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Old 28th February 2006, 11:51 AM   #1051
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Quote:
Originally posted by awpagan



agree with you totally

thought about extending connection so i could keep the pcb external while doing mods

coax connections are last

must be a major adventure for brent to remove pcb to mod

allan
Its great lol

I was an audio engineer in my previous job and working on mini systems with 8-10 pcbs connected with ribbon cables and mini disc and cd mechs all attached and spread out on the bench so I can scope the fault, I find a few pcbs attached on a few wires very easy indeed

I leave the back panel attached to pcb , my reg pcbs unclip from sides, remove front facia and flip the pcb over. sorted
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Old 28th February 2006, 12:16 PM   #1052
ash_dac is offline ash_dac  United Kingdom
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Default Re: Re: Analogue supply to the DAC

Quote:
Originally posted by 6h5c



Yes, they are digital
There's a nice 5V square wave on the outputs, but if the duty-cycle is 50% a voltmeter will measure 2.5V.
No analog reference whatsoever...

BUT....the "analog" supply IS as critical as you mention!

Hmmm...reclocking...don't know if that will gain something.
Need another stable clock then. And more stable PSU's.

Regards,

Ray.
Hi Ray,

The timing diagram from the datasheet suggests that iternally the outputs are reclocked to the system clock which I presume is buffered internally, and piped around inside the chip!

Yes it will require a bit of work to produce a pcb.

I need to look at the service manual, and player (both of which I don't have at work) but I think I could interrupt the signal at the 10K resistor after the dac (remove it), and patch in a 74hc74 based reclocker circuit, and feed with a tent or kwak clock.

One Tentlabs or Kwak clock would be used to drive the dac chip, decoder, and the two reclockers for the outputs. I hope they can drive this many gates!

What I may do is build the reclocker into one channel only to see if there is any change....
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Old 28th February 2006, 12:21 PM   #1053
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Quote:
I leave the back panel attached to pcb , my reg pcbs unclip from sides, remove front facia and flip the pcb over. sorted
Now, I have always assumed the rear panel has to be removed to take the PCB out - probably because that's what I did first time and I've stuck to it.
I wonder sometimes how I'd be if I had the ability to think!

Thanks for the tip! I am such a muppet, lol!

That solves the lovely chassis mount phono problem.

Thankfully, I've never had to work with anything more than two or three PCBs connected together at a time.
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Old 28th February 2006, 01:09 PM   #1054
SimontY is offline SimontY  United Kingdom
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Quote:
Originally posted by philpoole


Now, I have always assumed the rear panel has to be removed to take the PCB out - probably because that's what I did first time and I've stuck to it.
I wonder sometimes how I'd be if I had the ability to think!

Thanks for the tip! I am such a muppet, lol!

That solves the lovely chassis mount phono problem.

Thankfully, I've never had to work with anything more than two or three PCBs connected together at a time.
I did the same thing, always used to take the back panel off, and recently added proper phonos... but it's now 10x hard to take apart - the way it slots in mangles things under the pcb so you have to consider this. It may be the way I've modded it under there etc., but you are warned. New phonos after everything else I'd say (it's only a small improvement anyway).
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Old 28th February 2006, 01:41 PM   #1055
mickie is offline mickie  Germany
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Hello Ray,
thanks for clarification about the ceramics; actually i'm not planing to swap out all ceramics, but related to the diodes i did this once in my rega and it "helped";
Do you think the BG's will give me trouble in that position?

Some more questions to come, i'm afraid....

I swapped out DN03 + DN04 with Schottky by mistake, not realizing that they are not mentioned in the mod-list...can i leave them in?

I also changed the op-amps into OPA 2134 (i had them) - and the sound got worse (lifeless, grainy, harsh)!
I didn't expect that the 2134 are worse than the JRC...any of you had similar experiences?

thanks in advance,
mickie
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Old 28th February 2006, 01:43 PM   #1056
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Quote:
(it's only a small improvement anyway).
Not when you used the old phonos years ago for something elsewhere and ended up using the 'remote control' phonos instead! D'oh!
Besides, I started using the new phonos when bypassing the HDAM. That way I could do a comparison. Now the HDAM is completely disconnected, and I am happier with the new connectors.

I think with this kind of project you do reach a point when its going to get progressively harder to work on the board. That's just the way it is.
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Old 28th February 2006, 01:45 PM   #1057
6h5c is offline 6h5c  Netherlands
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I leave the rear panel on also, but I took off the hook-shaped thingies that lock into the side panels.
That way you can slide the PCB in quite easy.

Ray.
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Old 28th February 2006, 01:52 PM   #1058
6h5c is offline 6h5c  Netherlands
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Default Re: Re: Re: Analogue supply to the DAC

Quote:
Originally posted by ash_dac
Hi Ray,

The timing diagram from the datasheet suggests that internally the outputs are reclocked to the system clock which I presume is buffered internally, and piped around inside the chip!

Yes it will require a bit of work to produce a pcb.

I need to look at the service manual, and player (both of which I don't have at work) but I think I could interrupt the signal at the 10K resistor after the dac (remove it), and patch in a 74hc74 based reclocker circuit, and feed with a tent or kwak clock.

One Tentlabs or Kwak clock would be used to drive the dac chip, decoder, and the two reclockers for the outputs. I hope they can drive this many gates!

What I may do is build the reclocker into one channel only to see if there is any change....
Hi Ashley,

I think the output of the DAC is at 32*Fs = 1.411MHz.
You'll need some kind of synchronisation between the system and the PWM clock, otherwise the data will go out of sync. Or divide the sysclock by twelve to obtain 1.411MHz. And then use a latch to clock the data in and out. Should be possible. Maybe it can be put to work on a breadboard.

Regards,

Ray.
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Old 28th February 2006, 02:02 PM   #1059
6h5c is offline 6h5c  Netherlands
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Quote:
Originally posted by mickie
Hello Ray,
Do you think the BG's will give me trouble in that position?
Nah, no problem. That position is not critical. You should be careful around the digital chips though. Use a good electrolytic with an X7R ceramic or PPS (even better) in parallel, as close to the supply pins as possible.

Quote:
Some more questions to come, i'm afraid....

I swapped out DN03 + DN04 with Schottky by mistake, not realizing that they are not mentioned in the mod-list...can i leave them in?
No problem. They are rectifiers, so it won't hurt to have schottky's there

Quote:
I also changed the op-amps into OPA 2134 (i had them) - and the sound got worse (lifeless, grainy, harsh)!
I didn't expect that the 2134 are worse than the JRC...any of you had similar experiences?

thanks in advance,
mickie
Hmm, strange. When I first started modding I also tried these opamps, and OPA2604, and if I remember correctly I found them an improvement. Maybe it's because the rest of the player is not modded yet. Just put some turned-pin IC-sockets in and try again later. The power supply is also an important factor.

Regards,

Ray.
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Old 28th February 2006, 03:47 PM   #1060
poynton is offline poynton  United Kingdom
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Quote:


Hmm, strange. When I first started modding I also tried these opamps, and OPA2604, and if I remember correctly I found them an improvement. Maybe it's because the rest of the player is not modded yet. Just put some turned-pin IC-sockets in and try again later.

Hi Again.

Back after a day without my internet.........!!


I read an article which explained this. Unfortunately I cannot remember where - I'll post it when I find it!

The reason is the particular chips ability to handle the vast quantities of HF trash on it's input and what happens to this hash inside. For example, if the input acts as a rectifier and a cap as well, the RF is rectified and produces a DC component, however small, which affects performance downstream. Also, various parts of the chip can overload/clip due to the high level of RF.

Remember what frequencies we are talking about here. The chip may sound great in an audio preamp but was not designed to handle RF.

To be honest, I am surprised in does not happen more often.

Andy
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