Soundcraft Ghost subgroup distortions + other issues

[Gregory K]

Hello all,

I'm a happy owner of Soundcraft Ghost LE24 that I bought new 8 years ago. It came with CPS275 power supply.

I always used Subgroup Outs for tracking, but I recently discovered that the sound coming out from Direct Outs has noticeably different sound quality than ANY Subgroup Out. Direct Outs provide more low-end, and the "highs" seem to be clearer. After that, I decided to do some tests and found out some other issues: the signal is distorted on Subgroup Out 1-4 jacks, especially on Sub 4 (it's obvious on almost any music material).

Here is a picture of 1kHz sine wave test. I used Logic's test oscillator plugin as a source:

http://i61.tinypic.com/bexb7m.jpg


The only outputs that deliver no distortion from any subgroups are Group Inserts and Mix Outs (when groups are routed to Mix).

I also have to mention that one day (shortly after buying the console) I mistakenly turned on the PSU when the other end of the PSU cable was disconnected from the console. So, the PSU was working without a 'load' for 4 or 7 seconds. Currently, if the PSU is turned on, I can hear a kind of transformer buzzing sound at the distance up to 1 meter (3 feets) from the PSU. I don't know if this sound is normal, but otherwise the PSU "seems" to be ok.



With all this in mind, I have some questions:

1. The PSU was working without connection to the console for 4 or 7 seconds. Could the PSU be damaged as a result? Or could it cause a malfunction or any degradation of the console characteristics?

2. Subgroup out 1-4 jacks provide distorted sound, especially Sub 4 (no distortion on Group Inserts and Mix Out). Is there anything I can do myself to further diagnose a problem or fix a problem with a such symptom?

3. Direct Outs provide clearer highs and more bottom end than ANY Subgroup Out (links to audio examples are below). Is it a malfunction? To me, the difference is beyond the nature of an analogue console internal signal routing. It would be great to hear your opinions.

https://dl.dropboxusercontent.com/u/107246793/bottom%20end%20test_Direct%20Out.wav

https://dl.dropboxusercontent.com/u/107246793/bottom%20end%20test_Sub%201-2%20Out.wav

https://dl.dropboxusercontent.com/u/107246793/highs%20test_Direct%20Out.wav

https://dl.dropboxusercontent.com/u/107246793/highs%20test_Sub%201-2%20Out.wav

4. Please, see the picture of 158Hz Square wave test. Would you call these results normal for the console? I especially concerned about the slope.

http://i62.tinypic.com/2m5jpdg.jpg

I'm not an engineer, so maybe I'm missing something. I would greatly appreciate any advice or hint.
Thank you.

 

[PRR]

> 158Hz Square ... I especially concerned about the slope.

For NO slope you need response to infinitely low frequency (DC). We *never* want that in a large audio system.

It is less than 5% at 158hz, so the low-cut frequency is about 0.05*158Hz or 8Hz. That is entirely reasonable for a 20Hz-20KHz system which rarely really carries <50Hz.

Running the PS no-load "probably" did no harm. Most power supplies can do that all day and night for years.

Distortion on a "bunch" of paths suggests power supply trouble. But not all paths, so not the main power supply, but how it is distributed inside the box. Loose card contacts, sick filter caps, blown filter resistors.

 

[Gregory K]

Thank you for your detailed response, PRR! I appreciate it very much.

And just to clarify the slope subject: Did I get it right that you saw that it is less than 5% on Subgroups outs at the picture of my test?

 

[pucho812]

I used to service ghosts for a local audio school, most of the issues we ran into where as follow. Mind this is with kids banging on them constantly

1. the leds would go out in the meter bridges

2. the control room pot would get scratch over time. Yes you could deoxit but better to replace it.

3. loose connections, alot of times for no real reason the connection inside would randomly disconnect and you would loose things like no metering on the bridge and such.

I would venture to guess #3 is very likely the cause of your issues. Not to say other things will never go wrong but your more then likely going to run issues with connections coming out or being half connected causing a problem.  I would make sure all is seated properly. That in itself wil be enough of a pain as to get access to all that you will have to flip the board over and remove the bottom plate which is some 40 screws. Then you get access to the channels and the rest which are modular but all mount to the surface so you have to take all the knobs off and unscrew the pots just to take one out...

 

[Gregory K]

Thank you very much for your input, pucho812.

I will definitely look into the Ghost and check the connections.

 

[robomix]

i run a self overhauled ghost without problems for 3 years now. i would suggest the bus insert sockets.
running the power supply without a load should be no problem ;-)