good dac tweak

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I'm an italian new member and I'm looking for the best way to tweak the dac of my old Rotel 965BX.
This player have a philips 7310 as servodrive,saa7220 as digital filter and saa7323 as dac.
have anyone some idea schematics or experience about this player modification?
Thank you and sorry for my bad english:)
 
I have the datasheet of saa 7323 it has an internal oversampling filter infact it isn't bypassable.
The only modify possible is to get directly the I2s format out of 7310 pin37-38-39 or from the saa7323 output pin19-20-21so I need an I2s dac,I think.
Have you any good schematics?
 
My experience with a couple of the bitstream Philips players is that the "usual" mods will work wonders -- schottky diodes to power supply, improved capacitors, better dc blocking caps, etc, etc. The most dramatic improvements I experienced were from making sure that the power and power bypass caps to the dac chip (SAA7350 in my case) were improved. Better opamps, and class A opamp bias also help, but not as much as making sure power to the dac is robust and clean.
 
Hi Fin
I read your post,I Have the saa7323 datasheet and I can say it is a good DAC but it have at the output two poor quality opamps on board,the same quality of the old NE5532.This opamps are the filter following by another two NE5534 as voltage gain.
I have replaced the NE5534 at the output with 2 AD825 module by LCaudio and now it sound better but I can't replace the opamps inside the SAA7323.
I have only one way to modify it,to take the output before these opamps,pin10 and 44,but it is very dangerous because this pin is so small.
Have you any idea?
ciao Paolo
 
Hi Paolo

I've been thinking about this for some time and trying to find out as much as possible about these onboard opamps in the dac. If they are of the same quality as the original Sygnetics/Philips NE5532, that might not be so bad. Many people believe that the genuine NE5532 can produce good results in the right circuit. Some of the functionally similar (possibly inferior) replacements, may have given the NE5532 a bad name.

I'm not sure about their quality as I have not replaced them yet. I would like to try some others to find out for myself. The only way I can think of doing this safely is to follow the trace from the relative pins on the dac and access the signal at the closest outboard component. You could then build a new analogue board for the filter and gain stages. It would be easy to try different opamps and other components on this board without working on your main pcb too much. This way, you can even try bypassing the muting transistors without having to remove them.

I hope this helps a little but there are two mor opamps in the 7323 which are harder to get around - still thinking about those ones. It is also possible to improve the power supplies to this dac, but maybe they are quite good in the Rotel anyway.
 
I don't know if it is possible to get either the schematics for the Rotel 965 (and derivatives - think there was a 965 BXIISE Turbo injection Limited edition ........) or the Meridian 207/208 or 203 DAC.They all use the 7321 or 7323 . I would imagine that Rotel or meridian would do a pretty good job around the analogue sections of these chips.

I also noticed this web site (from google) My Italian is non existant but looks interesting

http://www.docethifi.com/dac3_e.htm
 
Accessing the i2s at the 7310 is one way to go if you want to put in a totally new dac into the player. Perhaps a non-oversampling TDA1543. Before you try this some mods to the existing player are worthwhile. The decoupling and supply for the DAC is very important. Rotel have given the saa7323 its own 5v supply and use some blackgates for decoupling. Taking their lead things can be improved upon - for example the blackgates are type F and are bypassed with smaller ceramics closer to the dac. Removing both and replacing with a single better blackgate (N, NX, or Hi-Q) where ceramic was (hence closer - even better direct to pins, but is fiddly obviously) will improve matters. Reading Guido Tents article is helpful
http://www.audiocraftersguild.com/AandE/Supply_decoupling.pdf


The digital supply is not well taken care of and can be improved upon with some decoupling. Also the Vref is something I will pay careful attention to in the future - either with a really decent cap very close to the pin or a dedicated vref circuit as documented somewhere here recently.

Do you like the sound of the Rotel? This is an important question. Changing the op-amps will almost certainly change the characteristic of the sound and may not actually be an improvement. I have tried quite a few in place of the NE5534 and to be honest prefer the 5534.

I had good results from shielding all chips with copper (grounded).

I will be looking into ways to improve the transport side of things. Or more accurately everything before the DAC. It has been sugested that the transport motor in the CDM4 is noisier than the brushless motors used in earlier CDMs. The addition of some caps could help here. As better decoupling of all chips on the transport side of things. I was thinking of an oscon and a ceramic directly across the supply and ground pins or something similar

As for the schematics - i had them and can remember parts of it, but lost it in a house move :(
 
Rotellian said:
This mod will not work for the SAA7323 as it is a bitstream dac. The oversampling is required to get the dac to actually work. The non OS mod is only suitable for multibit players that use chips such as the TDA1541a.

Just to clarify that, the pure digital I2S won't work, but using the optical from the multibit or bitstream cd player connected to CS8412/14 chip on the DAC, it will work fine?

Since the 8412/14 recognizes and derives the digital from the stream, it serves the purpose, I think.
 
You cannot perform a non-oversampling mod to work with the DAC chip itself as it is a bitstream DAC (the SAA7323) and hence requires a digital filter to even work (which some multibit dacs do not).

However you can get the I2S stream from the SAA7310 (or 7210) decoder chip and pipe it to a suitable replacement PCB/board with the TDA1543 dac (for example - its the easiest one to implement and build as its such a simple chip) on. Searching here will yield lots of results
 
Options, options, options......

Hi Paolo

pabiz said:
Thank youfor your replay I have consider it but I'm not sure for the result,this modification is irreversible.
I have think the possibility of I2s direct the saa7323 have this output but I don't have any schematics.

If you work carefully, it should be reversible - but - even better - on the CD624's pcb, there is a position between the decoder (7310) and the dac (7321), where a connector would normally be placed for the use of a separate audio board. The connector would be there if the pcb is used in a multi-board cdp like the CD850. You could quite easily access the 1*fs I2S at that point (if it is the same in the Rotel).


pabiz said:
I have the datasheet of saa 7323 it has an internal oversampling filter infact it isn't bypassable.
The only modify possible is to get directly the I2s format out of 7310 pin37-38-39 or from the saa7323 output pin19-20-21so I need an I2s dac,I think.
Have you any good schematics?

WRT the I2S from the 7323 - it is 4*fs. So you have the option to go Non O/S, change to a multibit with O/S, change to another 1-Bit dac or keep the existing dac and take it to the limit.

Rotellian said:
Accessing the i2s at the 7310 is one way to go if you want to put in a totally new dac into the player. Perhaps a non-oversampling TDA1543. Before you try this some mods to the existing player are worthwhile...........

Do you like the sound of the Rotel? This is an important question.........

I agree with Rotellian - you need to decide if you like the sound of your Rotel - if you do, then try to improve it. Going with the last option probably makes most sense - before you start comparing it to other dacs.
 
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