Unit-8

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #60 on: June 20, 2019, 09:09:22 AM »
Hi Bernd,

Thanks for the useful tips. This morning I started calibrating the compressor and I encountered the first problem. On test points B, C, D, E, I and J I have the same voltage on both channels between 297 and 300VDC which does not change using the VR103 and VR104 A-B trimpots. On the test points F, G, H the voltages measured are 0VDC and even here the trimpots have no effect. All the tubes do not glow up on both channels. No problem on relays and heater rails where I get 12 and 6.3VDC respectively. The tubes I used in the circuit are: RCA 6AL5, Mullard CV4024 (12AT7) and Brimar 6BQ7A (6BZ7 equivalent). Also, I checked all the components on the PCB to verify the values and their exact place on it and I viewed all the solders. No problems found. Any suggestions?

Ta

Andrea


bernbrue

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #61 on: June 20, 2019, 10:04:50 AM »
Maybe a stupid question, but did you do the heater wiring on the solder side of the pcb?
Bernd

« Last Edit: June 20, 2019, 10:12:41 AM by bernbrue »

Unit-8

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #62 on: June 20, 2019, 05:50:41 PM »
Yours is not a stupid question. I completely forgot to connect the heaters together :) now solved.
Progress to follow...

bernbrue

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #63 on: June 21, 2019, 06:09:06 AM »
 ;D

Unit-8

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #64 on: June 24, 2019, 11:43:32 AM »
Hi Bernd,

I started testing again today and unfortunately I haven't made much progress since last time.
First of all, the needles of the two VU meters do not move.
These are values ​​measured by the test points of the two channels:

CH-A:                 CH-B:

B: 295                 B: 293
C: 289                 C: 282
D: 289                 D: 286
E: 289                  E: 286
F: 14.46              F: 13.4
G: 0.90               G: 1.08
H: 0.81               H: 1.04
I: 285                    I: 283
J: 285                   J: 282

Furthermore, turning the trimmers these have only a slight effect on the voltages probably because of the above-mentioned VU meters problem.

Andrea

bernbrue

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #65 on: June 24, 2019, 12:06:52 PM »
1) Can you tell me more about your VU meter? In fact the unit needs an amperemeter (1mA or lower)
2) Does the meter react to the meter trimmer on the control pcb?
3) Is there a ground connection going from mainboard to control pcb?
4) Did you test, if the unit passes audio?
Pictures would be helpful. After powering up the unit needs about 5-6 seconds before the meter moves up.
Bernd
« Last Edit: June 24, 2019, 12:14:46 PM by bernbrue »

Unit-8

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #66 on: June 25, 2019, 06:18:23 AM »
Hi Bernd,

Thanks again for your valuable tips.
Even here I had forgotten to connect the grounding from the main board to the control boards ... damn it!
Now the measured voltages are close to those of your prototype.
However, the needles of the VU meters go to full scale and the trimpots have no effect on them.
It seems that the VU meters get more current than the one needed although they are 1ma fsd as required by the circuit.
What do you recommend: change the resistor from 270R to a higher value, or put another in series at the positive terminal of the VU meters, or what?
I have yet to test if the sound passes through the compressor.

Best

Andrea

bernbrue

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #67 on: June 25, 2019, 06:33:18 AM »
You could increase the value of the 220R resistor (470) or use a 1K trimpot as meter trimmer.
Bernd

Unit-8

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #68 on: June 26, 2019, 10:17:44 AM »
Hi Bernd,

I replaced R106 A and B (220R) with a 6K49 resistor, but it is a temporary solution because the VU meters need one with a slightly lower value than I currently don't have.
However, now they work even if they do not reach full scale.
The primary problem now is that the audio does not go through both channels and I still haven't managed to find the cause.
Any suggestions?
Meanwhile, I continue to investigate..

Andrea

Holger

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #69 on: August 03, 2019, 02:21:38 PM »
Some notes on this project:

- the PCB as well as the schematic have an error, the heater wiring for the 12AT7 is wrong.
Pin 4+5 of the two 12AT7 must be wired to F+, Pin 9 must be wired to F-.

- the 436 is built around attenuators. If a 1:1 input transformer ist used, these attenuators don't make so much sense because the internal level is relatively low.
The input TX for the 436 suggested by Sowter is the 1231 which is a 1:2.3 (15k:80k). Such a transformer rises the input level to a point where the attenuators are usable.
I'm currently playing with an Edcor 600:10k which gives a very high internal level, maybe a bit too much.

- I had to solder a 5k trimmer in series with the 220R meter resitor to get the value down to 1mA for the meter.

- The suggested OP TX for this project is the Sowter 8650 which is a 9CT:1 TX. Sowter has also the 1232 12.4CT:1+1 which could work here. Both are expensive (100 pound sterling).
I'm currently toying with an Edcor 15K:600 which I doubt has the right gap but it works.

The compressor is interesting. My version distorts the low end a bit but I don't have the right transformers right now. Can be improved.




bernbrue

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #70 on: August 03, 2019, 03:00:50 PM »
Thanks for pointing out your observation, Holger. When designing the pcb Tony and I were concentrated  on getting the details right and didnt see the more obvious things. Sorry for that.
I'm going to alter my prototype accordingly and report back. Please keep us informed about your progress.
Cheers
Bernd

Holger

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #71 on: August 21, 2019, 03:16:34 PM »
My observations, part 2:
I was wrong regarding the input transformers, a 1:1 transformer is OK. The compressor reacts on relatively low levels. My current measurements indicate that the compressor is made for a +4dBu/0VU environment. So it doesn't make sense to push up the input via a step up TX and then killing the signal with attenuators.
I'm going to test some more OP TX.


C_Meyer

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #72 on: September 17, 2019, 04:55:21 PM »
Hey guys! Has anyone had success in getting their unit properly working? What are your impressions, how does it sound?! I am very interested in doing this build but i'd very much like to see some success stories and comments on the sound and usability of the unit before throwing my hat into the ring!

Additionally: I think the "Mainboard & Control PCB" BOM has a minor error.  It would appear as if we're two rotary switches short. Are there suppose to be 6 of the 12 position Lorlins instead of 4?

Cheers!
Chris

bernbrue

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #73 on: September 18, 2019, 04:56:12 AM »
Hi,
my unit (prototype) is properly working (see video first post). During the prototype building process we realized some minor flaws that can easily be corrected. These were the relay circuit and the heater wiring of the output tube. The relay circuit has already been corrected on all the boards we have in stock, the heater wiring has been described here as well.
Zayance will check the BOM once again.
This Varimu compressor doesn’t need any further explanation.  I’ve got a few of them in my rack and use them very often.  Our pcb design is very well thought out and  offers  features you won’t find elsewhere.
Go for it.
Bernd

C_Meyer

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #74 on: September 18, 2019, 04:07:30 PM »
Thank you so much for your reply Bernd!

I will definitely order the boards in the next few weeks. I am looking to use this in mastering applications... should I plan on doing any modifications to the unit in order to make it more appropriate for this application?

Cheers!
Chris

PS: Thank you for all the hard work you and Zayance have done on your designs as well as providing support for them! Over time I plan on building them all!
« Last Edit: September 18, 2019, 07:47:46 PM by C_Meyer »

Unit-8

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #75 on: December 03, 2019, 09:00:42 AM »
These days I got my hands on the compressor where I checked again all the wiring, swapped the tubes, viewed the components on the pcb etc. but even now I can't get audio from both channels. The VU meters work as they should now by reaching 0 dB without audio at the respective inputs and I calibrated all the voltages on the test points obtaining good readings almost equal on the two channels. I also changed the output triode heaters connections as suggested by Holger, but still no audio. Any suggestions or help will certainly be appreciated.

bernbrue

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #76 on: December 03, 2019, 09:32:55 AM »
Assuming that you’ve put everything carefully and correctly together I would advise to start at the input side. Feed the unit with any kind of audio signal.  Build a simple audio probe (tip of audio jack, sleeve to ground)  and trace signal. Before you start you should check if XLR wiring is correct.

- Right in front of  the input transformer (no signal? Check input attenuator)
- right after the input transformer (no signal? Check transformer wiring)
- now be careful! ! Don’t probe anywhere on the output transformers primary side! High voltage!  Probe right after the output transformer (secondary side, output) , try one side of the R143 A resistor. (No signal, check output transformer wiring.)
- probe at  pin 2&3 audio out (no signal, check output attenuator for shorts etc.)
- check the switchboard connections to the main board once again. Probe at R120A for audio as well .
- finally check if the relays are working correctly and once again the output XLR wiring.

I’m quite sure there is some wiring issue. Don’t give up. It’s worth the time.
Bernd
« Last Edit: December 03, 2019, 09:36:49 AM by bernbrue »

Unit-8

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #77 on: December 04, 2019, 09:52:06 AM »
Hi Bernd,

Thanks again for your help.
However, I've already done most of the checks you recommended me to do, except check the 2 control boards again.
For tests I'm using a signal generator with a scope.
I do not have the sine wave oscillator signal on the secondary winding of the input transformer measuring it on R120 and between R100 and R101.
No signal on pin 2 & 3 from the 14 pin connectors on main pcb.
I checked all 4 flat cables going to the control boards without finding errors on the respective connectors.
Same thing on the two 436 control boards where there are no cold welds or wrong component placement. Is it possible that there are jumpers to be connected on the main pcb or the control boards that I have not done? All 4 relays are working. As input transformers  I’m using two Lundahl LL1540.
« Last Edit: December 04, 2019, 10:26:27 AM by Unit-8 »

Unit-8

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #78 on: December 05, 2019, 06:33:19 PM »
After banging my head several times I finally managed to find the cause of the lack of audio output.
The two input relays lacked grounding for the 12 V supply, so only the output ones worked.
I hadn't checked well before because I thought there was no such problem on the PCB.
I have attached a photo that will be useful to those who will face the same problem in the construction of the compressor.
The short blue leads at the top of the photo are the ground for the input relays.
In the first tests carried out I can say without exaggerating that the sound and the compression obtained are amazing.
I have only a slight difference of a few dB between the two channels that I will try to solve soon.

zayance

Re: [BUILD] NU VARIMU 436 build & help thread
« Reply #79 on: December 07, 2019, 06:03:58 AM »
After banging my head several times I finally managed to find the cause of the lack of audio output.
The two input relays lacked grounding for the 12 V supply, so only the output ones worked.
I hadn't checked well before because I thought there was no such problem on the PCB.
I have attached a photo that will be useful to those who will face the same problem in the construction of the compressor.
The short blue leads at the top of the photo are the ground for the input relays.
In the first tests carried out I can say without exaggerating that the sound and the compression obtained are amazing.
I have only a slight difference of a few dB between the two channels that I will try to solve soon.

Hi there,


The gnd link should have been there, but situated on the top copper, from the diode point directly to top copper plane, that's what i had done for rectifying the errata, maybe yours was missing this little solder bridge? Or this one was maybe broken by shipping or assembly handling?
If no present, please let me know so i can quadruple check that on my others boards.
Sorry about the headache


 

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