I posted already the suggestion for such stage but now I can confirm it works and it works fine. I tried it in my TDA1541A non-o/s DAC and it was better than the other things I tried which include a few classic opamp I/Vs and passive resistor I/V followed by the tube stage. Application is similar to that suggested by Kuei for the OPA660.
If used with JFET with Idss of 10-12mA, values between 200 and 500 Ohms for VR1 should be fine. Trimming should be redone after a few minutes of warming up.
Vuki had reported a successful implementation of this stage (without current injection) in the AD1865 DAC.
More info on my TDA1541A DAC page.
Pedja
An externally hosted image should be here but it was not working when we last tested it.
If used with JFET with Idss of 10-12mA, values between 200 and 500 Ohms for VR1 should be fine. Trimming should be redone after a few minutes of warming up.
Vuki had reported a successful implementation of this stage (without current injection) in the AD1865 DAC.
More info on my TDA1541A DAC page.
Pedja
Hello diyAudio,
Just wanted to say – though in the meantime I did have certain number of hits on my DAC page, I am completely disappointed by the reaction of The Forum. Ok, I know it happens that the people sometimes stay silent about the things they are in fact interested for, but…
Some interesting things I have dug lately.
http://www.stereophile.com/printarchives.cgi?840
I might be out of time, but I’ve never before heard for (or listened to) Ayre. In the review it was mentioned that the AD844 is used without feedback and the spectral content of the measured distortion is similar to those graphs I uploaded.
Another interesting case. Krell KAV-CD250 comprises AD844 and the trimmer (btw the same BI 67 you might note in my DAC) is aboard. The fact the trimming is done here and not downstream (I don’t see a coupling caps, hence it should be done somewhere) may and may not be related to the fact the AD844 is used as a common base since the PCM1702 puts out a bipolar (+/-) current. But if it is used this way, I’d expect to see the trimming circuit exactly here. The pictures I found are here:
http://www.webmedia.pl/maciejza/tuning/krell.htm
http://www.webmedia.pl/maciejza/tuning/img/krell/krell9.jpg
Unfortunately I don’t have any further info about this player. Fyi, the AD844 used like a classic I/V opamp is good but not spectacular.
Best regards,
Pedja Rogic
Just wanted to say – though in the meantime I did have certain number of hits on my DAC page, I am completely disappointed by the reaction of The Forum. Ok, I know it happens that the people sometimes stay silent about the things they are in fact interested for, but…
Some interesting things I have dug lately.
http://www.stereophile.com/printarchives.cgi?840
I might be out of time, but I’ve never before heard for (or listened to) Ayre. In the review it was mentioned that the AD844 is used without feedback and the spectral content of the measured distortion is similar to those graphs I uploaded.
Another interesting case. Krell KAV-CD250 comprises AD844 and the trimmer (btw the same BI 67 you might note in my DAC) is aboard. The fact the trimming is done here and not downstream (I don’t see a coupling caps, hence it should be done somewhere) may and may not be related to the fact the AD844 is used as a common base since the PCM1702 puts out a bipolar (+/-) current. But if it is used this way, I’d expect to see the trimming circuit exactly here. The pictures I found are here:
http://www.webmedia.pl/maciejza/tuning/krell.htm
http://www.webmedia.pl/maciejza/tuning/img/krell/krell9.jpg
Unfortunately I don’t have any further info about this player. Fyi, the AD844 used like a classic I/V opamp is good but not spectacular.
Best regards,
Pedja Rogic
Here's ML 30.6 DAC view:
http://madrigal.harman.com/image_library/marklevinson/30_6DAC_lo.jpg
Did you compare your stage against Kuei's OPA660 version?
http://madrigal.harman.com/image_library/marklevinson/30_6DAC_lo.jpg
Did you compare your stage against Kuei's OPA660 version?
No. I’ll compare it to some discrete (single end, not symmetrical) common base stages next weeks but OPA660 should wait a bit. Circuits are similar but in fact it will be easier to make a new board for the OPA660 than to change this I have with AD844.
Nice pic of ML, this is even better , but as I can see it uses the classic opamp IV.
😉
Pedja
Nice pic of ML, this is even better , but as I can see it uses the classic opamp IV.
😉 Pedja
Pedja said:No. I’ll compare it to some discrete (single end, not symmetrical) common base stages next weeks but OPA660 should wait a bit. Circuits are similar but in fact it will be easier to make a new board for the OPA660 than to change this I have with AD844.
Nice pic of ML, this is even better , but as I can see it uses the classic opamp IV.
Pedja
Pedja,
What is that R151 bent over backwards over that chip? Looks like a power R used to heat/temp stabilise the chip? What chip is that?
Jan Didden
Jan: Looks like Texas Component's TX2352. Essentially a Vishay S102 sans molded packaging.
PDF download link here:
http://www.texascomponents.com/Tx2352a.pdf
hth, jonathan carr
PDF download link here:
http://www.texascomponents.com/Tx2352a.pdf
hth, jonathan carr
Jonathan,
I suspected something like that, looks like a Caddock. But the intriguing thing is, what is that chip it tries to hide??
Jan Didden
I suspected something like that, looks like a Caddock. But the intriguing thing is, what is that chip it tries to hide??
Jan Didden
Hi Jan,
I meant originally that both OPA627 and AD826 can be used exclusively as a classic IV opamps.
As about the secret chip, I found this:
“The Reference DAC modules are based on the highest grade of the new 24-bit, multi-bit Burr Brown1 1704 DAC and OPA627AP I-to-V converters.”
http://www.marklevinson.com/products/overview.asp?cat=dap&prod=no30-6&details=yes
And in fact it looks like it is BB.
But for some reason, John Atkinson claims:
“The original UltraAnalog DACs have been replaced by new 24-bit DAC modules designed and built by Madrigal.”
http://www.stereophile.com/printarchives.cgi?159
Pedja
I meant originally that both OPA627 and AD826 can be used exclusively as a classic IV opamps.
As about the secret chip, I found this:
“The Reference DAC modules are based on the highest grade of the new 24-bit, multi-bit Burr Brown1 1704 DAC and OPA627AP I-to-V converters.”
http://www.marklevinson.com/products/overview.asp?cat=dap&prod=no30-6&details=yes
And in fact it looks like it is BB.
But for some reason, John Atkinson claims:
“The original UltraAnalog DACs have been replaced by new 24-bit DAC modules designed and built by Madrigal.”
http://www.stereophile.com/printarchives.cgi?159
Pedja
Pedja said:
And those are the pictured modules, featuring 1704 DACs.
I've built a DAC using paralleled 1704 K DACs, but the non-oversampling TDA1543 sounds better to me.
If it wasn't for all that NIGC controversy I would be bulding a DAC using 1541S2 chip right now😉
Hi Peter,
From the Strereophile’s test, one (me for example) could realize that ML invented something regarding the DAC chip and swapped the previous one with some their own module. Actually (if I am not again mistaken), the module comprises BB DAC chip and output stage, just like the previously used UltraAnalog's DAC (I guess) incorporates the DAC (strictly speaking) and the IV stage.
Don’t know about the PCM1704, but while we are at BB, compared against the SM5842/PCM63K, the TDA1543 non-o/s lacked some dynamics (and this was probably related to the fact the later used a resistor only I/V) but many other things, let’s say musicality, were on its side (I think I wrote this already somewhere).
Pedja
From the Strereophile’s test, one (me for example) could realize that ML invented something regarding the DAC chip and swapped the previous one with some their own module. Actually (if I am not again mistaken), the module comprises BB DAC chip and output stage, just like the previously used UltraAnalog's DAC (I guess) incorporates the DAC (strictly speaking) and the IV stage.
Don’t know about the PCM1704, but while we are at BB, compared against the SM5842/PCM63K, the TDA1543 non-o/s lacked some dynamics (and this was probably related to the fact the later used a resistor only I/V) but many other things, let’s say musicality, were on its side (I think I wrote this already somewhere).
Pedja
janneman said:
The chip it is hiding is DAC chip. Probably Burr Brown PCM1704
(from memory). You can see start of B for Burr and P for PCM.
ML used classic OPA I-V (627). R151/551 are I-V FB R's.
I would imagine tha dacs quiescent current (BP0)
may drift slightly with temp. This may be compensation.
Cheers,
Terry
Terry Demol said:
Sorry it's getting late! Wouldn't matter if FB R was thermally
tracking dac... no idea jan. I wonder if it measured
better like that?
T
Terry Demol said:
Beats me. The fact that the resistor has such long leads means it must have been deliberately done. Anybody has a schematic showing what drives this resistor?
Jan Didden
Note also that the DACs have pins 9 and 10 snapped off.
I'm sure they're not needed but can one really believe
the sound is better with them snapped off?
I'm sure they're not needed but can one really believe
the sound is better with them snapped off?
If you look closely at the uppermost leg of both 'resistors', then you can see a PCB track which goes directly to pin 2 on the OP627, which is the -in input termial of the op-amp. Very odd...😕
Great work Pedja,
I still need to try the OPA660.
If you got a few AD844's spare, I could try 'm as well.
I'm curious how it compares to the single ended discrete I/V.
I've almost finished the "complex" discrete, DC coupled folded cascode common base stage, got one channel up and running.
This one can be used with TDA1543 as well (again DC coupled).
Schematics and pictures will hopefully be posted this weekend.
I still need to try the OPA660.
If you got a few AD844's spare, I could try 'm as well.
I'm curious how it compares to the single ended discrete I/V.
I've almost finished the "complex" discrete, DC coupled folded cascode common base stage, got one channel up and running.
This one can be used with TDA1543 as well (again DC coupled).
Schematics and pictures will hopefully be posted this weekend.
Thanks Rudolf,
Unfortunately I previously ordered only one pair of the AD844. Will see how it compares with the discrete common base stages and will contact you if I’ll order it again.
Pedja
Unfortunately I previously ordered only one pair of the AD844. Will see how it compares with the discrete common base stages and will contact you if I’ll order it again.
Pedja
kiwi_abroad said:
Do you read the posts? I stated this R is FB R of I-V opamp
(627)... connects to opa - IP.
Any RF experts here? would there be some kind of RF
cancellation or attenuation with the I-V FB R mounted
very close to the switched current sources (R2R ladder)?.
Is it possible to mount the R so that fields are cancelling?
Just a crazy thought.
T
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