Joachim , I think the output buffer is the principal cause of the good results that your circuit achieve. Last week I have made a headphone amplifier with the same type of buffer , with opa134 , and I really, really love it .
Patrick, I must agree with dirk. Is not a good idea taking the output from the supply pins , I know some amplifiers that do that , like the Alexanders amplifier , but in that case the opamp is inside the feedback loop , and that is not the case with the circuit that you like. Tomorrow I will post a circuit that may serve you better.
I thought I got the OPA627 sounding as good as an opamp could for an I/V stage, nulling out the dc offset from the PCM1704 to it seemed to do a lot of good for them, don't ask me why, all I can say is that it seems the OPA627 as an opamp I/V doesn't like to see dc offset from the dac chip comming into it.
Then yesterday I got my sample LME49710 TO-99 tin can package, I thought no the specs are not as good for an I/V as OPA627 but I jerry riged them into the 8 pin dil sockets and low and behold they are today better than the 627's, cannot fault them, they make the OPA627 sound a bit restricted and not as open top to bottom.
They seem to be more transparent and extended through the top end, the bottom end is punchier yet seems to go lower and tighter and the mids are nice and relaxed and more followable for want of a better word.
I can't wait to get a discrete I/V, one that has cred, hopefully Sergio's once it's sorted and available.
But it seems discrete I/V's are still in there infancy design wise, then there are the prima donas who claim to have the holy grail of discrete I/V's but no one get's to hear them, they have to take their word on it. Are they scared to let them out? or are they waiting for the the offer of big bucks from manufactures to buy their designs even though unproven and unheard?. And never to be disected and appraised by those who can on these forums.
I'm glad I'm not up to designing one, all I can do watch from the sidelines and see the circus go round and round on this and other forums, thank you Serg for presenting yours and getting input from all the others who can, that can only be a good thing to make a design complete.
Cheers George
Cheers George
Then yesterday I got my sample LME49710 TO-99 tin can package, I thought no the specs are not as good for an I/V as OPA627 but I jerry riged them into the 8 pin dil sockets and low and behold they are today better than the 627's, cannot fault them, they make the OPA627 sound a bit restricted and not as open top to bottom.
They seem to be more transparent and extended through the top end, the bottom end is punchier yet seems to go lower and tighter and the mids are nice and relaxed and more followable for want of a better word.
I can't wait to get a discrete I/V, one that has cred, hopefully Sergio's once it's sorted and available.
But it seems discrete I/V's are still in there infancy design wise, then there are the prima donas who claim to have the holy grail of discrete I/V's but no one get's to hear them, they have to take their word on it. Are they scared to let them out? or are they waiting for the the offer of big bucks from manufactures to buy their designs even though unproven and unheard?. And never to be disected and appraised by those who can on these forums.
I'm glad I'm not up to designing one, all I can do watch from the sidelines and see the circus go round and round on this and other forums, thank you Serg for presenting yours and getting input from all the others who can, that can only be a good thing to make a design complete.
Cheers George
Cheers George
Last edited:
you may find they get tiring in the long-run, I did (the LME49710 to99) somethinga bit too flat about them, not neutral flat, just kinda lifeless flat. Great in regulators though.
then again I dont place quite as much ability on a single opamp swap to make extreme flavor differences in circuit if applied well these days as I did back then and I have more skill in applying them, so maybe it was more application. I do tend to prefer jfet opamps though, except for lme49990, which is rather special, but perhaps not the best for IV
then again I dont place quite as much ability on a single opamp swap to make extreme flavor differences in circuit if applied well these days as I did back then and I have more skill in applying them, so maybe it was more application. I do tend to prefer jfet opamps though, except for lme49990, which is rather special, but perhaps not the best for IV
Last edited:
I think your right qusp, I listened last night till midnight, and kept saying to myself how good is this bass, how good is the dynamics and micro detail everywhere, how extended/detailed are the highs, why am I not enjoying myself, maybe I'm not in the mood.
I'll swap back to the OPA627 later today or tomorrow to see what gives. Just in case I was not in the mood to enjoy
Cheers George
I'll swap back to the OPA627 later today or tomorrow to see what gives. Just in case I was not in the mood to enjoy
Cheers George
I have to say that all opamps for I/V seem to be a comprimise, I prefer for the long term the OPA627 but I just wish it had the bass power and tightness and dynamic swing of the LME49710. A proper discrete I/V could be the only way to go, but then this seems to be a black art in itself to design right, there doesn't appear to be set guidlines on how these are to be made either.
I'm over it, I just hope that Sergio (SMMS73) has the holy grail, can't wait to try it out once he get a kit going, I'll be in like Flyn (Errol) to try it out.
Cheers George
I'm over it, I just hope that Sergio (SMMS73) has the holy grail, can't wait to try it out once he get a kit going, I'll be in like Flyn (Errol) to try it out.
Cheers George
knowing op amp limitations I would rather point at the DAC - they often don't do a very good job on the datasheet of show limits, effects of offset V, termination Z
before widespread factory internal zener zap offset trimming some op amps benefited from selection for low offset, or those with trim pins could have input stage nonlinearity caused distortion minimized by the Vos trim
of course I have no idea what people are really talking about when attributing "frequency response" type "explainations" to op amp rolling - we can be fairly sure no "conventionally audible" frequency respose changes occur with decdent, "audio" op amps in DAC I/V circuits
but if some are so certain of these changes then why aren't they exploring really new op amps, composite op amp circuits instead of going down the descrete garden path, "nfb" rabbit holes
Hi JCX, no dc offset from the Dac's thanks to Abraxalito and the dac offset nulling circuit he posted, so the dac/s was zero'ed to within a tenth of a millivolt each time when each i/v opamp was listened to. And I listened to many not just these two mentioned.
http://www.diyaudio.com/forums/digi...help-needed-higher-dc-offset-one-channel.html
Cheers George
http://www.diyaudio.com/forums/digi...help-needed-higher-dc-offset-one-channel.html
Cheers George
I agree George, opamps for I/V just do not deliver transparency. I have changed my view based on experience, because I used to go for them a few years ago. Try a passive filter (steep one, based on inductors and capacitors) before discrete I/V and prepare to be surprised (Listening to passive I/V, 7th order elliptic filter now, can't go back).
(Listening to passive I/V, 7th order elliptic filter now, can't go back).
I agree George, opamps for I/V just do not deliver transparency. I have changed my view based on experience, because I used to go for them a few years ago. Try a passive filter (steep one, based on inductors and capacitors) before discrete I/V and prepare to be surprised
I would really like to do this Abraxalito, but please correct me if I'm wrong, the PCM1704's only have +-1.2mA output swing, this would die to nothing by the time it goes through a nice low 10ohms or so passive resistor i/v, then to bring it back up to 2v output with a decent low output impedance active stage maybe noise will become a big issue?
Cheers George
I've not played with the PCM1704 - why does the I/V resistor need to be as low as 10R? I know there are some issues with diodes conducting at the output which limits the compliance available. I have about 100mV signal on the output of my TDA1545s, noise doesn't seem to be an issue, but then I'm only feeding 16bits. The amp stage will dominate in noise terms for 10R source resistance so its worth exploring whether the resistor can't be bigger. AD603 works great for me, this has a built-in 100R resistor.
I've just read and been told that 10ohms passive I/V gets the best out of the PCM1704 I don't know who to believe to be honest anymore.
That AD603 looks the goods if 100ohms input is as good as 10ohms. 3v output at 2ohms with 50mA and I think most of the dac noise is taken out within the dac so maybe no low pass filter is required maybe?
Cheers George
That AD603 looks the goods if 100ohms input is as good as 10ohms. 3v output at 2ohms with 50mA and I think most of the dac noise is taken out within the dac so maybe no low pass filter is required maybe?
Cheers George
If you delete the low pass filter it'll still sound better than pretty much anything else except TDA1541A. But with the LP filter in place, the sound goes up into another league altogether - completely gob-smacking (at least with my TDA1545s). This does rather depend on the amp stage after it, AD603 might not be as great performance as a discrete stage done well. Once you've heard the sound through the filter, I can't believe you'd ever want to go back...
If you delete the low pass filter it'll still sound better than pretty much anything else except TDA1541A. But with the LP filter in place, the sound goes up into another league altogether - completely gob-smacking (at least with my TDA1545s). This does rather depend on the amp stage after it, AD603 might not be as great performance as a discrete stage done well. Once you've heard the sound through the filter, I can't believe you'd ever want to go back...
What's your take on filtering the output of a non-oversampling tda1541a with resistor as i/v?
I am currently not using any filtering (neither low pass nor otherwise to compensate the nos roll-off), and actually very happy as it is....but i read somewhere that bumping up the high frequencies make a huge positive difference ...
Definitely worth trying a filter, even with TDA1541A. Its definitely also worth bringing up the droopy top end by some means. You could do that by adding on two more TDA1541As (if you're feeling fairly rich) and feeding them with an HEF4517 delay line to create a 3 tap FIR filter. Thorsten also says undoing the droop is definitely worthwhile, I think he does it by some passive LC circuit, though not sure of the details.
Hi all,
This is my first post, so far and learned reading here.
I'm doing the mod in a CD player Technics SL-P999, is a great player.
This model mount a linear DAC converters: Four PCM56P (two per channel)
I replaced on I / V stage the original operational M5238 by OPA2604, and I'm not happy with the result ... sound, poor, muffled, dull, veiled.
I was thinking of replacing by AD825, because I need to be an double encapsulated SMD, and the power supply voltaje is a +7.9 and -8.1 (original design in factory)
I have skills and experience, it is worked in Panasonic/Technics/National for 15 years repairing audio, and I have instruments, parts, and Service Manual for these players
any suggestions?
greetings
http://i48.tinypic.com/5anex5.jpg
This is my first post, so far and learned reading here.
I'm doing the mod in a CD player Technics SL-P999, is a great player.
This model mount a linear DAC converters: Four PCM56P (two per channel)
I replaced on I / V stage the original operational M5238 by OPA2604, and I'm not happy with the result ... sound, poor, muffled, dull, veiled.
I was thinking of replacing by AD825, because I need to be an double encapsulated SMD, and the power supply voltaje is a +7.9 and -8.1 (original design in factory)
I have skills and experience, it is worked in Panasonic/Technics/National for 15 years repairing audio, and I have instruments, parts, and Service Manual for these players
any suggestions?
greetings
An externally hosted image should be here but it was not working when we last tested it.
http://i48.tinypic.com/5anex5.jpg
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.