dbx 160vu clone

[abechap024]

you the man Dy!

 

[abechap024]

Here is version one of BOM:

www.acsoundstudio.com/DIY/160vu/BOM/BOMMAINBOARD.html
www.acsoundstudio.com/DIY/160vu/BOM/BOMRMS.html
www.acsoundstudio.com/DIY/160vu/BOM/BOMVCA.html
www.acsoundstudio.com/DIY/160vu/BOM/BOMPWR.html

also for those who like to eat .xls files:


www.acsoundstudio.com/DIY/160vu/BOM/BOMMAINBOARD.xls
www.acsoundstudio.com/DIY/160vu/BOM/BOMRMS.xls
www.acsoundstudio.com/DIY/160vu/BOM/BOMVCA.xls
www.acsoundstudio.com/DIY/160vu/BOM/BOMPWR.xls

I'll Clean them up and arrange them better later, just wanted to get them up ;D

 

[David Kulka]

I'm back, it was just a short trip.

A VU meter will be very damped and slow compared to an original dbx meter. And, unless you remove the diode bridge from it, there will be no way to drive it "backwards". A VU meter is an AC meter; the dbx meters are a special DC type. To replicate the dbx meter, you'll be much better off with a DC meter and it will need to be very fast acting.

The dbx meter is not center tapped. The movement rests near the center when there is no current through the coil, but there is only one coil and there are only two terminals.

I think it will be near impossible to find a fast meter that rests at the 12:30 position like the original dbx meter. I would look for a fast meter that rests on the left and then mod / bias the drive circuit so that in gain change mode it goes to 12:30 when "idling". And of course you'd need to make a custom scale.

This is the opposite of what dbx did with the Beede meter. They let the mechanism take the needle to 12:30 in gain change mode, but DC biased the meter to rest at -40 with no audio in input or output mode. They must have had a good reason for going to all that trouble, so taking the easier way out will likely be a compromise, and any sub meter will probably have a different action than the original. But unless you have custom meters built or change to LED's, there's likely no way around this.

 

[damnyankee]

As I wrote on the other board, "welcome back!".  ;D

Thank you for explaining how VU meters work. I never thought of them as an AC meter; I always assumed they were all DC and I thought the more voltage they received, the more the needle moved to the red.  I see they are much more complicated than that - and I have a new appreciation for them other than to look at them as a "PITA cuz I have to change another light bulb".

Alot of thought must've went in to those dbx meters.  As for me, I'm used to meters which rest on the left, so that doesn't bother me.  I like to have a visual with my ear to confirm when I'm getting near the sweet spot and approaching squash zone.  I'm an analog guy - heck, even my stereo is a 1966 McIntosh tube preamp and tube amp.  I like meters better than LEDs.  But if the only option is LEDs, then I'll live with it because I've had to get used to LEDs on my other compressors (dbx 163x's, 166s, dbx 903s, aphex compellors, valley people dynamites).

I guess my question is given the schemo, can we just plug'n'play the LED meters?

Again, welcome back!  We are VERY VERY grateful for you sharing your experience and expertise, David!  Once we solve this, then it's time to find knobs and talk to one of the guys here to make the box.  This is getting very, very exciting!!!

DY

 

[David Kulka]

Thanks for the kind words.

Sure, VU meters are AC meters. Remember, they were designed to be connected directly to line level audio. Also remember, meters don't really respond to voltage -- they are all about current.

I'm sure you could come close to the dbx meter with an LED circuit, but you'll still be dealing with the same problem...it will be tricky to design the necessary RC circuits to simulate the ballistics of the dbx meter. And to get decent resolution you'll want a lot of LED's. The dbx 160 metering circuit had a whopping 60 dB of range, which was needed because the feed forward 160's were capable of such gain change extremes. Standard VU meters only have 23 dB of range.

 

[damnyankee]

Ok, so the db range is another problem besides the meter design.  Now I'm starting to understand why the dbx 160/161 cost so much new - it certainly wasn't because of the components!

So we're going to have to build something like this, correct?

http://www.electronics-circuits.net/60-db-led-vu-meter-vt69.html

Thank you, David!

DY

 

[bruno2000]

Ok, so the db range is another problem besides the meter design.  Now I'm starting to understand why the dbx 160/161 cost so much new - it certainly wasn't because of the components!

So we're going to have to build something like this, correct?

http://www.electronics-circuits.net/60-db-led-vu-meter-vt69.html

Thank you, David!

DY

The dbx 160 "VU" when new (mid 1980s IIRC) cost $300.  We bought 6 and still have them.
Best,
Bruno2000

 

[arska]

Arska,
I'm not having the option of more than one VCA at work at a time. Put another way, people will only have ONE VCA on the board at a time. So pin 2 of the 2180 will be driven by one of the 4558 thru a 4.7k resistor and a 200ohm resistor. Am I missing something here or that should work well? Or do we need to change the 4.7k resistor to a lower ohm is using the 2180? Plus I'll also make a note of different resistor changes when using the 2180 - Like I know the 100k input resistor should be changed to 20k.
Thanks
AC

You are missing a lot.........

Here´s tested schema...... everyone, how to drive 218X vca. 

 

[David Kulka]

Ok, so the db range is another problem besides the meter design.  Now I'm starting to understand why the dbx 160/161 cost so much new - it certainly wasn't because of the components!

So we're going to have to build something like this, correct?

http://www.electronics-circuits.net/60-db-led-vu-meter-vt69.html

Thank you, David!

DY

That looks like a pretty good candidate. But it will will have to be modded for a DC input and re-scaled to the VCA control voltage, which is log or near log (I'm not sure). I think it would be a combination of changing the circuit to run more or less linearly from a log DC input, and then re-labeling the LED's to fine tune the accuracy. Though it's not absolutely necessary, one or two little RC networks with the right design might give the LED meter "ballistics" that better match the original mechanical meter. (Maybe it would be a matter of changing RC values that are already in the LED meter circuit?)

 

[damnyankee]

[quote author=bruno2000]
The dbx 160 "VU" when new (mid 1980s IIRC) cost $300.  We bought 6 and still have them.
Best,
Bruno2000
[/quote]
I see we now have a source for original VU meters....YOUR six units! *LOL*

 

[damnyankee]

David,

I reviewed this ( http://www.oamk.fi/~archy/vu-meter/index.html ) to get better sense of what's involved with installing LED meters.  As you've pointed out, we're not going to be able to wire up a PICO LED setup for the original VU meter.  There are alot of other things that need to go in to it.

So basically: substituting an LED meter for the original dbx 160VU meter is going to be ALOT of work, isn't it...

DY

 

[haima]

is it worth looking at later dbx compressors with LED meters (903 160X etc...) for hints?

i have a vague memory of a string of comparators for the let meters on those...?

 

[damnyankee]

The more I become familiar with the 160VU, the more I'm realizing it's an animal all to it's own.  My gut reaction is, the LEDs from the newer generation comps aren't going to work just by wiring it in.  

I just don't have enough experience with AC powered gear to be of help.  In my mind, another pcb will need to be created for the LEDs, and that board will need to take the existing power normally fed to the stock VU meter and augmented to drive the LED meters.

The question is, how can that be done? 

 

[haima]

i would have expected the VCAs from the 160vu and 903/160x to have the same control law... but that's complete uninformed speculation, and i should probably butt out!

as you were  ;D

 

[damnyankee]

No - don't butt out.  This is a problem that needs solved.  If you have the LED expertise, any input would be greatly appreciated.

The way I see it: I'm used to working with a dbx 119 which doesn't have any metering; so if that's the case with the 160VU, then I'll learn to live with it.  But some type of pro metering device WOULD be nice...

DY

 

[Rybow]

David mentioned just using a fast acting DC meter in place of both the LED/VU/original metering, and re biasing it to sit at the 12:30 position. I am wondering, does it need to sit in this position? Can't we just set it up to do GR from left to right? That seems like the easiest option.

 

[bruno2000]

No - don't butt out.  This is a problem that needs solved.  If you have the LED expertise, any input would be greatly appreciated.

The way I see it: I'm used to working with a dbx 119 which doesn't have any metering; so if that's the case with the 160VU, then I'll learn to live with it.  But some type of pro metering device WOULD be nice...

DY

How about a 0 center dot based LED meter like on page 8 (or a variation there of)?
http://www.datasheetarchive.com/pdf-datasheets/Datasheets-25/DSA-483404.html
Best,
Bruno200

 

[David Kulka]

David mentioned just using a fast acting DC meter in place of both the LED/VU/original metering, and re biasing it to sit at the 12:30 position. I am wondering, does it need to sit in this position? Can't we just set it up to do GR from left to right? That seems like the easiest option.

It needs to sit in the 12:30 position ("0") when no gain reduction is occurring. That has to be somewhere near the middle of the meter because unlike a traditional limiter, the 160 also shows make up gain (gain addition) on the meter. So it needs to show gain reduction on the left, unity gain near the center, and gain addition on the right. To do that you need a DC meter that mechanically rests near the center, or a standard meter that rests on the left and is brought to the center with DC bias.

 

[abechap024]

You are missing a lot.........
Here´s tested schema...... everyone, how to drive 218X vca.
-arska 

thank you for clearing things up in my head concerning the 2180 implementation. I changed the schematic and will post the new one soon.

Thank you David once again for clearing up some more of the haze concerning the VU meters. Seems that DBX must of had a whole research team  devoted to the production of their VU circuits! lol
about the meters...I know some meters can be mechanically changed to rest in the center... if it messes with the ballistics or other side effects I don't know... But I did it to one of my meters in another comp (it had +/- control voltages) it seemed to work just fine.

Also I would personally like the VU option - even if that means only wiring it in GR mode.
Also the 160VU has 4 pots that DIRECTLY change the meter. I think that will give us a lot of control? also probably a PITA to set up correctly ;D

Haha the LED is also an option....but we'll have to start calling our project the 160LED  :

 

[damnyankee]

I think the 160LED would look very, very cool...but I'm an analog guy and I like looking at meters, personally.

What kind of meter would I look for (spec-wise)?  I'll start the search if someone can point me in the right direction...

DY