Audix 35102 Skewed Fequency Response Help

I have a pair of these racked in the early naughts by Boutique Audio & Design.

I have not used them in a while and upon testing noticed that both channels are exhibiting a skewed frequency response.

Here's a slow RMS metered white noise through one of the channels:

http://agatha-christie-fanclub.tumblr.com/post/158710104561

the other channel exhibits the same response (or similar enough not to see it very differently on the spectrum meter)

I'm at a loss to figure out why this is happening.

I thought it might have been the output transformers though disconnecting and coming directly from the card to the meter ins and bypassing the transformers yeilds a similar skewed response.

Something seems to be acting as a high pass filter on both the individual channels.

Where da low end go?

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A secondary seemingly unrelated problem is that a single channel has its 18k high cut malfunctioning - once the switch is engages at that point the signal drops out completely or near completely (sending a lot more gain seems to pass low level high frequencies) the 910 Ohm resistors after the switch seem to measure close as do all the others (in circuit) so I'm guessing it's the Wasp switch point that's most probably the culprit

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For reference these modules are the V03 35102 with single NE55 op amp in the mic pre section

The card with the Mic / Line transformers has D253 Issue B *AND* Issue F printed on the circuit board

The card with the Wasp switches has D258 Issue D

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P.S. There does not seem to be any extra electronics added for driving the electronics to the output as it seems many folks have installed for what it seems like is for headroom reasons


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If I had the extra cash I would hire a tech but It's not possible right now for me hence joining up here in the hopes of some kind guidance.

Sincerely,

Geoffrey

Are you sure you have it connected right? White noise is not the best to use for audio, try pink noise.
If you hook up a microphone does it sound alright?

white and pink both slope down like in the video I linked to

The rack was built by Boutique Audio & Design and sold via Vintage King in the early aughts

Without the device in the path white and pink noise is flat across the spectrum

It has XLR mic in XLR line in 1/4 in and then XLR out on each channel

here's the output and a little of the input

http://agatha-christie-fanclub.tumblr.com/post/158609399752

N.B. PIN 1 's on the XLR connect to chassis ground and are NOT  unattached

Whats the output impedance of your generator? Hint, if its a -10 device you shouldnt be trying to do this.

It's a loop coming from a PC out of and back into Lavry converters..the Lavrys are jumpered for balanced +4 operation

The problem was noticed running a mix from the same PC / converters in a similar loop (for eq processing)

mic signal or line signal with regular audio signal sounds exactly like what the noise is showing on the spectrum  analyzer to me..id est an unwanted high pass filter

One common cause for that would be bad coupling capacitors.

Bri

Thanks Brian


What are the chances the two individual channels would have the same symptoms /caps go out?

I'm not sure how to even ID the coupling caps. I have an idea of which they might be. I would guess the ones between the distinct circuit blocks and or ones coming from the power according to some reading I did yesterday and the coupling cap hypothesis seems possible and makes sense. I have very little experience with this kind of thing.