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Old 14th April 2006, 04:40 AM   #1
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Default Ideas, suggestions, and schem to improve Sony sdpep9 es?

I had picked up a brand new sony sdpep9 es a couple of years ago on ebay for around a hundred bucks and immediately shelved it because I didn't think it sounded great. The recent activity on the behringer DCX has inspired me to unpack it and have another look. Well, in 2 channel mode it actually sounds pretty good I guess...just not awesome. I'm thinking that maybe I can improve the analog section after the pulse dacs. Maybe I can integrate the New Ellis_Jens filter right after the dacs with balanced outputs right there in the sony chassis?

I have searched the forums and the only reference I could find on the unit was here by member wombat. He is talking about a different model but the guts look the same. Gotta send him a PM.

Does anyone have any schematics or experience with this unit? Geez, I'd like to eliminate the front output analog section and take the dac right into the active filter boards buffer..I couldn't do it without a bit more info though...well, maybe a lot more

Thanks,
Marc

By the way, those opamps are 5218A
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Old 16th April 2006, 05:11 PM   #2
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Maybe this will help....

a not so great schem here

or the zipped .pdf here 3.8Mb

any replies welcomed
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Old 17th April 2006, 02:43 AM   #3
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I'm not a digital expert, but I know enough to be dangerous.

It looks to me like the digital volume control takes a current signal and outputs current as well, looking at the output terminal designations, and the impedances at the next stage (LPF, IC415, etc.) This stage looks to be the I-V as well as the low pass filter.

Depending on your willingness to work, you can try anything from taking a balanced output after IC 415 (eliminating IC601 and all those switching transistors), splicing in your own I-V stage/ low pass filter before IC415 or getting rid of the likely biggest offender, the digital volume control and disconnecting IC409 and connecting your I-V stage to R25-28. Of course that means that you just signed up to build a 6 channel volume control. There are a couple of kits for that available here, though.

For all I know the DAC may be voltage output, judging by its 100R loads, but it seems odd to have a voltage output DAC with 2.6V of offset. If it is a current output DAC, the current is low and you'll need a heck of a low noise I-V stage. Sony doesn't seem interested in publishing a data sheets for its proprietary chips. Wonder why?

Maybe some of the digital experts will chime in.
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Old 17th April 2006, 03:24 AM   #4
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Thanks for the reply!

No 6 channel volume controls for me, thank you very much! I might as well start from scratch. You have given me hope though.

My goal is to get the active filter board in there somewhere on the front outputs as you know. I really don't want to kill the digital volume control or any real functions of the unit. I just want to 'kick it up a hifi notch', it's almost there IMHO. I could either kill the op relays or take it back into them...I don't know if it would be audible either way. Rather than just tag the active filter on the outputs I want to bring it as close to the digital stuff as possible. (Bob, I know you are aware and understand,I just wanted to re-emphasize for any digital expert that may happen along)


(not for Bob, you obviously know this already)
The active filter I want to use has an input buffer that can accept SE or balanced and can have a LPF function. The filter schem is posted here by Jens....
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Old 17th April 2006, 03:34 AM   #5
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Sounds like option 1 is the way to go - take the balanced signal to the active filter board, although you may want to buffer it before sending it out of the receiver.
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Old 18th April 2006, 04:16 AM   #6
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Quote:
Originally posted by BobEllis
Sounds like option 1 is the way to go - take the balanced signal to the active filter board, although you may want to buffer it before sending it out of the receiver.

Thanks Bob,

I'm confused though (surprise!). You had suggested taking the output from IC415 in your first post. Would that not act as a buffer?

Maybe you mean to take it right off of IC409 ?? If so, wouldn't the buffer at the front of the active filter board suffice?

I know you dont know the Sony chips, who does?? (Sony, the one and only, .. of course)

Thanks for putting up with my noobish-ness....
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Old 18th April 2006, 09:19 AM   #7
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Look at the feedback network and filter elements around IC415. There is 10R and 270R setting the gain. This low resistance along with the 10R-22nF-10R low pass filter is what makes me think that this is the I-V conversion stage - low impedance and high voltage gain (29.4 dB)

I suggested a buffer following that assuming that there is not much room and your filters would be in a separate enclosure. It is not strictly needed as long as the cable runs are short and you take the output from the output pins of IC415 (before the 10K resistors.

Looking at it again, you might find some improvement adding decoupling caps - it seems that IC415 and IC601 share a single pair. That's not the best practice, but it does save a few pennies per unit.

There might be some improvement just bypassing the electrolytics in the signal path C639, 640 etc.

Did you feed this beast a digital or analog signal? My Yamaha DSP-A1 sounds a lot better with digital input. This is probably due to the A-D conversion required going into the DSP. Notice that all of the signals are converted to digital, before being reconverted right before the volume control. Interestingly, the product literature calls it a "digital volume control", so that would have to be the DAC chip, despite the labels. The section labeled "High pass filter" is really a low pass and the section labeled buffer is really an adjustable gain high pass section, so there is some precedence for mislabeling (hoping to make it unserviceable?).
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Old 18th April 2006, 01:19 PM   #8
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Thanks,

The unit has no analog inputs at all, therefore I use the digital in (and it does sound pretty good as long as the dsp isn't doing anything 'useful').

I like:
Quote:
...........It is not strictly needed as long as the cable runs are short and you take the output from the output pins of IC415 (before the 10K resistors.
That's the direction I want to take. The boards will reside in the sony unit with no interconnects. I didn't know exactly where to grab the signal and your tips are priceless.

Now I gotta get working filters going then attempt the 'retrofit'. I could learn a lot on this one....thanks.

Marc
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Old 18th September 2008, 01:04 PM   #9
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Marc, did you ever proceed with this? On my workbench is a Sony TAE9000ES (http://home.online.no/~espen-b/ta-e9000es/); its DAC and output stage is very close to the SDPEP9s. Im trying to figure out how to improve the output stage. Did you have any success?
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Old 19th September 2008, 06:21 PM   #10
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Sorry -

Soon after, I started getting into vinyl and this unit became unimportant, as it has no analog. I still use it for movies though.

Please let us know how it goes!
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