tda1541a sound signature

[Marcelinho]

A class-A i can test quickly.
Further i plan to move the opa627 to the buffer and use a ad811 for the I/V, as i saw a circuit from someone who appears to be more knowlegdable than m

As there is also a deemphasize circuit attached to the i/v, it is beyond my capability to cut and paste some discrete stuff.

A better dem-reclocking i save for the last mile, not for the quantumleap i need now.

[Marcelinho]

Originally Posted by jazz

Hi,

I thought there was no dc servo and the cd80 uses a 220uF (c32) cap at the output anyway? Then again I don't care about caps in the signal path.

regards,
Joris

No output-cap, maybe you are mistaken for a philips. c32 is not a part on the list.

[jazz]

Hi,

Yup you are right. Checked the service manual and there is no cap. sorry.

I'd still try the Pass i/v stage though, it's simple and cheap enough to try out. Maybe a good idea anyway, prototyping various i/v stages and see what you like.

regards,
Joris

[GoranB]

I have CD40, with TDA1541 (not A), after i builded separated power supply for 1541 the sound improved a lot. I dont know how its in CD80, but if you have there 7220 and 7310 you can implement a separated PSU for both chips. Decopule the caps on 1541 (if its already not done) with 14 x 220 nF or 470nF.
These modes will result with deep and wide sound stage, natural highs and perfect mids.

[Marcelinho]

Originally Posted by danico

Try to bias the opamp into "class A ".
I use the opa627 just like you do. Put a 2k resistor on pin1 and pin4 (output and -15v).

That will be pin 6 and 4!

[danico]

Originally Posted by Marcelinho

That will be pin 6 and 4!

Not if you use Browndog adaptor with the 2x opa627.
But yes watch out for the right pins.
output to -V.

[Marcelinho]

Between the dac and the i/v there is somekind of dc-servo of which i don't understand how it works.
As the i/v process is so important, should i keep it or lose it?

[danico]

Originally Posted by danico

Not if you use Browndog adaptor with the 2x opa627.
But yes watch out for the right pins.
output to -V.

My bad,sorry. Marcelinho was right about pin2 and pin6 on Marantz cd80.

I should have to check the schematic first.

[Marcelinho]

Further investigation suggest that some 2mA is inserted before the i/v stage to negate a always present -2 mA that is present at the output of the dac even when there is no signal.
As long as i work with opamps, I keep that insertion.
For the discrete versions of i/v i don't see much mention of this always present offset, or it's compensation.

[ThorstenL]

Hi,

Originally Posted by Marcelinho

Further i plan to move the opa627 to the buffer and use a ad811 for the I/V, as i saw a circuit from someone who appears to be more knowlegdable than m

Beware, you must make significant circuit changes for the AD811 (or LM6181 for that) to work without oscillation.

Another problem could be if you replaced the 5534 Op-Amp's without removing the Frequency compensation capacitors, they may wreak havoc with an OPA627, while pin 8 is marked "no connection", for all we know it may connect to the substrate or something.

Also, the OPA627 is quite slow for I/V. I would recommend using an OPA637 instead and using Scott Wurcers trick circuit (I came up with the same incidentally a long time back) of having a suitable value cap to ground from the inverting input, 10nF in case of the player you have and the OPA637.

As for the "dark sound", also have a look at the DEM Filter capcitors, also, I personally would consider DEM Reclocking and I2S attenuation as essential.

FWIW, the AMR CD-77 uses special PECL based reclocker/drivers for the TDA1541 which among others also perform attenuation, DEM reclocking, passive I/V and ton's of individual regulators, including some tuned to offset the temperature coefficient of the circuit they supply.

The regulators use a wide variety, from current source fed shunts to fully discrete super low noise feedback free ones, each matched precisely to the circuit they supply - there just is no such thing as a "super regulator" that is super in each and every application. They are followed by very carefully selected and designed decoupling and bypassing.

I would say the power supplies account for around 50 - 60% responsible for the final sonic result in the CD-77.

More on the principle design (block diagram) can be seen here:

Abbingdon Music Research - Product - CD - 77 Freatures

A picture of the whole DAC/digital board is found here:

Abbingdon Music Research - CD - 77 Photo Gallery

Over- and/or up-sampling are selectable as well as deflatable. Finally, for PC connections it comes with a USB input (CD Standard only) and in more recent versions also with SPDIF inputs having very low jitter on either input...

A lot of attention has also been paid to the mechanics, which avoid traditional damping and use multiple material sandwiches and application of certain geometric rules to avoid resonant reinforcement of any modes.

So in many areas it is a tour de force of what can be done.

The sound will not please everyone, nor is it meant to, it is a Player that is firmly "Digital to Analog" in sonic nature. Those who actually LIKE digital sound will be disappointed.

Ciao T