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Old 16th September 2005, 01:43 PM   #1
wreeve is offline wreeve  United Kingdom
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Default Harsh trebble after clock upgrade on Pioneer PD9700

Hi all,
I have recently acquired a Pioneer PD9700 which is one step down from a PD93 and from what I can see have the same internals, transport and DACs.
I carried out my usual mods of op-amps and signal capacitors. In fact the high-end Pioneers are equipped with my favorite signal cap (Elna Silmic) from the factory so I only swapped the horrid NE5534s with my favorite AD8066s. Big improvement in clarity and instrument separation. The player was sounding very nice indeed.

Last night I had a couple of hours spare so decided to swap the Trichord Clock2 and Clock2 PSU from my old Pioneer CD into this one.

The Clock circuit on the PD9700 is different to the lesser models in that it's a crystal and some logic gates (a discrete square wave generator circuit in effect). It has separate logic buffered three channels of clock output for the input filter and two DACs.
The circuit also has a copper grounded CAN surrounding it.

Anyway. I modified it by adding the clock2 signal to the input of the first logic gate removing the crystal, caps and resistors.

Sound: Horrible, well not horrible I am listening to it now, just harsh and so precise it sounds artificial, you can hear everything, it's directed the sound into complete clarity, even low level "pin drops" are audible under louder stuff. In fact I am hearing imperfections on a lot of CD's and it's not the player as I can rewind and yes there are little clicks here and there on some CDs which must have been mastered in!

Suggestions: Go back to standard clock which I think I liked better.
Try some different op-amps, maybe BB will warm the treble up a little? Try some home made copper screen around the Clock2?

Your comments are most welcome!

Keep well,

Will
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Old 16th September 2005, 02:32 PM   #2
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I remember once replacing the output opamps (NE5534) in an older top end Pioneer, can not remember the model something like yours, with the AD847's same thing happened, over detailed harsh, it turned out that in this circuit the AD was oscillating it's brains out in the high mhz region and I only picked it up on a 100mhz scope, if you have a scope look at it, or put back the NE5534 and see if it goes away. If it does try an AD825 (smd) on a Browndog adapter board, I swear this opamp is the best I've heard.

Cheers George
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Old 16th September 2005, 02:41 PM   #3
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Hi Will,

well BB opamps will warm up the sound (the 2604 in particular), but before you try that I'd suggest paying attention to power line decoupling.

Make sure the logic chip (HCU04 or similar I'd guess) is well decoupled with a ceramic cap close to power input pin, and use a ferrite bead or two in series. In fact I'd make sure all local chips are so powered to minimize rfi distribution. Also keep in mind that the AD chip is much faster than the NE5532/4 and so will need better decoupling to prevent oscillation.

You could also try using copper tape to shield these chips. A good mains input filter and perhaps power cord might help too.

All these mods should do nothing but help the sound even if they don't completely cure the brightness you are witnessing, so are worth doing anyway. Good luck, and let us know how you get on.
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Old 16th September 2005, 07:59 PM   #4
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Default Re: Harsh trebble after clock upgrade on Pioneer PD9700

Quote:
Originally posted by wreeve

Anyway. I modified it by adding the clock2 signal to the input of the first logic gate removing the crystal, caps and resistors.
Suggestion: connect the new clock directly where the old clock circuitry "ended" and not at the input of the first logic gate.

Edit: I changed the brand name as mentioned in the thread title to Pioneer.
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Old 19th September 2005, 07:26 AM   #5
Ruach is offline Ruach  Singapore
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The AD8066 may be oscillating. Touch it if it is hot after 10 minutes of use.

My experience - OPA627 works and sounds wonderful with the Pioneers. The AD825 sound great too.
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Old 21st September 2005, 07:14 PM   #6
wreeve is offline wreeve  United Kingdom
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Those bloody browndog single SO8 to DIL8 converters. I again (due to tiredness) managed to plug in a couple of op-amps 180degrees out! The orientation marking on these adapters isn't obvious is it!

Luckily Pioneer anticipate such stupidity and fit some nice electronic fuses to the + and - 12v op amp rails!

As suggested I completely removed the original clock circuit and inverter IC. Feeding the new clock signal direct to the three clock lines (one to the digital filter (and off to the laser electronics), one to each DAC. Result...nearly.

Looking at the op-amps (AD8066) they were not happy chappies in this circuit. They were indeed oscillating. Pioneer fit a pair of nice 470uF decoupleing caps to the rails but they are a good 1" away. If I had the time I would decouple them on the adaptor boards to see if that improved matters.

I had run out of SO8 to DIL8 converters so needed a DIL packaged DUAL op amp in a hurry! The Pioneer circuit uses two op-amps per channel for the audio processing, passing the signal through a single IC twice.

After a search I bought a couple of OPA2107's from farnell. WOW! I had not listened to a BB op-amp before. The bass is nice and rounded, not quite as fast and snappy as before, but sharp enough not to smear. The treble is now tamed. And they measure well (no oscillation on the 'scope).

I am so happy I am going to listen to a few hundred hours before I reach for the soldering iron again! At which point I will be fitting the copper shield around the clock circuit which I will make out of the sheet I have ordered from RS. I will also transplant the filtered IEC socket over from my old player.

I am at this moment listening to the Alison Moyet live CD (a limited edition with her greatest hits album) through Senheiser HD600s and a lightly modified Creek OBHIISE amp. I know from auditing friends players and other players I have owned that this is a difficult recording to play for some reason. It used to induce fatigue after the first three tracks. No it sounds sublime with the '9700 with a cuddly bass/midrange.

Outlay: 50quid from eBay for the player, 24quid for the OPA2107s! Bargain!

Thanks for all your help guys,

Will
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Old 22nd September 2005, 04:48 AM   #7
Ruach is offline Ruach  Singapore
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Good to hear that you have fixed the "harshness".

If you have spare time, you can wire in a dedicated transformer (9V on the secondary) for the DAC stage easily and there will be significant sonic improvements
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Old 22nd September 2005, 06:15 AM   #8
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Quote:
Luckily Pioneer anticipate such stupidity and fit some nice electronic fuses to the + and - 12v op amp rails!

Wow, those Pioneer cats are really smart. The stuff they use while all other cheapskates stick to 3-terminal regulators. You should easily get a job at their marketing department
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Old 22nd September 2005, 07:47 PM   #9
wreeve is offline wreeve  United Kingdom
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Gnarr they still use the three terminal regulators, but stick an ICPN15 in front! A right pain to source as well. A nice little device I may well use in some of my commercial electronics (none audio!). There are dire warnings in the schematics to replace these with an identical part otherwise your house will burn down.

Keep well,

Will
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Old 23rd September 2005, 06:54 AM   #10
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Quote:
but stick an ICPN15 in front

I retract my smart-*** remark. Still, can't see the point of having an additional current protection. Paranoia? Can't be too good for the sound.
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