Discrete output for my cd player!

wandelblu

Member
2007-05-30 2:08 pm
Hi!

I'd like to make a discrete output stage for my cd player. It's sound too harh in the highs. I'm looking for a tube sound.
I've just tried LM4562 in the place of NE5532 but It sounds quite the same... Someother people advice me to put the OPA2134 ... Actually I'm not so sure that changing opamp I can really get the sound I'm looking for.

What do you think about an A class transistor (or Tube EERP) output stage?

Who wanna help me? Do you have any ready schemes?


Regards, Enzo.


P.S. In attached you'll find cd player scheme.
 

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poynton

Member
2005-03-10 11:57 pm
UK
wandelblu said:
Hi!

I'd like to make a discrete output stage for my cd player. It's sound too harh in the highs. I'm looking for a tube sound.
I've just tried LM4562 in the place of NE5532 but It sounds quite the same... Someother people advice me to put the OPA2134 ... Actually I'm not so sure that changing opamp I can really get the sound I'm looking for.

What do you think about an A class transistor (or Tube EERP) output stage?

Who wanna help me? Do you have any ready schemes?


Regards, Enzo.


P.S. In attached you'll find cd player scheme.


Moderators : this thread should be in the DIGITAL section
 
wandelblu said:
What do you think about an A class transistor (or Tube EERP) output stage?

Who wanna help me? Do you have any ready schemes?
If you don't have a lot of experience modding, I'd stick with "plug-n-play" op-amps for a while -- the aforementioned OPA2134 is decent and inexpensive; AD825 is also good, but it’s single channel so you'll need an adapter (Brown Dog). Opamp performance can be further improved upon using effective bypassing techniques as well as using dedicated power regulators.

Discrete is not necessarily better -- esp. if you implement "blindly". Matching impedances and putting the ckt under the o'scope are, IMO, important tools/techniques to get discrete stages to sound best. All that said, and when you're ready for the "next step", here are a few discrete IV's to keep you busy:

Peufeu's discrete IV

Jocko Homo's discrete IV

Rudolf Broertjes' discrete I/V

(You noted "tubes". But I don't like them because, to me and all else being equal, they do not reproduce accurate sound when compared to carefully-designed SS ckts, like the ones above)

Your schematic shows an opamp-based output buffer. Buffering may or may not be needed depending on certain "criteria". Can someone with knowledge and/or experience -- or just a humble opinion! -- comment on when buffering is or isn’t necessary?
 

poynton

Member
2005-03-10 11:57 pm
UK
wandelblu said:
Hi!

I'd like to make a discrete output stage for my cd player. It's sound too harh in the highs. I'm looking for a tube sound.
I've just tried LM4562 in the place of NE5532 but It sounds quite the same... Someother people advice me to put the OPA2134 ... Actually I'm not so sure that changing opamp I can really get the sound I'm looking for.

What do you think about an A class transistor (or Tube EERP) output stage?

Who wanna help me? Do you have any ready schemes?


Regards, Enzo.


P.S. In attached you'll find cd player scheme.

Hi.

What CD player are we talking about here.?

Your schematic does not show the DAC so I think recommendations are a little premature.

Andy
 
Hi Enzo,

I see you are now trying a different angle.

Be patient! Do some research, something called "Due Diligence".

You said in the other thread you started, that you are trying to warm up the analog output stage to a "tube like" sound. http://www.diyaudio.com/forums/showthread.php?postid=1417952#post1417952

This might be do-able with some info: Model we are working with... DAC we are working with.... the right op amp choices that offer a "warmer sound" (AD op amps are very accurate and revealing but I wouldn't say "Tube like") and a bunch of other mods before you decide to go to a "Discrete" output stage. You tried the LM, but did you research the Data Sheet to see the optimal values on the decoupling caps? This can bring the most out of these and other op amps. Not all op amps are just swap and play (op amp rolling). Ignoring to check this isn't the way to see if they are right or wrong. You have to look at the whole output stage when making mods! (most of the time) Also start with op amps that have the desired traits you are looking for (research this, it is all here on DIY somewhere).

Andy is right. If we know which CD Player it is, we know what we have to work with and the max potential and if it can be anything special with mods or if it needs replacing the output stage (not to mention everything else). Or if you want to make this kind of commotment, maybe a different used cd player might offer more potential because this one might not be worth it, other than the experience! This is TBD.

This can be a great experience and a huge learning opportunity!

Good luck!

Regards//Keith
 
Hi,
the output stage is not a buffer. It is a 2pole unity gain Sallen & Key low pass filter.
Prior to that is a shelving filter.
Normally these active filtering opamps need high input impedance to ensure the filter poles are accurate, but Rotel may have altered the component values to take account of the 5532's limited impedance.

Simply swapping to a FET input opamp could be undoing Rotel's ingenuity or worse, causing the better opamps to become unstable.

How does the MFB looking filter in the I/V section operate? Is it a pure I/V section or does it also operate as a filter?

I note that to protect the final opamp in mute mode that Zout=470r has been added and then a further 220r before the RCA fixed outputs.
What circuit follows the tappings into the variable output PCB?
These unknown loads on the final opamp and the high total source resistance (Rs=690r) will limit what equipment can be supplied with signal.
 
KP11520 said:
Not all op amps are just swap and play (op amp rolling). Ignoring to check this isn't the way to see if they are right or wrong. You have to look at the whole output stage when making mods! (most of the time)
Yup -- something I should've noted in my response above! Indeed, opamp rolling can lead to some very bad consequences if, say, a CFB (current-feedback opamp) opamp (e.g. AD844) is simply (accidentally) rolled-in.
 
Andrew,

The only Rotel CD schematic you have ever seen is mine (I think anyway)! No worries! In fact, one of the main reasons I can even give what little advice I can is because of all the help I have gotten from you!

You are always out there helping! Thanks!

Enzo, you got a great group of helpers here! (me not included) Run with it and take this where you can be really satisfied!

Regards//Keith
 

poynton

Member
2005-03-10 11:57 pm
UK
wandelblu said:
.......... What do you advice me?

I am not familiar with this chipset.

I think I am correct in assuming that the main (first) Dac chip is followed by a pair of DACs used to provide the variable output.
(this is what is used in my Revox)

If that is the case, you need to be looking at the output of that DAC (+L, -L, +R, -R)

Thorsten Loesch did some designs for this.

http://www.fortunecity.com/rivendell/xentar/1179/theory/vasfda/vasfda.html#




Andy