[BUILD] NU VARIMU 436 build & help thread

[rockinrob86]

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!

Your build looks great! Where did you get the facepanel? It is the only thing holding me back from building this (I hate metal work!)

 

[HerbertR]

Your build looks great! Where did you get the facepanel? It is the only thing holding me back from building this (I hate metal work!)

Hi, Frank from frontpanels.de has done the frontpanel on green anoidizised Alu. If you need a .fpd file for the frontpanel designer software I can mail it to you. Totally easy free software to modify the holes, signations....Br

 

[sbranco]

I am gonna go slow but am trying to convince myself that I really need the iron before I order some.

For the input transformer, the pcb allows for an API2622, which is a mic input transformer. From what I can gather, the EA2622 and the Altran C3402-2 are pretty much equivalent. UTM seem nice but the pins don't match the pcb configuration. Am I missing something as to why the Altran would not work?

 

[sbranco]

Feel like I am being cheap trying to reuse parts but cheap is relative. Would many use this site if they could just go out and buy what they wanted? Well OK some guys just like to do this stuff regardless. And I am thankful for all the info. Wish this project had as much activity as the Sta-Level or the transformer-less varimu!

Anyway, my plan is to gut an Altec 1707c, a powered PA mixer/amp. To that end I would like to recycle/reuse what makes sense from it.

This is the EI power transformer. It is wired for 120V. For the secondary I am reading 50Vac for the blue wires. I get 80Vac between the larger red wires. 228Vac between the red wires after what I think is the yellow/black center tap? And 113Vac between each red wire and the yellow/black center tap? Haven't tested the smaller red wire because I'm not sure what to test it against. It is soldered to a post on the pcb marked "AC". This transformer has a copper flux band around it. It is a pretty large case so I think it could be far enough to keep anything audible from creeping in. 3.5 Amp fuse by the IEC inlet, 165 Watts maximum. I have read a lot about transformers but was wondering if anyone has repurposed these. The 50Vac is too hot but that can be reduced fairly easy no? Anyone know if I am right about the secondaries? The schematic is readily available for the 1707c but not much info on the power transformer.



Plan to try using the Alltran input transformers but have ordered some UTM output transformers designed for this.

 

[Rob Flinn]

I am gonna go slow but am trying to convince myself that I really need the iron before I order some.

For the input transformer, the pcb allows for an API2622, which is a mic input transformer. From what I can gather, the EA2622 and the Altran C3402-2 are pretty much equivalent. UTM seem nice but the pins don't match the pcb configuration. Am I missing something as to why the Altran would not work?

Not quite sure why they use a mic amp transformer. The original RS124 uses a 1:1. I haven't built this box or used these pcb's, my builds are more an exact copy of the RS124 circuit but my own point to point layout, but I definitely didn't need any extra gain using a mic transformer would have supplied.

 

[sbranco]

Hey Rob,
Just wondering if there was something I overlooked. You are far ahead of me with this stuff so thank you for your thoughts. I will probably need more help as I get further along. The answer is probably already on this forum - somewhere.

 

[Rob Flinn]

Hey Rob,
Just wondering if there was something I overlooked. You are far ahead of me with this stuff so thank you for your thoughts. I will probably need more help as I get further along. The answer is probably already on this forum - somewhere.

I haven't built this particular project. It is quite close to the Altec 436 & possibly the RS124 both of which I have built. Therefore I can't speculate on the reasoning behind the component choices they made.

 

[FreqFarm]

London (UK) based and need a little help with the calibration of a vari mu I am finishing off - hopefully it will just be the final calibration steps as I don't have a distortion meter or scope and have promised not to buy any more kit I will only use occasionally (and this time I really mean it )

Can anyone recommend a good shop or DIYer who would be able and willing? Of course I am happy to pay in one or more of the following: cash, beer or spirits for someone's time.

 

[Rob Flinn]

London (UK) based and need a little help with the calibration of a vari mu I am finishing off - hopefully it will just be the final calibration steps as I don't have a distortion meter or scope and have promised not to buy any more kit I will only use occasionally (and this time I really mean it )

Can anyone recommend a good shop or DIYer who would be able and willing? Of course I am happy to pay in one or more of the following: cash, beer or spirits for someone's time.

You could just apply more signal into the box.

 

[Holger]

#3

 

[Holger]

PSU

 

[studiosus]

Hi all, kind of finished with mine. Works and sounds nicely, but the output is a little low. I also used the 1232 sowters. Herbert vor Holger, what values did you put in R143&R144. I don't know how to calculate these for the 1232 sowters.

 

[Masuto]

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..

 

[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.