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| Searching for high audio quality low noise low power opamp for DI box upgrade |
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| 3dBi:
Hello, I have Behringer DI20 direct box and I wanted to make it a bit less noisy, so decided to swap out crappy TL064 opamps. I had in hand OPA4134, so i soldered them in. All is well until you try to power the box with 48V phantom power, I think two OPA4134's draws too much current (Iq = 4mA per amp) and that is why circuit fails. Battery power works good as it should. I've attached a schematic, so you can check, if my logic is sound. So, could anybody point me in direction to high quality low power opamp? I found OPA1692, but quad version OPA1694 is still in development. :( Closest low current audio opamps I could found is OPA1664 with Iq = 1.5mA per amp, but it's nowhere close 200µA per amp on original design. |
| Alex Nikitin:
OPA4196 or OPA4191 Cheers Alex |
| Mark Hennessy:
That particular DI box is notoriously noisy. Many other DI boxes use the TL06x op-amp, yet they don't have a noise problem. I've built many myself. The TL06x is perfectly adequate for this role. The TL07x is better if you can afford the higher current consumption (which you usually can if you use a dual rather than a quad). Rather than focusing on the op-amp, look to the (rather dumb) design of the DI20 to see why an op-amp swap is likely to be disappointing :-+ |
| 3dBi:
I must have got a good DI20, it worked for me very acceptable with original TL064 too, noise I was talking about is opamp hiss, all these opamps (TL06x, TL07x, TL08x) have it so better opamp should get better results. In my main usecase I can loose phantom supply feature too, as it is powered by power supply trough battery connection all the time and reside on my bass guitars pedalboard. The reason I'm asking for this, is for any other usecase I might have one day, where phantom powering could be useful. Using dual opamp is out of question, because of existing board layuot. It has two quad opamps in SOIC-16 package. |
| Mark Hennessy:
Yes, I know it uses quad op-amps. I mentioned duals because many DIs use a dual opamp. Some even use a single (usually in conjuction with an output transformer). From memory, the DI20 is at least 10dB noisier than other DIs using the TL06x op-amp (I have the actual figure written down elsewhere - I have researched DI boxes extensively recently). So how do other DI boxes manage to be so much quieter, despite using the same op-amp? The DI20 is acceptably quiet if you're lucky with the signal level and don't need to put too much gain after it. Running from batteries limits the headroom, which might require the attenuator to be switched in, which in turn needs the desk gain to be increased, and up comes the noise. Really, it's a very poor design, and it's quite hard to improve it you need to maintain a high-ish input impedance. But if you're feeding this from a pedal, then hi-Z in isn't an issue, so that at least gives you some scope to reduce the noise... I don't know if they're available where you are, but this is a much better DI for not much more: http://orchid-electronics.co.uk/classic_DI.htm - it's only single, but based on what you've said about your application, that might be all you need. There's an in-depth review of it on SOS here: https://www.soundonsound.com/reviews/orchid-electronics-di-boxes - despite the excellent test (and subjective) results, it uses a TL072 - nothing fancy needed in a DI box that's properly designed. I'm just hoping to save you a lot of messing around and disappointment :-+ |
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