dbx 160vu clone

[haima]

perhaps the meter bias circuit could be something like the one in the later 1176 opamp meter driver?

maybe mike hairball could supply the meters - or perhaps his existing SSL meter would work with a different scale...

 

[damnyankee]

Hairball Audio - good call!!!

He does the 1176 4 button switches...maybe he has some ideas about the 3 button meter switches...

I don't know him, do you???

DY

 

[haima]

he's a super nice guy - just send him a email or pm!

 

[damnyankee]

he's a super nice guy - just send him a email or pm!

Done!

I've sourced the thread, so hopefully Mike/Hairball Audio will drop in. 

Man, I would love take (4) of those VU meter clones off David's hands (he's been a big help here) but as those clones were expensive to have manufactured, their inclusion in this project would create a price point near to what a genuine 160VU would cost. *sigh* 

It's like having aubrey O'Day's  http://cdn.complex.com/blogs/wp-content/uploads/2010/02/aubrey-o-day1.jpg phone number but knowing you can't afford to take her out.

DY

 

[abechap024]

It's like having aubrey O'Day's  http://cdn.complex.com/blogs/wp-content/uploads/2010/02/aubrey-o-day1.jpg phone number but knowing you can't afford to take her out.

DY

What an analogy ! Haha if you play your cards right you get her to take you out AND source some custom meters for a group buy!

 

[Echo North]

Hi All,

First let me say I know very little about this compressor, but I do know a fair bit about sourcing parts.  

The 3 gang switches shouldn't be a problem.  My current 1176 supplier isn't really an option because of the high MOQ but someone like C&K can do it for a reasonable price.  If you're asking me to stock them, I would need a little more info about cap dimensions and switch spacing.

With VU's you obviously get what you pay for, but cost isn't always the best indicator of quality.  For example I think my AL29-WF clone is as good as the Sifam version and is a fraction of the price.  My AL19 meters are good but the Sifam's are a fair bit better (although 3X the price).  The issue with the GSSL type meter is that I can not get the 90 degree deflection of the original without spending $$$$ on custom molds and buying a very high quantity.  The closest option I can provide would be the 19-WF style:
http://hairballaudio.com/shop/product_info.php?cPath=25&products_id=59

I'd need to know the DBX dimensions to be sure.  I can get a custom scale made but it would be the 78 degree type so it would look a little smaller than the original.  I could get it in the "B" style bezel but the pictures I'm seeing show something closer to a thick "WF" style.  Again if you're asking me to source them I can get the meter to VU spec with a rectifier or a straight DC meter.  I'll need to know what resistance and scale (in mA) the meter should be.

If someone is willing to run a group buy they can contact me directly for info.  Only if you're serious though!

Thanks guys!

Mike

 

[damnyankee]

Hi Mike

I doubt if this will help...but here goes:

Meter range is 60db (-40db to +20db).
The rear panel pot sets the VU meter at "0db" for any level from -10db (250mV) to +10db (2.5V).

Matthias, can you help with dimensions on the gang switches and the VU meter - plus help determine the resistance and scale in mA???

 

[damnyankee]

I think this black VU meter looks really bada$$...

http://hairballaudio.com/shop/product_info.php?cPath=25&products_id=61

 

[David Kulka]

Here are the specs for the dbx meter:

A - 1.2 ma current will deflect it to -40.
A + .6 ma current will deflect it to +20.
The coil resistance is 1.4K.

But, it is not -- repeat not -- a VU meter. VU meters are AC meters with very specific ballistics. The dbx meter is a DC meter, and it is much faster than a VU meter.

 

[abechap024]

I think until we get a working circuit up and running, or until someone wants to try out different dc meters on their DBX, we won't really have a clear idea on what meters will work or not. Unless I'm missing something here (which wouldn't be the first time!)

I know DC meters are usually cheaper? I will be happy to set up a bunch of meters and see if we can fandangle something....when the time for fandangleing comes

I know its been said, but let me say it again. Thanks for all the info you guys are contributing for this project!

AC

 

[haima]

I think this black VU meter looks really bada$$...

i'd assume that black "SSL compression" meter is a fast-ish moving DC meter - with a different scale glued on there and a bias/driver circuit i think it might be able to work for a 160ish style comp, not an exact match by any means though (different look, size, mounting style, the needle has less movement range etc).

 

[Echo North]

Thank you for the info David!

abechap024,

Well DC meters are a lot cheaper than true VU meters.  As David mentioned "True VU" is a very specific standard.  Even Sifam meters do not meet this standard.  A true VU will usually start in the $100 range for a single unit (if you're lucky).

90% of the "VU meters" you see are usually DC meters with a bridge rectifier slapped in there.  The ballistics can range from awful to pretty close to true VU.  In these cases the only difference in cost between a DC meter and this type of VU meter is 4 germanium diodes.

Mike

 

[damnyankee]

Here are the specs for the dbx meter:

A - 1.2 ma current will deflect it to -40.
A + .6 ma current will deflect it to +20.
The coil resistance is 1.4K.

But, it is not -- repeat not -- a VU meter. VU meters are AC meters with very specific ballistics. The dbx meter is a DC meter, and it is much faster than a VU meter.

I am learning alot, David - and I'm sorry for boring you with another question but I'm learning...

Am I correct that if I were to measure the audio output amperage with my DMM, the mA/dbx meter should read:

-40 = -1.2 mA
-30 = -0.9 mA
-20 = -0.6 mA
-10 = -0.3 mA
  0 = 0 mA  <-- needle reads "0" on the scale
+10 = +0.3 mA
+20 = +0.6 mA

Thanks!

DY

 

[Walrus]

Would it be possible to use something like the top meter here...http://www.esr.co.uk/electronics/test-panel.htm
and then use the mechanical zero adjust to offset to 12.30?

 

[damnyankee]

Would it be possible to use something like the top meter here...http://www.esr.co.uk/electronics/test-panel.htm
and then use the mechanical zero adjust to offset to 12.30?

the dbx meter is 1.2mA to 0.6mA; the scale on that meter goes -50 to 50.  I suspect that in its stock form, you probably wouldn't hardly see the needle move on the meter.

 

[damnyankee]

Anyone know who makes this meter???  This one goes up to +60db as well...

http://www.jackenhack.com/pics/vumeter.png

 

[David Kulka]

Here are the specs for the dbx meter:

A - 1.2 ma current will deflect it to -40.
A + .6 ma current will deflect it to +20.
The coil resistance is 1.4K.

But, it is not -- repeat not -- a VU meter. VU meters are AC meters with very specific ballistics. The dbx meter is a DC meter, and it is much faster than a VU meter.

I am learning alot, David - and I'm sorry for boring you with another question but I'm learning...

Am I correct that if I were to measure the audio output amperage with my DMM, the mA/dbx meter should read:

-40 = -1.2 mA
-30 = -0.9 mA
-20 = -0.6 mA
-10 = -0.3 mA
  0 = 0 mA  <-- needle reads "0" on the scale
+10 = +0.3 mA
+20 = +0.6 mA

Thanks!

DY

Your table of currents and meter readings is correct, but practice repeating these words 100 times "Audio is AC. VU meters are AC. dbx meters are DC."

Forget this "audio output amperage" stuff. dbx used a DC meter, driven by a 3 mode metering circuit. In Gain Change mode it basically displays the DC control voltage going to the VCA. In Input mode you are seeing the DC output of the RMS Detector. Output mode (as I recall) is a sum of the RMS Detector DC and the VCA control voltage (input level plus VCA level equals output level).

There is never AC or audio signal connected to this meter. It only measures, depending on mode, different DC voltages within the side chain circuit.

 

[arska]

It´s dc-current meter not voltage meter, take any 100uA or 1mA meter and make new dB scale . redesign mea amps with bias setup to give meter offset as needed.
Easy task .... no problem........

 

[damnyankee]

[quote author=David Kulka]

Your table of currents and meter readings is correct, but practice repeating these words 100 times "Audio is AC. VU meters are AC. dbx meters are DC."

Forget this "audio output amperage" stuff. dbx used a DC meter, driven by a 3 mode metering circuit. In Gain Change mode it basically displays the DC control voltage going to the VCA. In Input mode you are seeing the DC output of the RMS Detector. Output mode (as I recall) is a sum of the RMS Detector DC and the VCA control voltage (input level plus VCA level equals output level).

There is never AC or audio signal connected to this meter. It only measures, depending on mode, different DC voltages within the side chain circuit.
[/quote]

Ok, I wrote it on the board Bart Simpson-style 100 times.  ;D

Depressing one of the buttons on the 3 button gang allows us to select DC voltage going to the VCA, DC voltage out of the RMS, or sum of the voltages of the VCA & RMS - which is being read as "decibels" on the dbx DC meter.  

So here's a few stupid questions..

1. Why is current (mA) being measured at various points along the meter scale instead of voltage?  I know when I troubleshoot pedals, I look for voltages...

2. Bridge rectifiers are used in AC applications and true VU meters, correct?  

3. Would it be safe to say DC voltage meters do not have these rectifiers?  

4. As the dbx meter is a DC amperage meter, we would measure the mA rating along the meter points, correct?

Thank you again!

DY

 

[damnyankee]

It´s dc-current meter not voltage meter, take any 100uA or 1mA meter and make new dB scale . redesign mea amps with bias setup to give meter offset as needed.
Easy task .... no problem........

Awesome!  It's unanimous - you got the job! *haha*  ;D