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Old 6th November 2003, 11:21 AM   #1
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Join Date: May 2002
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Default DVD + aleph analog stage?

hi All

I have been reading about a tweak for a pioneer dv525 dvd player by "modwright" or Dan Wright

see http://www.underwoodhifi.com/stimespioneer.html

In short part of the upgrade process he uses is to replace the audio IC's in the output stage with higher quality units.
I wonder if instead of doing this one could replace the existing op-amps with what is essentially an Aleph Preamp stage Aleph P for example. or even just taking the audio feed from prior to the low grade IC and passing it straight out of the box and to say an Aleph preamp anyway.

Gain issues aside , are their any comments out there.

What I am trying to do is really get my DV525 sounding real good.
Replacement not an option ($)

Thanks and regards
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Old 6th November 2003, 11:54 AM   #2
Klaus is offline Klaus  Germany
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Default each Op is to much

Hi,

The related functions in digital equipment are: I to V conversion, filtering and buffering for output. In your DVD the I2V is surely done by an OP amp. The filter will be just passive or another OP amp. Output buffer for sure another OP. So OP-sound is in – so IMHO one OP more or less is not the big break through.

To get rid of all OP-sound disadvantages – if willing to be seen – the complete chain has to be replaced – zero OP at all! For specialists no problem, one can use the combined I/V and buffer stage from Pass D1 DAC are similar schematics using bipolar transis or added by CCS´s. Or even passive solutions. But this really is hardcore DIY for not specialists…

So make your mind what kind of operation you are daring to start. I currently build a D1 stage completely added with CCS and will check it out soon starting on my TDA1547 DAC. Lets hear!

Best regards

Klaus
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Old 6th November 2003, 10:07 PM   #3
Hans B is offline Hans B  Denmark
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Hi George

Good idea with the DV525 - get rid of those nasty opamps - remove them all

Here is how I see it:

Your DAC should be the PCM1716 (from a short search on the internet), which is a stereo DAC with single voltage output for left and right channel.

The center voltage out, is 0.52*Vcc and a signal voltage is 0.62*Vcc. This gives 2.6V center voltage and 3.1Vpp voltage out @Vcc=5V.

Now you mention Aleph P - is that because you want balanced outputs?? if so - I think the Aleph P might be shaped to fit PCM1716. For unbalanced the Aleph L might be modified to fit.

The problem is that the AC load impedance should be 5kOhm, which neither of Aleph P and Aleph L has (as well as you mention, the different gains). As I see it, it is easier to make a BOSOZ that fullfills that need than the Aleph L og P. Also the BOSOZ can have balanced as well as unbalanced output. Unfortunately I don't know enough about these voltage output DAC's - The datasheet states that the AC load should be 5k, but what about the DC load - what should that be? - inifinity?? - 5k as well?? - anyone?

By the way, this whole idea uses the BOSOZ right after the DAC, and don't use any opamps at all.

As Klaus said - if you are not that comfortable with electronics, this can turn out to be quite a mouthfull.

Anyways - just my 2kr (danish currency)

/Hans
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Old 7th November 2003, 06:35 AM   #4
Klaus is offline Klaus  Germany
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Default one OP is to much...

Hi again,

As far as I understand any DAC with voltage output has already integrated the I/V stage realized by more or less bad OP amps. So the "OP sound" – maybe caused by this complex feedback monsters - is already in. The after burn Aleph or whatever circuit can do the best conversion job to symmetrical and so on – but the limiter stays this dammed OP in the DAC and the not given symmetrical signal input. The magic of Pass sound can IMHO never be achieved this way – even on OP is way too much!

I found exactly the same situation with my older stereo DAC: the TDA1547 converter (stereo, symmetrical, multibit – not bad sounding) is designed for using the 2 x 2 voltage outputs of internal OP amps. But lucky, the load resistors for this I/V stage are external – so the outputs of the current sources are lead to pins. Just 0,1mA sources, but should work. So I just have to through out this resistor to stop the OPs from working and then pick up the pure current at this pins. A nice D1 stage converted to 0,1mA and added by CCS will hopefully do the same fantastic job like my Aleph P1.7 and Aleph4 mono powerblocks already do. No OP at all, over all 4 FET gain stages with no "complex" gain feedback scenarios at all. Thanks Nelson for this audible dream!

To come back to your story – I think the only "real" way would be the same like I do (if the PCM1716 has external resistors for I/V) – hard core… Half a step but also very healthy would be – my current status before the D1 stage is finished – to tweak around the PCM1716. Better Caps, maybe through out filtering behind the output, better external OP amps… I use just one OPA637 (stable at g=1 with a simple RC between in_+ and ground – setting gain to e.g. 15 from above 100kHz on. Sounding much better than OPA627, more focus, clearer, more "flow" of music) as buffer behind my TDA1547 voltage output with lean passive 6dB filtering and the sound could already be a dynamical dream – if not this "OP amp sound" was in…

Complex stuff!

Klaus
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Old 7th November 2003, 12:38 PM   #5
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Hi Gentlemen
It seemed like such a simple question and I sincerely thanks you for your replies.

I mentioned the Apleh L because of its simplicity and the P.1.7 because I am currently working towrds assembling one.

I looked over the PCM1716 datasheets and found the following diagram to be interesting:
Please forgive my ignorance.
Pins 13 & 16 appear to be signal out.
Post low pass filters should be easy enough to implemnt and the analog mute is i assume the highly undesirable muting transitors often reffered to in other posts.
There may well be other circuits after those indicated.
I hoped we could attach a good quality anaolgue stage to pins 13& 16 and use pins 11,14 & 19 as analog grounds.
Can someone please explain what "center voltage" is please.

Is my ignorance making me hope for too simple a solution?

Ps input impedence of aleph L is approx 10Kohm i think

Thanks again

ps I think Modwright does replace the Op amps as suggested by klaus
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Old 7th November 2003, 04:56 PM   #6
Henrik is offline Henrik  Denmark
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Take a look at this http://thunderstoneaudio.nav.to/ and goto the "Thermionic Valve Analogue Stages for Digital Audio" link.

Regards
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Old 7th November 2003, 05:20 PM   #7
Hans B is offline Hans B  Denmark
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Hi again

I am "afraid" that Klaus is right. As far as I can tell the I2V conversion DOES happen in the DAC, with no means to get the current out feature as the TDA1547 has. As Klaus mentions, this means that you will have to put up with at least one OP amp (the internal opamp in the DAC).

The center voltage is just a DC voltage out, which means that the signal swings from 2.6V-1.55V to 2.6V+1.55V (3.1Vpp).

I found this link describing a tube analog output stage, where the DAC is pcm1716:
http://www.geocities.com/fuherb/taiwan.htm


Also LC-audio has a description of how the pcm1716 can be coupled to their zapfilter:
http://www.lcaudio.dk/zf2setuppcm1716.jpg


And I was wrong about the 5k - I should have read the datasheet more carefully - it states minimum 5k, so just keep the impedance above 5k and it should be alright. This means that you can use Aleph L as the output analog stage, where the signal is taken from pin 13 (right ch.) and 16 (left channel). This should work fine.


So your initial question should be answered with a simple yes afterall. The question is, as Klaus mentioned, will the sound improve significantly. I wish I had an input to this - the truth is - I don't know.

But....... if you are building an aleph P or L anyway, you might try to connect pin 13 (right ch.) and pin 16 (left channel) to the Aleph P or L and have a listen.



I actually have the DV525 and I disassembled it ½ hour ago - it uses pcm1716E as DAC and a 8pin chip labelled "4560" close to the RCA plugs. My guess it, that it is an NJM4560. Before the output a couple of mute transistors are placed.



/Hans


PS. Marantz CD17 MKIII uses the pcm1716

NB. This was written before Henriks link, showing what a opamp TI uses as the internal opamp.
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Old 25th January 2004, 10:00 AM   #8
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Hi Guys

No I haven't got round to doing any of this stuff yet.
Aleph P bits nearly here!

Another question if I may ask.
The issue of the "centre voltage" - to quote Hans B

"The center voltage is just a DC voltage out, which means that the signal swings from 2.6V-1.55V to 2.6V+1.55V (3.1Vpp). "

I assume this means that some DC is present at the output of the DC much like offest in a power amp output-
Can this problem be simply overcome with a blocking capacitor in series with the output?? (high quality of course)
or is something more sinister required...pardon my ignorance

Thanks in Advance
George a
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Old 3rd February 2004, 11:27 AM   #9
ljordan is offline ljordan  United States
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Default I have a Sony dvps-7700 same DAC pcm1716

I am running the dac out pin to a trw oil 1.5uf cap. (Original board had a 47uF and a .22 film.) Then to a 100k pot then a opa637 in my headphone amp drivers 2 groups of 5 buf634s.

What do you think could be the smallest coupling cap? I want to try a teflon.

Lewis
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