Universal Buffer achieving -140 dBc (0.00001 %) THD

[tvrgeek]

Yes, I saw the Victors oscillator. Got me thinking. ( My old HP Ultra low distortion oscillator was .1%)
I do not get the acquisition side. I have a Focusrite that is pretty good, but we are talking .001 , not .000001. Noise floor 120, not 150. If doing A2D, we are going to need a lot of bits.

Now, I can see, if you cascaded 100 of them, the cumulative distortion would be measurable. I am not seeing how a notch filter gets the resolution being discussed. Flat not enough dynamic range for a start even if you were filtering out the noise floor.

What notch are you using? Variable, or multi-pole fixed? Q?

 

[NicMac]

I use a fixed twin-t notch filter (also from Victor).
Have a look at this blog post which explains better than I can do.

 

[Stony]

Is anyone having experience of AVC or TVC with Neurochrome preamp ?

I mean amps of course 😳

 

[itsikhefez]

I'm planing on building a preamp with the Universal buffer and I/O switch boards. I'll be using dual boards to support both balanced and unbalanced connections.
I have a spare pair of Jensen JT-11P-1 and was wondering if there would be any benefit to using them in this build.
Per AN-003:

This interface uses an input transformer to effectively replace the "active balanced" input stage. The input transformer, unlike the input stage, can tolerate source impedance unbalances with very little CMRR degradation.

If the transformer can be installed inside the "pro" equipment, the resulting balanced input will give outstanding CMRR performance from either balanced or unbalanced (using the adapter cable) sources.

1 option is to use them between one of the unbalanced inputs and the selector board.
Another option is to connect it between the selector board and the potentiometer so that it is used on all inputs.

Thoughts?

 

[tomchr]

The distortion of the transformer is likely to be 40-60 dB higher than that of the Buffer. I wouldn't put a transformer into the audio path.

Tom

 

[tomchr]

Just my point
"Residual THD+N (22 kHz BW)
–117 dB + 1.0 µV
Typically <–120 dB (1 kHz, 2.0 V)"

Right. THD+N is not the same as THD.

The THD (no +N) of my B-series APx555 measures about -148 dBc (1 kHz, 1 V). The 20 kHz THD comes in at -140 dBc (1 V).

The THD+N is about -119 dBc (1 V, 20 kHz BW).

Tom

 

[Studley]

Tom, if I put your buffer on the output of a DHT preamp then I’m assuming it would preserve the harmonic profile of the signal and that it would not somehow flatten it. Is my assumption correct?

 

[tomchr]

Correct.

Tom

 

[Studley]

Correct.

Tom

Thanks Tom.

 

[killie99]

Looking for a little bit of advice/guidance here. I currently have one of Tom's 8x2 differential preamps.
I'm looking for a project to keep me busy so is there much, if anything, to be gained by me building a preamp with his universal buffer, input selector, selector switch/volume control and power supply or even going the full hog and use 2 input selectors and differential volume control?
The 8x2 is super quiet, no hiss/noise, would I actually notice any difference?
I'm using it into a 686 dual mono which I built.

 

[Simon1972]

Nope

 

[tomchr]

The Universal Buffer is even lower noise than the DIFF PRE 8x2, but if you don't currently have issues with noise, you won't notice much, if any, improvement.

Tom

 

[killie99]

Thanks

 

[CageyH]

I am looking at building a preamp to replace the Topping Pre90 I purchased, to go with my Mod 686.
I need at least one balanced and 1 unbalanced input, and the same with the output.

So If I understand correctly, I need the following parts:
Input Selector
Volume control
Power supply
2 x universal buffers
Case & connectors.

 

[otto88]

Is there a case you can suggest that fits the buffer?

I searched on case, but there were several dozens of hits, mostly on use case

 

[Baffless]

Nice, good and impresive numbers. But 0.00001% compared to speaker 0.1% numbers feels unfair…

 

[Hvy69Mtl]

I didn’t fully get what you you meant at first.



In regards to this specific quote, I am referring to using DSP products in car audio setups. These are often necessary in vehicle which is just about the worst listening environment imaginable. DSP allows us to change things in the time domain, make custom crossovers, align phase of drivers in multi way setups to play as cohesive as possible at the driver seat to place the best stage possible on the center of the car dash. Nearly all The leading automotive DSP products allow users to also adjust individual channel gains. So that makes amp gain pot becomes redundant. Hence the answer to the proposed question of why no gain pots on certain Biketronics amps.

I use Biketronic amps on this.
6 8” soon to be 8 8”
6 horns soon to be 8
2 Hertz ST35’s & 4 Hertz ST25’s

 

[BrianL]

I'm sure the speaker guys would be quite happy if they could make drivers with 0.0...1% distortion.

Just because speakers are not as low in distortion isn't a good reason to not make low-distortion electronics.

 

[poseidonsvoice]

I am looking at building a preamp to replace the Topping Pre90 I purchased, to go with my Mod 686.
I need at least one balanced and 1 unbalanced input, and the same with the output.

So If I understand correctly, I need the following parts:
Input Selector
Volume control
Power supply
2 x universal buffers
Case & connectors.

Post 459 has an excellent implementation if you need ideas. And of course Tom’s Guide is an excellent synopsis.

Best,
Anand.

 

[tomchr]

So If I understand correctly, I need the following parts:
Input Selector
Volume control
Power supply
2 x universal buffers
Case & connectors.

Yep. You'll also need a Selector Switch. That comes with the Selector Switch & Volume Control board.

Is there a case you can suggest that fits the buffer?

The ModuShop Galaxy series springs to mind. Hammond also has some decent options around the $30-40 mark.

Tom