CLX-VU Build Thread (DBX 160VU ) UPDATE: REV 3

[Spencerleehorton]

Hi,
I'm getting 24v when connecting Gnd and touching the outer case of the transistor, so this seems fine.
I didn't however pre amp the mic!!! Let me test it with a sine wave.

Regards

Spence.

 

[Bowie]

For the Stereo link, you have to press both the link and the meter function you want, I wish there was a more elegant solution than this, but it works.

Could someone please elaborate on the wiring of the stereo link?  I understand which switch to use and that it's the + side of the Tant cap but how exactly are we wiring the switch? I imagine that the "off" position returns the + leads back to each board, respectively, but what is happening when the link is engaged?  Thanks!

 

[Spencerleehorton]

I would very much like a picture of the link wiring as what Bowie has said if someone is able to draw it out please, if I get a chance and figure it out I will put it up.

Regards

Spence.

 

[Spencerleehorton]

Hi,
When probing the offset pin setting up rms with no input I get 20khz oscillation anyone have an official word on how to fix this please?

Regards

Spence.

 

[Bowie]

Unfortunately, the CT trace (at the PT connection) on one of my boards is defective or damaged, with no continuity to ground.  Could someone please recommend a way to repair it?  If there is no way to fix, should I jump the molex to the negative pin on C2, underneath the board?

 

[Spencerleehorton]

Hi all,

Have replaced  CA3083 and all lm301 chips and still get oscillation of 20khz when setting up rms!
Have changed the caps but nothing changed?
Anyone have any ideas?

Regards

Spence.

 

[Spencerleehorton]

Hi,

Do I need to install the R1 100r 0.5w resistor?

Regards

Spence.

 

[Bowie]

Hi,

Do I need to install the R1 100r 0.5w resistor?

Regards

Spence.

From what I've read, it's not needed if you're using an LED illuminated meter.
BTW, I PM'd Abe a couple days ago and asked him to check in on this thread regarding there stereo link, etc.  He's been responsive in the past so we'll hopefully get some info soon.  I'm still wondering to do about the dead trace in my board.

 

[Spencerleehorton]

Hi Bowie,

Where is your dead trace, maybe both my pcbs have the same problem?

Regards

Spence.

 

[Bowie]

Hi Bowie,

Where is your dead trace, maybe both my pcbs have the same problem?

Regards

Spence.

I have 2 boards but the problem lies in only one of them, at the CT trace for the power trans.  I'm trying to find out if jumping a wire over to C2 is the best fix.
As far as your oscillation goes, I can't say but I would check the polarity of all relevant components, make sure none of your chips are backwards or wires are crossed, and that you have no stray solder blobs.

 

[Spencerleehorton]

hi all,

this is where im at with this project.

Well, at the moment both amplifiers behave the same. The RMS section of the design is oscillating at about 20kHz. The power rails are correct and appear to be noise-free. All the component values are correct (except the 27Meg resistors in place of 22Meg but that is not important) and assembly is fine.

I can stop it oscillating by introducing mods that reduce the gain of the LM301s but that will, I assume, stop it performing as intended.

I am at a loss to think of a way forward.

can anyone help please, pretty please

regards

Spence.

 

[Dr Gris]

Stereo link:
See post #160 & 161 in this thread. Also mentioned in some other posts spread out in this thread.
You still need to set the controls similar in both channels.

Oscillation:
Did you populate C39 (needed for That chip build)?
And increaced C14 to 150pF?
No cold solder joints where the ceramic caps go in the RMS area?
If you put the lid on and probe the output, same problem?

I still haven't got as far as you guys have, and to be honest I don't know anything ;D
Just speculating....

Good luck!!!
//Magnus

 

[Spencerleehorton]

Hi,

The oscillation advice is perfectly sound but would only make sense if the oscillation was at a much higher frequency. In this case the oscillation is at 20kHz.

Anyone else like to chip in with any ideas?

Regards

Spence.

 

[Spencerleehorton]

Hi,

There isn't a cap in C39 but putting in the specified 100pF makes no difference.

C14 is a long way from the RMS section, so, unsurprisingly, it made no difference when increased to 150pF.

This is starting to be Lost cause!!!!


Regards

Spence.

 

[Spencerleehorton]

Hi,

It's seems no one has anything to add about this rms unit 20khz oscillation.
The rms unit is self contained and taking out all other chips makes no difference to getting rid of this problem?
All components are correct, would really do with pointing in the right direction with this design it seems it is floored.

Regards

Spence.

 

[Bowie]

Hi,

It's seems no one has anything to add about this rms unit 20khz oscillation.
The rms unit is self contained and taking out all other chips makes no difference to getting rid of this problem?
All components are correct, would really do with pointing in the right direction with this design it seems it is floored.

Regards

Spence.

Must be frustrating.  Maybe post a few pics?  Being that this isn't a common problem, and it exists in both of your boards, maybe someone can spot the error.

 

[Spencerleehorton]

I will take a picture of it, see if anyone can spot anything?

No word from abe yet either?

Regards

Spence.

 

[Spencerleehorton]

This is where I'm at with this:

Well, to change the frequency I removed C2(10pF) and to stop it oscillating I reduced the gain of the first amplifier by putting a 68k resistor from output to input. However, although this is not going to alter the signal path performance, it will change the compression algorithm which claims to behave like the human ear(whatever that means). So it is best that the problem is solved without mods like these.

If someone could please advise on this rms unit mod please, as I would really like this unit to work how it should behave.

Regards

Spence.

 

[Spencerleehorton]

Hi all,

I am still pulling my hair out with this rms unit!
Attached pic is the waveform from the offset pin without anything on input.
The rms unit is oscillating on its own?

Resistor wise the only ones that are different are the 27meg instead of 22meg, would this make much difference?
also the 6k04 ones measure 6.7k


Could anyone help me get this sorted please?

Regard

Spence.

 

[Spencerleehorton]

Hi,

This is a picture of my pcbs, have put in C39 since this picture was taken but not tested.
If you spot anything please let me know!!!

Regards

Spence.