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

ethervalve said:

baadc0de said:

Interstage. There have been reports of the compressor picking up more hum/noise there.

Click to expand...

Hey thanks for the advice, I decided to go all-Lundahl for the rev 1. My rev 2 is very quiet with the Edcors.

Click to expand...

Really!?! I need to get my rev 2 working with edcors (I have a box of them) for some reason it wouldn't, and when I switched out the transformers with mu-metal covered ones, it was dead quiet.

Maybe cause I live in the city and there is tons of junk in the air??

IDK I'm going to build another one with edcors and see, I love the tone of the steel core edcors, nice and warm.

Hi Abe!

Thanks for the help, really appreciate it!

Before my stepped pot for Threshold I put now trimmers, like this I can adjust it perfectly!

No stereo link at all for it

Stereo pots, stepped, but no link! I connect direct S and C point together on channel 2.

One more thing.

I'm using the same meter as in my Gssl, 1mA one! No move at all, really small move in fact almot 1db when full compression. And when unit is fired up, the meter goes for full reduction even with no signal in!

Best regards.

Chris.

labak said:

Hi Abe!

Thanks for the help, really appreciate it!

Before my stepped pot for Threshold I put now trimmers, like this I can adjust it perfectly!

No stereo link at all for it

Stereo pots, stepped, but no link! I connect direct S and C point together on channel 2.

One more thing.

I'm using the same meter as in my Gssl, 1mA one! No move at all, really small move in fact almot 1db when full compression. And when unit is fired up, the meter goes for full reduction even with no signal in!

Best regards.

Chris.

Click to expand...

Great!

And just to verify bout the meters...you know they respond like the 1176 meters right? basically they are full deflection with no gain reduction.

Great!

And just to verify bout the meters...you know they respond like the 1176 meters right? basically they are full deflection with no gain reduction.

Click to expand...

I've seen that and think that!

But finally 1ma meter is not made for it? Moves are too small with, aren't they?

Anyway, I will update to something else.

I'm thinking about doing a kind of tube and harmonic box! What do you think if we had a switch to cut the tube HT, and run audio thru tubes?

Thanks for all.

Best regards.

Chris.

labak said:

Great!

And just to verify bout the meters...you know they respond like the 1176 meters right? basically they are full deflection with no gain reduction.

Click to expand...

I've seen that and think that!

But finally 1ma meter is not made for it? Moves are too small with, aren't they?

Anyway, I will update to something else.

I'm thinking about doing a kind of tube and harmonic box! What do you think if we had a switch to cut the tube HT, and run audio thru tubes?

Thanks for all.

Best regards.

Chris.

Click to expand...

1ma should be fine...but vu seem to work ok too..just changes your scale.

True! 1mA is ok!

My meters do not have enough internal resistances!

Just put a trimmer in between + and - and it rocks.

All the options and settings are rocking. Thanks for all Abe!

Best regards.

Chris.

abechap024 said:

ethervalve said:

baadc0de said:

Interstage. There have been reports of the compressor picking up more hum/noise there.

Click to expand...

Hey thanks for the advice, I decided to go all-Lundahl for the rev 1. My rev 2 is very quiet with the Edcors.

Click to expand...

Really!?! I need to get my rev 2 working with edcors (I have a box of them) for some reason it wouldn't, and when I switched out the transformers with mu-metal covered ones, it was dead quiet.

Maybe cause I live in the city and there is tons of junk in the air??

IDK I'm going to build another one with edcors and see, I love the tone of the steel core edcors, nice and warm.

Click to expand...

Hey Abe, I haven't done measurements but under use I've never noticed objectionable noise or hum. Subjectively, it's quieter than my LA2A clones and about on par with RevD 1176 clones. I do mainly record to tape with no noise reduction tho, so I'm seldom listening for post-nuclear-holocaust-esque digital silence. I'll do some measurements after I finish the 2nd one (tonight hopefully!)
I also would really like to know the attack and release specs. For measuring release, would an above-threshold tone followed by a below-threshold tone be the way to go?
One last thing, I found a couple THAT1646 chips in my junk drawer. Has anyone tried these chips out in place of DRV134s?
PS I just noticed Mouser stocks a switched 100k liner pot should anyone wish to do a build with bypass on the attack pot (like the original 176): http://www.mouser.com/ProductDetail/Alpha-Taiwan/RV170SF-10-15R1-B100K/
 

Hey Abe - when are you going to do another run of kits?

Hi,

have a problem with the psu .... i only get +6.3V but -0. I don´t find the fault ... any ideas?

thx

dogma said:

Hey Abe - when are you going to do another run of kits?

Click to expand...

Soon I hope, as soon as there is enough interest.

RYM said:

have a problem with the psu .... i only get +6.3V but -0. I don´t find the fault ... any ideas?

Click to expand...

Start measuring the voltage out of the transformer (carefully!) And follow it into the regulators. Also remember to trim the regulators they are multiturn, meaning about 25 turns from one end to the other. I know you probably know this but don't want to take anything for granted. That should fix it.

abechap024 said:

Hi! Yea the DRVs do seem to pass DC. They supposedly are supposed to negate it by having the caps near the output but I guess not. (from the data sheet) I would put a cap between the opamp and the DRV chip. Bi-polars are ALWAYS a fine choice when dealing with audio, or anything for that matter.

Click to expand...

Hi all,
I just noticed that my Rev 2 also has some DC on the outputs. In my case, I'm using ne5534s rather than DOAs; as far as I can tell the DC seems to be coming from that last ne5534 prior to the DRV134. Has anyone else had this problem and successfully fixed it? Would Abe or anyone else have a suggested cap value to try?
And pardon my ignorance, but would the offset nulling application example in the ne5534 datasheet be applicable here?

ethervalve said:

abechap024 said:

Hi! Yea the DRVs do seem to pass DC. They supposedly are supposed to negate it by having the caps near the output but I guess not. (from the data sheet) I would put a cap between the opamp and the DRV chip. Bi-polars are ALWAYS a fine choice when dealing with audio, or anything for that matter.

Click to expand...

Hi all,
I just noticed that my Rev 2 also has some DC on the outputs. In my case, I'm using ne5534s rather than DOAs; as far as I can tell the DC seems to be coming from that last ne5534 prior to the DRV134. Has anyone else had this problem and successfully fixed it? Would Abe or anyone else have a suggested cap value to try?
And pardon my ignorance, but would the offset nulling application example in the ne5534 datasheet be applicable here?

Click to expand...

I would put a cap between the output of the NE5534 chip and the DRV chip. The DRV134 is supposed to null any DC offset as per Application data sheet, but doesn't seem to always work.

Hey thanks Abe,
would you have an idea of a cap value I should try?
(I'd like to read up more on general troubleshooting this issue, as I also realized my DIY 169 EEQ has a little bit of DC on the outputs -- has anyone come across a good document on the topic?).

ethervalve said:

Hey thanks Abe,
would you have an idea of a cap value I should try?
(I'd like to read up more on general troubleshooting this issue, as I also realized my DIY 169 EEQ has a little bit of DC on the outputs -- has anyone come across a good document on the topic?).

Click to expand...

10uf up to 100uf would be fine, 22uf, 47uf....Whatever you have handy

Has anyone found a simple single transformer option to power these from US mains?
-s

I'm looking to build a stepped, stereo only version... In this case, could I reduce on cost by:
-Eliminating the stereo switch and jump the connections as if the switch was in the 'stereo' position,
-Using only the LEFT side pots (switches in my case), and eliminating the right side controls.
-There would be no need for a second meter, correct?
-Are the HPF and Bypass controlled at all by the stereo switch? If not, I would just use a single DPDT switch for each.

Is there anything else I'm not thinking of? Are there any key components I should be keen on matching?

Thanks in advance,
Greg

GregNey said:

I'm looking to build a stepped, stereo only version... In this case, could I reduce on cost by:
-Eliminating the stereo switch and jump the connections as if the switch was in the 'stereo' position,
-Using only the LEFT side pots (switches in my case), and eliminating the right side controls.
-There would be no need for a second meter, correct?
-Are the HPF and Bypass controlled at all by the stereo switch? If not, I would just use a single DPDT switch for each.

Is there anything else I'm not thinking of? Are there any key components I should be keen on matching?

Thanks in advance,
Greg

Click to expand...

Yes I've thought about doing the same. You would need separate switches for the HPF and Bypass. IF you really wanted to save money, you could find a good mix of threshold and make up gain and only have attack and release controls and then how hard you hit it would determine the GR...but that might be to constraining, and input control would come in handy..

bluesbaz said:

Has anyone found a simple single transformer option to power these from US mains?
-s

Click to expand...

Yes....pretty much any....18v dual primany and dual secondary....there are lots that will work!

HI
any of you know recommend a toroidal for Europe?
I want to build another 176 mastering version .
In the first I used a custom toroidal bought on prodigy ..
thanks

abechap024 said:

ethervalve said:

Hey thanks Abe,
would you have an idea of a cap value I should try?
(I'd like to read up more on general troubleshooting this issue, as I also realized my DIY 169 EEQ has a little bit of DC on the outputs -- has anyone come across a good document on the topic?).

Click to expand...

10uf up to 100uf would be fine, 22uf, 47uf....Whatever you have handy

Click to expand...

Hey thanks for the tip Abe! I somehow missed this message. I got very busy all of a sudden, but I'll try this out and report back.

bluesbaz said:

Has anyone found a simple single transformer option to power these from US mains?
-s

Click to expand...

I built two with this inexpensive triad model: VPT36-1390
They have them at Mouser if you're ordering other parts from there.