Serious issues with MPC 2000(classic) 8-output board... Can

In my case its a 2000(classic) distorting the outputs...

Main L/R are fine... digital IN is fine.
what is NOT fine is the digital output( sends clock, but zero audio) and analog outputs 5 & 8 intermittently distorted with 7 being totally dead. Ive pulled the board, seeing zero obvious damage measured the voltage regulators outputs, put every output playing a 1kHz sine into my ocilloscope, and spent hours trying to research the issue.... all 8 analog outs can go twist for all i care.... i want the SPDIF working!!! I know which chips run the analog section... 2 opamps and the PCM D/A chip, along with associated external components... what im not sure of is which chip(s?) to try and test on the digital side.

When i plug the SPDIF jack directly into my scope, i get the clock signal, and what looks like a shadow or reflected image whenever i trigger that same sampled sine wave. I havent checked to see what the SPDIF output of my computer does, but i imagine its similar.

Before you ask: YES, ive tested the cable and SPDIF input to the computer from another source, and it passed audio just fine!

jimmyklane wrote:When i plug the SPDIF jack directly into my scope, i get the clock signal, and what looks like a shadow or reflected image whenever i trigger that same sampled sine wave.

The SPDIF cable might need termination at the scope end.

You will not see a sine wave when looking at the SPDIF signal on a scope, as it is a digital signal, not analogue, a sine wave in a digital signal will not look anything like a sine wave in an analogue signal.

SimonInAustralia wrote:

jimmyklane wrote:When i plug the SPDIF jack directly into my scope, i get the clock signal, and what looks like a shadow or reflected image whenever i trigger that same sampled sine wave.

The SPDIF cable might need termination at the scope end.

You will not see a sine wave when looking at the SPDIF signal on a scope, as it is a digital signal, not analogue, a sine wave in a digital signal will not look anything like a sine wave in an analogue signal.

Let me clarify: I am seeing a square wave at the clock frequency... thinking about it now (not in front of the scope). It's probably NOT the "clock" of 44.1kHz I'm seeing but the raw 2.8MHz signal. When I'm viewing that square wave, and trigger a sample(I'm using a 1k sine that was useful for testing the analog outputs) the square wave gains a "shadow"....but it is STILL another square wave! Simon, I appreciate what you're getting at here... I'm an EE, but analog filter design(power supplies and audio) was my focus, not digital interfacing or design. I'm seeing a nice .5V p-p square wave in my scope.

What I am most certainly NOT any kind of expert in is the MPC electronics, as I've only ever had my 2000 apart and have only owned that for about 10 days. I can afford another 8-out card, but two things are stopping me: academic interest and straight up cheapness! Any ideas Simon or anyone?

jimmyklane wrote:Let me clarify: I am seeing a square wave at the clock frequency... thinking about it now (not in front of the scope). It's probably NOT the "clock" of 44.1kHz I'm seeing but the raw 2.8MHz signal. When I'm viewing that square wave, and trigger a sample(I'm using a 1k sine that was useful for testing the analog outputs) the square wave gains a "shadow"....but it is STILL another square wave! Simon, I appreciate what you're getting at here... I'm an EE, but analog filter design(power supplies and audio) was my focus, not digital interfacing or design. I'm seeing a nice .5V p-p square wave in my scope.

The digital clock signal and the digital audio data get transmitted together, using biphase mark encoding.

The digital audio data is also broken up into blocks, frames, and subframes, with the audio data only being part of each subframe, it also includes header, aux data, and status bits.

So, there really is no way to see the analogue audio signal inside the SPDIF digital data stream on a scope.

I think that it is supposed to look like a .5V peak to peak square wave when idle.

What you are seeing as a shadow is possibly an audio signal being encoded along with the clock, and the scope trying to lock onto the original square wave frequency which is no longer a simple square wave, so it is jumping around and causing the shadow.

The first three sections on this page discuss some of the detail of the SPDIF protocol...
http://www.ni.com/white-paper/3255/en



Not sure about your MPC SPDIF issues, but do you have any other devices with an SPDIF input that you can test the MPC SPDIF output with?

There are two solid state fuses on the expansion board (FS501 and FS502) that are located next to the ribbon cable. Check those for continuity to make sure they are not blown.

Typically the distortion on the analog outputs is caused by the opamps not getting power and passing the low-level signal through unamplified. You could have a faulty op-amp.

As an EE with access to a scope you should be able to trace the audio signals through the circuit and see where they are getting lost. It's a pretty straight forward circuit on the analog side.

Thanks, MPC-Hunter!!! Sorry for the late reply.

Got the analog side working....went a bit overboard and recapped and replaced the opamps with some decent ones I had in the parts bin.

I will absolutely get on checking those fuses tomorrow! Standard TO-92 package over by the SPDIF outputs I'm guessing? Not looking at it now, but I remember 3 large chips(one fairly oddball one) and some little bit of external components.

That's great info and I'm very grateful!

RESOLUTION!!!

My MPC Digital out works just fine.... This is one of the oddest issues I've ever ran into! My MPC 2000 classic SP/DIF output was NOT working when plugged into an M-Audio 24/96, regardless of driver settings, card position, cable choice, or computer....however the 24/96 digital input worked with every other source I could test it on....I purchased a MOTU 828mkII (initially for use with Silent Way) and because it has built in SMPTE thought it would be ideal as a tracking device for my MPC. The Digital output that was previously not functioning works like a charm now!!!

For those of you wondering why I'd bother to use the SPDIF output, if you own Maschine(or any sampler/effects unit with digital input) it is an IDEAL way to add a stunning effects "board" to your setup! I'm passing samples back and forth digitally for processing, and when I track them out I use my stereo outputs with individual tracks soloed (use the click track "count in" on play as a visual sync source) for my drums (they go through my Neve) and then all the instruments via individual outputs in 1-3 passes, and then the hardware synths in a last pass.

To those that read this: I've read of some issues with M-Audio+MPC combos in the past, and before trashing your 8-output board, try testing with another interface as well as the usual suspects(cables, inputs 2 outputs, power, volume, etc)

Feel free to PM me if you want some help troubleshooting!

-Jim