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Old 18th March 2015, 09:21 AM   #1
diyAudio Member
 
Join Date: Apr 2007
Default sparkling distortion on less loud passages

Hello,
I hope there is someone who could help me.
Yesterday i connected my Revox225 dac TDA1540 to i/v resistor, and to valve stage. Before i use normal OP-Amp output.
I tried 100ohm because sound with this nominal is a best,but... there is a sparkling distortion(strong enough) on less loud passages.I also try 50,70ohm resistors.Later i connected back to opamp.Distortion still but quiet.
I check all voltages,also i burned 1000hz cdr and tested output with osciloscope.Voltages ok,sinus wave ok,but when i put musicCD, i can hear sparkling distortions on less loud passages.
I did same thing with Philips104 .Very similar schematics.Any noises !!!
Maybe somebody come across with this problem and can help me?
Best Regards
Ram
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Old 18th March 2015, 12:21 PM   #2
marce is offline marce  United Kingdom
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Location: Blackburn, Lancs
How are you connecting to the valve, twisted pair? how far is the connection, is the DAC output filtered for HF before going to the valve....
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Old 18th March 2015, 06:22 PM   #3
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Default Re: Sparkling distortion on less loud passages

Hi,
I have tried a lot valves.Last one is HL4. My cabel lenght is about 40cm from dac to valve stage.I using same valve stage also for Philips104 (very similar schematics) without any backgroud noises.I dont use any HF filter.
Best Regards
Ram
P.S. i try conect dac only with 100ohm resistor straight to transistor amp input.Still same noises, so reason somewhere in a player.
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Old 18th March 2015, 06:56 PM   #4
sesebe is offline sesebe  Romania
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Standard problems with not using a low pass filter.
Some amplifiers can filter these components without inter-modulations in audio frequency, some will put some noise in audio frequency.

If you will use low pass filters at, lets say 50-100KHz, all problems must disappear.
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Old 18th March 2015, 07:10 PM   #5
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Default Re: Sparkling distortion on less loud passages

Hi,
what kind of HF filter you can recomend?
Maybe you can share time proof schematic?
Best Regards
Sioko

Last edited by vismantas; 18th March 2015 at 07:15 PM.
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Old 18th March 2015, 07:22 PM   #6
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Default Re: Sparkling distortion on less loud passages

Hi,
i connected 2 weeks ago 2 players Philips304 and 303 with same 100ohm resistor and same valve stage, same amp.Any noises.How it coud be?
Best Regards
Ram
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Old 19th March 2015, 12:41 PM   #7
marce is offline marce  United Kingdom
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EMI probably from a 40cm (ridiculously long) cable from your DAC, I would hope this cable is at least tightly twisted so the HF return current has a decent path back to its source, filtering the HF firsts would be a help.
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Old 19th March 2015, 09:39 PM   #8
danico is online now danico  Hungary
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Location: Hungary
Quote:
Originally Posted by vismantas View Post
Hello,
I hope there is someone who could help me.
Yesterday i connected my Revox225 dac TDA1540 to i/v resistor, and to valve stage. Before i use normal OP-Amp output.
I tried 100ohm because sound with this nominal is a best,but... there is a sparkling distortion(strong enough) on less loud passages.I also try 50,70ohm resistors.Later i connected back to opamp.Distortion still but quiet.
I check all voltages,also i burned 1000hz cdr and tested output with osciloscope.Voltages ok,sinus wave ok,but when i put musicCD, i can hear sparkling distortions on less loud passages.
I did same thing with Philips104 .Very similar schematics.Any noises !!!
Maybe somebody come across with this problem and can help me?
Best Regards
Ram

Hello there,

I have had the same problem on my B225 recently.
Low noise crackling kind of sound at on very low passages.
on one side. Do you hear noise on both side or just one?
I had one bad (extra) capacitor on the MSB pin underneat the original fim cap. After I changed it the noise was gone.

I also use DEM reclocking with 6k8 resistors if the DEM clock not in syncron can cause distortons,too.


Ckeck the board for dry,cracked solder around the dac.
Good ground connection is important. at the psu cap,too.

OOps I just realized you using tubes. I did not tried yet,altough I have some tubes for that reason.
There are two biasing resistors between dac output and opamp input. That goes from +12V.
I dont know if those can be a problems for the tube or not.


I just upgraded the dac psu caps for elna silmic II and it was a huge update in sound clearness and smoothness.
I had changed all the caps in the player couple years ago,but I used the same kind of philips bc116.
not bad but the elna in another leage
Also just recently find some optimization guide for the LM337/317 psu. Needed to put some low value cap on the adjusting resistor. LM317 (100-120nf +12V) (68-100nf +5V)
LM317 (39-47nf -12V) (33nf -5V on dac board) I changed the -5V reg capacitors to tantalum it just sounds better,low esr caps are no godd after the regs.
Another look at the LM317 and LM337 regulators

Now the cd sounds extremely dinamic and clear bottom to top and very sweet at the same time. Drums kicks is right in your guts.

Regards.
Bardos

Last edited by danico; 19th March 2015 at 09:53 PM. Reason: adding more info
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Old 20th March 2015, 05:57 AM   #9
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Default Re: Sparkling distortion on less loud passages

Hi Danico,
i have same noises on both chanells.This evening i will try check those capacitors.
Thanks alot.
Best Regards
Ram
P.S.On the decoder board a find some modifications.I think these changes made with cd player when it was serviced.Maybe you can check on your player these modifications.2 extra diodes,pcb trace cut in one place and c31 missing in supply board.For fun i put back c31 3300nf back to pcb and distortions was slighly different.
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Old 20th March 2015, 11:23 PM   #10
danico is online now danico  Hungary
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Location: Hungary
Hi Vismantas,

If you talking about the c31 on the servo 1 board,then its not needed if you have the 1.769.315 number on the board. also q13 and r60,r61 not needed. on the 300 series board it should be there.

About the noises, it was there before you tried the tube output?
I assume it was working fine. I can only think about those biasing resistors R109-R108 // R209-R208 and C118 // C218 capacitors between them. I'm not good with tubes but can be a problem with the biased dac output or the caps leaking and you have some DC on it.

I would try disconnecting the resistors or just change the caps, if they original they should be dried out already.

I remember revox made some mod but cant remember to what board it was. I will check on the german revox forum,they had the mod schematic.

I just saw you are already on that side. I'm sure they can help you better then me :-))

Last edited by danico; 20th March 2015 at 11:30 PM.
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