Audinc Velvet Boost Frequency discrepancy

[Diamondj421]

I have what appears to be a fairly uncommon EQ; the Audinc Velvet Boost. I say this as I can't seem to find any information about it. While I'm not sure anyone will know the exact fix for this unit, I'm sure that someone's basic knowledge of the inner workings of an EQ should get me pointed in the right direction.

I've had this EQ for about a year and have had issues balancing the left and right signals of my stereo bus. The left channel is always a few dB louder than the right. I always assumed it was due to using different cables or from one of the other pieces that I had built. Today, I decided to investigate further and realized that the problem is in fact the Audinc. The left channel's low frequency knob, while labeled 30, 60, 100, 160, 250 and 350 is reading at approximately 20, 40, 50, 65, 75 and 110 Hz. The bandwidth is also much wider with both Qs set to the same width.

I bought this used and the last owner says that nothing has been modded or repaired on it. Upon opening the unit up, all components that should match do. Anyone have any idea what could be causing this?

Thanks!
Jeff

 

[ruairioflaherty]

Without information on the topology or schematics it will be hard to help...

Why not start with a picture of the insides and the outside?

Does it have pots or stepped switches?

Is it a solid state EQ or tube based?

Pics will help us to determine the type of EQ and then possible solutions, for example if you have an LC based EQ then your frequency center discrepancies from Left to Right may not be fixable (or at least not easily).

Help us to help you.

 

[pucho812]

did a quick google...

Audinc EQ-HFB4 "Velvet Boost"

From great slutz I found the following

This was a cutom eq made by John Schmitt who I believe worked at Universal Recording in Chicago. It's a nice piece and there are only a handful of these around. Don't know where John is these days or what he's up to, I haven't seen him for many years. I think he made these in the late 80's or early 90's.

 

[Diamondj421]

Here you go gents. It's technically 4 individual EQ channels, 2 low and 2 high bands that can be switched to work as 2 channels, each with one low and one high.  A switch for shelf/bypass/peal on the low, peak/bypass for the high then boost knob, Q knob and 6-way selectable frequency switch per band. It's solid state. Here are the guts. I'll post another view of the front.

 

[Diamondj421]

Front view.

 

[ruairioflaherty]

Ok, that's a little better.

So - first question is does this EQ sound great?  If it doesn't sound great then it's not worth fixing IMO because there will be some figuring out involved.

Next

- I can tell the frequencies are on a rotary switch, are the gain and Q controlled by pots or switches?

- What are you using to measure the frequency response?

- With all bands flat and EQ inline is there a difference in level between the left and right channels?

Cheers,
Ruairi

 

[abbey road d enfer]

Anyone have any idea what could be causing this?

Since the PCB is adequately labelled, it should not be too difficult to trace the signal and find out where the difference is located; then you would find either a defective component, most likely a capacitor, or, even more likely, one of the switches.