Why are servo power supplies often unregulated? - diyAudio
Go Back   Home > Forums > Source & Line > Digital Source

Digital Source Digital Players and Recorders: CD , SACD , Tape, Memory Card, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 22nd September 2006, 09:41 AM   #1
diyAudio Member
 
Join Date: Oct 2004
Default Why are servo power supplies often unregulated?

Hi all,

I've noticed on a few CDP schematics, that some circuits, (I think) mainly servo circuits, are powered with unregulated supplies.

Why is this? Is it because motors are being driven, and the current demands require that the supply is unregulated.

Surely, if the supply is regulated, the supply lines will be steadier, and this would offer more precision to the servo driver, not to mention improvements in PSRR and noise reduction in general?

If bigger current demands were required, couldn't a regulated supply with large local decoupling capacitance suffice?

Or, as another alternative, have I just completely missed the point?

I appreciate that some things really don't work well with regulated supplies (i.e. many power amps) but this is using much less power.

Cheers,
Phil
  Reply With Quote
Old 22nd September 2006, 11:58 AM   #2
diyAudio Member
 
Join Date: Jul 2003
Location: Bath, UK
There's simply no benefit. The positioning is sensed separately, so regulating the supply lines adds nothing in the way of needed accuracy, so manufacturers leave it out.

In a CD player the current demands are nothing plain old 78xx/79xx regs couldn't handle.

Now - in terms of stopping motor noise getting back into a weedy supply, yes regulation or other passive measures (e.g. small value inductors in the raw servo supply lines could make a lot of sense - and there's nothing to stop you if you like DIY.
  Reply With Quote
Old 22nd September 2006, 12:45 PM   #3
diyAudio Member
 
Join Date: Oct 2004
Hi Martin,

Thanks for the reply.
That confirms my suspicion (I did see one schematic were the IV conversion was also unregulated! So it does scream cost cutting).

One of my favourite CDP mods is to use a daughterboard with seperate regualtion for different parts of the circuit. Now I know I can extend it to the servo circuitry.

Thanks again!

Phil
  Reply With Quote
Old 22nd September 2006, 03:18 PM   #4
diyAudio Member
 
Join Date: Jul 2003
Location: Bath, UK
Quote:
did see one schematic were the IV conversion was also unregulated!


Let us know how it turns out if you try this. You can always lookup the datasheet for the servo drivers and find out the max. current that will supply. I bet it will be under 0.5A - servos are usually only weedy little 3v motors anyway (Mabuchi or similar).
  Reply With Quote
Old 27th September 2006, 10:21 AM   #5
diyAudio Member
 
Join Date: Oct 2004
Hi Martin,

I think as a start I will rearrange the regulation at the power supply.
On this CD player (Philips CD940), all power rails (ignoring the VFD display), regulated or not, are derived from +/- 10V after rectification.
I am, at some point, going to try feeding a +/- 10v regulated supply to the PSU, just after the rectification (and oviously decommision the original relevant secondaries on the transformer). That way, everything should be regulated at least once.
The only regulators on board are +/-5V, so 10V should have ample headroom for them to work properly.

I did replace the 5V supply with seperate regulation to several chips on my, alas now defunct, Marantz CD63, and the difference was actually very surprising.

I'm hoping to not mod this player so much. I just want to use it as a transport with I2S output to feed a DAC. All those regulators made it a real pain to perform maintenance.


Cheers,
Phil
  Reply With Quote
Old 27th September 2006, 04:14 PM   #6
diyAudio Member
 
Join Date: Jul 2003
Location: Bath, UK
Quote:
I am, at some point, going to try feeding a +/- 10v regulated supply to the PSU, just after the rectification (and oviously decommision the original relevant secondaries on the transformer). That way, everything should be regulated at least once.
I think I'd cut tracks as required then rewire so that the original regulated PSU remains to power the servo and control ciruitry, and the new PSU supplies the clock, decoder and SPDIF output devies - really go for the separation between servo and audio you intend. Of course if you only want to use it asa fransport, you can unhook power to the aduio output stage(s) you don't need also...

Quote:
I did replace the 5V supply with seperate regulation to several chips on my, alas now defunct, Marantz CD63, and the difference was actually very surprising.
Oh I know...but the 5v rail in a standard cd63 is a total mess
  Reply With Quote
Old 28th September 2006, 09:40 AM   #7
diyAudio Member
 
Join Date: Oct 2004
Hi Martin,

I think you're absolutely right, and that's probably the best way to go. From my experience with myCD63, and requiring extra boards with regulators kicking around, I think it will be the last mod I do to it (best to do it properly).
I was running under a stupid assumption that, because its a bitstream CDP, all the ICs in the chain are required (because the clock is fed back from the DAC to the decoder - the only chip I want), I would leave all the power rails in tact. But, you're right, there is a lot that can be switched off, especially the analogue output.
I guess it depends on time, and/or how big a job I want to do on the machine.

Cheers,
Phil
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Parallel a dual power supply or two power supplies? Thunau Power Supplies 12 16th February 2007 04:21 AM
unregulated wallmart power supply cap size ash_dac Power Supplies 11 17th August 2005 11:39 PM
Power Supplies guitargully Parts 0 6th February 2004 03:45 AM
HV power supplies santa Swap Meet 3 12th May 2003 02:01 AM
Regulated Power Supplies for Low Power Amps PTL60 Solid State 18 6th February 2002 06:24 AM


New To Site? Need Help?

All times are GMT. The time now is 05:52 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2