A. Hopefully I’m covered in that department.

For the meters I bought Sifam Tinsley Vista series with custom scales from Ram Meter. They were very pleasant to deal with! I was able to sneak two soft white LED’s in the bottom and they look great lit up. I pointed them down and painted the inside of the cover white, and it’s a nice glow. I couldn’t have these be the only meters in my rack that aren’t illuminated haha.




I’m really excited about finishing this one. I just need the case and front panel, and assembly should go much quicker than other projects I’ve built lately.

 

[petermontg]

RMOD on attack is it quicker attack times or slower attack times? I know it halves the release. So will it half the attack time and will 1meg suffice here also?

 

[thelivingroom]

Hi Peter,

I replaced my meters with 1mA ones.

I left Rtrim empty and I get 330VDC on A point, 261 on B channel A, and 260 on B channel B.
Pretty high? I'm supposed to make the calculation to have Rtrim giving something like 245 on B+ ?

Other points readings, respectively on A and B channels, are as follow:
C 267,7 C 268,7
D 176,6 D 171,2
E 168,5 E 170
F 3,22 F 3,26
G 3,65 G 3,59
H 3,93 H 3,68
I 266,6 I 268
J 266,9 J 266,9

Looks like VR104 and VR103 tweaking have no impact on read values???

Thanks for your help ;-)

Regards,
Jerome

I know this is an old post, but I’m going back through this thread while awaiting my case and front panel and noticed something that wasn’t mentioned in the replies about your B+ issue. You stated that you left RTrim empty, but I remembered while doing my initial homework for this project that RTrim either has to be jumped or fitted with a resistor. If you leave it empty than R3 (47k) is also taken out of the circuit for the TL783 adjustment. I hope this helps you or others in the future who may come across this!