MPC 3000 record input impedance issue?

Anyone had similar issues or have any thoughts on how to cure this..

I have Cambridge Audio 651P phono pre-amp for my MPC 3000. It has sounded great for some time now but just recently started to distort when connected directly to the 3K inputs. It didn't used to do this. It used to connect straight in, work fine, sound great.

After testing everything it turns out that the 3k inputs are fine when hooked up to a different source. The pre-amp output also sounds fine when connected to my portable recorder (Olympus LS-11). So if I hook it up through the LS-11, just leaving the LS-11 record ready so that it outputs what the phono pre-amp is feeding it, I can sample to the 3K with no distortion.

I'm guessing it's some kind of impedance issue that is causing the 3K inputs to distort when connecting the phono pre-amp directly and that when I'm sticking the LS-11 between them it's somehow acting as a DI or whatever. I don't want to have to use the LS-11 AD/DA between the pre-amp and my 3K every time I want to sample something though.

Any thoughts on a little something (perhaps some kind of DI) that I could stick between them to cure this.. I don't know too much about impedance etc so am not sure what I should be trying. Also, am a bit mythed as to why is used to work fine when connected directly in.



Thanks in advance!

its strange that it DID work ok for you but now doesn't.

I know you said its working ok with other items, but are you sure nothing else in your MPC chain has changed?

I've got a similar chain

audiophile cart + headshell >technics 1210 >Angle Audio phono stage >MPC3000

then after that am planning on going MPC3000 >stereo outs >DI >Glensound BBC mixer mic pre's >audio interface

Yup I'm sure I've not changed anything. It makes absolutely no sense to me! Also, I can't think of any reason that the phono pre-amp shouldn't work plugged directly into the MPC 3K inputs.

Like I said, when I stick the LS-11 between them it does work fine and I get a good signal to input. So adding that to the chain fixes it for now. I don't want this as a permanent solution though - as much as I don't want the extra AD/DA in the chain, it's also just a waste of batteries for the LS-11 and another thing to have switched on etc

Maybe there is an issue with my 3K inputs but only with certain impedances or something? I really don't know much about these things though and thought that a phono pre-amp would output line level anyhow.

Nice set up. How's that Angle Audio phono stage?

Could be a grounding issue. Have you tried using different power outlets?

Haven't had a chance to mess with this in a couple of weeks so sorry I'm a bit slow on the reply.

I've just tried connecting both the MPC 3000 and the phono pre-amp to 3 separate main sockets (in all possible combinations) to see if I get any different results. Sadly, no joy. Wherever I plug either of them in I'm still getting a distorted signal when running the pre-amp directly into the 3K.

I guess a stereo DI box would be the next thing to try but any other suggestions would be welcome..

Tried different gain settings with the rear panel Record In Gain switch?

Dude you fixed it! Hadn't ever even noticed that switch there. Flicked it back to low gain and all is well. A million thanks. Owe you a couple of schooners.

No problem, glad to see you sorted it out.

I should have suggested it earlier, as I was thinking it might be the problem right from the start of the thread, but thought it was too obvious, especially since you were plugging in cables right next to the rear panel Record In Gain switch.

Something like the Display Contrast rotary dial doubling as an LCD backlight on/off push button is easy to miss, if pressed accidentally, and I thought that the rear panel gain switch was a little more obvious, but you didn't seem to mention it in your troubleshooting attempts.





If you want to get a little technical...

The rear panel Record In Gain switch sets the gain level of the first of four op-amps (operational amplifiers) that the input signal goes through, in the internal signal chain, before being converted from analog to digital in the AD converter chip.

The front panel Record Level knob sets the gain level of the third op-amp in this internal signal chain, before the signal reaches the AD converter.

The rear panel Record In Gain switch is really setting the main input gain, to one of three different ranges, while the front panel Record Level knob is more of a trim control of gain, within each of those three main gain ranges that are set by the switch.

So, if you don't set the rear panel Record In Gain switch correctly for each different input signal that you are recording, then you might get a distorted signal at an overloaded first op-amp in the signal chain, as you did, which you can't fix with the front panel Record Level knob, as that is just turning an already distorted signal up and down within the third op-amp in the signal chain.

Or, you might get a very low signal through the first op-amp, and therefore might not be getting an optimum signal-noise ratio through the internal signal chain and into the AD converter.

Good info. Thanks man.