PRR-176 Vari-Mu REV 2 - *Group Buy 7/13!*

[astroschnautzer]

Caold anybody give a hint on good quality meters that fits the 1u case from collectivecases..? hopefully from europe or ebay...

http://www.ebay.com/itm/Panel-VU-Meter-TN-73-0dB-1-288V-76x59mm-LED-lamp-NISSEI-/130384936913?pt=LH_DefaultDomain_0&hash=item1e5b8c3fd1


you have to take off the front cover and cut the bottom off of it for it to fit. Not that hard, just don't huff the fumes!

thanks, not really sure I understand exactly what to do but I trust I will get it when I see them in front of me...

+ one more question, about caps, Is a good practice to elna/mundorf caps on audio path and for example panasonic fc for the rest, or should the PSU caps be high quality or how do you peeps do with your capacitors?

 

[astroschnautzer]

Caold anybody give a hint on good quality meters that fits the 1u case from collectivecases..? hopefully from europe or ebay...

http://www.ebay.com/itm/Panel-VU-Meter-TN-73-0dB-1-288V-76x59mm-LED-lamp-NISSEI-/130384936913?pt=LH_DefaultDomain_0&hash=item1e5b8c3fd1


you have to take off the front cover and cut the bottom off of it for it to fit. Not that hard, just don't huff the fumes!

I'm not really sure how to cut the bottom off of these and still keep the meter mechanism working since the mechanism is in the part that is supposed to be cutted off, can you ellaborate a little on this one? + I think you have given a bad hint on meters, havent got the case yet but these look alot bigger than would fit that case (looking at the pictures...)


EDIT: Yep, definitely not the right meters.... looks like these would go in a 1176 case....

 

[abechap024]

Sorry, my mistake,hard to tell from those pictures. I would just get them from hairball unless you have a local nessei dealer.
best,
abe

 

[astroschnautzer]

Sorry, my mistake,hard to tell from those pictures. I would just get them from hairball unless you have a local nessei dealer.
best,
abe

Ok, too bad, maybe I find a project these fit into.... :-[

 

[usekgb]

I finally got around to begin this build today.  I installed all of the parts that I had on hand, and order most of the rest of them.  I'm so excited to get this going!

 

[Edward]

I finally got some time to finish the PSU part, so last night i powered it up with a VARIAC.

I increased the input some 20% at a time and did some measuring and at first everything looked fine except that Heater - was not showing up.

At 60% i noticed a familiar smell and R32 (or was it R16), the 120 Ohm resistor was starting to glow up... I decided to quit because i was not in the mood to make lighting effects.

So my questions are: What exactly are VR7, 8, 10 and 12 doing? And does anyone have a hint on how to trouble shoot the Heater - line?

I would be really thankful for any help on this.

 

[usekgb]

Heater - should be at 0V, as it is tied to the power transformer's center tap.  All of those trimmer resistors in the power supply are setting the voltages that you will need on the main pcb.  Set your volt meter for Scott, and measure the voltages compared to ground.  Adjust the trimmers until you get the voltages that you need.  Also, the BOM calls for three LM317's, but the silk screen on the power supply calls for two LM317's and one LM337.  The LM337 is required for the -18V rail.

 

[Edward]

I see, thank you very much for clearing that up for me. I noticed it said LM337 on the PCB but I doublechecked the BOM and went with LM317. Guess that explains the glowing resistor.

I was expecting +6.3 and -6.3 for the heater +/- but I don't know where I got that from.

 

[abechap024]

Ah! Let me correct the BOM. Sorry bout that gents.

And like you found out, heater needs to have 12.6v difference between them

 

[usekgb]

No problem.  Easy typo to make.

 

[Edward]

Replaced one LM317T for a LM337T and one burned 120Ohm resistor and now it's working like it should. A reminder for me to keep checking the schematic whenever in doubt. I blame no one but myself for that.

However, I have one more stupid question regarding this PSU. Hopefully I can soon move forward and do the fun part, i do hate building PSUs...

On the Plate V+ line i measure 120VDC with ~115VAC on the input side. Expecting ~100VDC i now wonder what kind of problem I have here?

 

[Rellister]

Hi Edward,
Are you building this in a 1U chassis? If so, were you able to fit two toroids for euro power in there with the pcb?
Just wondering how to solve this case-wise.

 

[Edward]

Hi Edward,
Are you building this in a 1U chassis? If so, were you able to fit two toroids for euro power in there with the pcb?
Just wondering how to solve this case-wise.

Yes, my plan is to fit it into a 1U case, but I don't have a case yet so I can't tell you how. It's been done before thou, just scroll through the Rev 1 build thread. I can post pictures when I'm done but i think it's gonna take a while.

 

[Kingston]

Hi Edward,
Are you building this in a 1U chassis? If so, were you able to fit two toroids for euro power in there with the pcb?
Just wondering how to solve this case-wise.

Needs a deep case. I used 280mm, but consider this a bare minimum. There will be problems with heat especially if high rail voltages and DOA's are used. 1U needs a vented cover and a spare 1U (or at least half U) area in a rack for reliability.

If I had to choose now I would do 2U instead and would recommend it to others as well.

 

[ilfungo]

Hi
I've tried to make a stepped version of input but now the compression kick in very early...
what is the problem?
Thanks

 

[abechap024]

Hi
I've tried to make a stepped version of input but now the compression kick in very early...
what is the problem?
Thanks

Well maybe 30db pad isn't enough? Or it is enough, but you have to possibly hit it softer if you don't want it to compress. Also try raising the threshold so you have more breathing room.

You can configure it however you like!

Me, I like to be able to compress things to the extreme. Though, maybe not the best thing all the time I'm beginning to find. Things to consider is the higher the threshold, the potential for better noise floor, but too high and you might get some weird distortion on fast peaks  that overload the circuitry because you have to gain it so got to get the desired compression. Probably easier for me to lay down hard rules, but were is the fun in that?

 

[earl]

This is interesting the unit comes on: tubes glow can hear the output pot working: unit is showing gain (not passing
input signal though) BUT after about a minute the tubes shut off and big noise.  Ideas? anyone? Thanks

 

[Holger]

I assume that you have two problems. Check the heater regulator. Is it possible that the regulator gets too warm and is collapsing after a minute? If so, exchange it, maybe mount it off board on a heat sink. After that problem is solved, you should check where you can trace an audio signal in the signal path.

 

[earl]

Thought stuff was getting warm there.  I will try that out thanks Holger.

 

[Axelerator]

..hm..also interested in a hybrid comp like this..
is there a pcb left ?

axel