Cayin CDT-17A

[psam]

Die Schaltung ist ausgelegt für RCA und XLR!
In dieser Konfiguration ist nur noch RCA, für alles andere MÜSSEN die OPAs voll bestückt sein. Ich dachte das wäre klar rübergekommen.
Nochmal, diese Modifikation ist nur bei alleiniger Nutzung der Cinchausgänge gedacht! XLR ist tot und die Röhren nehmt Ihr besser auch gleich raus.

Hello guys,
Things are getting weird on my CD 17A...
I removed all six op amps and the CD player sounds fine....
I started by removing the AD843s on position (1) of the photo circulating, then I removed the OPA627BP on position # 2 and then the last OPA627BP of position #3 on one channel. It was playing OK and afterwards I removed all 3 from the other channel with no audible effect on the sound...
Am I missing something here? I am using the RCAs only, so is it maybe that the 6 op amps are only doing something through the XLRs and they have nothing to do with the RCAs?
Is it maybe that the op amps under the red heat sinks are delivering the RCA signal? Are they supposed to be replaced as an upgrade?
One more thing, all the CD17A users who replaced the Op amps, do they all listen through the XLRs? Isn't it strange that people hear differences using different opa amps which have no effect even when removed completely?

Regards,
Panayiotis, Athen.

----------------
Cayin CD17A, Cayin A88T, RCA 6SN7/6SL7 -TungSol 6550, Coincident Technology super Eclipse III, Kimber 8TC, Kimber KCAG.

[Erzkanzler]

Hello Panayiotis,

the Operational Amplifiers under the red heatsink (5) work as double I/V-converter, as the following stage (3) is the differential amplifier.
So maybe it works, but I would strongly recommend not to remove this OPA.

Best regards
Martin

[Mas Teringo]

If the OPA are needed I'm wondering why it works without them. I thought that if I interrupt the signal path there couldn't be a sound.

[psam]

Hello Panayiotis,

the Operational Amplifiers under the red heatsink (5) work as double I/V-converter, as the following stage (3) is the differential amplifier.
So maybe it works, but I would strongly recommend not to remove this OPA.

Best regards
Martin

OK, I understand that, but what do the opamps in the positions originally equipped with the OPA604s do? How is it possible for the CD player to work without any of them in its socket?
MfG, Panayiotis

[psam]

If the OPA are needed I'm wondering why it works without them. I thought that if I interrupt the signal path there couldn't be a sound.

Exactly! This is the reason I am wondering whether we are playing around with opamps which have absolutely no effect in the sound if only RCA are used...
I hope this in not the case, otherwise I will feel rather silly ...

[Erzkanzler]

Mal ein Schaltungsbeispiel:

Nichtinvertierender Verstärker (Buffer):

[img:191:184]http://www.roehren-und-hoeren.de/phpBB/ ... /opa_1.jpg[/img]

Wie Ihr seht gibt es keine Verbindung vom Ausgang zum Eingang.


Invertierender Verstärker:

[img:251:173]http://www.roehren-und-hoeren.de/phpBB/ ... /opa_2.jpg[/img]

Das Signal geht über den Gegenkopplungswiderstand zum Ausgang. OPA 1


Differentialverstärker:

[img:286:177]http://www.roehren-und-hoeren.de/phpBB/ ... /opa_3.jpg[/img]

Das selbe Spiel wie der nichtinvertierende, allerdings wird nur ein heißer durchgeschaltet, das nichtinvertierte Signal fehlt.

In our case, stage 3 is the differential amplifier.

[img:820:608]http://www.roehren-und-hoeren.de/phpBB/ ... /opa_4.jpg[/img]

[Tom_H]

I know that my experience is not on the 17 Cayin.
Just for your reference, when I remove all the OPA's (#2) from my Music Van, the sound remains more or less the same but at a lower volume level. Normally the Volume of my Amp is running at roughly 9 o clock and without the OPA's the same volume level is reached at about 11 o clock position of the knob.

So also the Jolida works without Operational Amps.

[teiki arii]

Yes, but what about quality of the sound? Because changing OPA on "filter's stage" #2 & #3 or on "desymetrisation = single ended stage for RCA" #1 is efficient on changing the sound output!

[teiki arii]

And again for everyone:
Here is the scheme (according to 00940, momois and flom):
[img:955:389]http://www.roehren-und-hoeren.de/phpBB/ ... eiki_d.jpg[/img]

So, I changed the OPA604 on #1, #2 & #3 sockets on that configuration by:
- AD843 full
- AD843 on #1 and OPA627 on #2 & #3
- OPA627 full
- OPA134 on #1 and OPA627 on #2 & #3
As we didn't touch to dualchips under red heatsinks: AD827/NE5532...
[img:642:668]http://www.membres.lycos.fr/sst00940/numeros.JPG[/img][/quote]

[teiki arii]

Perhaps you are right according to the scheme that we don't need Op Amp in #1 #2 #3 sockets...
But on What is the goal of "filter's stage: sockets #2 & #3"?

[psam]

Perhaps you are right according to the scheme that we don't need Op Amp in #1 #2 #3 sockets...
But on What is the goal of "filter's stage: sockets #2 & #3"?

OK, I hope that you electronics experts can figure whether the 6 opamps are required.
I've just performed a simple test with an OP627 on position 2 only. Nothing on 1 and 3.
It seems to me that without any opamp, the treble is slightly reduced. Percussion looses weight. I used the Ry Cooder Mambo Sinuendo and the older Buena Vista Social Club CDs.
It has gotten late in Greece and I 've already stressed the nerves of my neighbours with the loud music lately, so I cannot proceed with the tests tonite. I will get back to you later this week with more results, but I really think that IC and Opamp experts could help us by clarifying the necessity of the opamps for RCA only.

Thanx!
Panagiotis

[teiki arii]

I've just performed a simple test with an OP627 on position 2 only. Nothing on 1 and 3.
It seems to me that without any opamp, the treble is slightly reduced. Percussion looses weight. I used the Ry Cooder Mambo Sinuendo and the older Buena Vista Social Club CDs.

It is exactly what I have noticed but I am waiting for other forumeurs to tell us....So less widestage, less dynamic and less accurate for me.

[Erzkanzler]

Hello Teiki,

unfortunately the scheme is not - let's say - complete.

As you may have seen, the Cayin is using 2 pc. of PCM1792, each of them has a right and a left channel.

I have just a Cayin for repair and the PCB is out of the cabinet.
I'll try to write down the exactly electronical diagram later this week.

Regards
Martin

[teiki arii]

Hello Teiki,

unfortunately the scheme is not - let's say - complete.

As you may have seen, the Cayin is using 2 pc. of PCM1792, each of them has a right and a left channel.

I have just a Cayin for repair and the PCB is out of the cabinet.
I'll try to write down the exactly electronical diagram later this week.

Regards
Martin

Dear Martin,
I think you have the answer on pages n°34, 35, 36 of PCM1792's Datasheet and on the first page of our french topic,
best regards.
http://focus.ti.com/lit/ds/symlink/pcm1792.pdf
http://www.homecinema-fr.com/forum/view ... 7a&start=0

APPLICATION INFORMATION of PCM1792 : (EXTRACT of PCM1792's Data Sheet)
- APPLICATION CIRCUIT
The design of the application circuit is very important in order to actually realize the high S/N ratio of which the PCM1792 is capable. This is because noise and distortion that are generated in an application circuit are not negligible. In the circuit of Figure 36, the output level is 2 V rms and 127 dB S/N is achieved. The circuit of Figure 37 can realize the highest performance. In this case the output level is set to 4.5 V rms and 129dB S/N is achieved (stereo mode).
In monaural mode, if the output of the L-channel and R-channel is used as a balanced output, 132 dB S/N is achieved (see Figure 39). Figure 38 shows a circuit for the DSD mode, which is a 4th-order LPF in order to reduce the out-of-band noise.
- I/V Section
The current of the PCM1792 on each of the output pins (IOUTL+, IOUTL–, IOUTR+, IOUTR–) is 7.8 mA p-p at 0 dB (full scale). The voltage output level of the I/V converter (Vi) is given by following equation: Vi = 7.8 mA p?p × Rf (Rf : feedback resistance of I/V converter) An NE5534 op amp is recommended for the I/V circuit to obtain the specified performance. Dynamic performance such as the gain bandwidth, settling time, and slew rate of the op amp affects the audio dynamic performance of the I/V section.
- Differential Section
The PCM1792 voltage outputs are followed by differential amplifier stages, which sum the differential signals for each channel, creating a single-ended I/V op-amp output. In addition, the differential amplifiers provide a low-pass filter function. The op amp recommended for the IV circuit is the NE5534, and the op amp recommended for the differential circuit is the Linear Technology LT1028, because its input noise is low.

[Erzkanzler]

Hello Teiki,

I'm just drawing together a detail-scheme of the outputsection.
Hope that fits.

Best regards
Martin

[teiki arii]

00940 answered us about taking the AOP off. Thanks to him:

"If we withdraw 1 and 2, we use simply of a half pcm1792 by channel. Punch is lost but especially the distortion is increased. If one withdraws 1, 2 and 3, we use for final only one of the exits of the pcm1792. Increased loss of punch, increase again in the distortion."

It's a google translation...

[Mas Teringo]

It doesn't sound like a good tuning...

[Erzkanzler]

Versuch macht kluch..... und kostet nix.

If one withdraws 1, 2 and 3, we use for final only one of the exits of the pcm1792. Increased loss of punch, increase again in the distortion."

I agree, withdraw of OPA3 will increase distortions dramatically.

Regards
Martin

[Mas Teringo]

So the conclusion is only to remove OPA #1?

[teiki arii]

So the conclusion is only to remove OPA #1?

My conclusion is to remove no one...
except if you use XLR exclusive outlet since the #1 is used for RCA...
Best regards.