Cambridge Audio Azur 651p Pre-Amp Not Working

[Mark_71]

I have a Technics SA-700 receiver and normally I use the built-in phono stage. It's always worked well, in fact, the built-in phono input has worked on all my old vintage gear. But I've always been curious about what an external pre-amp would sound like.

I tried this once before. I already had a Cambridge Audio 651p that I bought a few years ago when I tried it on a Technics SA-DX750 (c. 2001) that had no phono input I probably hooked it up through the tape input. I got no sound. I figured it was my used receiver or my mistake. I wasn't too savvy audio wise at the time. Then I got a cheaper pre-amp (1/3 price of the Azur), hooked it up the same way, and that one worked fine.

Back to the Azur, I really wanted to see if I noticed any difference. So today I tested the Azur 651p again, but on my Technics SA-700. I set the switch to MM and plugged an Audio Quest Black Mamba RCA cable into the Azur and then into my Aux input on the receiver. Turned it on... again no sound. This can't be that hard - TT to MM inputs, Pre-amp output to Aux on the receiver, power on, switch input selector to Aux on the receiver... what am I doing wrong? Did I just get a bad Azur 651p?

The reason I was testing out the Azur on my SA-700 was if it sounded better than the built-in phono stage, then I was going to buy a Pro-ject Audio Tube Box S, but I don't want to spend that type of money if I don't see any noticeable improvement.

 

[Mark_71]

UPDATE

I went out and bought a cheap $20 preamp and it worked just fine on my system. Once again, I swapped back the Azur 651p and no sound. I took it apart to look for any glaring issues, but nothing jumped out. Maybe just a bad unit.

Anyone have any troubleshooting suggestions. I bought it a while ago so no returning it.

 

[Audiofreak71]

Have you tried to connect preamp output to a different input on your receiver besides aux like the tape or cd? To rule out if it's possible the auxiliary input that's bad? Just a thought.

Audiofreak71

 

[guiller]

Do you have a multimeter? Is the external power source providing the correct voltage?

 

[cre009]

Just to make sure of the basics - does the purple LED light up when powered up? On mine I find the plug into the unit is prone to slide off the unit if I move it around.

There are separate outputs for MM and MC with an MM/MC switch which dictates which output is being used.

 

[Mark_71]

Thanks, everyone. I verified the power was on, the power light was illuminated. I plugged the TT into the MM inputs and then the outputs to the Aux on my Technics receiver. It's a 1970s receiver so I don't have other inputs, no CD, etc. I know the Aux input works because I've tested it with many cassette decks, a R2R, and other external preamps (which worked fine). I also verified the MM switch was set correctly. I tried the subsonic filter in both positions. Well, that's about all you can try. The directions are pretty simple. Still no sound.

I opened it up and looked around for anything obvious, I cleaned the contacts, resealed it, tried again, still no sound.

I have a Fluke multimeter and it's about time I learned to use it. Thanks for everyone's suggestions.

 

[HypnoToad]

First of all check you are using the proper AC wall wart and not a DC one. If the unit has ever had a DC wall wart plugged in some of the capacitors in the PSU are damaged. Plug it in and listen, there should be an audible click from the relay, if no click there is a problem, usually in the PSU.

The next step is to check the PSU with the AC wallwart plugged in, there are two voltage regulators 7818 & 7918 (see red arrows in picture below) attached to an aluminum shroud / heatsink around the PSU.

Set your DMM to DC voltage and check the output voltages between ground (aluminum heatsink) and the output pins (pin 3 on each which is the right hand of the three pins on both looking from the front of the unit, make sure you don't short the pins out) on these voltage regulators they should be similar and around +18vdc on the 7818 and the other -18vdc on the 7918.

 

[Mark_71]

First of all check you are using the proper AC wall wart and not a DC one. If the unit has ever had a DC wall wart plugged in some of the capacitors in the PSU are damaged. Plug it in and listen, there should be an audible click from the relay, if no click there is a problem, usually in the PSU...

Thank you so much for the detailed instructions. I almost tossed it. I have a Vincent 701 on the way, but now I can play around with this and not worry about doing too much damage. Thanks, again!

 

[Mark_71]

UPDATE
I have the correct AC wall wart. I opened it up and listened carefully for the "click" after powering it on and it was indeed audible. I'm certain I never noticed it before, but I never had the cover off. Tried every possible setting - still no sound. I've tried it on other systems with a p-mount cart (no sound) and my vintage rack with a Grado Green. Nothing. Whether I set it for MM or MC (and swap the cables to the correct inputs). I tried both cause those Grados are not quite MM I suppose, but either way it didn't work on either setting. I've tested the cables too. They're fine. New Blue Jeans. Work on my other $20 phono stage.

I guess it's time for the DMM. I bought a Fluke last year and haven't even tried it yet.

Interestingly enough, I prefer my built-in phono stage (Technics SA-700) to the LKG PRE600 external phono preamp. It was only $20 though and I only bought it to help troubleshoot the Azur and see if any preamps worked on my system. Kind of surprised too, even though I assumed they made a good phono stage in the 70s, I expected it to have degraded over time, all I've done w/ the Technics SA-700 is clean it, DeoxIT, and replace light bulbs, everything is original.