Have you ever considered using a DOA (Discrete Op Amp)? There are some very good ones out there.
Why do you say that? Discrete opamps have never been easier to build. Granted, the king of audio FETs (Toshiba SK170, SJ74) have been discontinued, but you can find them all over eBay, including matched sets. Yes, more expensive, but easy to get. Don't write off discrete opamps!
LME49720 is still available, fortunately. I believe in both pdip and soic8 (in which case you could use an adapter to pdip).
There are a wide number of very excellent IC's out there, (never been a better time, in fact) especially if you're willing to solder soic8, which isn't that bad at all. Have a look at the OPA16XX opamps from TI, to start. One could almost standardize on the OPA164x for line-level applications and be pretty well squared away. Low noise, low distortion, excellent input impedance behavior, decent drive-capacity, jfet input. Not much more you need for general use.
Most DOAs are derived from so called 'classic' designs such as the Jensen 990 and API 2520. I have two favorites that I have settled on. When I want FETs I use a variation of the MOX circuit found on this forum and for BJTs I use the SGA-SOA2 by Samuel Groner. Both are excellent sounding. I have raw PCBs and finished versions on hand for both should you be interested. Schematics for both are online.
For a JFET solution: http://www.diyaudio.com/forums/analog-line-level/27651-mox-active-crossover.html
For BJTs I use an SGA-SOA2: Analog Circuit Design · Samuel Groner · Resources · Discrete OpAmps
They both plug into the legacy 2520 sockets established years ago in Pro Audio applications as do most commercial DOAs.
Carl,
I have a few spare PCBs to build the mox discrete opamp.
http://www.diyaudio.com/forums/grou...over-discrete-opamp-group-buy.html#post369900
send a PM if you are interested.
Does letter post get through customs in Brazil?
I have a few spare PCBs to build the mox discrete opamp.
http://www.diyaudio.com/forums/grou...over-discrete-opamp-group-buy.html#post369900
send a PM if you are interested.
Does letter post get through customs in Brazil?
Hi Andrew,
Thanks, but those pcbs had a 2SK389 at the input, which is expensive and rare nowadays.
They looked like very promising indeed.
Carlos
Carlos,
You can edit the PCB layout to accept NEC uPA68H matched FETs. Salas is doing that on his DCG3 preamp here on DIYAudio. I took his suggestion and mapped the uPA68H into the MOX op amp and configured the circuit as a 2520 DOA plug-in. It works very well.
AndrewT,
I appreciate your offer. The MOX project that you describe makes for a very nice active crossover. However in my case I have adjusted the packaging of the MOX op amp to be a '2520 plug-in' and recreated the Linkwitz-Riley circuit using them.
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The question is where to get them if they fail, and that's not so difficult to happen.
If I am not wrong, the uPA68H came in the top Luxman power amps from the early '90s. Superb amps. A friend of mine has one.
The dual FET was hard to find when it blew. It came on a piggy back board that Luxman used, sometimes encapsulated.
In the case of those discrete ICs that were mentioned, I got to get a schematic, This uses two K170s. and a trimmer to balance DC offset. It should drift, though.
A cap or DC servo might be necessary to block DC offset. But you can use higher voltages.
If I am not wrong, the uPA68H came in the top Luxman power amps from the early '90s. Superb amps. A friend of mine has one.
The dual FET was hard to find when it blew. It came on a piggy back board that Luxman used, sometimes encapsulated.
In the case of those discrete ICs that were mentioned, I got to get a schematic, This uses two K170s. and a trimmer to balance DC offset. It should drift, though.
A cap or DC servo might be necessary to block DC offset. But you can use higher voltages.
Attachments
These are the discrete ICs:
New Dual Channels Full Discrete Op Amp Module Replace OPA2604 LME49720 | eBay
New Dual Channels Full Discrete Op Amp Module Replace OPA2604 LME49720 | eBay
You can still find uPA68H as NOS (New Old Stock) if you go looking for it. You will pay roughly $2 each in small quantities. Of course the LSK389 is back in production, this time by Linear Integrated Systems.
The best place that I have found to buy them is here: https://www.trendsetter.com/Transistors-s/23000.htm
The best place that I have found to buy them is here: https://www.trendsetter.com/Transistors-s/23000.htm
Anyone like the Analog Devices op amps for audio?
I have used AD822 ,823 and 827
all have a unique sound and are quite different to audio op amps but mostly enjoyable (the AD827 is nothing special), the colouration makes them a lot of fun to explore.
although tonally inaccurate I feel these op amps can have very realisitic and immersive soundstage. possibly just distortion adding a ''realisitic'' effect but its sounds good nonetheless.
AD have a huge range of op amps, is there any others worth checking out?
I have used AD822 ,823 and 827
all have a unique sound and are quite different to audio op amps but mostly enjoyable (the AD827 is nothing special), the colouration makes them a lot of fun to explore.
although tonally inaccurate I feel these op amps can have very realisitic and immersive soundstage. possibly just distortion adding a ''realisitic'' effect but its sounds good nonetheless.
AD have a huge range of op amps, is there any others worth checking out?
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Evidently Burr-Brown. My impression is that both AD and Burr-Brown have been bought by TI so if you check TI's list you have many of the good items.
A bit more exotic in EU/US is Japan Radio Company (JRC). They also have very good OP-AMPS.
I am the trivial type mainly using NE5532, OPA2134 and LM4562.
A bit more exotic in EU/US is Japan Radio Company (JRC). They also have very good OP-AMPS.
I am the trivial type mainly using NE5532, OPA2134 and LM4562.