Swapping opamps in a WM12, worth it?

[Treb]

I've been doing some reading on opamps. I've found that there are better opamps than the (six) TL072's that are in my first generation WM12. The OPA2604 is mentioned as a drop-in replacement and a better sounding one too. The OPA2604 advertised as: Very low distortion, low noise and wide bandwidth provide superior performance in high quality audio and other applications requiring excellent dynamic performance.

Anyone ever done such a modification? Any improvements to be gained? Worth the money and trouble?

[Passinwind]

Before you do this, please Google "OPA2604 instability" and make sure you understand why this is not a straight drop-in replacement part. Works OK in many circuits, but could be catastrophic in others. Be sure to check circuit integrity with an oscilloscope if you do the swap. Also be aware of the increased current draw, which might be a deal breaker in some cases.

After you sort that out, will it sound better? Maybe, maybe not. FWIW, I have found that I generally prefer OPA2132 to OPA2604 by a little in most of the stuff I've tried both in.

best,

--------CE

[12bass]

Originally Posted by Treb

I've been doing some reading on opamps. I've found that there are better opamps than the (six) TL072's that are in my first generation WM12. The OPA2604 is mentioned as a drop-in replacement and a better sounding one too. The OPA2604 advertised as: Very low distortion, low noise and wide bandwidth provide superior performance in high quality audio and other applications requiring excellent dynamic performance.

Anyone ever done such a modification? Any improvements to be gained? Worth the money and trouble?

IME, replacing op-amps can produce a very audible improvement in the sound of some gear. There are some issues to consider before doing such a swap, however. Stability of high-performance parts is one issue (noted above). Stability problems can often be addressed by using small capacitors between the op-amp's power leads and ground. Also, most of the higher quality chips use more current, so you might need to look at the ability of the amplifier's power supply to provide enough current without sagging under the increased load.

Op-amps I have tried which should work as a drop-in in your application include the TLE2072, OPA2134, OP2604, and AD823 (all FET input). I also like the LM4562 quite a bit (most transparent op-amp I've found), but it can be tricky in some TL072 circuits because it is bi-polar, whereas the TLO72 is FET. I've found that the sound of any given op-amp depends on the surrounding circuit, although they do tend to have certain identifiable sonic characteristics. One nice thing about the TLE2072 is that it only uses slightly more current than the TLO72, but sounds more lively overall.

What sort of improvement are you after?

[PilbaraBass]

TL072, IMO is not a bad opamp, and given the application, can perform quite well.

If OPA2604, is truly a drop-in replacement, then yes these do have better signal-noise specs than TL072 and more importantly, faster slew rate (that's where most harmonic distortion comes from, slow response time).

You have to make the decision, will the cost of 6 Brown-Burr OPA2604 chips improve the sound quality to your liking on the WM12....6 of them will set you back about $25-$35...

12bass critique of the TLE2072 is interesting...they draw a slight bit more power than the TLO72, but that in turn gives you a faster opamp...they're also 2/3 the price of the OPA2604

[mikeboth]

Originally Posted by Treb

Worth the money and trouble?

If the ICs are in sockets, doubtful; if they aren't, then no - IMHO. Bass isn't exactly a hi-fi application, and any improvements in dynamic response would be minimal at best.

I'm not sure I'd want a 'clearer' sound from *my* rig (Yamaha PB1 preamp stuffed full with 4558 opamps) anyway - is that what you are after.

[12bass]

My recent project has been improving the sound of my Eden WT-500 bass amplifier. To that end I've replaced most of the electrolytics in the signal path with film capacitors and bypassed those which could not be replaced. I've also replaced the (8) murky sounding TL072s with (6) LM4562s and (2) TLE2072s. Two of the sockets seem to work best with FET input op-amps, so I've used the TLE2072s there, with the LM4562 in all of the other positions. I've also removed some of the high frequency roll-off to extend frequency response from 12 kHz to 20 kHz, as well as changed the overall gain structure to reduce noise. Overall, I think it sounds quieter, and far more open and natural.

Whether such an endeavor is worthwhile will depend on how particular one is about their tone....

BTW, the OPA2604 didn't wow me, especially considering the price.

[mikeboth]

Originally Posted by 12bass

Whether such an endeavor is worthwhile will depend on how particular one is about their tone....

I'm particular about my tone - however, I doubt I *personally* would find much benefit in extending the frequency response of a bass amp to 20kHz from 12kHz. On my rig I imagine this would just let more noise through.

I think the OP is only going to know if it's worth it or not AFTER he's done it.

[12bass]

Given that I have a Pedulla Rapture with a Q-Tuner and Lane Poors in my Hamer Chaparral 12, I think extending the frequency response to 20 kHz is worth it for me. I'm starting to think I might want a more hi-fi cabinet though....

That said, I think that better op-amps can significantly improve the sound. When I swap out a TLO72 or NE5532 for an LM4562, the increased clarity is instantly noticeable. All of the sudden I can hear subtle nuances like the ringing harmonic overtones of the roundwound strings.

[Treb]

Thanks for all your input, much appreciated. First off, I'm not an electronics whiz, hence the need for a drop-in replacement preferably without the need of soldering skills.

I found a webpage that mentions a power consumption of 12 mA for a OPA2604 whereas a TL072 only takes 4 mA. That's quite a bit more current for the OPA2604. The TLE2072 sounds interesting though, its datasheet states it's a direct upgrade to the TL07x opamps.

I'm looking for a general improvement in sound quality.

[Trevorus]

Well, I have to talk about this one a bit. I had a Conklin GT-4 bass with a mighty-mite preamp system. It had a TL072 in it, and I never liked the sound. The TL082 had the same pinout, though it drew more current. At the really low draw of the circuit anyways, I didn't think it would be an issue. Turns out it wasn't, and I liked the TL082 MUCH better overall.

[PilbaraBass]

Originally Posted by Trevorus

Well, I have to talk about this one a bit. I had a Conklin GT-4 bass with a mighty-mite preamp system. It had a TL072 in it, and I never liked the sound. The TL082 had the same pinout, though it drew more current. At the really low draw of the circuit anyways, I didn't think it would be an issue. Turns out it wasn't, and I liked the TL082 MUCH better overall.

generally speaking, for FET opamps, if they draw a little more current, they generally have a faster slew rate...it's the slew rate that will be the most important in determining the sound quality of the opamp....the more volts per unit of time, the better.

[mikeboth]

Originally Posted by PilbaraBass

generally speaking, for FET opamps, if they draw a little more current, they generally have a faster slew rate...it's the slew rate that will be the most important in determining the sound quality of the opamp....the more volts per unit of time, the better.

With the data sheets I have the TL082 has typical slew rate of 13V/us, and the Tl072 is exactly the same. Noise characteristics are slightly better for the TL072 ... but all of this stuff is 'golden-ears' in magnitude to *my* way of thinking / experience.

I'm sure my bias is because I once bought 1000 4558s for about a cent each and still have plenty in stock for building stuff with. Need a dual opamp? Use a 4558.

[Passinwind]

Originally Posted by unbeliever

With the data sheets I have the TL082 has typical slew rate of 13V/us, and the Tl072 is exactly the same. Noise characteristics are slightly better for the TL072 ... but all of this stuff is 'golden-ears' in magnitude to *my* way of thinking / experience.

I'm betting he actually meant TL062 vs either 072 or 082. TL062 is common in low voltage battery powered applications. But individual chips from any of those families could have better performance than a bummer one from any other family.

I'm sure my bias is because I once bought 1000 4558s for about a cent each and still have plenty in stock for building stuff with. Need a dual opamp? Use a 4558.

I have tons of pulled 4558s kicking around my shop. They work OK in some things, not so much in many others though. Bill Thompson at Ashly posted in another forum about how guys were subbing expensive chips into his gear in place of 4558s and actually hurting performance in some cases. As I said above, at the very least I'd use a scope to confirm that you haven't made things worse anytime you do a substitution. I actually test noise and distortion these days too sometimes, since it's so easy to do nowadays with a computer.

[Stuggi]

I've used the OPA2134 in a lot of circuits, andall I can say it that it's next to impossible to design something where it won't work. It's gain-stable and very nuclearproof OPA2132.

Generally, any of Burr-Browns OPAX1XX would be fine as long as it has enough opamps in the package (first X, so the OPA2132 has two opamps of model 132 in the same package)

[Treb]

I found that the TLE2072 draws a lot less current (1.8 mA per channel) than the OPA2604 and has a much higher slew rate (45 V/microsecond) than the stock TL072 opamps (13 V/microsecond).

I'm gonna see if I can lay my hands on six TLE2072's locally this afternoon.

[PilbaraBass]

Originally Posted by Treb

I found that the TLE2072 draws a lot less current (1.8 mA per channel) than the OPA2604 and has a much higher slew rate (45 V/microsecond) than the stock TL072 opamps (13 V/microsecond).

I'm gonna see if I can lay my hands on six TLE2072's locally this afternoon.

they're cheaper than the 2604's, too...

[Mark Reccord]

There's also the AD OP275 and 285. Both unity-gain stable and pretty transparent. I'm a big fan of the LM4562 and OP2134 as well. Like Stuggi said, the 2134 is quite stable under most conditions and as a bonus because its input bias current is so low it hardly generates any DC offset even with considerable gain and less than ideal Req.

I recently got my hands on some AD8599 low noise dual opamps and they're very promising. I'm in the process of designing a phono stage and I've pretty much decided on 8599s. They offer noise characteristics previously only seen in single channel devices and sound very transparent to boot. Don't think they're on the market yet, though.

[12bass]

I've got the OP275 and AD8599 here as well....

At first I liked the sound of the OP275, (it seemed to add a nice character to the bass) but after a while I found it exhibited some odd tonal characteristics. I'm not sure how to describe it exactly, but it almost sounds like it compresses or distorts in an odd way. Maybe it's the Butler front end??? After a while I grew to dislike the colored sound of the OP275. I was impressed by the improvement found in replacing the OP275 in my RNC with an LM4562. IMO, the RNC sounds more natural and open now. The LM4562 remedied the previously veiled highs when engaged.

As for the AD8599, I've tried it in various sections of my Eden WT-500's preamp and also in the RNC. From what I can tell, it sounds fairly natural, and less noticeably colored than the OPA2134 (which I find does something odd with the dampened sounding highs), but not quite as transparent as the LM4562. So, I'd take the AD8599 over the OPA2134 or OPA2604. Still, from my limited testing, I prefer the LM4562 - it sounds more like straight wire to my ears.

[alexclaber]

Whilst there is a host of opamp experts present, what would y'all suggest for the filter opamps and the input and output buffer opamps in this active crossover design (planning to DIY for my bass rig):

http://sound.westhost.com/project09.htm

I'll have an Avalon U5 feeding it and the high and low outputs running into a QSC PLX. I think I'll be simply unbalancing the U5 output by wiring the XLR to a TS 1/4".

Thanks!

Alex

[Mark Reccord]

Originally Posted by 12bass

I've got the OP275 and AD8599 here as well....

At first I liked the sound of the OP275, (it seemed to add a nice character to the bass) but after a while I found it exhibited some odd tonal characteristics. I'm not sure how to describe it exactly, but it almost sounds like it compresses or distorts in an odd way. Maybe it's the Butler front end??? After a while I grew to dislike the colored sound of the OP275. I was impressed by the improvement found in replacing the OP275 in my RNC with an LM4562. IMO, the RNC sounds more natural and open now. The LM4562 remedied the previously veiled highs when engaged.

As for the AD8599, I've tried it in various sections of my Eden WT-500's preamp and also in the RNC. From what I can tell, it sounds fairly natural, and less noticeably colored than the OPA2134 (which I find does something odd with the dampened sounding highs), but not quite as transparent as the LM4562. So, I'd take the AD8599 over the OPA2134 or OPA2604. Still, from my limited testing, I prefer the LM4562 - it sounds more like straight wire to my ears.

So far, tonally I like the 4562 best for clarity as well, very neutral, at least in a dual device. However, it can't touch the 8599 in terms of noise and when you're looking at 70-odd dB of gain, that's really important. The AD797 is probably the best of both worlds. Very neutral, very low noise but it's prone to oscillation, it's a single channel and it's expensive as hell.

I really like the 2134 too, but for different reasons. It's got a bit of a tube-ish quality to it, maybe a bit rolled off in the top end.