Low-distortion Audio-range Oscillator

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#5,162
1audio said:
It doesn't show on the simulation but M8 drives an active shield around the high impedance output of the VAS. It also drives C6 as part of the stabilization network. I'm not sure now whats on the PCB. I may have used a gimmick https://www.youtube.com/watch?v=v1wWL6TGWOE . The sim is a mod on the original that had 20 dB of gain and a larger feedback cap there. The sim works with a pretty small error on the RIAA curve. I'm not sure I would make a phono preamp this way today. The FET buffered opamp may be a better choice. It would address the level dependent input cap on the opamp, which is the dominant remaining distortion source, probably for all of this stuff. And I would be tempted to use DSP and correct for the actual response of the phono cartridge.
Click to expand...

Nice trick. I can use this for vari cap trim.
30 AWG wirewrap wire works very nicely.
 
#5,163
#5,164
Its simulated since there is almost no way to measure such low distortion. Simulations really break down when looking at ultra low distortion. Even the resistors would need more involved models. I don't invest a lot into distortion from simulators, just build the thing and see what happens with real parts.
 
#5,165
1audio said:
Its simulated since there is almost no way to measure such low distortion. Simulations really break down when looking at ultra low distortion. Even the resistors would need more involved models. I don't invest a lot into distortion from simulators, just build the thing and see what happens with real parts.
Click to expand...

Yes, an inch of wire in the wrong place can ruin the performance. At <-130dB no two realizations of the same circuit are going to match. It would be embarrassing to say how many times the output stage and the offset null circuit sharing current inadvertently on an IC op-amp caused a need for a mask rev.
 
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#5,168
scott wurcer said:
At <-130dB no two realizations of the same circuit are going to match.
Click to expand...

It may turn out that a hand built amp/buffer will need to be made. I spent a lot of money and time on that HPA to get the THD so low. I liked the results so much I made another using same pcb layout. I didnt do the due diligence which I did on the first one and ended up with slightly below -100db. Still fine for HPA.

However, I could not do it to extreamly low levels without the best test equipment available. When I get the gen from David, I am going to use the first HPA with it. Part of the problem for me was the low-ish feedback amount. Should be less critical to do if slightly redesigned. Maybe as a buffer only? But still individual tweaking with best analyzer to get it to nill thd. Not a project for the DIY'er with simulation alone.

What levels of thd/harmonics was produced with LME type? How far off was it?

ULDHB.jpg Buffer contender. http://www.diyaudio.com/forums/solid-state/240239-ultra-low-distortion-hp-buffer.html


THx-RNMarsh
 
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#5,169
RNMarsh said:
It may turn out that a hand built amp/buffer will need to be made. I spent a lot of money and time on that HPA to get the THD so low. I liked the results so much I made another using same pcb layout. I didnt do the due diligence which I did on the first one and ended up with slightly below -100db. Still fine for HPA.

However, I could not do it to extreamly low levels without the best test equipment available. When I get the gen from David, I am going to use the first HPA with it. Part of the problem for me was the low-ish feedback amount. Should be less critical to do if slightly redesigned. Maybe as a buffer only? But still individual tweaking with best analyzer to get it to nill thd. Not a project for the DIY'er with simulation alone.

What levels of thd/harmonics was produced with LME type? How far off was it?

View attachment 576611 Buffer contender. http://www.diyaudio.com/forums/solid-state/240239-ultra-low-distortion-hp-buffer.html


THx-RNMarsh
Click to expand...

Was that ever built, or just simulated? I am not sure I'd trust those numbers if simulated...
 
#5,171
EUVL said:
http://www.diyaudio.com/forums/equi...on-audio-range-oscillator-55.html#post3497666



I know it was from a long time ago, but has this ever been built ?
Such elegant circuit, would be a shame not to ......


Patrick

.
Click to expand...

Thank you. Really the shame 🙂
Today I made this prototype by modifying my serial generator's schematic.
Here are the spectrums measured via passive twin T (the scale is properly adjusted at 3kHz):
traditional schematic - http://content32-foto.inbox.lv/albums/e/elterra/TwinWienB/TrWienB.jpg
twin Wien bridge modification (same board, same opamp) - http://content32-foto.inbox.lv/albums/e/elterra/TwinWienB/TwinWienB.jpg
system noise (input short) - http://content32-foto.inbox.lv/albums/e/elterra/TwinWienB/SysN.jpg
As we can see, the main difference is the lower noise. This modified schematic may has good potential...

Victor.
 
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#5,172
vicnic said:
Thank you. Really the shame 🙂
Today I made this prototype by modifying my serial generator's schematic.
Here are the spectrums measured via passive twin T (the scale is properly adjusted at 3kHz):
traditional schematic - http://content32-foto.inbox.lv/albums/e/elterra/TwinWienB/TrWienB.jpg
twin Wien bridge modification (same board, same opamp) - http://content32-foto.inbox.lv/albums/e/elterra/TwinWienB/TwinWienB.jpg
system noise (input short) - http://content32-foto.inbox.lv/albums/e/elterra/TwinWienB/SysN.jpg
As we can see, the main difference is the lower noise. This modified schematic may has good potential...

Victor.
Click to expand...

WoW


-RNM
 
#5,178
1audio said:
It doesn't show on the simulation but M8 drives an active shield around the high impedance output of the VAS. It also drives C6 as part of the stabilization network. I'm not sure now whats on the PCB. I may have used a gimmick https://www.youtube.com/watch?v=v1wWL6TGWOE . The sim is a mod on the original that had 20 dB of gain and a larger feedback cap there. The sim works with a pretty small error on the RIAA curve. I'm not sure I would make a phono preamp this way today. The FET buffered opamp may be a better choice. It would address the level dependent input cap on the opamp, which is the dominant remaining distortion source, probably for all of this stuff. And I would be tempted to use DSP and correct for the actual response of the phono cartridge.
Click to expand...


"https://www.youtube.com/watch?v=v1wWL6TGWOE ."

Demian I tried this yesterday using some 30 AWG wire wrap. It works marvelously.

I did it a bit differently. Rather than twisting the wires I folded the wire in half then rapped a coil around the other end of the folded wire. Soldered in place and cut the shorting loop at the end. I wanted a trim cap. To tune it just cut some of the coil off the end. For fine tuning slide the inner strait piece of wire out of the coil.

I suppose one could fix it with a bit of glue but once soldered in, it will stay in place.

Total cost 0.006 dollars and a bit of labor.
 
#5,180
1audio said:
The circuit I used in the NuForce preamp is pretty close. This gives the basic idea. I can send you the complete simulation. Adding the bipolar pair will have higher voltage gain at the input. The low noise pair from Linear Systems worked fine in the NuForce with very low distortion.

I can send you the complete simulation but its a pain to get the transistors into the database. I may have some assembled boards around here as well. It uses more real estate and has more output drive than the Shibasoku.
Click to expand...

What's the noise like with this?
 
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