hi i own a qed digit running off two 12 volt batterys the opamp is a dual type but i want to use a good opamp the AD826AN is very good but my digit has distortion when used with this chip. is there any way around this? is it not getting enough voltage or is therer too much going to it ? and is there any opamps as good i can try thanks for your time john
Hi, sorry its a bit late, but I just saw a digit on ebay going with a Burr-Brown OPA2134 op amp in it. May be worth trying. Don't know what it sounds like though.
While we are on the subject, I have a digit with split power supplies (ie with 2 positrons. this opens the sound out nicely.) I now have the option of another positron. Obviously a case for one supply for each channel., Any recomendations which side to beef up, the digital or analogue section?
Frank
While we are on the subject, I have a digit with split power supplies (ie with 2 positrons. this opens the sound out nicely.) I now have the option of another positron. Obviously a case for one supply for each channel., Any recomendations which side to beef up, the digital or analogue section?
Frank
I had a Digit a while back (split supplies, Oscons, extra regulation) etc. Great fun & good sound. I tried a number of OpAmps including the Burr Brown.
IMHO I ended up with a JRC version of the original 5532. The other opamps tended to sound too bright to me. I still have quite a bit of info from those days in the form of mail threads I will happily forward. I now use the Cambridge ISOmagic but the Digit has found a new home witha good friend.
IMHO I ended up with a JRC version of the original 5532. The other opamps tended to sound too bright to me. I still have quite a bit of info from those days in the form of mail threads I will happily forward. I now use the Cambridge ISOmagic but the Digit has found a new home witha good friend.
QED Digit upgrades
Jives11,
If you could forward those threds onto me I would be grateful -
fa.jb(at)virgin.net EDIT: removed @ /peranders
I fancy a period of tweaking! You mention many other op ampds to the JRC were bright - did you try the Burr Brown I mentioned?
I also have a Marantz 63SEKI player which has already been modded a bit, but I have just seen another site which gives excelent details on doing some more. More "cheap" fun awaits...
Lets see if I can get the Digit to out perfor m the Marantz..
By the way, I seem to remember that a company called Nene Audio (or something like that) took the digit circuit & added ca 6 or so power supplies etc etc & charged a bomb for it - but got v. good reveiws. Was that true?
Cheers
Frankie
Jives11,
If you could forward those threds onto me I would be grateful -
fa.jb(at)virgin.net EDIT: removed @ /peranders
I fancy a period of tweaking! You mention many other op ampds to the JRC were bright - did you try the Burr Brown I mentioned?
I also have a Marantz 63SEKI player which has already been modded a bit, but I have just seen another site which gives excelent details on doing some more. More "cheap" fun awaits...
Lets see if I can get the Digit to out perfor m the Marantz..
By the way, I seem to remember that a company called Nene Audio (or something like that) took the digit circuit & added ca 6 or so power supplies etc etc & charged a bomb for it - but got v. good reveiws. Was that true?
Cheers
Frankie
Regarding split supplies. I remeber that the DAC chip (7323 Bitstream) is one of those square multilegged beasties. Even if you did the well aknowledged Analogue/Digital split, the DAC chip was still entirely supplied from the Digital supply. Really it was an Output Vs Everything else split. Some of the pins on the DAC were decoupled with small inductors as they were feeding analogue modules in the DAC. Maybe mileage in exploring truly split supplies.
The Opamps I tried was the BB 2604AP which was good but bright.
I settled on the JRC 21140 as combining the best characteristics of several and was very cheap.
I've emailed the guy who may still have the Digit hacking web site to see if he still has the content as the site was retired some years back.
I settled on the JRC 21140 as combining the best characteristics of several and was very cheap.
I've emailed the guy who may still have the Digit hacking web site to see if he still has the content as the site was retired some years back.
Thanks John = I did have a good look around the web a few years ago - obviously not that good though!
Would appreciate any help there..
Any ideas to improve an opto version I am thinking of getting to link into my new Sony freeview box? - Apparently the weakness of optical links are in the sending & receiving bits on each end.
Anyone know of best practice here?
Cheers
Frankie
Would appreciate any help there..
Any ideas to improve an opto version I am thinking of getting to link into my new Sony freeview box? - Apparently the weakness of optical links are in the sending & receiving bits on each end.
Anyone know of best practice here?
Cheers
Frankie
Yes - as did some of the Meridians (207 & 208 ) I think
It's always a good idea to get the Chip schematics. The 7323 was designed I think for Discman type applications. The chip has onboard pins for I/V conversion and I think for output buffers too. This enables discmans to have the minimum of components other thasn the DAC.
I recall Kelvin Labs did a blackbox DAC where the outputs ran directly of the DAC chip ! No external opamps at all but it only produced 0.5v output
In the QED Digit the I/V conversion is done "on chip" , hence my earlier comment about not all legs being digital, even if you do the HiFi World split PSU mod.
I found that I prefered the JRC over other opamps I tried ( I soldered a socket for easy swapping) but 2 things to bare in mind.
1) The Opamp is providing the buffer for each channel. High slew rate may not be so important here.
2) I hate brightness and can happily live with sloped off treble response (I ended up getting a Quad 44 for the tone controls) , so I am terribly out of fashion ;-)
It's always a good idea to get the Chip schematics. The 7323 was designed I think for Discman type applications. The chip has onboard pins for I/V conversion and I think for output buffers too. This enables discmans to have the minimum of components other thasn the DAC.
I recall Kelvin Labs did a blackbox DAC where the outputs ran directly of the DAC chip ! No external opamps at all but it only produced 0.5v output
In the QED Digit the I/V conversion is done "on chip" , hence my earlier comment about not all legs being digital, even if you do the HiFi World split PSU mod.
I found that I prefered the JRC over other opamps I tried ( I soldered a socket for easy swapping) but 2 things to bare in mind.
1) The Opamp is providing the buffer for each channel. High slew rate may not be so important here.
2) I hate brightness and can happily live with sloped off treble response (I ended up getting a Quad 44 for the tone controls) , so I am terribly out of fashion ;-)
jives11 said:
A very experienced DIYer recommended the following approach to me. I should be trying it soon:
In the CD624, all of the 5V supplies to the SAA7321 are taken from the main 5V digital supply. The digital side of the chip is supplied through pins 22 and 23 (digital and osc). The analogue side is supplied by pins 39, 11 and 43. It should be possible to separate each of these and even provide separate regulators for each side. Each supply pin could also be directly decoupled to its corresponding ground pin.
jives11 said:
Did you get any reply wrt the above?
not yet but will try again.
I think the most important thing is to get the data sheet for the chip. Another mod which I have seen is providing a better voltage ref. a few pins provides a +2.5v ref voltage out and another is the voltage ref in. I think using an external voltage reference is worth pursuing. I think audo synthesis did a 3 pin V ref, rather like a small transistor that could be used.
The real problem is that the legs are so tiny and so close together.
I think the most important thing is to get the data sheet for the chip. Another mod which I have seen is providing a better voltage ref. a few pins provides a +2.5v ref voltage out and another is the voltage ref in. I think using an external voltage reference is worth pursuing. I think audo synthesis did a 3 pin V ref, rather like a small transistor that could be used.
The real problem is that the legs are so tiny and so close together.
I have the data sheet for the 7323. It is available on the net at:
SAA7322-3 PDF
Yes, the pins on the smd 7321/3 are really small, but it might be possible to access them via the trace on the board - a little further from the chip. Not ideal - but better than the existing setup and safer than risking damage to the dac.
SAA7322-3 PDF
Yes, the pins on the smd 7321/3 are really small, but it might be possible to access them via the trace on the board - a little further from the chip. Not ideal - but better than the existing setup and safer than risking damage to the dac.
Just out of interest & I knew I remember reading about it somewhere - anyone with a copy of "Audiophile" (a 90's UK hifi rag) did a reveiw of a certain Nene Valley Audio's DACon in their November 1992 issue.
I don't have the issue unfortunately, but later summaries stated thus:
"The DACon is essentially a souped up QED Digit. NVA has added its own electronics, power supply & casework. With a good transport, the DACon gives a detailed informative sound that does justice to all types of music"
Bearing in mind at the time the Digit retailed for £139 while the DACon retailed for £730 and £960 - it must have been one hell of a souped up version. Memory has it that there were at least 6 independant power supplies...
By the way the makers NVA are currently up for sale according to their web site..
FrankJB
I don't have the issue unfortunately, but later summaries stated thus:
"The DACon is essentially a souped up QED Digit. NVA has added its own electronics, power supply & casework. With a good transport, the DACon gives a detailed informative sound that does justice to all types of music"
Bearing in mind at the time the Digit retailed for £139 while the DACon retailed for £730 and £960 - it must have been one hell of a souped up version. Memory has it that there were at least 6 independant power supplies...
By the way the makers NVA are currently up for sale according to their web site..
FrankJB
Re: QED Digit upgrades
Hi all
How do they compare now?
I doubt it - and I wouldn't trust myself soldering a 44 pin SMD. Jocko does it all the time, but I'm not that brave. If you want to use a different chip, it's probably easier to access the signal going into the 7323 and the bypass it completely. That's quite a significant change and it would no longer be a QED Digit - but it would open up a lot of possibilities.
It might be a good idea to see what the 7323 is capable of with the best implimentation - maybe along the line of the NVA. Being an external DAC, jitter reduction might be at the top of the modding list - along with the power supplies.
BTW, there is a discussion on the 7323 in the Rotel 965 at
good dac tweek
Also, the review of the Digit and the PS upgrade are below:
QED Digit review
QED Digit PS upgrade
Hi all
Frankieno3 said:
How do they compare now?
Frankieno3 said:
I doubt it - and I wouldn't trust myself soldering a 44 pin SMD. Jocko does it all the time, but I'm not that brave. If you want to use a different chip, it's probably easier to access the signal going into the 7323 and the bypass it completely. That's quite a significant change and it would no longer be a QED Digit - but it would open up a lot of possibilities.
It might be a good idea to see what the 7323 is capable of with the best implimentation - maybe along the line of the NVA. Being an external DAC, jitter reduction might be at the top of the modding list - along with the power supplies.
BTW, there is a discussion on the 7323 in the Rotel 965 at
good dac tweek
Also, the review of the Digit and the PS upgrade are below:
QED Digit review
QED Digit PS upgrade
My recollection was that the NVA player was basically a Sanyo Transport and a Digit on a single board with very large torroidal power supplies. The whole thing was in acrylic case work which was the epoxied tight shut. NVA did admit that the DAC was a Digit but said they had made some upgrades. No idea what. The player was well reviewed at the time despite it's humble roots. NVA did a few strange things - I recall there amps were not unconditionally stable and could only be used with certain cables !?!?
I think the Digit is worth tweaking but not worth going overboard (pardon the pun). Better PSU regulation/decoupling- usual stuff is worth doing. However you could probably pick up a Meridian DAC203 on ebay for not too much which is the same chip in a better implementation (and box). The Digit was a great beer money DAC emphasising the smooth bitstream sound (plus some engineered rolloff) , but was not the most advanced implementation of this chipset. You will also find the box does not stand up well to being repeatedly unscrewed/rescrewed together and the thread will strip.
That said - mine is gving good service in a friends mp3 system
I think the Digit is worth tweaking but not worth going overboard (pardon the pun). Better PSU regulation/decoupling- usual stuff is worth doing. However you could probably pick up a Meridian DAC203 on ebay for not too much which is the same chip in a better implementation (and box). The Digit was a great beer money DAC emphasising the smooth bitstream sound (plus some engineered rolloff) , but was not the most advanced implementation of this chipset. You will also find the box does not stand up well to being repeatedly unscrewed/rescrewed together and the thread will strip.
That said - mine is gving good service in a friends mp3 system
Alas it looks like the old QED Tweaking web site ("Digitalis" - geddit ?) has no backup - thanks Dieter for trying.
But I think most of the tricks have been covered here, i.e:
Better Dual (or 2 single + daughter board) Opamps.
valve output ? (WARNING : watch that plastic box - it could melt !)
Swap the tantalum caps for OSCONS.
Split supplies , even 3 supplies (Output 12v, 7323 Dig, 7323 Analogue).
change the 7805 for something better (LT ?)
Run off over 12v lead acids
Remove/replace the DC blocking caps.
Replace/remove the rolloff caps
There were a few variants The Opto had a Toslink digital input, while there was Digit in a full width case with 2 positron PSUs inside. Think is twas called the Digit Pro or something. NVA had a digit based DAC and a full player which had a Digit inside
But I think most of the tricks have been covered here, i.e:
Better Dual (or 2 single + daughter board) Opamps.
valve output ? (WARNING : watch that plastic box - it could melt !)
Swap the tantalum caps for OSCONS.
Split supplies , even 3 supplies (Output 12v, 7323 Dig, 7323 Analogue).
change the 7805 for something better (LT ?)
Run off over 12v lead acids
Remove/replace the DC blocking caps.
Replace/remove the rolloff caps
There were a few variants The Opto had a Toslink digital input, while there was Digit in a full width case with 2 positron PSUs inside. Think is twas called the Digit Pro or something. NVA had a digit based DAC and a full player which had a Digit inside
QED Digit website Found ! (Part 1)
Thanks to Dieter , who kept looking and found a backup on an old PC.
------------------------------------------------------------------------------------
Guten Tag and welcome to the unofficial QED home page
You are visitor number since June 1998
This is intended as a home page for all users of the QED Digit DAC and specifically aimed at individuals who are interested in the numerous modifications that can be made to this remarkable device.
--------------------------------------------------------------------------------
Contact
To let us know that we are not the last Digitalics on this planet please contact
Jonathan Ives & Dieter Strecker (auch in Deutsch)
--------------------------------------------------------------------------------
Background
In 1982, QED released the "Digit", as a cheap upgrade to existing CD players which featured an electrical digital output, complying with the S/PDIF format. It featured the (then) latest Philips Bitstream technology: 7323 DAC, 7274 interface receiver and used the humble Signetics 5532 to drive the output. It was sold as a means of curing some of the nasties associated with early CD players i.e. gritty treble, fatiguing sound. It clearly met this design goal, but was also capable of sounding very good, embarrassing many higher priced DAC's. A number of magazines recommended partnering a Digit with a much higher priced dedicated CD transport as a fast route to high quality CD sound. The Positron followed, an upgrade to the standard sealed plug power supply. Later came the Digit Reference , until production ceased in 1996.
The Digit was really the first affordable budget DAC, and set the market for the likes of Audio Alchemy and Musical Fidelity.
--------------------------------------------------------------------------------
Variants
QED Digit Original DAC, electrical input, basic power supply. Small black plastic box
Positron Uprated power supply
QED Digit Opto As Original, but including support for Toslink optical connection as well
QED Reference Full width chrome plated front and 2 Positrons
DAC Pack Digit + Positron + Digiflex cable
Digit Plus Digit + Incon interconnect Digiflex cable
A number of commercially available DAC's were rumored to be based on the Digit, where companies strengths lay in Analogue rather than Digital design. A number of Companies offered upgraded power supplies the most notable being the NVA single and twin PSU upgrades. It is also claimed that NVA were involved in the novel design of the Positron.
--------------------------------------------------------------------------------
Basic circuit description
The Digit uses the complement of Philips SAA 7274P ADIC (digital receiving chip) and SAA 7323 convertor. The 7274 is fed from the Digital Input (S/PDIF format) via an LC resonator filter to extract the clock signal. The 7224 supplies the 7323 in I2S format. The converter chip is a 1-bit 256 times oversampling DAC, incorporating a version of the 7220 Digital filter & noise shaper. The de-emphasis networks employs polystyrene capacitors feeding the Signetics NE 5532 dual OpAmp to drive the outputs. A 100uF cap provides blocking for any DC present on each output, while a final 4700pF provides a degree of high end roll off. The later OPTO model included an additional optical digital input using the Toslink format favoured by mostly Japanese CD players. This then feeds the same LC resonator and 7224.
Thanks to Dieter , who kept looking and found a backup on an old PC.
------------------------------------------------------------------------------------
Guten Tag and welcome to the unofficial QED home page
You are visitor number since June 1998
This is intended as a home page for all users of the QED Digit DAC and specifically aimed at individuals who are interested in the numerous modifications that can be made to this remarkable device.
--------------------------------------------------------------------------------
Contact
To let us know that we are not the last Digitalics on this planet please contact
Jonathan Ives & Dieter Strecker (auch in Deutsch)
--------------------------------------------------------------------------------
Background
In 1982, QED released the "Digit", as a cheap upgrade to existing CD players which featured an electrical digital output, complying with the S/PDIF format. It featured the (then) latest Philips Bitstream technology: 7323 DAC, 7274 interface receiver and used the humble Signetics 5532 to drive the output. It was sold as a means of curing some of the nasties associated with early CD players i.e. gritty treble, fatiguing sound. It clearly met this design goal, but was also capable of sounding very good, embarrassing many higher priced DAC's. A number of magazines recommended partnering a Digit with a much higher priced dedicated CD transport as a fast route to high quality CD sound. The Positron followed, an upgrade to the standard sealed plug power supply. Later came the Digit Reference , until production ceased in 1996.
The Digit was really the first affordable budget DAC, and set the market for the likes of Audio Alchemy and Musical Fidelity.
--------------------------------------------------------------------------------
Variants
QED Digit Original DAC, electrical input, basic power supply. Small black plastic box
Positron Uprated power supply
QED Digit Opto As Original, but including support for Toslink optical connection as well
QED Reference Full width chrome plated front and 2 Positrons
DAC Pack Digit + Positron + Digiflex cable
Digit Plus Digit + Incon interconnect Digiflex cable
A number of commercially available DAC's were rumored to be based on the Digit, where companies strengths lay in Analogue rather than Digital design. A number of Companies offered upgraded power supplies the most notable being the NVA single and twin PSU upgrades. It is also claimed that NVA were involved in the novel design of the Positron.
--------------------------------------------------------------------------------
Basic circuit description
The Digit uses the complement of Philips SAA 7274P ADIC (digital receiving chip) and SAA 7323 convertor. The 7274 is fed from the Digital Input (S/PDIF format) via an LC resonator filter to extract the clock signal. The 7224 supplies the 7323 in I2S format. The converter chip is a 1-bit 256 times oversampling DAC, incorporating a version of the 7220 Digital filter & noise shaper. The de-emphasis networks employs polystyrene capacitors feeding the Signetics NE 5532 dual OpAmp to drive the outputs. A 100uF cap provides blocking for any DC present on each output, while a final 4700pF provides a degree of high end roll off. The later OPTO model included an additional optical digital input using the Toslink format favoured by mostly Japanese CD players. This then feeds the same LC resonator and 7224.
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