[pmillett]

An interesting discussion about the audibility of inverted polarity:

https://hydrogenaud.io/index.php/topic,55323.0.html

Pete

 

[Desert Rat]

Are you saying that for the line in and line out connections on the board the positive is actually the negative and the ground is the positive? That's my understanding of reversed signal polarity. If that's the case then that would mean the signal would be connected to ground if the negative is actually the positive surely or am I missing something?

This is AC, not DC. You can tie either 'positive' or 'negative' of an AC signal to circuit ground to unbalance the signal. Reversed polarity in this case means that the audio signal comes out of the circuit 180 degrees out of phase from the way it went into the circuit.

This can be corrected in loudspeaker systems which use 4 separate conductors, 2 per channel, by reversing the balanced wiring connection between the amplifier and the loudspeaker, either at the amplifier end or at the loudspeaker end of each channel's 2-conductor wire. Since headphones typically tie the "negative" from each channel together and use a 3-wire system, it is impossible to do this unless you take the headphones apart and then reverse the connections at the transducers themselves.

 

[Desert Rat]

Personally, I think someone's getting mixed up, here (could be me, though!).

AFAIK, inverting the signal is actually what allows negative feedback. If the signal was not inverted, a feedback connection back to the input would blow up, become unstable, runaway, etc. It is the inversion of the signal that allows the feedback loop to close, and thereby work. In other words, the music signal is inverted by the OPA551 opamp in the NuTube Millett Hybrid circuit. That signal becomes negative. It's then fed back into the input side of the opamp as a negative music signal. Now the opamp has two signals that are input, one positive and one negative. The opamp is then able to compare/correct to minimize the voltage offset between the two. That minimizes distortion and noise. As I understand it, that's how negative feedback works.

I am not familiar with Nelson Pass's Korg preamp, but if it is simply an amplifier circuit without feedback, I'm guessing that trying to eliminate the signal inversion at the input to the NuTube hybrid is not the way to go about creating a zero-feedback circuit.

The BJT input buffer does not invert the signal. The signal comes out of the Korg triode 180 degrees out of phase from going in, thus inverted. The opamp buffer does not invert the signal. The opamp in the Millett NuHybrid circuit is configured as a non-inverting unity gain buffer. The signal is connected to the non-inverting (+) input of the opamp. The opamp output is tied both to the center pin of the output jack (via a capacitor for DC blocking) as well as directly back to the inverting (-) input of the opamp with zero resistance in the connection. This is how the gain of the opamp is set to unity.

 

[Desert Rat]

An interesting discussion about the audibility of inverted polarity:

https://hydrogenaud.io/index.php/topic,55323.0.html

Pete

He does make a point about clean vs distorted signals. The way I have the triode set up in my build, with 332K plate resistors and +9.75V at TP1 and TP2, the circuit is theoretically producing about 1.5% negative phase second order harmonic distortion at 1V out. I posit that with that level of distortion, you can hear the difference between an inverted and a non-inverted signal. I have yet to try listening to the uncorrected (inverted) polarity output with the same amount of positive phase second order harmonic distortion, established by going to the high side of the half-supply plate voltage point. I'm not sure that would be valid since the tube characteristics might be different in other ways with +13 or +14V on the plates, especially since the amount of distortion generated seems to be dynamically dependent on the signal level going through the tube.

I feel that there is validity to maintaining the polarity of the original recording due to the way the transient wave fronts are reproduced. Not just at a high level, like kick drum beats, but also at a low level within the stereo mix. I realize I haven't done any blind A-B testing, and may just be "hearing what I expect to hear" but I'm a musician, a piano tuner, and was in the pro audio industry as a systems and loudspeaker designer for 40 years. And yes, my ears are not what they used to be as regards high frequency response but I can still hear differences in imaging, detail and clarity and I personally find that correct polarity at the transducers just sounds better.

 

[tomb]

The BJT input buffer does not invert the signal. The signal comes out of the Korg triode 180 degrees out of phase from going in, thus inverted. The opamp buffer does not invert the signal. The opamp in the Millett NuHybrid circuit is configured as a non-inverting unity gain buffer. The signal is connected to the non-inverting (+) input of the opamp. The opamp output is tied both to the center pin of the output jack (via a capacitor for DC blocking) as well as directly back to the inverting (-) input of the opamp with zero resistance in the connection. This is how the gain of the opamp is set to unity.

OK - I was the one getting mixed up, apparently. Thanks for the explanation.

 

[RestlessZombi]

Can someone answer a quick question, half way through the build and will be finishing it tonight (yay !) but I just checked and the adaptor I have is 24v but 2.91A DC, is this going to cause issues and i should hold off testing till i have something lower?

I'm guessing something more like 24V 1A is more suitable?

Sorry if this has been asked before, read the last 10 pages and the first 15 so far and not seen an answer.

 

[pmillett]

Can someone answer a quick question, half way through the build and will be finishing it tonight (yay !) but I just checked and the adaptor I have is 24v but 2.91A DC, is this going to cause issues and i should hold off testing till i have something lower?

I'm guessing something more like 24V 1A is more suitable?

Sorry if this has been asked before, read the last 10 pages and the first 15 so far and not seen an answer.

That should work fine.

Pete

 

[Alkolor]

That should work, provided the polarity is also correct, meaning that the + and - connections on your alternate supply physically match (which one is on the outside or inside of the connector). From the spec sheet, it looks like the one on the BOM has + on the inside. Adaptors usually have the symbol for polarity on them.

Amps are more like a maximum supported spec. The device will draw as much as it needs, and your adapter needs to be rated high enough to supply what’s asked for. So, having a higher amperage rated adaptor is fine. There’s some posts earlier on where I learned the stock adapter is even way over as someone else was considering a lower power supply.

 

[RestlessZombi]

Thanks for the reply, it was perfectly timed...

It's Alive

Thanks for the design, Instructions and BOM, Much easier to make.. Time for some listening..

 

[Geezer Rock 001]

Hello to all who visit this thread and especially to Pete.

I discovered this branch of the rabbit hole after I got interested in a NuHybrid build that Torq had for sale on the board. He is great to deal with and the amp delivered today. Torq's build was flawless and it sounded excellent!

I was interested in the NuHybrid because I was looking for a hybrid amp that I could roll Sparkos op amps into. I have a set in a Burson Fun and imo they are far superior to any of big B's offerings.

I rolled the Sparkos in this afternoon and they take a great sounding amp to another level. Again imo.

Pete, thank you for sharing so much of your expertise with the general public. I am so impressed with the performance of the NuHybrid that I plan to try my hand at building a Butte amp very soon.

 

[slowpogo]

I'm about to pull the trigger on this project and have just a few questions.

C3, C5, C6, C11 are designated 470uf 35v. Would 680uf 35v be okay in any of these positions?

Like many around here I like the Dale RN55 resistors. Some of the values for this project are only available in the 1/5 watt resistors from that series. Would 1/5w be enough for this project?

 

[Alkolor]

Hello slowpogo,

I think the upsized capacitors would be fine. I used 1000uf for C3 and C6 in mine since some had done the same for a stated increase in bass response. I used the billed 470uf for C5 and C11, but have upsized capacitance in similar circuit placement for other builds. From what I could gather when researching for my build, increased capacitance on a decoupling capacitor can improve ripple smoothing on the line, but capacitance is also selected based on the frequency it is meant to filter.

 

[pmillett]

I'm about to pull the trigger on this project and have just a few questions.

C3, C5, C6, C11 are designated 470uf 35v. Would 680uf 35v be okay in any of these positions?

Like many around here I like the Dale RN55 resistors. Some of the values for this project are only available in the 1/5 watt resistors from that series. Would 1/5w be enough for this project?

Yup, that is fine, if the caps will fit in the space available. Dale RN55 are fine too.

Pete

 

[slowpogo]

I built the NuHybrid, fully populated the board. Plugged my adapter in, turned it on. The choke started smoking. I turned it off quickly.

Wondering what the hell went wrong, I double checked polarities of everything, solder joints, etc. and it all looked fine. Turns out...I was using the same Triad wall wart that I used with my Millett Hybrid Max, thinking it was 24VDC. It's actually 24VAC. **many expletives***

So I briefly put 24VAC into the amp. Obviously the choke is toast, but what else is likely damaged?

 

[docentore]

Check electrolityc caps