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SOUNDCRAFT 200 DELTA MODIFICATION
Old 3rd January 2010
  #1
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golden beers's Avatar
 
2 Reviews written
🎧 10 years
SOUNDCRAFT 200 DELTA MODIFICATION

Hai slutz if any of you have this board here’s a mod for you:
I was going for best bang for buck, which basically involved me handing over a few channels to my very good electronics expert friend. He looked at the design and found the best cheapest way to improve things. This basically involves changing a few caps, changing the input ICs and removing some caps and replacing them with links.


What I ended up with was: more head room and unity gain. i didn't touch the EQ or the mic inputs.

Input channels, what I did
I replaced some capacitors with link wire (which is in effect the same as putting in a massive capacitor - only extremely cheap).
I changed the line input IC to the latest model, it's basically the same but much, much faster. And a couple of other changes..

Which components where?:
· Link replacement of C14 and C24
· Swapped over C25 to 22pF
· Swapped over IC2(TL0272CP) to TLE20272CP
· Connected a 47pF capacitor across R22
See photo for the locations (this is AFTER I changed the components)


input channel, what I didn't do
OK there may be marginal gains to be made by swapping out other ICs you can go ahead and swap all of them if you like as the new replacement IC will not make any difference in terms of circuit component values. as I said I didn’t touch the mic input (IC1) so that would help

Also there is room for improvement to the signal by swapping out some of the blue polarised caps with bigger non-polarised 100mF ones. They are using polarised caps with AC. Polarised caps should only be used with DC. But in this particular circuit it doesn't make much difference. ie they figured they could get away with cheaper caps. I’m sorry but I can't remember which caps could be swapped, I didn't bother as the difference is so marginal. But if you wanted to change the mic input you should change the relevant caps to non-polarised. I think there’s 2 of them right next to IC1.

Group module, what I did

I replaced some capacitors, with links. removed others completely and changed an IC

which components where?:

· link C6, C12, C18
· swapped C14 with 94pF and C16 with 47pF (note the 94pF is 2x47pF in parallel - saves on ordering another baggy)
· swapped IC5 (TL0272CP) to TLE20272CP
· removed completely C29 and C10
See photo for the component locations. There’s 2 photos here to show the location of the IC and the caps I changed hidden by the Fader





what I didn’t do

The problem with the group channel is they have a badly designed circuit with amps facing each other. This creates a 'ring' or self oscillation in the amps. All over the circuit the soundcraft guys put Caps in to slow down the signal (low pass filter it) so it wouldn't ring. Now the new IC made this a allot better but the key caps- C14 and C16 still cause ringing with higher values. You want to make these caps as small as can be to get the high freqs, I found 94pf and 47pf did the trick but really I wanted to go to 22pF. Unfortunately the bloody thing kept ringing! Also, as before changing some caps over to non polarised 100mF caps could also potentially improve things marginally. Also changing more ICs wouldn't hurt but I changed the only one that really matters...
Old 28th September 2012
  #2
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tvsky's Avatar
 
🎧 10 years
nice post . did you do anything to your psu ? was just the little cps 150? Lots of people seem to say to upgrade that first.
Old 28th September 2012 | Show parent
  #3
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golden beers's Avatar
 
2 Reviews written
🎧 10 years
Quote:
Originally Posted by tvsky ➡️
nice post . did you do anything to your psu ? was just the little cps 150? Lots of people seem to say to upgrade that first.
no i didn't touch the PSU. there's allot you can do there and allot you need to do there if you start seriously modifying the rest of it.

it's something i want to look into, thanks for reminding me.
Old 25th April 2013 | Show parent
  #4
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golden beers's Avatar
 
2 Reviews written
🎧 10 years
the answer from my engineer:
Quote:
What they are doing is using a long tailed pair as an input to an operational amplifier, which already has a long tailed pair as an input. The circuit is unnecessarily complicated and will ring with slow amplifiers so the feedback has to slow the circuit down to prevent the ringing. What they are trying to do is increase the input impedance of the amplifier but there is no need for it. Using a higher speed amplifier in the feedback loop reduces the ringing so you can reduce the values of the stabilising capacitors thereby increasing the high frequency response.

The capacitors that are linked out are not necessary because there is no significant direct Voltage across them. The purpose of having those capacitors is to isolate the direct Voltages and allow the alternating signals to pass. Since the Voltages are as near as makes no difference equal, there is no need to isolate them and the capacitor just reduces the low frequencies without any benefit.
Old 25th April 2013
  #5
Gear Maniac
 
🎧 5 years
Quote:
Originally Posted by golden beers ➡️
What I ended up with was: more head room and unity gain
do you mean 'more headroom at unity gain'?
confused
Old 25th April 2013
  #6
SEED78
Guest
the Delta is meant to respond well to upgrades - good choice.

I looked at Delta, but ended up with a more OTT option, a Siemens C4 that needs money chucked at it - currently waiting in line at my tech's place.
Old 26th April 2013 | Show parent
  #7
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golden beers's Avatar
 
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🎧 10 years
Quote:
Originally Posted by sad computer ➡️
do you mean 'more headroom at unity gain'?
confused
no i mean every channel and the master has more headroom.

also

a much wider range on the gain control will equate to unity now.

Meaning:
before modification, 0 dB on the input gain would be close to unity. every other gain level would have an uneven frequency response. so if you want to turn the gain up, you would get a colouration. like a very subtle eq. after modification, the frequency response was the same where ever the gain was set.
Old 26th April 2013 | Show parent
  #8
Gear Maniac
 
🎧 5 years
Quote:
Originally Posted by golden beers ➡️
no i mean every channel and the master has more headroom.

also

a much wider range on the gain control will equate to unity now.

Meaning:
before modification, 0 dB on the input gain would be close to unity. every other gain level would have an uneven frequency response. so if you want to turn the gain up, you would get a colouration. like a very subtle eq. after modification, the frequency response was the same where ever the gain was set.
Oh sweet. Thanks for clearing that up for me
Old 31st August 2014
  #9
Here for the gear
 
zenman666's Avatar
 
🎧 5 years
master section

been recently modding a Delta with great results -was just wondering about what u said--"edit: the latest from my engineer is yes, you should link (short) C6 and C106, but better to link C5 and C105." Does that mean u linked both C6/C106 and C5/C105 or better to just link c5/c105? Great post by the way.
Old 12th September 2014 | Show parent
  #10
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golden beers's Avatar
 
2 Reviews written
🎧 10 years
Quote:
Originally Posted by zenman666 ➡️
been recently modding a Delta with great results -was just wondering about what u said--"edit: the latest from my engineer is yes, you should link (short) C6 and C106, but better to link C5 and C105." Does that mean u linked both C6/C106 and C5/C105 or better to just link c5/c105? Great post by the way.
the only things I have done to the desk are in my original post, everything else is theoretical. my engineer came to the 'link C5 and C105' conclusion after looking at the schema, this was not tested in the real world.

I think there's value in looking more closely at the master, what i did to the channels is solid, but the master, although sounding great may have some asymmetry in the output due to that C6 / C106 change... i would link both and see if you get ringing. if you do, this must have been why we went for that cap instead - cant remember. but anyway, i've been using the desk for a few years now, still good and any lopsided audio certainly does not get noticed by a human. maybe a bat would hear it.
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