I blew a opamp and wondered since I have to replace it if there is anything in the same package that higher quality?
Here's the spec sheet http://www.analog.com/static/import...heets/AD744.pdf
The circuit was originally designed for a LF351N A friend had suggested the 744 series way back then. Maybe there's something even better?
Here's the spec sheet http://www.analog.com/static/import...heets/AD744.pdf
The circuit was originally designed for a LF351N A friend had suggested the 744 series way back then. Maybe there's something even better?
I post your link (corrected)
http://www.analog.com/static/imported-files/data_sheets/AD744.pdf
Personally, I think AD744 is a very high class op-amp.
Think you should stick to that one.
Not much to improve using anything else.
Regards 🙂
http://www.analog.com/static/imported-files/data_sheets/AD744.pdf
Personally, I think AD744 is a very high class op-amp.
Think you should stick to that one.
Not much to improve using anything else.
Regards 🙂
Thanks for fixing the link. Don't know what happened. If that's the best - I'm using the KN series then I'll order those. Just want to get the best part for the job. Oops. Just went to order them at Digikey and its a non stock.
Know where I can order from in the US?
Know where I can order from in the US?
you could see what people think. google search:
http://www.google.com/search?q=ad744+audio+op-amps
for example this topic AD744 Revisted
http://www.fixup.net/talk/topic.asp?TOPIC_ID=1475
where is compared to some other, like AD829, AD8397
Now, what op-amp will 'be perfect' is a lot depeding on the circuit in question
What you should avoid, is to replace one JFET input op-amp
with one using higher bias current Bipolar input.
It may be possible to do so. But may not work at all in other cases.
This has to do with that some circuits are supposing JFET very low input bias currents.
http://www.google.com/search?q=ad744+audio+op-amps
for example this topic AD744 Revisted
http://www.fixup.net/talk/topic.asp?TOPIC_ID=1475
where is compared to some other, like AD829, AD8397
Now, what op-amp will 'be perfect' is a lot depeding on the circuit in question
What you should avoid, is to replace one JFET input op-amp
with one using higher bias current Bipolar input.
It may be possible to do so. But may not work at all in other cases.
This has to do with that some circuits are supposing JFET very low input bias currents.
Do you think this is a correct sub for a LF351N? I have been using the AD744 series but it could be causing issues I'm not aware of. It goes into an Audio Note board. Here's the ps schematic
http://www.audionotekits.com/PDF/Schematics/DAC_Digital_Sheet_2_PDF.pdf
Thanks for the links. I'll read through them.
http://www.audionotekits.com/PDF/Schematics/DAC_Digital_Sheet_2_PDF.pdf
Thanks for the links. I'll read through them.
Yes, I think AD744 is an excellent upgrade for LF351 in that DA-Converter +- 5.000 volt regulator supply.
http://cache.national.com/ds/LF/LF351.pdf
Looking at the simplified internal diagram of LF351 and AD744, they are almost identical.
But AD744 should be the better one. LF351 is an old JFET amplifier.
AD744 also has about same supply voltage range as LF351:
+-4.5 to +-18 VDC.
For example input voltage offset (precision) is 0.5 mV vs. 10 mV max offset.
This is 20 times lower offset.
http://cache.national.com/ds/LF/LF351.pdf
Looking at the simplified internal diagram of LF351 and AD744, they are almost identical.
But AD744 should be the better one. LF351 is an old JFET amplifier.
AD744 also has about same supply voltage range as LF351:
+-4.5 to +-18 VDC.
For example input voltage offset (precision) is 0.5 mV vs. 10 mV max offset.
This is 20 times lower offset.
Thanks again. Looks like the kn series was replaced by the KNZ. Don't know if that's a touch different or not. Good news is digikey has them.
How did you blow it up ?
With the greatest respect to Lineup, I would stick to the original device type 🙂 here.
Power supplies like this can be surprisingly fussy on the device used, and I did some work on this a while back.
Is this a commercial product ? built by a manufacturer.
The AD744 may well be unstable in this configuration.
With the greatest respect to Lineup, I would stick to the original device type 🙂 here.
Power supplies like this can be surprisingly fussy on the device used, and I did some work on this a while back.
Is this a commercial product ? built by a manufacturer.
The AD744 may well be unstable in this configuration.
I was going to ask the same question.
If AD744 did get blown in that circuit, then you have 2 options:
1. As Mooly suggest, stay with LF351.
It will probably perform very well enough. And will not oscillate & get destroed.
2. Study the datasheet and/or consult some that knows such circuits
and modify the circuit using (compensation- and bypass-) capacitors to get AD744 stable.
If AD744 did get blown in that circuit, then you have 2 options:
1. As Mooly suggest, stay with LF351.
It will probably perform very well enough. And will not oscillate & get destroed.
2. Study the datasheet and/or consult some that knows such circuits
and modify the circuit using (compensation- and bypass-) capacitors to get AD744 stable.
Hello Lineup,
I don't think this is a commercial design, not that that matters. There are a few things that are odd.
The LED used as a reference, it's not stable enough as it is fed from an unreg supply via a resistor. LED's generate noise ! There is no filtering of this on the LED. The output voltage is too dependant on the exact type of LED and temperature etc.
The 100 mf cap that feeds back to the opamp. This can be a problem, some opamps will go unstable with this arrangement.
You need to measure ( scope ) the output of the opamp and the reg to see what is happening.
Sorry to be a bit negative pharod.
I don't think this is a commercial design, not that that matters. There are a few things that are odd.
The LED used as a reference, it's not stable enough as it is fed from an unreg supply via a resistor. LED's generate noise ! There is no filtering of this on the LED. The output voltage is too dependant on the exact type of LED and temperature etc.
The 100 mf cap that feeds back to the opamp. This can be a problem, some opamps will go unstable with this arrangement.
You need to measure ( scope ) the output of the opamp and the reg to see what is happening.
Sorry to be a bit negative pharod.
I would also be careful here... the ad744 might indeed not be stable on a pcb designed for the (way) slower lf351.
You might have a quite safe improvement by simply replacing R21,22,23 by 5ma CRD's (1N5314 ?).
You might have a quite safe improvement by simply replacing R21,22,23 by 5ma CRD's (1N5314 ?).
Yes, those 100uF lyts across R30/31/32 looks too way much.
I usually try with 1nF, 2.2, 4.7 or 10nF here.
Also there are no 100nF supply film caps from V+ and V- (pins 7, 4) to GND.
I usually try with 1nF, 2.2, 4.7 or 10nF here.
Also there are no 100nF supply film caps from V+ and V- (pins 7, 4) to GND.
lineup said:
And what do you expect a 1nf cap to do there ?
Read again the articles by Walt Jung (freely available on his website) and you will understand why a 100uF cap isn't a bad idea at all in those positions.
this design violates the common mode restrictions of most opamps. Even the chosen LF351 may only work by accident.
Wild opamp swap is risky!
regards
Wild opamp swap is risky!
regards
This is a great discussion. The board is a commercial product. Its the Audio Note kit dac board. I'm building a new one because of issues. I put three ps in my ps box from twisted pair so each section would have its own separate supply.
When I turned it on one section blew either the LED or diode. A friend fixed it so I'm not sure which. When its working its fine although at times when I do mods to other things it can get fussy. I blew one just by trying to diagnose it. I noticed I'm getting voltages (5v and -5v) that aren't in spec. When I use some spare but different opamps it settle back so I though I would just get all new ones.
I have a spare pcb and plan to build a new one from scratch as this one is a little beat up. Since its the heart of the unit I would love to make any improvements I can.
When I turned it on one section blew either the LED or diode. A friend fixed it so I'm not sure which. When its working its fine although at times when I do mods to other things it can get fussy. I blew one just by trying to diagnose it. I noticed I'm getting voltages (5v and -5v) that aren't in spec. When I use some spare but different opamps it settle back so I though I would just get all new ones.
I have a spare pcb and plan to build a new one from scratch as this one is a little beat up. Since its the heart of the unit I would love to make any improvements I can.
00940 said:
00940
If you know, which I doubt 😉 until you can tell us with your own words
.. then why not tell me and others.
Why keep your secrets, if you are a sharing DIY Member.
What dicussion would be, if we always reply with a link to somebody who knows better
😀 😀
Actually, I have several great working Regulator circuits using 1nF - 10nF for feedback resistor.
This is why I think you may not be 100% correct.
Regards, Lineup
You could probably do a lot worse than to use the lm337/317 regulators or something on those lines.
Juergens comments are spot on.
It's a flawed design I'm afraid.
But don't let that put you off, things can only get better 🙂
Juergens comments are spot on.
It's a flawed design I'm afraid.
But don't let that put you off, things can only get better 🙂
I've wrestled with this board for many years now wanting to just replace the whole thing unless I could improve it. Kind of frustrated. The 744s sounded less grainy and smoother than the original opamps.
Since I'm building a new one with one of their pcb's I'm open to improvements. I had thought of just replacing it with a buffalo dac board/iv from Twisted but I can't find reviews on it apart from "sounds good".
Little frustrated. This grew from a lowly dac kit to a two box monster with dual mono for the analog, separate fils trans for the ps and the analog tubes, now 3 separate supplies for the dac board. Switchable to run off battery. Its pretty elaborate. The flaw has always been this board.
Since I'm building a new one with one of their pcb's I'm open to improvements. I had thought of just replacing it with a buffalo dac board/iv from Twisted but I can't find reviews on it apart from "sounds good".
Little frustrated. This grew from a lowly dac kit to a two box monster with dual mono for the analog, separate fils trans for the ps and the analog tubes, now 3 separate supplies for the dac board. Switchable to run off battery. Its pretty elaborate. The flaw has always been this board.
The aim of the power supply is to provide a stable output voltage independant of load variations, temperature, mains fluctuations etc.
Why not try the IC regulators ? Look up the datasheets and have a go.
Discrete regulators can perform very well, but you can't just throw a few bits together and hope it will outperform a device that's had 100's of thousands or more spent developing it.
Even easier, the 7805 and 7905 regs.
Why not try the IC regulators ? Look up the datasheets and have a go.
Discrete regulators can perform very well, but you can't just throw a few bits together and hope it will outperform a device that's had 100's of thousands or more spent developing it.
Even easier, the 7805 and 7905 regs.
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