I built a "proper" 4 channel amplifier for biamping. All four channels have 47K input impedance. That provides maximum flexibility. I will never need an external buffer to drive it no matter what the application.
My tube amps have 90k input, the Yorkville is 10k.
My buffer circuits are 510k input though, with 600R driving ability.
My buffer circuits are 510k input though, with 600R driving ability.
Yes, I call that the Super Buffer.
I use buffers extensively. They clean up a whole lot of trash.
That's right ladies and gentlemen, op amps add distortion to a circuit. Except when they drastically reduce distortion.
Tube amps from back in the day had to have high input impedance. Tube preamps couldn't drive low impedances. Today it's trivial to build a buffer capable of swinging 10 volts RMS into 600 ohms with ultra low distortion.
My last tube amp (from the 70s) had box stock input impedance of 47K in order to work with a solid state preamp. And work well it did. It had way, way less noise than typical tube amps of the era: no hiss, pops or hum. Its noise performance was on par with solid state amplifiers of the time.
I use buffers extensively. They clean up a whole lot of trash.
That's right ladies and gentlemen, op amps add distortion to a circuit. Except when they drastically reduce distortion.
Tube amps from back in the day had to have high input impedance. Tube preamps couldn't drive low impedances. Today it's trivial to build a buffer capable of swinging 10 volts RMS into 600 ohms with ultra low distortion.
My last tube amp (from the 70s) had box stock input impedance of 47K in order to work with a solid state preamp. And work well it did. It had way, way less noise than typical tube amps of the era: no hiss, pops or hum. Its noise performance was on par with solid state amplifiers of the time.
I should mention I build buffers with triodes, not opamps... But if the OP doesn't want to use an opamp buffer, I doubt they would want to use with tubes.
Here's the circuit. This one is designed as a line amp for use with an amp with 10k input. Input inpedance is 1M/3 == 333k
If you need more "driving" capability, replace 6N24 with 6N6, and 240R with 100R, and change 10u to 100u (but then you're into electros)
Here's the circuit. This one is designed as a line amp for use with an amp with 10k input. Input inpedance is 1M/3 == 333k
If you need more "driving" capability, replace 6N24 with 6N6, and 240R with 100R, and change 10u to 100u (but then you're into electros)
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Now that's cool! Do you use parallel cathode followers? Have you considered hybrid tube/FET output stage? Erno Borbely made a "super triode" with a cascaded triode and JFET or MOSFET.
I see what you did. That simple circuit is more elaborate than anything I've seen in commercial equipment. They didn't like to "waste" a section of a tube on frivolities when just a resistor will do.
I see what you did. That simple circuit is more elaborate than anything I've seen in commercial equipment. They didn't like to "waste" a section of a tube on frivolities when just a resistor will do.
I don't have any built with parallel cathode followers. I have considered it. I have boards for this buffer, too. Mono ones, and a stereo one I call the Business Card Buffer (it's the size of one).
https://www.diyaudio.com/community/threads/photo-gallery.71300/post-6783689
I have IXTP08N100D2 depletion MOSFETs that would plug in with a change to the biasing point.
By using the tube as a load, you move the heat outside of the chassis 🙂 I don't ventillate my cases.
https://www.diyaudio.com/community/threads/photo-gallery.71300/post-6783689
I have IXTP08N100D2 depletion MOSFETs that would plug in with a change to the biasing point.
By using the tube as a load, you move the heat outside of the chassis 🙂 I don't ventillate my cases.
Well I'm £90 lighter and got everything I need to make 4 copies of the buffer from here on the way https://theslowdiyer.wordpress.com/2013/09/02/project-files-opamp-buffer-for-icepower-asx-modules/
But having a hard time choosing op-amps that will work with them that don't cost an absolute fortune, I don't suppose anyone has any suggestions around the $1 to $5 price range, need to be singles and available in the UK, and low distortion/noise obviously.
But having a hard time choosing op-amps that will work with them that don't cost an absolute fortune, I don't suppose anyone has any suggestions around the $1 to $5 price range, need to be singles and available in the UK, and low distortion/noise obviously.
What on Earth cost 90 quid??
NE5532: Buy 10 and they're 96p each.
https://uk.farnell.com/texas-instru...dual-low-noise-5532-dip8/dp/3117310?st=ne5532
NE5532: Buy 10 and they're 96p each.
https://uk.farnell.com/texas-instru...dual-low-noise-5532-dip8/dp/3117310?st=ne5532
That was for all the parts for the boards, 10 PCB's and the resistors for my stepped attenuators, without the resistors it was £70. And that wasn't going with fancy parts, pretty much the cheapest to spec that were in stock in the UK. Mouser would have been about £60 but they wanted to bend me over on postage.
And ne5532's are duals, i need singles.
I think I'm after something a bit newer than from the 70's, i reckon I'm gonna step away from this project for a couple of weeks, that's the estimated date of my PCB's anyway so no point in buying the op-amps today. Hopefully by then I'll have forgotten how much money I'm sinking into this 😂
I don't recommend the TL081 (although it will work fine) but age doesn't mean it's bad. It's true that newer generation op amps have improved specs etc. But even the old 5532, which has some clear limitations, is still an excellent audio op amp. It was designed in fact for audio; some of its specs (like input bias current) are deplorable but it's low noise and unlike general purpose devices its output stage is designed for minimum crossover distortion. Plus it's easy to use in regards to stability.
I noticed your boards use DIP-8 devices. This rules out some of the newest devices which aren't always available in DIP-8. Breakout/adapter boards (which convert PDIP packages for a DIP board) can cause stability issues with cranky devices.
FWIW the "modern" audio op amp I like is the LM4562 https://www.ti.com/lit/ds/symlink/l...92210&ref_url=https%3A%2F%2Fwww.mouser.com%2F or if I need low input bias current OPA2134.
I noticed your boards use DIP-8 devices. This rules out some of the newest devices which aren't always available in DIP-8. Breakout/adapter boards (which convert PDIP packages for a DIP board) can cause stability issues with cranky devices.
FWIW the "modern" audio op amp I like is the LM4562 https://www.ti.com/lit/ds/symlink/l...92210&ref_url=https%3A%2F%2Fwww.mouser.com%2F or if I need low input bias current OPA2134.
I have some of those.
I also like AD712 but they cost more.
Could always just use LM741 LOL
@Fast Eddie D What do you think of the LF411?
I also like AD712 but they cost more.
Could always just use LM741 LOL
@Fast Eddie D What do you think of the LF411?
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@timreeves if you use an external PSU, you can quite easily get something that will power all four boards - you don't really need more than 100mA of current in total here.
You could technically also power all the boards from the internal PSUs of the AS2, but you'd have to be careful with the amount of load capacitance you add and also the grounding of the boards. If you can fit a small dual PSU in you chosen enclosure, I think that will be the easiest and safest to get working.
You could technically also power all the boards from the internal PSUs of the AS2, but you'd have to be careful with the amount of load capacitance you add and also the grounding of the boards. If you can fit a small dual PSU in you chosen enclosure, I think that will be the easiest and safest to get working.
All the opamps you mentioned are duals, except for the one you said I shouldn't use which was suggested after I mentioned this board needs singles, not duals 😂
I'm not worried about the PSU at the moment, pre made +\- 15v boards aren't hard to find if the aux power doesn't look suitable 🙂