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Old 6th February 2006, 03:37 PM   #561
6h5c is offline 6h5c  Netherlands
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Quote:
Originally posted by poynton
HI.

To find the source of the noise and so reduce / eliminate it, you need to measure earlier preferably just after the dac.

Andy
Hi Andy,

I've done that already, the DAC's outputs show a nice square wave .
After that, a 1kHz sinewave on a test cd gets clearer and clearer after the first stages of passive filtering. The first opamp is supposed to subtract both signals, but at it's inputs, the two waves seem to be in phase (???).
There's still too much HF at this point to discover any noise (on my simple 20MHz scope that is...).

Ray.
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Old 6th February 2006, 03:50 PM   #562
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I am changing every thing in the HF amp tomorrow with nice parts and then the RF later in week.

Has anyone thought about changing the xtal on the servo or is this a waste of time?
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Old 6th February 2006, 03:56 PM   #563
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Quote:
Originally posted by Bas Horneman
Haven't started yet...maybe tonight

NO hurries mate.

Thanks...but that would be a waste of a great sounding CD player..since I'll would probably end up using it as a transport for my RAKK DAC.
Yeah, that 63 it's a bit overdone....

The tubestage sounds great, but it also has a few minor disadvantages. The amplification is low (1x), and since the signal is divided by the passive filter, the output is not all that.
I'm going to see if I can solve that by using a long-tailed diff. input stage with a low-mu tube. Then I can sum the input signals also. The tubes are not in series then, so B+ can be lower. If I use one with low Ri then the output impedance should be low enough so I won't need a kathode follower buffer. I already tried with a ECC82 (I simply modified the exsisting circuit) and got a HUGE output. It needs some tweaking .

Regards,

Ray.
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Old 6th February 2006, 04:02 PM   #564
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Quote:
Originally posted by 6h5c



I'm going to see if I can solve that by using a long-tailed diff. input stage with a low-mu tube. Then I can sum the input signals also. The tubes are not in series then, so B+ can be lower. If I use one with low Ri then the output impedance should be low enough so I won't need a kathode follower buffer. I already tried with a ECC82 (I simply modified the exsisting circuit) and got a HUGE output. It needs some tweaking

Regards,

Ray.

Hi Ray.

So now you have something similar to mine but without the cascode???


Andy

PS
I read, in one of the many articles on modding the '63, that it is VERY important to have matched components after the dac to give a balance. Of course, any imbalance would give rise to residual noise.
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Old 6th February 2006, 04:03 PM   #565
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Quote:
Originally posted by rowemeister
I am changing every thing in the HF amp tomorrow with nice parts and then the RF later in week.

Has anyone thought about changing the xtal on the servo or is this a waste of time?
Hi Brent!

Like your pictures! You did a nice job on the PSU.

In my 67 the servo/decoder is one chip fed from the DAC clock, so that's that for me .
If the PSU around the 63's servo is improved it may have a positive effect since less noise will be present in the player.

Ray.
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Old 6th February 2006, 04:09 PM   #566
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Quote:
Originally posted by rowemeister


Has anyone thought about changing the xtal on the servo or is this a waste of time?
Since the servo osc. is 8.46Mhz, divide the dac clock by 2 and use 1 clock ?????

Andy
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Old 6th February 2006, 04:14 PM   #567
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Quote:
Originally posted by poynton
Hi Ray.

So now you have something similar to mine but without the cascode???
Yep, that's right. I tried it with one channel only. I re-arranged the wiring of Thorstens circuit and upped the current through the FET to 8mA. I used 10k anode resistors.

Quote:
I read, in one of the many articles on modding the '63, that it is VERY important to have matched components after the dac to give a balance. Of course, any imbalance would give rise to residual noise.
I know that one. My tube-proto is not that balanced, but my 67 and 63 use 0,1% resistors and 1% matched caps. But there's still noise. Have you found it as well in your player?

Regards,

Ray.
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Old 6th February 2006, 04:27 PM   #568
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Quote:
Originally posted by 6h5c
[B]

Yep, that's right. I tried it with one channel only. I re-arranged the wiring of Thorstens circuit and upped the current through the FET to 8mA. I used 10k anode resistors.



I know that one. My tube-proto is not that balanced, but my 67 and 63 use 0,1% resistors and 1% matched caps. But there's still noise. Have you found it as well in your player?

Regards,

Ray.
Hi Ray,

Sorry, I cannot be of help in that respect right now!!
I have just started to rip the audio stages off my board in preparation for the tube stage.

I am also rewiring the redundant +-12v opamp supply to give +12v only as a preregulator for +5v.

Andy
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Old 6th February 2006, 05:56 PM   #569
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Ah, good luck with that. Didn't do that yet. There's enough possibilities to mount Thorsten's filter on the PCB, using the original holes and traces. It will be nicely close to the DAC.

I was hoping to use the 12V for heater supply . Not enough current i'm afraid. Maybe the windings can be paralleled?

Anybody heard from Michael yet, regarding our custom toroid?

Hey Michael, how are you ?

Regards,

Ray.
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Old 6th February 2006, 06:14 PM   #570
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Quote:
Originally posted by 6h5c
..............I was hoping to use the 12V for heater supply . Not enough current i'm afraid. Maybe the windings can be paralleled?...........
Hi,

Windings are centre-tapped except, maybe, the KI. It may be possible by removing the TX and checking out the wiring but I would not think so.

Andy
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