I hope this is the correct forum for asking for help with an Op Amp ? I recently bought a genuine Lehmann Audio Black Cube Linear Headphone Amplifier with some modifications. Mods include a larger transformer, Mundorf capacitors and some circuit changes, but most intriguing is the op amp has been replaced with what appears to be two Burr Brown op amps on a carrier. The text reads BB (Burr Brown logo) and SL232 but I can't find any info on this on-line. It's possibly an older amp ? It comes as stock with an OPA2134 which isn't bad at all, so I'm surprised it's been replaced.
Any info much appreciated.
Any info much appreciated.
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Many thanks ! I've just checked and there's a pair of OPA111AM op-amps.
There's a chap here discussing them: https://rockgrotto.proboards.com/thread/6842/give-whirl-opa111 His are marked UK but mine have a USA stamp, the same 2-1 mounting board. Basic details here: https://uk.farnell.com/texas-instruments/opa111am/op-amp-difet-precision-to-99-111/dp/1097523
The reason I'm interested in these is the second hand, modified, Lehmann BCL amp with these in I recently bought sounds noticeably better than my Burson Soloist 3X GT ! I'll try some other op-amps and see how the amp sounds with those, it might just be the Lehmann is better sounding or the op-amps really do make the improvement.
There's a chap here discussing them: https://rockgrotto.proboards.com/thread/6842/give-whirl-opa111 His are marked UK but mine have a USA stamp, the same 2-1 mounting board. Basic details here: https://uk.farnell.com/texas-instruments/opa111am/op-amp-difet-precision-to-99-111/dp/1097523
The reason I'm interested in these is the second hand, modified, Lehmann BCL amp with these in I recently bought sounds noticeably better than my Burson Soloist 3X GT ! I'll try some other op-amps and see how the amp sounds with those, it might just be the Lehmann is better sounding or the op-amps really do make the improvement.
Strange choice is that one. It looks like quite a 'slow' device for audio (poor slew rate and very poor full power bandwidth). Its uses lie elsewhere in very specialised applications. It also has very limited output drive ability.
The opamp rollers have been at it! Even one of the heatsinks is upside down.
However I note the OPA111AM can drive 1nF of capacitive load directly - not many opamps can do that. Perhaps stability was an issue without series resistance on the output (which degrades damping factor).
However I note the OPA111AM can drive 1nF of capacitive load directly - not many opamps can do that. Perhaps stability was an issue without series resistance on the output (which degrades damping factor).
Opamp rolling and then judging them by ear seems the favorite pastime of persons that "just want to do something".
Anyway there are many opamps suitable for use in the Lehmann Audio Black Cube Linear. Like the quite good OPA2134 Lehmann used in it 🙂
Anyway there are many opamps suitable for use in the Lehmann Audio Black Cube Linear. Like the quite good OPA2134 Lehmann used in it 🙂
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Indeed, that's what's going back in. I suspect the previous owner had those in his spares and decided to have a go.
But it does sound very good. One thing I did hear is what sounds like digital artefacts, mainly at higher frequencies and only at very high volume, which I thought was the improved resolution of the amp showing poor recordings but now might just have been the op-amp limiting the quality, maybe distortion or noise. The bass was better than my Burson Soloist with the Burson V6 op-amps, the midrange was less coloured and forward and the treble about the same apart from a sort of halo effect around louder, high frequencies. If you only listened to organ music it would be a useful ap-amp to have !
But it does sound very good. One thing I did hear is what sounds like digital artefacts, mainly at higher frequencies and only at very high volume, which I thought was the improved resolution of the amp showing poor recordings but now might just have been the op-amp limiting the quality, maybe distortion or noise. The bass was better than my Burson Soloist with the Burson V6 op-amps, the midrange was less coloured and forward and the treble about the same apart from a sort of halo effect around louder, high frequencies. If you only listened to organ music it would be a useful ap-amp to have !
They are going for big money... if you can actually sell them. £100+ 😱
Only you can decide if you really like them or not. A scope check on the output would be useful to see if they are clipping and if they are stable.
Wow.. then again, given that at modest volume the Lehmann beats the Burson, maybe I'll keep them. I will get the scope on the output, maybe that's a job for this evening before I swap them out. I'm also swapping parts on a Whammy headphone amp and that's got a 5532 currently, but overall it's not a patch on the Lehmann.
I only got it a few days ago 🙂 To me, the ultimate measure of an amplifier is how it sounds. If the OPA111 does have a low slew rate or maybe higher noise, but it still makes the lower frequencies sound so good, then that's possibly part of the compromise which makes it a winner and audio so much fun.
Well worth scoping. If the opamp drives additional output transistors then the limited drive ability may be of little importance, if it drove them directly (which many opamps can achieve) then it would be struggling I suspect.
Absolutely. Used correctly and within their performance envelope and the old TL071/72/74 series of opamps can sound excellent. Don't discount those until you have tried them.
Gain-bandwidth, slew rate, etc. were not the major design points here. This is where the money is:
You're quite unlikely to find a modern opamp that has been 100 % tested for noise down to 10 Hz and if you do, expect to pay through the nose for it. Measuring 1/f noise takes forever (several tenths of seconds) which makes that a very expensive test.
Also note the space grade 'SM' version. I bet that would fetch a pretty penny on the used market.
The 5.5 mA (worst case) output current would mean that this part would be challenged in many audio circuits.
There's something to be said for that. "They don't make 'em like they used to". Yeah... Sometimes there are good reasons for that. But there are also exceptions.
For example, the OPA627 is an amazing opamp. It offers very low distortion and is well liked by the subjectivists. In SOIC it runs about $30/each as I recall. In the (now obsolete) DIP and TO-99 versions it'll set you back $60-100/each. The OPA627SM space grade sets you back $150ish/each.
Also, as we discussed over here, the NE5532 is still a very good opamp, especially considering it launched in 1979. I'm not sure I would use it today in a new design, but I also wouldn't slam anyone who did. You sure get a lot of audio performance for your ~$0.15/each (reel quantity).
The OPA111 here seems to follow the 4 Os, though. It strikes me as an "ooh! special!" type of modification.
You wanna be a bit careful with random opamp swapping, especially with discrete opamps. Even though many of them are unity gain stable, they're often only stable near unity and will have severe ringing and overshoot if used away from unity gain, for example in phono stages. I give some examples here:
Tom
Indeed so. I'm also looking at the date on the data sheet... 1984, so it really is quite an oldie.
Totally the right features/specifications for the wrong application 🙂 This is not an audio opamp, it is a 741 on steroids for precision instruments.
It would have been an adequate measure to have a different pinout for specialty opamps to prevent swapping in both directions (like red bank tubes versus normal) tubes.
It would have been an adequate measure to have a different pinout for specialty opamps to prevent swapping in both directions (like red bank tubes versus normal) tubes.
Somewhat curiously the data sheet gives an RIAA front end as an application which might have been interesting back in the day but yes, I agree its not what we would tern an audio opamp. A TL071 would be much more capable.
The boys at BB always had a weak spot for audio 🙂 I would not advise to use it in a headphone amplifier though as it is wimpy with regards to output current and by far not RRO. +/- 12V output voltage (minimum +/- 11V even) at +/- 15V supplies. Typical 10 mA output current and a minimum of 5.5 mA so it would not even drive a 1984 LED. Maybe that explains the artefacts at higher volume?! There are better opamps for that purpose it seems.
Got some new OP90 and OP77 for free. Same story. Very nice parameters for non audio.
Got some new OP90 and OP77 for free. Same story. Very nice parameters for non audio.
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A lot of that is copy-n-paste by the applications engineer without much thought, though. For ages the National Semiconductor audio data sheets showed a tape head preamp. Now the RIAA stage is the audio darling, even in the LM4562 data sheet even though the LM4562 isn't a super hot candidate for a phono stage due to its higher current noise.
Tom