Hi All,
I am hearing noise from the servo circuits performing focusing and disc spinning tasks during the playing of disks. It is low level compared with the music but it is there. Any ideas on how to get rid of this?
Some detail on the machine:
A Rotel 955 16 bit with the following mods:
1. 2x TDA1541 in parallel
2. Zero-oversampling
3. Passive IV concersion through a 25 ohm resistor. There is no post IV conversion filter and the DAC pushes out about 0.3 V (I think)
4. The DACs are powered by two separate transformers, one for the -15/-5V pins and one for the +5V pin. The powersupplies consist of LM317 pre-reguilatioon followed by TL431 shunt regulation
5. The SAA7210 and processor have their own power supplies and transformers each! These are decoupled by 1000uF low impedance caps (Panasonic). These also use LM317
6. The clock is by Guido Tent and has its own transformer/power supply. The supply is TL431 based with LM317 pre-regulation
7. Everything that sits on the unregualetd 9V line (which includes teh servo circuits) are now powered from a separate transformer and sit at about 12V. These are not regulated...
8. The original transformer is only powering the LED display now!
9. 80% of wire links in teh CD player have been replaced with inductors having DC resistance of about 0.2 ohms and all have been threaded with ferrite beads.
10. Despite all of the above, the CD player still sits in its original box and with its lid on you'd never guess all the nasty stuff happening inside, except for the weight which is now around 15kg!
11. So in total 7 transformers and lots of capacitors and inductors with zero oversampling and no op-amps after the DAC.
12. The Sound? Very good. Tight bass, clear highs and good depth to sound. Just that very low level servo noise that gets to me sometimes. If there is no real solution, I will live with the player as is!!
13. One final thing is that I do not really have any space left for anything else inside the player!!
Thanks for any help
Ryan
I am hearing noise from the servo circuits performing focusing and disc spinning tasks during the playing of disks. It is low level compared with the music but it is there. Any ideas on how to get rid of this?
Some detail on the machine:
A Rotel 955 16 bit with the following mods:
1. 2x TDA1541 in parallel
2. Zero-oversampling
3. Passive IV concersion through a 25 ohm resistor. There is no post IV conversion filter and the DAC pushes out about 0.3 V (I think)
4. The DACs are powered by two separate transformers, one for the -15/-5V pins and one for the +5V pin. The powersupplies consist of LM317 pre-reguilatioon followed by TL431 shunt regulation
5. The SAA7210 and processor have their own power supplies and transformers each! These are decoupled by 1000uF low impedance caps (Panasonic). These also use LM317
6. The clock is by Guido Tent and has its own transformer/power supply. The supply is TL431 based with LM317 pre-regulation
7. Everything that sits on the unregualetd 9V line (which includes teh servo circuits) are now powered from a separate transformer and sit at about 12V. These are not regulated...
8. The original transformer is only powering the LED display now!
9. 80% of wire links in teh CD player have been replaced with inductors having DC resistance of about 0.2 ohms and all have been threaded with ferrite beads.
10. Despite all of the above, the CD player still sits in its original box and with its lid on you'd never guess all the nasty stuff happening inside, except for the weight which is now around 15kg!
11. So in total 7 transformers and lots of capacitors and inductors with zero oversampling and no op-amps after the DAC.
12. The Sound? Very good. Tight bass, clear highs and good depth to sound. Just that very low level servo noise that gets to me sometimes. If there is no real solution, I will live with the player as is!!
13. One final thing is that I do not really have any space left for anything else inside the player!!
Thanks for any help
Ryan
Ryan,
Is it possible that with so much tweaking done to the player, the tracking and focusing of the laser pick up head has been misaligned electrically (too much offset?) to force the servo circuit to work especially hard (& thus the "noise") to try to get back to read the disc properly. Try a badly scratched or warp disc and see if it'll play. If you hear a lot of "noise" from the pick up head, it's most likely that the pick up head needs some major alignment. Get a service manual and hook it up to a scope and just follow the alignment instruction in the manual. Let us know how it turns out.
Is it possible that with so much tweaking done to the player, the tracking and focusing of the laser pick up head has been misaligned electrically (too much offset?) to force the servo circuit to work especially hard (& thus the "noise") to try to get back to read the disc properly. Try a badly scratched or warp disc and see if it'll play. If you hear a lot of "noise" from the pick up head, it's most likely that the pick up head needs some major alignment. Get a service manual and hook it up to a scope and just follow the alignment instruction in the manual. Let us know how it turns out.
Re servo noise
Thanks for your replies.
1. The servo noise was not there before the mods, but i think that it is now audible because the output from the DAC in the CD player is so much lower. Remember that befoire my mods, the CD player was pushing out 2V. Now its just 0.3-0.6V, so any DAC independent noise is going tp appear louder
2. The noise is not like when the servo first searches a disk (i.e. the whining noise that one sometimes hears). It is more like a whirring sound in the background, I'd say around 300-500 Hz.
3. It is in the background and only really audible when the machine is paused. During music, it is too soft to be noticed, except in between tracks. I must say that I'm not sure that other people have noticed it unless I paused teh Cd player and turn the volume up.
4. I was thinking that regulating the +-9V lines to the servo may help. Any thoughts on this?
Thanks for your ideas.
Ryan
Thanks for your replies.
1. The servo noise was not there before the mods, but i think that it is now audible because the output from the DAC in the CD player is so much lower. Remember that befoire my mods, the CD player was pushing out 2V. Now its just 0.3-0.6V, so any DAC independent noise is going tp appear louder
2. The noise is not like when the servo first searches a disk (i.e. the whining noise that one sometimes hears). It is more like a whirring sound in the background, I'd say around 300-500 Hz.
3. It is in the background and only really audible when the machine is paused. During music, it is too soft to be noticed, except in between tracks. I must say that I'm not sure that other people have noticed it unless I paused teh Cd player and turn the volume up.
4. I was thinking that regulating the +-9V lines to the servo may help. Any thoughts on this?
Thanks for your ideas.
Ryan
Ryan,
Looks like you have to adjust your tracking and focus gains and focus offset of your player. Obtain a manual and perform the adjustments, you will probably need a signal generator and a scope (60 Mhz min.) This is assuming that your player does not have a digital servo.
Excess servo noise could also be an indication of a weak pickup(laser) assembly.
Jam
Looks like you have to adjust your tracking and focus gains and focus offset of your player. Obtain a manual and perform the adjustments, you will probably need a signal generator and a scope (60 Mhz min.) This is assuming that your player does not have a digital servo.
Excess servo noise could also be an indication of a weak pickup(laser) assembly.
Jam
At first I thought you were complaining about acoustical noise, but with yesterday's post it becomes clearer that you are talking about servo noise on the analog out signal. My best guess is that you have a botched grounding scheme, the servo circuits and the analog out sharing some common ground impedance. But it may also be radiated interference...
For starters:
1. try to connect some decent low-ESR electolytics (220/16 or up) in parallel with 1µF ceramic chip between the +/- supplies of the power servo drivers and the ground return of the servo coils. If those are BTL drivers, there will be no ground return. In this case make sure the electrolytic is connectet between + and - supply of the driver (the latter may actually be ground).
2. Define separate star grounds for servo, digital, analog. Tie them together at one central ground.
Have fun!
Eric
For starters:
1. try to connect some decent low-ESR electolytics (220/16 or up) in parallel with 1µF ceramic chip between the +/- supplies of the power servo drivers and the ground return of the servo coils. If those are BTL drivers, there will be no ground return. In this case make sure the electrolytic is connectet between + and - supply of the driver (the latter may actually be ground).
2. Define separate star grounds for servo, digital, analog. Tie them together at one central ground.
Have fun!
Eric
Thanks Eric,
I will certainly take a closer look at teh grounding scheme, which admittedly I have paid VERY little attention to.
I must tell you that putting a resistor 10 ohm between chassis ground and circuit ground seemed to lower the noise floor and made the sound more relaxed (sorry no other way of describing it).
But even more was gained by adding a cap (2.2 nF I think or may be it was 22nF) across the resistor (i.e. in parallel with the R). This seemed to have teh effect of increasing transparency in the system and lowering teh noise floor.
I guess that the cap is shunting AC noise on the cirrcuit ground to chassis ground.
I'll let you guys know how it pans out, but am still open to ideas!
Regards
Ryan
I will certainly take a closer look at teh grounding scheme, which admittedly I have paid VERY little attention to.
I must tell you that putting a resistor 10 ohm between chassis ground and circuit ground seemed to lower the noise floor and made the sound more relaxed (sorry no other way of describing it).
But even more was gained by adding a cap (2.2 nF I think or may be it was 22nF) across the resistor (i.e. in parallel with the R). This seemed to have teh effect of increasing transparency in the system and lowering teh noise floor.
I guess that the cap is shunting AC noise on the cirrcuit ground to chassis ground.
I'll let you guys know how it pans out, but am still open to ideas!
Regards
Ryan
Jocko,
I've had a brief look at some of your postings.
Everyone to his own opinion. I can say that based on empirical evidence, I LOVE the sound of the zero-oversampled TDA1541 and so does everyone that I know that has tried it.
I owuld strongly recommend that you obtain a cheap 16 bit CDP with SAA7220/TDA1541 and do just the following:
1. Disconnect the DAC output from the op-amp output stage and use a 50 ohm resistor to do IV conversion (with no post IV filter)
2. Disconnect the 7220 from the DAC input pins (word, clock, etc) and connect pin1 of the DAC to pin1 of the SAA7220. DO teh same for pin 2 and 3 of the SAA7220. This gives zero-oversampling.
3. Listen and if you really want, measure (It should sound great and measure poorly)
4. Let us know what you hear!
Regards
Ryan
I've had a brief look at some of your postings.
Everyone to his own opinion. I can say that based on empirical evidence, I LOVE the sound of the zero-oversampled TDA1541 and so does everyone that I know that has tried it.
I owuld strongly recommend that you obtain a cheap 16 bit CDP with SAA7220/TDA1541 and do just the following:
1. Disconnect the DAC output from the op-amp output stage and use a 50 ohm resistor to do IV conversion (with no post IV filter)
2. Disconnect the 7220 from the DAC input pins (word, clock, etc) and connect pin1 of the DAC to pin1 of the SAA7220. DO teh same for pin 2 and 3 of the SAA7220. This gives zero-oversampling.
3. Listen and if you really want, measure (It should sound great and measure poorly)
4. Let us know what you hear!
Regards
Ryan
One final thing:
As I have noted in previous posts, the "servo noise"I refer to is really at low levels and I can live quite happily with the CDP as it is at present.
My initial query was based on determining whether someone had heard the same thing and solved the "problem". I guess I'm being a bit of an audiophile, you know try to get to 100% when you have 98%! The whole thing just gets asymptotic!
As I have noted in previous posts, the "servo noise"I refer to is really at low levels and I can live quite happily with the CDP as it is at present.
My initial query was based on determining whether someone had heard the same thing and solved the "problem". I guess I'm being a bit of an audiophile, you know try to get to 100% when you have 98%! The whole thing just gets asymptotic!
Are you sure that you have not made a ground connection(s) an inductive one.
Follow Capslock's (the other Eric) advice regarding defining grounds of various stages and then making them common at one point (star grounding).
Make the central ground common of massive copper - 1mm sheet with largeish area (volume/mass) makes a good solid central reference earth, only it's a bitch to solder to.
Two soldering irons helps.
Regards, Eric.
When you actually have feedtrough from the servoes, who knows what else ends up in your output stage that you cannot discern expressly? RF rectification is definitely a source for intermodulation distortions. There is nothing audiophilic about this!
You would probably have the feedtrough even with a decent digital and post filter. But probably the intermodulation is acerbated by the presense of RF from the DAC that keeps those poor little input transitors of your output buffer or power amp input buffer close to or at their slew rate limits...
Eric
You would probably have the feedtrough even with a decent digital and post filter. But probably the intermodulation is acerbated by the presense of RF from the DAC that keeps those poor little input transitors of your output buffer or power amp input buffer close to or at their slew rate limits...
Eric
Doc:
If you are new to the forum, then "well come". I've only been here a month or so, and have managed to really stir things up.
I've been doing this stuff long enough to know how it is going to sound/work/etc. Tube retro, I can understand. But this stuff makes no sense at all. Digital audio may be flawed from the get-go, but going 14 years backwards isn't going to fix it. And will only make the things I rant about worse. You'll just have to trust me.
Jocko
If you are new to the forum, then "well come". I've only been here a month or so, and have managed to really stir things up.
I've been doing this stuff long enough to know how it is going to sound/work/etc. Tube retro, I can understand. But this stuff makes no sense at all. Digital audio may be flawed from the get-go, but going 14 years backwards isn't going to fix it. And will only make the things I rant about worse. You'll just have to trust me.
Jocko
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