[BUILD] NU VARIMU 436 build & help thread

[Holger]

I'm currently building a second unit. As you can see, I've did a couple of mods.
I used an external PSU to get rid of the usual power transformer AC hum.
I rewired the tubes for 12.6V heaters, I use an SMPS here.
I'm actually measuring -80 dBu noise floor flat.I omitted the output attenuator section and replaced it with a simple 1k pot (Ian's Neve trick).

In this build I use a Lundahl 1540 which works fine. OP TX is a Sowter 1232. The meter is an old Weston 301 stamped May 1964 on the back.
Note: in an earlier post I wrote that the meter circuit needs to be modified. I was wrong. The meter circuit works well
for the Sifam meter in my first build as well as for the Weston meter when the meter is strapped with a resistor.
I used a 22R which works perfect for both meters.

 

[petermontg]

Holger, where did you get the cans? Were they from Sowter when you got the trafos.

I am down to -80 flat also. I am going to shield up the toroidal and try get another -5db or so out of it. Mine is still in the chassis. I can some psu noise in there on the scope.

Best
Peter

 

[Holger]

Holger, where did you get the cans? Were they from Sowter when you got the trafos.

...

Sowter, story told here:


https://groupdiy.com/index.php?topic=75702.msg964557#msg964557

 

[Rob Flinn]

Sowter, story told here:


https://groupdiy.com/index.php?topic=75702.msg964557#msg964557

Apparently they have taken on more staff according to their website.

 

[electrisizer]

Note: in an earlier post I wrote that the meter circuit needs to be modified. I was wrong. The meter circuit works well
for the Sifam meter in my first build as well as for the Weston meter when the meter is strapped with a resistor.
I used a 22R which works perfect for both meters.

hello holger can you explain a bit more. what do you mean with a strapped resistor?
have you used a 500R trimmer for the meters as suggested?

 

[Ayman59]

Hello guys, I hope everything is OK on your side ;-)
Can you tell me please if heater wiring correction on the 12AT7s is as simple as this (and the same on the other channel):

 

[petermontg]

Hello guys, I hope everything is OK on your side ;-)
Can you tell me please if heater wiring correction on the 12AT7s is as simple as this (and the same on the other channel):

Yes! The correct wiring of the output tube heater should be somewhere in earlier in the thread.

Best
Peter

 

[labak]

Hello all,

Some news.

First of all my unit works good.

The 1689-PP works well...What is good, is it's configurable to have different output ratios.

@Peter : indeed 1540 does not work in this design.

I tried different Transformers : 600:600 (old Altec output transformers), and the Edcor 10k:600 as a 600:10k.
I have had, surprisingly, great results using a 5402 setup as 1:1 configuration. I tried it as 1:2, backward, and it was too strong for the circuit, for me.

I tried with RCA 6bc8 and Siemens PCC189. I prefer the articulation of the PCC189.
To be able to use the PCC189, I removed the Rmeter resistor (270r) and I put a 1k trimpot instead.

I still have to pass it throughout tests.

I hope this helps.

 

[petermontg]

Hello all,

Some news.

First of all my unit works good.

The 1689-PP works well...What is good, is it's configurable to have different output ratios.

@Peter : indeed 1540 does not work in this design.

I tried different Transformers : 600:600 (old Altec output transformers), and the Edcor 10k:600 as a 600:10k.
I have had, surprisingly, great results using a 5402 setup as 1:1 configuration. I tried it as 1:2, backward, and it was too strong for the circuit, for me.

I tried with RCA 6bc8 and Siemens PCC189. I prefer the articulation of the PCC189.
To be able to use the PCC189, I removed the Rmeter resistor (270r) and I put a 1k trimpot instead.

I still have to pass it throughout tests.

I hope this helps.

That great news Labak. going to try the trim option on the output shortly. Might be a nice option to have when dealing with a hot output. Mine is pretty solid now. Took awhile to for everything to settle down and burn in.  It has a lovely color to it. I am a fan of its box tone. The compression isn't overly strong. Ideal just tapping the compression is the way to go.

Its definitely a keeper.

Best
Peter

 

[Cosmonaut]

Hello guys, I'm doing my homework to make a complete BOM including transformers, meter, case and all that. The idea is to use it in my msatering studio, so looking for some flavour but the most linear and transparent the better.
-So options for transformers would be Lundhal 1540 (somebody said that doesn't work?) and which other lundhal would work for the output?
-For meters anything 1mA right?
-Is there any vector file (not FPD) for the front panel?

Thanks in advance

 

[Holger]

...

@Peter : indeed 1540 does not work in this design.

...

I wonder why. Can you explain that a little bit?
In my current build, I use the  Lundahl 1540/Sowter 1232 combo. Attached is the frequency response.
THD+N @ 6 dBu input
0.130 @ 1000 Hz, 0.160 @ 50 Hz  Right
0.120 @ 1000 Hz, 0.167 @ 50 Hz  Left
I can live with that.

 

[petermontg]

I wonder why. Can you explain that a little bit?
In my current build, I use the  Lundahl 1540/Sowter 1232 combo. Attached is the frequency response.
THD+N @ 6 dBu input
0.130 @ 1000 Hz, 0.160 @ 50 Hz  Right
0.120 @ 1000 Hz, 0.167 @ 50 Hz  Left
I can live with that.

Mine were a fairly old set. The unit would lose bottom and boost the top. I didn't really investigate much as I spent too much time chasing the fault.

Trafos still read correct out of the unit. I thought it could have been something to with the CT strapped across the input with those hard to know. I just put it down to an old trafo.

Best
Peter

 

[petermontg]

Hello guys, I'm doing my homework to make a complete BOM including transformers, meter, case and all that. The idea is to use it in my msatering studio, so looking for some flavour but the most linear and transparent the better.
-So options for transformers would be Lundhal 1540 (somebody said that doesn't work?) and which other lundhal would work for the output?
-For meters anything 1mA right?
-Is there any vector file (not FPD) for the front panel?

Thanks in advance

You can use it in a mastering environment if you change the threshold. The units shines when driven hard but the threshold is too strong even in first position for mastering.

I changed my threshold pot from the 47k Log. It's far too much in reality.

I took the 3K resistor in position 1 and calculated that as my strongest compression in position 6 I think I ended up with a 7k log in there. Perfect for mastering!!  487R, 768R, 1K21, 1K96R, 3K which when calculated should be 3K090 (splitting hairs).

Best
Peter

 

[Cosmonaut]

You can use it in a mastering environment if you change the threshold. The units shines when driven hard but the threshold is too strong even in first position for mastering.

I changed my threshold pot from the 47k Log. It's far too much in reality.

I took the 3K resistor in position 1 and calculated that as my strongest compression in position 6 I think I ended up with a 7k log in there. Perfect for mastering!!  487R, 768R, 1K21, 1K96R, 3K which when calculated should be 3K090 (splitting hairs).

Best
Peter

Thanks a lot Peter, I will continue studying the project and it will go to the cue, after the Porter eq.

 

[Holger]

 

[dasnevestheo]

Love the switches !

 

[Grooveteer]

Gentlemen,

I'm slowly gathering parts for this build.

Has anyone tried the AVD Audio TR2622 as input transformer? 
http://www.avdaudio.com/catalog.htm?id=1367

It's certainly cheaper than Sowter or Lundahl, but I've never heard their transformers. The reviews seem to be all right.

Also: I have some Sifam AL20SQ meters laying around.  I know this build requires a 1uA meter, The specs of these meters confuse me. It looks like the Sifams are not suitable?
http://www.sifam.com/meterDetails.asp?modelNo=AL20SQ

Cheers,
Stefan

 

[PermO]

Datasheet direct link; http://www.sifam.com/Downloads/Content/Vintage_AL%20Meters-A4_web.pdf

Yeah, they say just strap them across a 600 Ohm output with a resistor....

But that will not show you gain reduction.

I wonder if there's too much current in the circuit for the meter to handle, could this be fixed with a resistor ?
It will at least move once  ???

 

[Grooveteer]

It will at least move once  ???

;D ;D

I'll look into proper 1ma meters then. 

 

[Grooveteer]

Bernd, Tony,

I'm playing with the FPD file provided earlier in this thread.  I see that the scales and the drill holes for the Lorlins are little offset.  (scales are slightly lower on the Y-axis than the drill holes)

Not a problem as I like to do my own scales, but I would just like to be sure that the drill holes are still correct.
Can any of you confirm this?