[BUILD] NU VARIMU 436 build & help thread

[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]

The release should vary from 2.5 to 250ms.

I stuck mullard in GR and SC. Phillips on the out if I remember. I know it's heading microphonic so I might roll something else there.

The calibration definitely needs FP mounting.

I settled on 15k/15k input. Tried lundahl and some Sowter 10k/10k Going to roll a Sowter 15k/15k against what's in there but I am super happy with the current 15K/15k. Great colour and plenty of vibe. That lowend seems to like the 15k drive better. It reacts now as it should really from now observations. Noise floor is super quiet. I also used the CT on the input secondary side.

Was the original a 15K input? I know TC comp has a 15k input so that's why I ask.