cambridge isodac s700 mods/upgrades

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#43
JohnW said:
Dan,

🙂 Glad to hear - that you also hear what I do....

John
Click to expand...

I'm glad you kept saying it. 😉

I have one question I hope you'll answer for me John. When you say to upgrade the IsoMagic psu, do you mean the parts in the brick, or are there some power supply parts inside the box.?

I still don't have a schematic for the IsoMagic, so if anyone can oblige I'd greatly appreciate it. I have the DiscMagic cct if anyone needs it.
 
#45
I plan to order a pair of DACT CT102 power supplies later this week. What do you think? http://www.dact.com/html/power_supplies.html

Expensive I know, but I think it will be money well spent. I've been comparing the DiscMagic/IsoMagic to a couple of more expensive players lately. I've always thought highly of the Magic pair, but now I realize it's even better than I thought. Two of these DACT units won't come close to the price I would have sunk into another player.
 
#46
Hi Dan,

The Isomagic (and CD4SE) are the best designs I did for Cambridge Audio, so I'm glad you are also discovering there Magic!!!

Forget ordering the PSU you Linked too, these are switching units, and as there Switching Frequency is not Sync. to the DAC operating Frequency you will get Spurie due to "beating" between Clocks - go for a simple LM7815 / LM7915 type PSU.

John
 
#47
I have just put together two P05 power supplies from Rod Elliot, I am sure that most of you know that they use LM7815/LM7819 regs.

I think they sound just fine, although I have never heard the DAC with the original PSU as I bought the DAC without one.

I am going to rig up another +15v supply in a few days for the digital supply, this time using a LM317.

Dose any one have any preferences for LM317 over LM7815 or vice versa? Any particular reasons?

Thanks
Mark
 
#48
Hello John,

I've upgraded the IsoMagic with a nice LM7815 & LM7915 type PSU and am really pleased with the results. Trouble is I think I heard you say the next big upgrade was a discrete output circuit? Any clues as to the circuit you used?

I have the IsoMagic running on the end of a M-Audio Transit at the moment and I keep coming across the term 'galvanic isolation' to isolate it from the PC. I'd love to know how to acheive this as the PC ground must be connected for the transit to work.

You've probably heard this a million times John but I think the IsoMagic is an amazing design for the money and it's given me many hours of beautiful music and lots of fun trying to tweak it. You must get quite a buzz from your acheivements!

One last plead: has anyone got a circuit diagram for a IsoMagic?

Thanks,

Gray.
 
#49
JohnW said:
Forget ordering the PSU you Linked too, these are switching unitsPSU
Click to expand...

Thanks again John. It must be tedious for you talking with a mechanical guy. 😀

I thought the DACT unit might work if I used the existing IsoMagic PSU to feed it instead of the switching supply. There was a link on the DACT site showing a DIY DAC where he's fed the PSU with a 12V wall wart. I'm not sure where the third +15V supply would come from though. Split it off from the analog +15?

What about this Welborne Labs unit? http://www.welbornelabs.com/ps1.htm

I know you're saying a basic LM7815/LM7819. I'm not trying to be thick, but I'm looking for maximum impact, without worrying too much about price. Regardless of the regulators used, would two power supplies be likely to improve the sound at all?
 
#52
JohnW said:
Expensive but OK, you would need 2 of these units one for each channel, and one POSREG version for the Digital section,

John
Click to expand...

Expensive is OK, as long as the performance is there. Welborne has a good reputation. I like the component quality and the bypass caps. I'm going to go ahead with these. Thanks for your help John.
 
#54
Hi there,
I have decided to upgrade my power supply. Apart from the little issue of not realising that 7815's have different pin outs to 7915's, I am just about ready to go.

However I don't want to mess about inside the S700 and am going to use the power lead from the existing power unit. However having taken this apart I see a group of wires

White red and blue to +15V
orange and brown to -15V
green purple and 2xblack to 0V

The question is how are they paired up within the S700. I really don't want to start mixing up my carefully constructed 3 independant supplies.

Any help would be appreciated.

Shoog
 
#59
Thanks for that link. Unfortunately that only refers to the internal S700 power wiring.

I buzzed out the cable to the inside of the S700 and this is what I found.

Orange -15V Channel one
Red +15V Channel one
Purple OV Channel One

Brown -15V Channel Two
Blue +15V Channel Two
Green 0V Channel Two

White +15V Digital
Black 0V Digital

Thick black - Power Cable Screen

I cannot be certain of the 0V because they all seem to be tied together in the S700.

I used the existing S700 power transformer for the digital supply, through a LM7815 and 1Kuf before and after, with 0.01uf of MPE bypass before and after.
I used a 30VA 12V toroidal for the audio channels. I have made up two supplies for left and right but because of a problem with the LM7915 I am only using one for the two channels.
I would guess from looking inside the S700 that when I go for seperate left and right channels there will probably be only a marginal improvement in sound. I would also guess that going for more expensive regulators will probably be a waist of time because within the s700 there are various LM78xx type regulators further smoothing the supply and bringing things down to 12V.

Having done this I did a test with Becks-"Mutations", which is a HDCD.
It was quite a revelation. Previously I would have described the sound of the s700 as warm and rich. With the new power supply it sounds like a different DAC. There is a level of detail that I had never heard before. I am hearing things that were previously lost in the mix. The improvement is especially noticeable on the vocals which are nuanced and more intimate. The warm veil has disappeared, to be replaced by enhanced imaging and an expanded soundstage. Possably the bass is a bit lighter.

Altogether well worth the effort, and I cant wait to see if adding the second channels separate powersupply will bring further enhancement.

Shoog
 
#60
I forgot to look what the output opamps where when I had the case open lastnight. Are they standard single opamps. If so would I see an improvement by substituting some OPA627's.
If its worth it, whats the best way of dropping in a replacement. I
wouldn't really want to desolder with all of the inherant risks to the board. Could I chop the legs and solder the OPA627 to the stumps.

Shoog
 
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