I would like to replace this dual op amp with new op amps but it has some features I am not familiar with and I having difficulty find sutitute(s). I'm not looking for pin to pin replacement.
Look at the LAG PINS, it seems to have more in's and out's than a typical op amp. I'm used to Vin+ Vin- and Vout+ Vout-
Cheers,
Shawn.
Look at the LAG PINS, it seems to have more in's and out's than a typical op amp. I'm used to Vin+ Vin- and Vout+ Vout-
Cheers,
Shawn.
Attachments
uA739
from the data sheet of the uA739:
These three stage amplifiers use Class A PNP transistor output stages with uncommited collectors
Uncommitted colectors! I guess the uA739 has extra connection possibilities that are tied up and committed inside of a regular op amp. Can we eliminate some of this external circuitry knowing it already exists inside the modern op amp version? Or is it critical to this particular circuit?
Pin for pin replacement is way out of the question.
Shawn.
from the data sheet of the uA739:
These three stage amplifiers use Class A PNP transistor output stages with uncommited collectors
Uncommitted colectors! I guess the uA739 has extra connection possibilities that are tied up and committed inside of a regular op amp. Can we eliminate some of this external circuitry knowing it already exists inside the modern op amp version? Or is it critical to this particular circuit?
Pin for pin replacement is way out of the question.
Shawn.
Has the uA739 gone bad, or are you looking for an upgrade?? They can still be found as old new stock, usually on dusty backroom shelves. Other comparable numbers are MC1303 and ECG725 (not to be confused with the uA725). An NE5532 would probably work as well in the application with some circuit tweaking (basically removing the components unique to using the 739, e.g. Q119, C102, D111, etc). There isn't really enough of the surrounding circuit in your pic to know for sure in terms of oscillation issues though. The 5532 also draws a bit more current, though I doubt that'd be an issue. If it were me, I'd just replace the 739 if it's gone bad. I don't think I'd bother trying an upgrade. I sort of liked the sound of the 739 in its day anyways, though yes, it is obsolete by current standards.
Hi Tomwaits,
have you read the WJung series on cascading opamps to get the benefits of superlative input/voltage amp parameters combined with the excellent current ability of a buffer on the output.
eg. a FET opamp driving 75ohm terminated cables using a buffer.
Extrapolate that practical advice to an ICopamp input into a power amplifier used as the buffer and you have the makings of excellence while sticking sort of loosely to the Crown philosophy.
At bit at odds with my vote to rebuild the DC300, but close(ish).
I am thinking about (I do too much thinking and not enough making) modifying my Sugden P128s to exactly this. They have separated stages, 5534 input followed by the power amp. I would like to hear the benefit of integrating the amplifer with the input opamp as Jung.
have you read the WJung series on cascading opamps to get the benefits of superlative input/voltage amp parameters combined with the excellent current ability of a buffer on the output.
eg. a FET opamp driving 75ohm terminated cables using a buffer.
Extrapolate that practical advice to an ICopamp input into a power amplifier used as the buffer and you have the makings of excellence while sticking sort of loosely to the Crown philosophy.
At bit at odds with my vote to rebuild the DC300, but close(ish).
I am thinking about (I do too much thinking and not enough making) modifying my Sugden P128s to exactly this. They have separated stages, 5534 input followed by the power amp. I would like to hear the benefit of integrating the amplifer with the input opamp as Jung.
Hi,
uA739 had an internal resistor to the - supply , uA749 had no connection so the resistor was mounted on the PCB. However, some manufacturers were smart (Marantz 3600 / 3800) and used a constant current source instead in this location. This made the stage far more linear and lowered the distortion.
So, to use a normal op amp, remove all the "lag" components and any pull down resistors if they exist. Compensate the op amp and go. With this amp you may or may not need an op amp that can deliver some current, or a buffer stage. I have never tried this as I've always put in the original. They can tend to go very noisy over time.
-Chris
They look like a current boost for the output.
uA739 had an internal resistor to the - supply , uA749 had no connection so the resistor was mounted on the PCB. However, some manufacturers were smart (Marantz 3600 / 3800) and used a constant current source instead in this location. This made the stage far more linear and lowered the distortion.
So, to use a normal op amp, remove all the "lag" components and any pull down resistors if they exist. Compensate the op amp and go. With this amp you may or may not need an op amp that can deliver some current, or a buffer stage. I have never tried this as I've always put in the original. They can tend to go very noisy over time.
-Chris
Hi Tom,
saving you some Googling:-
http://waltjung.org/PDFs/ADI_2002_Seminar_Ch6_Audio_Drivers_I.pdf
http://waltjung.org/PDFs/WTnT_Op_Amp_Audio_1.pdf
http://waltjung.org/PDFs/WTnT_Op_Amp_Audio_2.pdf
http://waltjung.org/PDFs/WTnT_Op_Amp_Audio_3.pdf
http://waltjung.org/PDFs/WTnT_Op_Amp_Audio_4.pdf
http://waltjung.org/PDFs/Composite_Line_Driver_with_Low_Distortion.pdf
http://waltjung.org/PDFs/ADI_1992_Seminar_Audio.pdf
http://waltjung.org/PDFs/Op_Amps_in_Line_Driver_and_Receiver_Circuits_P2.pdf
http://waltjung.org/PDFs/ADI_1993_Seminar_Audio_Drivers.pdf
The first is an extract from the ICopamp tome. Worth downloading the whole document if you are interested in the gospel according to the various experts (edited by Walt).
The last three are older documents that look in more detail at what Walt is trying to achieve.
I think all of this is transferable to ICopamp+power amp as a composite pair.
Sorry to be adding to any confusion, Walt calls them composite, I suppose I should conform.
saving you some Googling:-
http://waltjung.org/PDFs/ADI_2002_Seminar_Ch6_Audio_Drivers_I.pdf
http://waltjung.org/PDFs/WTnT_Op_Amp_Audio_1.pdf
http://waltjung.org/PDFs/WTnT_Op_Amp_Audio_2.pdf
http://waltjung.org/PDFs/WTnT_Op_Amp_Audio_3.pdf
http://waltjung.org/PDFs/WTnT_Op_Amp_Audio_4.pdf
http://waltjung.org/PDFs/Composite_Line_Driver_with_Low_Distortion.pdf
http://waltjung.org/PDFs/ADI_1992_Seminar_Audio.pdf
http://waltjung.org/PDFs/Op_Amps_in_Line_Driver_and_Receiver_Circuits_P2.pdf
http://waltjung.org/PDFs/ADI_1993_Seminar_Audio_Drivers.pdf
The first is an extract from the ICopamp tome. Worth downloading the whole document if you are interested in the gospel according to the various experts (edited by Walt).
The last three are older documents that look in more detail at what Walt is trying to achieve.
I think all of this is transferable to ICopamp+power amp as a composite pair.
Sorry to be adding to any confusion, Walt calls them composite, I suppose I should conform.
Symmetry
Thanks
Mr.T where is your avatar? You look kind of skinny without it. You Ma's getting worried and she's going to start sending cookies in the post.
Shawn.
Before I give this a try I still have to deal with the non symmetrical part of the circuit. I'm a little lost with the change in symmetry from the left channel to the right channel? Picture down below.anatech said:
AndrewT said:
Thanks
anatech said:Hi Andrew,
Always the librarian!Thanks.
That would be a good avatar for you.
-Chris
Mr.T where is your avatar? You look kind of skinny without it. You Ma's getting worried and she's going to start sending cookies in the post.
Shawn.
Attachments
ua739
I guess I see the ua739 as a design flaw. I see an engineer obsessing over some new technology and going off-the-rails to design it in to his work. It is signature and I think it is the only weak spot in the amp, if you want to call it a weak spot; some do, some don't. Overall the amp is not weak by any stretch.
If I put Humpty Dumpty back together why not breathe in some new life. It could provide some other DC300A's a possible upgrade path. There are many DC300's out there and they can be had cheap. What a great power amp to mess with without investing too much. I don't want to do this but I feel I have to do it. I think the ua739 and it's support components give the DC300A a particular sound that many frown upon. I can't be certain and the only way to find out is to displace it and there are many fine opamp's on the market now.
Cheers,
Shawn.
hughmon said:
I guess I see the ua739 as a design flaw. I see an engineer obsessing over some new technology and going off-the-rails to design it in to his work. It is signature and I think it is the only weak spot in the amp, if you want to call it a weak spot; some do, some don't. Overall the amp is not weak by any stretch.
If I put Humpty Dumpty back together why not breathe in some new life. It could provide some other DC300A's a possible upgrade path. There are many DC300's out there and they can be had cheap. What a great power amp to mess with without investing too much. I don't want to do this but I feel I have to do it. I think the ua739 and it's support components give the DC300A a particular sound that many frown upon. I can't be certain and the only way to find out is to displace it and there are many fine opamp's on the market now.
Cheers,
Shawn.