Kijanki, the technician knew that the AD818 is a video amp. He uses it on purpose because he says it´s faster. I´ll talk your recomendations with him. I suppose the decision of which one to use will be taken once he opens the poweramp and sees what the circuit is like. Thanks again! |
Input offset current is 11nA typ and offset voltage 0.1mV. Total of 0.3mV giving generous 10k unbalance. Gain after DAC is practically none. Sub 1mV offset might be a problem for some power amps but not for mine (5Hz-65kHz). |
Typical bias current for LM4562 is 10nA. Taking into account possible unbalance of 10k we get 0.1mV unbalance. Good, keep going. Calculate the effect of the input offset current based on the higher of the two source impedances, and add that. Then add the input offset voltage. Then multiply by the the sum by the DC gain of the circuit . . . you now have the number you're after. A mV or two of offset gets pretty scratchy-clackety on the source-selector and volume controls of a following preamp (provided they're DC coupled). Again, it COULD work fine if you change to DC output coupling to accompany your opamp sub (10nA is pretty low for a bipolar opamp) . . . but like any modification, a full analysis of the particular circuit as it pertains to your particular mod is required if you want to be confident of a positive outcome. |
Typical bias current for LM4562 is 10nA. Taking into account possible unbalance of 10k we get 0.1mV unbalance.
LM4562 has excellent AC characteristics but the sound is what matters. Benchmark uses it as a driver for XLR outputs because of the ability to drive 600 ohm (not necessarily because of sound). Getting rid of output cap would be a good thing but my Benchmark is still under warranty. NE5532 has bad rap on DIY forum - perhaps because it is so cheap. Somebody tried already replace NJM2068 with OP2132 and complained about metallic sound.
I do not have experience with LM4562 so I would not push for replacement of OPA627 or OPA2134 but original question was about replacement for NJM2068 - pretty old dual amp. Bias current runs here 150nA typ. and 1000nA max (it doesn't get much worse than that) - LM4562 is good candidate here. |
Change to LM4562 and you might be able to remove this cap. With emphasis on "might", like in bold print, or a big neon sign. The LM4562 is indeed a good sub candidate for the 5532, even though it's not for the TL072. And the 5532/5534 is definately not known for its DC performance -- I agree that most newer designs are much better. But the input bias currents of these medium-impedance bipolar opamps are far from negligible, and it is extremely rare to find balanced DC impedances in an audio opamp circuit that features an output capacitor - and this is what to look for (in addition to low DC gain) if you're planning on removing this capacitor in a circuit without a DC servo. I take it you're fond of this part for its sound quality . . . maybe I'll have to add it to my list of things to play around when I have some time. |
I was refering to Joaco post about power amp that has TL081. As for 5532, it depends - if it's thin sounding Philips amp I would replace it, but if it is TI amp I would leave it. But if your amp has 5532 it probably has output capacitor (like Benchmark DAC1). Change to LM4562 and you might be able to remove this cap.
Joaco - AD818 is a video amp. It could be used in audio applications (Rowland uses video amps in Capri preamp) but care must be taken. Pinout of the NULL pins is different so verify if NULL feature is used. In addition bias current is much higer. 100MHz bandwidth in not always a blessing. Wide bandwidth amps can often oscillate since small circuit capacitance at 100MHz can "eat out" phase margin. |
I was referring to the original poster's question - the OPA134 family is excellent, and I can see no reason to sub . . . other than the convienence of what parts one has lying around.
While I don't think the reason of "it's newer!" is in and of itself a valid reason for swapping opamps around, I am also very much NOT a fan of the TL0xx devices - they have an internal resistor in series with the output that can in many applications severely affect phase margin. But it's still a good idea to consider why they were chosen for the original design - and the same reasoning applies to the TL0xx opamps - they're FET-input, and the LM4562 is . . . not. So the current noise for an LM4562 will be MUCH higher than the TL0. A much better choice would be something like an AD845.
Also, with single opamps you generally have to be more careful with subbing - because of those extra pins. In the case of the TL071, it's still internally compensated, and the extra pins are just offset null or something - almost always unused in an audio application. But the PCB designer may still have routed a trace across an NC pin that's not NC on your sub, so you still need to check before you swap.
And something like the 5534 (unlike its dual-opamp brother, the 5532) has external compensation, so you DON'T want to sub around willy-nilly in this case - that and the 5534, despite its age, is still an outstanding opamp. |
What's wrong with using the original part? - without going into technical stuff let just say that Texas Instr. introduced this part in October 1976 and LM4562 was introduced around 2006. Not only 30 years difference but also TL081 was design as universal amp while LM4562 was designed specifically as an audio amp (with incredible DC spects). |
Generally, not a good sub. OPA2134 is FET-input (higher noise voltage, lower noise current) and NJM2068 is bipolar (higher noise current, lower noise voltage). This means that they're optimized for different circuit impedances.
What's wrong with using the original part? |
Joaco - TL081 is a single amp. It is very old and very cheap amp designed as a improvement over 741 type (one of the first op-amps). It is not an audio amp. LM4562 comes in single version with completely different number starting with LME.... - I have to check again. |
Kijanki, I recall he said they were 4 TL081. I´m sure he said they were 4 and not absolutely sure the model. I think the TL081 are the single versions og the TL082. Another technician advised me to use AD818. Do you know them? I have them in a DAC. Thanks for all the other advise. I´ll use it when I take it to the technician I choose. |
TL... is probably TL082 or 72 or 62 or something from this family (pretty bad for audio). If you can go with OPA2134 (dual) then go with LM4562 - it is exceptional amp. It is probably 8 pin DIP thru hole plastic package (2 rows 0.3" apart of 4 pins each 0.1" apart. Pinout of packages is standard - always the same. Both OPA2134 and LM4562 are dual and pinout is the same. Be sure that package is plastic DIP as I described a not a metal can. Metal can package (not very common) can be soldered into DIP (same order of pins) but not the other way around. LM4562 is available in all versions. When you change amps go for the best and most expensive. Few dolars more won't make any difference to you. It makes often difference to manufacturer but sometimes reason is different. They just simply cannot constantly change amps when new and better once are released (every year). It would require prototype testing over and over again and create nightmare in service. I suspect that they never change to better amps without a big reason. Design is treated as closed. Be sure to test your amp with cheap speakers. In spite of op-amps being stable there is always a chance as with any repair of bad solder joint or short - very small chance but still.. |
Thanks for the info, Kijanki! My technician advised me to change the opamps of a Hafler P3000 poweramp. I think he said it had TL... and advised to change them by the OPA 2134. As I started investigating a little bit, they seemed to be not the last word in audio opamps. I don´t know anything about electric nor physical configuration of them. Any other advise? Thanks. |
LM4562 is the newest audio amp from National Semiconductor (they got awards for it) intended for hi-end audio. It has excellent AC (THD=0.00003% IMD=0.00005%) and DC (0.2uV/degC) specifications. Unity Gain Bandwidth is 55MHz and slew rate is 20V/us. It work from 5V to 36V. Power supply rejection is excellent. It has pretty strong drive (600 Ohm specified). As for the known product - Benchmark DAC1 USB uses it in the output stages replacing previously (DAC1) used NE5532. Replacing all chips in Benchmark is probably too expensive for Benchmark ($5 for LM4562, $0.55 for NE5532) since there is a lot of them (about dozen packages) and NE5532 is very decent in the AC (pretty bad at DC).
It is difficult to talk about sonic character since I have never heard it (new product) and Benchmarks design objectives are very specific (promoting natural sound and avoiding warm sound). My audio experience is also very limited.
How it compares to OPA627 - I don't know. According to Benchmark's technical director John Siau they tested OPA627 and got worse results than NE5532. Mr Siau even stated in details which harmonics got worse. On the other hand Steve from Empirical Audio who moded a lot of Benchmarks says that OPA627 is better since it performs better/cleaner at low levels (microdynamics). Steve is probably the person to answer question about sonic characteristic of LM4562.
OPA627 is, as far as I know, a single package amp while LM4562 is dual amp available in DIP, Metal Can and SOIC (SMT) packages from Digi-Key for about $5. LM4562 is very good at AC and DC and having wide banwidth and wide supply range can replace any audio op-amp in the dual package. I think that National created also single packages but with different part number - I can find out.
Word about NE5532 - it was initialy designed by Signetics. Signetics became member of Philips Company and early Benchmarks used thin sounding Philips NE5532. Around year 2001 Philips factory burned down and they stopped making NE5532 selling license to Texas Instruments. TI redesigned them with larger die and the newer Benchmarks that use them have much fuller sound. Benchmark has output cap since NE5532 has pretty bad DC offset and drift.
In general audio OP-Amps are a very narrow class of all OP-amps. If you're not sure if amp belongs to this class download data sheet in pdf and check for THD vs Frequency and THD vs Output Voltage charts. Don't even bother if you don't see it. |
Kijanki, can you please tell us about the LM4562? Which are its sonic characteristics? Is it used in any known audio product? Is it better than the OPA 627 as well? Thanks. |
I'm not sure about repair cost but he is offering very old op-amp not even half as good as OPA2134. I suspect he might have this amp handy. My advice is to replace it with LM4562 - much better amp than both. Be sure to replace it in both channels - this is dual amp but might have both amps in one channel. LM4562 can be purchased from Digi-Key for about $5. Be sure to order right suffix (DIP, SOT8 ...). OPA627 is a single amp (won't fit).
If you still want to go with NJM2068 ask this guy about supply voltage since OPA2134 starts at 5 volt minimum while NMJ2068 starts at 8V minimum.
NMJ2068 datasheet looks pretty old. They claim better performance than 4558 type amps. Nobody remembers Rayteon 4558 since it was designed/used more than 20 years ago. |
Amdb9, aren´t you meaning the OPA 2134? I´m not into opamps but I know that one is one of Burr Brown´s usually used ones. Another one that is better for some and not for others is the OPA 627.
Give us your feedback when you are done. I´m thinking of changing opamps in a Hafler poweramp. |
HI Amdb9,
I checked the web, and couldn't find anyone, but a place in australia that was selling the 2143, so it's either out of production, or scarce. I couldn't find it on the TI website either. So your repair guy's apparently found a suitable replacement..as for the sound, it's hard to say how it will effect it. If he's an experienced audio tech, then he should know whether these parts sound good, or whether another currently avaiable burr brown op amp would be a good substitute. What's the tech's hourly charge, most shops will have this posted prominently. It might take 30 minutes to replace the parts, or an hour and a half to replace the parts (depends on how easy the parts are to get to). Then the thing will have to be bench tested, and burned in -- just to make sure the new parts are okay. It's been so long since I've had any equipment repaired, I don't know what's being charged lately -- but don't expect it to be cheap. How much is the "estimate" ??
Good luck. |
