[BUILD] NU VARIMU 436 build & help thread

[Rob Flinn]

Help.. i got a non working diy 436.. the project is the pcb is on another thread here. It passes signal ok, but compression is totally unnoticeable. At switch on, the meter goes all the way right. When signal passes, the meter goes towards the middle but alas, it doesnt move along with the signal.. very slow movements to the right when signal is drastically reduced. Any hints where i could look? Replace tubes? They may have been damaged in transport..

If the meter is moving left then the bias on the 6bc8 will have changed & it will be compressing. In my experience the 436 stock doesn't really work that well with modern gear. I built a few over the years & always dismantled them, I would never have used them because they sounded awful. I built some RS124's & they are a different ball game much more controllable & very usable.

 

[Masuto]

Hey thank you! Super helpful! Ok so i just have to bias that one tube? Great.. theres two trimmers on board.. actually this is a somehow jazzed up 436.. unfortunately the seller couldnt help and just linked to this thread Altec 436C Build Project (PCBs, schemes)

 

[studiosus]

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..

 

[MaxSquare]

Where did you get this really nice case for nu varimu 436?

 

[MaxSquare]

I have also finished my build. I ve used LL1540s the Sowter 1232 for my build. I could grab a pair of small 1mA Honeywell MM1 Meters on Ebay for about 65 Euro. I also tried to buy directly from Jewell Company NOS MM2 Meters. But their behavoir was so rude - neeeevvvveerr again. So a snooty, disgusting company. Bäaah...
The Compressor is in my opinion super clean, really fast, it has a very expensive sounding texture. Its difficult to get this piece really dirty sounding, hard to get it pumpin'. Like SSL on Tubes.... Wow....

Nothing to mention, no real problems with the build. It works excellent.
My Power TX is a customer made TX, with 0.2A 215V secondary, 4A 8V secondary and 1A 12V secondary from Audiophonics France. I have 315V DC after the B+ Bridge and about 15V Voltage Drop over R1. As for B+ Rtrim I ve used 1K -> total 48K for R3+Rtrim to get about 260V. That works super and the Components like the heatsink and resistors only gets slighly warm within the B+ PSU circuit. The heater PSU Circuit also works perfectly. My secondary shows 8.3V AC. The Input Voltage before of the TL338 regulator shows no necissitiy to tweak the Voltage down. The heatsink gets not really hot.
As for the meters I also think you will really need a 1mA DC Meter or they will not get adjusted within the range. The Meter adjustments also affect the other calibration adjustments. So it required more calibration cycles. I used a 1kHz Signal with +5dBu on the input and adjusted a 5dB Compression / Voltage Drop to 0dBu on the Output with the compressor. After that I adjusted the Meter Zero with the Multiturn Potentiometer and tried different Resistor in parallel to get the 5dB GR on the Scale and Zero in Bypass. It ended with 100 Ohms parallel between the Meter. Its a funny work. I also "slowed down" the meterspeed with a 10uF Capacitor parallel to the meter. Okay, you should not expect a high precission device. But it works pretty well. Only on high Compression Values bigger 15dB my two Channels show a difference of about 1.5 dB and more due my 6BZ7 Tubes are not really matched and should be replaced as last part. Changing of the 6BZ7 Tubes between the two channels clearly showed the difference.
Thanks to Bernbrue and Zyance - you are amazing!

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

 

[MaxSquare]

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

Does anybody, have the universal frontpanel design still accessible? Please, share!

 

[studiosus]

It's in one oft the first posts. Maybe you need to change the filenending. It's not a PDF. Frank from frontpanels.de does nice panels.

 

[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.

 

[petermontg]

I have some spare Sowter 8650 going spare for this project. Check the black market.

 

[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