I'm looking for the most suitable, commonly available op amp for driving a 600 ohm 1:1 ratio output transformer. I prefer to be able to drive it cleanly to +10 dB.
There's obviously the NE5532, but the distortion is too high for my tastes. The 4580 comes to mind, but that one isn't the best in terms of slew rate, despite the low impedance capability.
Any suggestions?
There's obviously the NE5532, but the distortion is too high for my tastes. The 4580 comes to mind, but that one isn't the best in terms of slew rate, despite the low impedance capability.
Any suggestions?
The output transformer will have at least an order of magnitude more distortion than an NE5532. Do you mean +10dBu or +10dBV ? The NE5532 can drive 600 ohms at its full swing with little degradation of distortion. Its basically what it was designed for.
@Mark Tillotson I was actually aiming for +20dBu. That was about the max out of the NE5534 running 18V rails into 600 ohms.
While this is an acceptable application, I wanted cleaner performance without needing fancy coupling caps, which is the case with higher end transformers.
The transformers I chose.have considerably lower HD than most caps with most residual HD being mostly even order type. They're the Jensen high permalloy model JT11-DMCF and have extremely low HD throughout their bandwidth. I measured F-3 points to be 3 hz - 500 kHz into 600 ohms with virtually no phase shift in the 10 hz - 40 khz BW.
I wanted something a little cleaner than NE5532/34 and SSM4122/DRV134. I was going to try discrete buffers, but these can be higjly dependent on circuit layout.
While this is an acceptable application, I wanted cleaner performance without needing fancy coupling caps, which is the case with higher end transformers.
The transformers I chose.have considerably lower HD than most caps with most residual HD being mostly even order type. They're the Jensen high permalloy model JT11-DMCF and have extremely low HD throughout their bandwidth. I measured F-3 points to be 3 hz - 500 kHz into 600 ohms with virtually no phase shift in the 10 hz - 40 khz BW.
I wanted something a little cleaner than NE5532/34 and SSM4122/DRV134. I was going to try discrete buffers, but these can be higjly dependent on circuit layout.
OPA1655 (dual is OPA1656)
Has low distortion and 100mA output.
It is in SOIC, not through hole.
Has low distortion and 100mA output.
It is in SOIC, not through hole.
The transformer will dominate distortion, there is no point going for better opamp THD if they are far better than the magnetics anyway. The JT11-DMCF graphs show 0.03% distortion or so at 600 ohms source impedance, upto 5dBu or so, then rising to 0.3% or so at 20dBu.
what are the actual target specs? sounds like you have ideas for distortion and slew rate at least...
Running the two halves of the 5532 in parallel will reduce distortion into 600R, an added benefit is a reduction in noise.
Yes, driving true 600 ohm load will make distortion worse. The 0.03 is worst case scenario for the average levels I'm pushing. Thats about 2 - 4V leaving some headroom. I want flat phase from 10 hz - 40 kHz without any noticeable loss in low end. Most gear speced at -3 dB limits starts rolling off well before those points. In the case of an.F-÷3 limit of 10 hz, the rolloff starts already at 30 hz which is noticeable.
I'm actually driving a 5k load. The main purpose of having the xformer is to have a balanced signal coming from the crossover buffer. Thats the circuit which drives the xformer, which also serves as a DC blocking point.
Doing both halves of a 5532 is a good idea, but in theory also doubles noise. 4nV/hz isn't much and isn't that noticeable, but it can be with high sensitivity drivers.
I'm actually driving a 5k load. The main purpose of having the xformer is to have a balanced signal coming from the crossover buffer. Thats the circuit which drives the xformer, which also serves as a DC blocking point.
Doing both halves of a 5532 is a good idea, but in theory also doubles noise. 4nV/hz isn't much and isn't that noticeable, but it can be with high sensitivity drivers.
A couple of others that might suit your needs would be the OPA891, 12V/200 ma into 250 ohms, and if no gain is needed - LMH6321 - 12 V/300ma into 50 ohms.
Though if galvanic isolation is not needed and the money for a transformer hasn't been spent, then maybe a THAT 1646 Balanced Line Driver could be used. It would meet your THD requirements. The noise level is a bit higher than the JE-990/OPA891 options.
Though if galvanic isolation is not needed and the money for a transformer hasn't been spent, then maybe a THAT 1646 Balanced Line Driver could be used. It would meet your THD requirements. The noise level is a bit higher than the JE-990/OPA891 options.
Why would you waste time with an ancient OPA like 5532?
OPA1612 drives 600R with no sweat and is not even a high current model. OPA1602 is cheaper. OPA1692 is rated for +-50mA
Go to Texas Instruments homepage and search for higher current outputs. Plenty of options, all are better as a 5532.
A dedicated buffer stage is only needed when you aim for low impedance <100R like headphones.
Can you hear that difference ... better save as sorry for DIY 🤓
OPA1612 drives 600R with no sweat and is not even a high current model. OPA1602 is cheaper. OPA1692 is rated for +-50mA
Go to Texas Instruments homepage and search for higher current outputs. Plenty of options, all are better as a 5532.
A dedicated buffer stage is only needed when you aim for low impedance <100R like headphones.
Can you hear that difference ... better save as sorry for DIY 🤓
If you are driving a 5k load thru a 1:1 transformer you see also a 5k load at the primary. Even if the transformer was designed for 600 ohms. I have no idea what the impedance characteristic does at 10 Hz or 40 kHz when the secondary load is 5k. But it won't be 600 ohms.
All are more costly with no audible benefit.
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Nobody liked my joke. OK then.
I built a headphone amp line pre off the Maxim/Analclog Devices MAX97220
It sounded like a wire...nothing was there.
Silence.
Had enough brass to drive a little speaker. Boy it has heart!
Didn't like it at all.
I built a headphone amp line pre off the Maxim/Analclog Devices MAX97220
It sounded like a wire...nothing was there.
Silence.
Had enough brass to drive a little speaker. Boy it has heart!
Didn't like it at all.
Besides 5532, 4556/60/80 are all good but if you're looking for even lower THD, then you could pick video amplifiers for example, AD8056:
+/- 5V
300 MHz
1400 V/μs
60 mA, drives 4 simultaneous video loads (37.5 ohms)
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Agree. 5532 is completely transparent at audio frequencies and levels that the op amp is designed to handle.