Soundcraft 200B

[mervaka]

hey all,

 

just picked up a soundcraft series 200B the other day. all seemed well until I tried the EQs however.. :(

 

I turned the channel gain right up (70dB or so) and turned up the HF on the channel EQ right up (15dB) and something rather bizzare happened - the peak light for the channel came on permanantly, the L/R VU meters swang far right, and there was a loud crack in the PA (lucky the mains were down!)

 

this seems to happen on all the channels, so am I right to assume it might be some sort of design flaw involving saturation from positive feedback? its a bloody nice desk apart from this problem :(

[StevieR]

The 200B is also quite an old desk.

 

As such, the problem could be due to component degradation somewhere. As this is affecting all channels, this could be in the power supply. Worth also checking that you have the right PSU with the desk (Should be a CPS450 or 650) methinks. A good service may be in order.

 

Steve

[mervaka]

well worringly its a CPS150 supply, but its recently been replaced, and I know the guy I got it off pretty well, and he's not the type to go out and buy the wrong supply

 

the CPS150 supplies +-17v@1.25A and 48v@125mA. would an underpowered set of rails cause this problem? :/

EDIT: did a bit of research, seems the CPS150 is the correct supply for this desk.

[Bobbsy]

Back in the early 90s I used the 200B quite a lot--the place I was working used a 24 channel version as the sound desk in one of its smaller studios. I really quite liked the board at the time and am pretty sure I would have noticed the effect you describe had it been a design fault present in every board.

 

I suspect that StevieR is on the right track when he talks about components degrading...the desk could be over 20 years old.

 

It's probably worth a phone call to the nice people at Soundcraft's service centre who may have encountered this and be able to advise if it would be economic to repair.

 

Bob

[Mixermend]

It sounds as though you have created an oscillation, or stimulated an instability - with all of the mic amp gain followed by another 15 dB of HF eq that is a lot of gain (75dB) so perhaps it is not surprising.....!

 

Probably if you terminate the channel microphone input with a microphone - in a box - or covered with cushions - (or a short circuit on pins 2 & 3) - you will almost certainly find that this doesn't happen.

[mervaka]

It's probably worth a phone call to the nice people at Soundcraft's service centre who may have encountered this and be able to advise if it would be economic to repair.

 

 

a call might be in order I think. I got the desk and supply for a mere £50 so I definitely have some money to burn on repairing it. could this mean a complete recap of the channels and master section?

[MarkPAman]

Is this realy a problem? Full gain & 15dB boost on the eq are not something you are going to do often, if ever in real life. As Mixermend says, have you tried this with a mic plugged in?

 

I used to have an old Studiomaster that did something along these lines. In practice though, it was never a problem, as I never had to run it at the levels that caused this.

 

Give it a go in a real life situation, and I suspect all will be well.

 

If not, try Soundcraft, though I've found that once all of a discontinued desk model had reached the end of their guarantee period, service prices, & turn around time, went up (I understand there was no longer any dedicated bench space or staff for a particular model). It may be that the job could be done cheaper elsewhere ;) .

[mervaka]

true, there's a guy I know whos about 10 minutes away who does mainly backline repair, but also does the old A&H stuff. I might just throw it at him if I gain little ground with contacting soundcraft directly.

 

I've just found another bizarre fault with this desk where the power supply seems to spack out and send a series of loud cracks out. I'm still trying to find out what causes this problem, as its only happened twice, but nearly blew my studio monitors ;) sounds like the power supply again.

 

I think I can learn to live with the old problem as you say, but I'm hesitant to bring it out with this new problem that just arisen.

[paulears]

Just a thought - and memory could be mistaking this with an another desk I had, but worth checking the problem still occurs with phatom power off. I seem to remember something like this, that sounds very similar. Could have been a soundcraft 200 or a Sountracs project 8 can't remember which.

[mervaka]

wasnt using phantom on any of the channels, or do you mean physically disconencting it inside?

[paulears]

Memory tells me that it was a known dodgy component in the phantom network - I think it was an out of spec diode in the pair that was letting dc back into the pre-amp making it unstable. whate triggered the memory was the description. normal operation until you turned the gain up, when it just instantly lit the led and went 'mad' - I'm sorry I can't remember more.

P