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Old 24th February 2012, 07:52 AM   #421
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It's probably more likely that the oscillations are caused by the feedback loop. I'd look at this before the decoupling.
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Old 24th February 2012, 11:22 PM   #422
gvelim is offline gvelim  United Kingdom
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Hi aptsys, any suggestions on fixing the feedback loop would be greatly appreciated. AD797 sounds so good that I am decided to go all the way.


On another topic I reworked the clock supply and now have a) Crystek XO relocated to DAC PCB, b) removed the FBs for both XO & Schmitt inverter and powered both from the flea 3.3Vdc, c) replaced XO & Schmitt inverter ceramic bypass caps with film Panasonic ECHU 0.1nf/50V (0805).

With this change the whole clock chain is in clean supply except of the DSP. The AD797 on the flea PSU gets warm but nothing to worry.

This feels to have added further improvement to the sound stage, definition and bass.
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Old 25th February 2012, 12:18 PM   #423
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@gvelim
- you can replace regular diodes with schottky diodes (green circle)
- use SP-Cap, glue it on the top of Potato chip and connect to pins 14 in 7 (yellow circle)
- for VMIDL and VMIDR you need low leakage type capacitor and Oscon's are high leakage: http://www.saga-sanyo.co.jp/oscon/cg...de.cgi?id=SEPC. I tried different caps there, including Nichicon KL (lowest leakage). Personally I like Panasonic FC or FM there (white circle). You should try different caps and values in this position and decide for yourself

For AD797, try to lower power supply lines to 12V to minimize power dissipation.
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Last edited by stormsonic; 25th February 2012 at 12:20 PM.
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Old 26th February 2012, 01:28 PM   #424
gvelim is offline gvelim  United Kingdom
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Thanks Stormsonic for the good advise, will try out the rest but AD797 since I am bit stuck on +/- 15Vdc as otherwise I have to change the SuperRegs so not sure whether I have any option here.


My last mod (flea PSU -> XO+HexInv) although it improved on bass and stage detail I noticed that caused the highs to be distorted, particularly the sound of the hi-hat was sounding muddy.

I reworked the mode to add the ferry beads which fixed the problem and made the sound pristine again, "hi hat" sounds as a "hi hat", etc. Seems some HF return spoiling something there, not sure though what happened.

I attached photos of the final change as I hope that I am done with the clock (can't get any better, or is it ?)
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Old 26th February 2012, 04:54 PM   #425
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Great, you isolated chip and crystal with ferrite beads. Maybe bigger capacitor after ferrite beads (SP-Cap parallel to C32 and C121).

You can also rework digital input buffer for Coax Digital input 1 and Coax Digital input 2, but you will need 0805 SMD resistors:
R20, R22 = 4.7K
R21, R23 = 68K
R65, R86 = 2.2K
R87, R125 = 10K

While there, please remove capacitors C17 and C18, they are doing a lot of harm in this position.
If you want to improve things further, C126 and C127 should be replaced with piece of wire.
You can also move output film capacitors to new position, solder them across C12, C14, C215, C222. Recycling
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File Type: jpg gv3.jpg (72.6 KB, 311 views)
File Type: jpg gv4.jpg (80.7 KB, 282 views)

Last edited by stormsonic; 26th February 2012 at 05:08 PM. Reason: pictures
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Old 28th February 2012, 08:41 AM   #426
gvelim is offline gvelim  United Kingdom
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Nice one Stormsonic

Quote:
Originally Posted by stormsonic View Post
You can also rework digital input buffer for Coax Digital input 1 and Coax Digital input 2
Considering the re-clocking and up-sampling that takes place in the DSP would any improvements in the input make any difference ?

Isn't the purpose of the DSP/memory buffer to cancel all those bad effects of the input ?
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Old 2nd March 2012, 10:48 AM   #427
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Quote:
Originally Posted by gvelim View Post
Hi aptsys, any suggestions on fixing the feedback loop would be greatly appreciated. AD797 sounds so good that I am decided to go all the way.
Hi,

Is the AD797 in place of all the op amps at U55, U56, U59 and U60, or are the ones for differential to single ended also replaced?

Do all of the AD797's run hot or is it only certain ones?
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Old 3rd March 2012, 10:34 PM   #428
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Stormsonic, can you please make a summary of which mods you recommend for the best possible sound? You seem to be the one to ask!

I have made the basic mods with super regs for 5+ and 15-volt, and bypassed the output caps, now I want more!

The relays at the output, are they affecting sound quality in a negative way? Can they be removed in some way?

I only use toslink-input and xlr-output. Will I gain anything from disabling usb,coax and the rca-outputs?

Last edited by Rajapruk; 3rd March 2012 at 10:41 PM.
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Old 4th March 2012, 03:45 AM   #429
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@Rajapruk

About relays : I have bypassed relays 3 ,4 , 5 ( mind not relays 6 ) last week with no noise on switch on/off, nor when switching sources too ( tanks to WOLFSON'S guys for well implemented digital mute ) . Don't know if is a big change because, in same time, I made a couple of more mods....


ciao.
Nice
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Old 4th March 2012, 07:02 AM   #430
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Thanks Bicefalo! I probably will do that then.
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