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Soundcraft Delta 200 Mod Questions
Old 25th May 2009
  #1
Gear Head
 

Soundcraft Delta 200 Mod Questions

I just bought 2 Soundcraft Delta mixers, a 24 channel and an 8 Channel. The 24 channel did not come with a power supply, and the 8 channel came with a CPS-150 which I hear is ****. I will be using the 8 channel board for remote recording to an Alesis HD24 XR, and I will come home to mix on the 24 channel board as well as record/mix my own music with it.

I am really interested in modifying both boards to be all they can be, I know how much Jim Williams loves these boards; and I know that he does wonderful work to them. I definitely plan on getting the master section on the 24 channel modified by Jim as well as my HD24XR when funds allow. But I really need some good pre's for a record I am recording really soon and I really don't have the money to pay for any mods right now, I am getting married in a week and have already spent a ton on my HD24 and these two boards; and I still don't even have all the cabling bought yet...

Plus, I absolutely love tinkering around with this kind of stuff; and considering I am a student out on summer break I have a lot more time than money, so I would like to try and do some of this myself.

I have researched all over the net to try and piece together what people are doing to these boards but all the info is so scattered; from what I've gathered I should...

-replace all 47uf electrolytics with 220uf 25v Panasonics
-replace eq film caps with WIMA's
-replace the pair of transistors with something better
-buy a better power supply for both boards

Here are my questions

-I know the TL072's should be replaced with something more modern, but should I replace all of them or just specific ones? And also, what is the purpose of bypass caps and other additional capacitors when putting in different op amps?

- What are the power decoupling resistors on the delta 200 boards for??? There are 2 raised resistors labeled power decoupling on all the mono channels.

-What kind of transformer (brand/model and or ratio) does the optional transformer input take? I may like to try that on a couple of channels, I have a number of transformers laying around. Does using a transformer require me to modify the circuit at all?

-How can I change the High Pass filter to a different frequency? I would like to take a couple channels down to about 80 hz for guitars , and then a few more to 120hz or so for high hats etc. Is it just resistors, or does the capacitor value effect the frequency as well?

I really appreciate the help, I can't wait to get these boards up and running.
Old 25th May 2009
  #2
hi i don't have answers for your questions just yet. but i'm in the process of modding my delta (24deluxe channels). when i'm done, i'll post what i did and how. i won't be touching the mic inputs as i wont be using them. i've been told that the circuit design of this part of the channel is not good.
please check my thread out here, post #24 is where i'm at now and there's an audio comparison test there to listen to.
Old 25th May 2009
  #3
hi, my genius electronic engineer friend sent me an email about this, i'll copy and paste what he told me.
Quote:
Originally Posted by ian1101 View Post
from what I've gathered I should...

-replace all 47uf electrolytics with 220uf 25v Panasonics
-replace eq film caps with WIMA's
-replace the pair of transistors with something better
-buy a better power supply for both boards
The 47microF capacitors are polarised electrolytics. This is quite wrong, you should use non-polarised capacitors of a higher Voltage preferably 35V. You should also note that electrolytics have a high inductance so they exhibit a high impedance at high frequencies. If you connect a 0.1 microF capacitor in parallel with them, it will reduce the impedance at high frequencies. This has a much greater effect on the high frequency response than changing the operational amplifiers. You will find that increasing the values to 100microF will do the trick. The output decoupling capacitor should be 220microF except, of course that it needs to be non-polarised and have a 0.1microF capacitor connected across it.

You should note that the transistor pair in the microphone pre-amp circuit are a matched pair. They should not be replaced with transistors that are not matched.

Quote:
Originally Posted by ian1101 View Post
Here are my questions

-I know the TL072's should be replaced with something more modern, but should I replace all of them or just specific ones? And also, what is the purpose of bypass caps and other additional capacitors when putting in different op amps?
The TL072's are actually quite good even though they are old. If you really feel the urge to replace them, use TL2072's. These are about 3 times faster but otherwise have similar characteristics (both in frequency response and slew rate). Both IC's are low noise. Generally speaking very high speed amplifiers use more current and have lower input impedances. In view of the large number of amplifiers being used, it would not be prudent to use high current amplifiers because of the additional load on the power supply and the increased effect of the amplifiers talking to each other through the power supply. If you are going to replace them, replace all of them [in any given channel]. Changing the op-amps does not have any effect on the capacitors.

Quote:
Originally Posted by ian1101 View Post
- What are the power decoupling resistors on the delta 200 boards for??? There are 2 raised resistors labeled power decoupling on all the mono channels.
The power decoupling resistors together with their associated tank capacitors reduce the effect of the boards talking to each other. Without them there is a high probability of unwanted oscillations probably in the radio frequency range together with a general increase in noise.

Quote:
Originally Posted by ian1101 View Post
-What kind of transformer (brand/model and or ratio) does the optional transformer input take? I may like to try that on a couple of channels, I have a number of transformers laying around. Does using a transformer require me to modify the circuit at all?
I don't know about the transformer.

Quote:
Originally Posted by ian1101 View Post
-How can I change the High Pass filter to a different frequency? I would like to take a couple channels down to about 80 hz for guitars , and then a few more to 120hz or so for high hats etc. Is it just resistors, or does the capacitor value effect the frequency as well?
Increasing the capacitor values in the high pass filter circuit will reduce the cut-off frequency of the circuit.
Old 25th May 2009
  #4
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memphisindie's Avatar
 

Bigger caps, lower hz knee of the cutoff freq. There is a calculation for it, but, I don't have that handy.

If you do change the chips to TL2072's, do you still need to have HF suppression caps, are they a problem because of increased bandwidth and speed?

If you like the tonal character but want a tighter sound, keep TL072's or do the switch to TL2072's (probly sound the same, never used them) and you keep the "British Sound (Tridents and Neoteks use them too, only really well decoupled and supplied).
The first thing you should do is get a bigger power supply. Listen to the board with that and no modifications. If you like (it will be different) great, why keep going, but, if you don't, start the cap upgrades first, including decoupling and HF suppression. All the caps in the channel path can use upgrades to bigger value and higher voltage rating although, soundcraft does a pretty good job to start. But once you up the PS you should up the caps.As I understand it al the caps on the channel strips could use an upgrade. I've read that there are some spots you can add some caps.
Oh and the material of the cap make a big difference in the lower powered areas, like the pre amp, where there is going to be significant amplification going on. Use low esr caps where ever you are using electros except the PS where you can use low impedance.
The powersupply can be upgraded pretty easily, by either swapping one out or modding the CPS150, get two better rated bridge rectifiers, a 2.7k resistor for the regulator transistor, and some 10,000uf caps to replace those 4700uf stock smoothing caps. Make sure you have properly rated fuses, solder the cable onto the board instead of using the connector, check the voltage on the meter, connect the board to the cable and measure again, dial it up from 15volts to + - 17, or 17.5 volts and you're done. Take a listen. Record something.
Old 26th May 2009
  #5
BTW haw much did the 24channel cost you?
mine was $980 including PS and it's half 200 deluxe, half DLX channels
Old 20th July 2009
  #6
Here for the gear
 

direct out mods?

all. there's some awesome info in this thread. right now i'm working in a club with a 24 channel delta and now i may look into some of this stuff. but i was wondering, i'm just getting a recording system hooked up right now and saw that the direct outs on the board are all post fader. does anyone know why that is? there's no way this will work in a live situation. i don't need to put anymore of that marshall full stack into the mains in a tiny room. really, i want to know if anyone has seen the direct outs rewired to be pre EQ? i haven't seen anything but it doesn't seem like it would be that hard. something like this?

Pictures by fledspictures - Photobucket

or am i completely off? i'm just getting into the electronics/wiring thing so if this way off let me know.

cheers,
fled
Old 1st November 2010
  #7
Here for the gear
 

In line nightmare

Yeah. Why did they put the out so far back? There must be a work around here.......
Old 1st November 2010
  #8
Gear Maniac
 

i cant remember but i think at least the dlx is able to route the direct outs internaly.

i have a 8ch dlx. use it as a recording desk with low end ad-da sound interface. i like the caracter a lot but i am planning on a small upgrade soon.

changing all electros to panasonic fc
bypassing the electros between each audio section with a 0,01uF wima
and bypassing electros close to any opamp with a 0.1uF ceramic disc

i alredy upgraded my cps150 with good results in noise reduction and sharper bass. measured with my ears and a pair of adam a7.

all info of this is obtained from gearslutz forum.
Old 1st November 2010
  #9
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memphisindie's Avatar
 

Quote:
Originally Posted by 5.333V View Post
i cant remember but i think at least the dlx is able to route the direct outs internaly.

i have a 8ch dlx. use it as a recording desk with low end ad-da sound interface. i like the caracter a lot but i am planning on a small upgrade soon.

changing all electros to panasonic fc
bypassing the electros between each audio section with a 0,01uF wima
and bypassing electros close to any opamp with a 0.1uF ceramic disc

i alredy upgraded my cps150 with good results in noise reduction and sharper bass. measured with my ears and a pair of adam a7.

all info of this is obtained from gearslutz forum.
Excellent news.
I have a CPS 150 modified with MUCH higher capacity and quality rectifiers, better resistors on the voltage regulator, and new low impedance electros. It stopped humming at all, I modified my board beyond the scope of a cps 150's output (major chip upgrade), so, I need to sell it. I doubt it will ever break if used on a board within it's scope.
Old 14th September 2016
  #10
Gear Maniac
 

i just did some sweeps through my delta dlx master module with my new tektronix fg504 generator.

transistors, resistors, caps and opamps are replaced with better. two electrolytic caps in the signal path remains, the rest are replaced with wire.

on a fluke meter i read, @ -3db, 148khz at the summing amp. there is a smoothening effect on the wave form from about 35khz that slowly and gradually filters and distorts the signal when frequency rises.

the fader amp and linedriver read about 250khz and seemd much cleaner to about 100khz.

not a very proper test but i liked what i saw. and the sound is amazing.
Old 19th September 2016
  #11
Lives for gear
 

To test it properly you need to use a 1kHz square wave. The test procedure was explained in an article in a magazine called "Studio Sound", June 1985. The title of the article is: "How to check if it Sounds Good without Actally Listening". You may still be able to find it on the web somewhere. Personally, I roll off at around 40kHz. It's comfortably beyond 20k and it makes sure I'm not picking up any RFI.
Old 7th September 2019
  #12
Gear Head
 

Does anyone what might cause a Soundcraft Delta 200 channel to not output (or to output a VERY weak signal) to the Direct Output? I'm hardly getting anything from like half of my 24 channels from the Direct Out. Inserts are working fine, and when I plug an instrument cable halfway into the Insert jack it actually boosts up the volume out of the Direct Output jack a bit.. any ideas?
Old 7th September 2019
  #13
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Radardoug's Avatar
 

Quote:
Originally Posted by golden beers View Post
hi, my genius electronic engineer friend sent me an email about this, i'll copy and paste what he told me.


The 47microF capacitors are polarised electrolytics. This is quite wrong, you should use non-polarised capacitors of a higher Voltage preferably 35V. You should also note that electrolytics have a high inductance so they exhibit a high impedance at high frequencies. If you connect a 0.1 microF capacitor in parallel with them, it will reduce the impedance at high frequencies. This has a much greater effect on the high frequency response than changing the operational amplifiers. You will find that increasing the values to 100microF will do the trick. The output decoupling capacitor should be 220microF except, of course that it needs to be non-polarised and have a 0.1microF capacitor connected across it.

You should note that the transistor pair in the microphone pre-amp circuit are a matched pair. They should not be replaced with transistors that are not matched.



The TL072's are actually quite good even though they are old. If you really feel the urge to replace them, use TL2072's. These are about 3 times faster but otherwise have similar characteristics (both in frequency response and slew rate). Both IC's are low noise. Generally speaking very high speed amplifiers use more current and have lower input impedances. In view of the large number of amplifiers being used, it would not be prudent to use high current amplifiers because of the additional load on the power supply and the increased effect of the amplifiers talking to each other through the power supply. If you are going to replace them, replace all of them [in any given channel]. Changing the op-amps does not have any effect on the capacitors.


The power decoupling resistors together with their associated tank capacitors reduce the effect of the boards talking to each other. Without them there is a high probability of unwanted oscillations probably in the radio frequency range together with a general increase in noise.



I don't know about the transformer.



Increasing the capacitor values in the high pass filter circuit will reduce the cut-off frequency of the circuit.
Now this is how WRONG information spreads on the Web. The caps are polarised for a reason. When the board is built, the builder did not know which way the offset on each opamp would be, plus or minus. So they specified a non polar capacitor. Of course, you could go through, check what the offset is on every stage, and then fit polar caps appropriately. But if the offset changes polarity with temperature, what do you do? As Jim Williams says, the best cap is a wire. But this requires more work. And then, what are you going to put through this board? The highest quality pure instruments recorded with the finest mikes? Or grunge? Professional musos or amateurs? Lots to think about, before you start the soldering iron up!
Old 8th September 2019
  #14
Glad you said it first. Console manufacturers do not match mic preamp transistors. I do, but that's my job. They don't because it's too expensive and time consuming. Besides, the large gain pot blocking cap eliminates the DC gain that a matched pair can tolerate. Even matched discretes wander with temperature variations. All the precision matched transistor pairs are made on the same die to avoid that. Those are rare in recording consoles.

As for caps, a bipolar cap is two in series for twice the losses. That's why they sound so dull. Manufacturers blindly place them without regards to DC offset polarity. The Soundcraft 6000 master mix section has a negative 2 volt DC offset but the blocking caps are placed + pin towards the opamp output pin like most of them. This causes noises and sputtering on those consoles. Reverse that cap and all is good.

TL072 opamps have 40 db loop gain at 10k hz. That causes excessive THD. It's the same as a 1970 era 741 opamp. Modern opamps have up to 90 db gain at 10k hz, 50 db less THD and you hear that difference when taking gain. Crank up a 072 based hi EQ +15 db's and you only have 25 db's for error correction.

Input impedances are all very high in the meg ohm range, even for the bipolar devices. That is also not an issue in modern line level audio design. Jfet opamps are selected for their low bias currents, not for very high input impedances unless you are doing specialized work on I/V designs or strain gauges.

Higher current opamps do not talk to each other through the power rails unless the decoupling is poorly done. I tend to use rather large caps with local .1 uf bypasses to avoid that.
Old 8th September 2019
  #15
Gear Addict
 
audiospecific's Avatar
 

Its the bipolar electrolytic cap or equivalent circuit (two polarized caps, with the negative terminals tied together) that has a lot of ESR that causes the dull sound. There is certain combinations of other non polarized caps and the circuit that its applied in can cause loss (dull sound) because of the construction techniques. On those, the characteristics change under circuit application.
Old 8th September 2019
  #16
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nosebleedaudio's Avatar
Looks like the OP never came back to follow up ect...
Old 8th September 2019
  #17
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audiospecific's Avatar
 

The thread is ancient. But its always good hearing feedback from Jim Williams
Old 5th August 2020
  #18
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White Falcon's Avatar
I find it very annoying (for my workflow) that the Control room monitor out (CR MON L & R) gets muted when headphones is inserted.

Also, the headphones socket needs cleaning from time to time as it cuts and distorts the signal from the CR MON even if no headphones is inserted (even more annoying).

How would I disable this 'mute function'? Schematics of the master module (and more) is attached.

Attached Files
File Type: pdf Sndcft_DeltaDLX_Schems(1).pdf (1.16 MB, 7 views)
Old 5th August 2020
  #19
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nosebleedaudio's Avatar
The signal goes thru the headphone jack before going to the CTR line output, cant use both at the same time.
I would get a good gold 1/4" jack and replace the old one.
To have access to both make a headphone extension box and split off to both a separate headphone amp and CTR monitors.
Old 5th August 2020
  #20
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White Falcon's Avatar
Thanks nosebleedaudio!
Old 5th August 2020
  #21
Quote:
Originally Posted by White Falcon View Post
I find it very annoying (for my workflow) that the Control room monitor out (CR MON L & R) gets muted when headphones is inserted.
A local guy had me install a small DPDT toggle switch in his master module to switch cans or monitors.
Old 5th August 2020
  #22
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White Falcon's Avatar
Quote:
Originally Posted by Jim Williams View Post
A local guy had me install a small DPDT toggle switch in his master module to switch cans or monitors.
Thanks Jim, that's cool
Old 10th August 2020
  #23
It's not easy, very thin traces are cut and the mechanical fitting is not very strong. It's best for fixed situations.
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