[CatalinM]

Hey guys!

I'm looking to start a build using some "premium" components (because why not?), but I'm having some issues sourcing an R8/9. So I need to ask: what would be the impact of replacing this with a "slightly" larger resistor, say 2R2? Cause if it's something like a volume drop, that might actually be a good thing.

 

[pmillett]

Hey guys!

I'm looking to start a build using some "premium" components (because why not?), but I'm having some issues sourcing an R8/9. So I need to ask: what would be the impact of replacing this with a "slightly" larger resistor, say 2R2? Cause if it's something like a volume drop, that might actually be a good thing.

It won't make a big difference. More than a volume difference, it sets the output impedance - or damping factor - of the output.

Some people prefer an even larger resistor, depending on the headphone impedance. It changes the sound. For high impedance headphones some people go as high as 150 ohms, though this is too much for most modern headphones. On the other hand, if you are driving inefficient low impedance headphones, you want this to be as low as possible, even 0 ohms.

Pete

 

[CatalinM]

Thanks, Pete!

My target cans right now (and probably for the foreseeable future) have a 64ohm impedance, so I'll probably be fine with 2R2 then.

PS: One more question. Can I use a bigger bypass cap (C4 and C7) on the output caps? Say 0.68uF.

 

[AddiDub]

Hey Guys,

few weeks ago i ordered everything i need for my nuhybrid headphone amp. I want to run it together with my old AKG240 Studio - which has 600 Ohm impedance. Any suggestions for parts value changes like R8/R9? I got the following resistor values at home: 10R, 12R7, 33R, 49R. Which one would fit best to drive a 600 Ohm Headphone? Any further suggestions?

You are spot on about R8 and R9 - some people will like zero ohms better than 1 ohm, and some might also prefer 10-33 ohms there. It depends on your headphones and listening preferences.

Many thanks to Pete for creating this kit and making the nutube available!

 

[pmillett]

I don't think it will make a big difference. As I recall the K240 was designed to the old IEC standard that specified a source impedance of 120 ohms. But you might like the sound better with a low source impedance.

If it were me, I'd stick in 33 ohms...

Pete

 

[Wyd4]

Very interested in this, but would have more chance soldering with a cannon .

 

[CatalinM]

Finished mine some 20 mins ago. Really happy with the overall sound, even though it's really microphonic. I kinda regret soldering the volume pot on the board as it sends vibrations when you hit it's minimum stop - I'll probably desolder it and add some wires to decouple it from the board.

I had to change some parts though, namely C10, C12 and C15... the Elna's I got were too large and didn't fit, so I changed them with some Nichicon's that were rated at 25V and thus smaller. I checked the schematic and these 3 didn't have any high voltage on them so the switch seemed safe... and it hasn't blown in my face, so we're good.

PS: I noticed a significant channel imbalance at very low (barely audible) levels. I'd blame it on the TKD pot, even if it's really disappointing for such an expensive pot (the Alps Blue Velvet I have in my Aikido preamp doesn't have such issues).

 

[Dule]

Hello,
I am having trouble with my nuhybrid amp. Can't get 11 V on the right channel, I get around 4.4 max. Left channel is fine. I tried plugging headphones and right channel is noisy, a humming sound.

I have measured voltage on both R13 and R14 and on one side they both have 23.77V but on the other sides of resistors one (R14) is 10.72V and the other (R13) is 6.28V . Both resistors are 475k checked and rechecked few times.

Does anybody know what might be the problem?

 

[HiGHFLYiN9]

You might want to flip-flop the op-amps, that's an easy thing to check.

 

[Dule]

Hello,
I am having trouble with my nuhybrid amp. Can't get 11 V on the right channel, I get around 4.4 max. Left channel is fine. I tried plugging headphones and right channel is noisy, a humming sound.

I have measured voltage on both R13 and R14 and on one side they both have 23.77V but on the other sides of resistors one (R14) is 10.72V and the other (R13) is 6.28V . Both resistors are 475k checked and rechecked few times.

Does anybody know what might be the problem?

Solved One of the pins on op amp was not soldered properly. I have checked all the joints something like 10 times and missed this every time, only when I changed angle of light I saw it . Anyway, it is working now all good.

 

[CatalinM]

I finally had a chance to test this out with my main headphones, a pair of Audio Technica A500, but I can't say I'm very happy with the sound. These headphones always had a light bass - it goes really low, but it's not powerful, unless you apply some EQ. They're also very open and detailed. Unfortunately, through the NuHybrid, the bass remains light, but the brightness is just a little too much. I'll let the amp run for a day or so to burn it in and see if that changes anything.

On another note, I'll build a separate linear power supply and I was thinking about putting it in a different case. Now, I've never done this before and I'm not sure how I should handle grounding / earth connection between the two cases. The power supply would not be floating, so it'll probably have GND connected to mains earth through a filter most probably. Should I connect the amp's aluminium case to the power supply GND?

 

[CatalinM]

After some 50hrs of almost continuous music playback through the amp I feel it has gotten slightly better, but it's still too bright. With the Samson SR850, it's just a little too glassy, but with the Audio Technica it gets some really searing highs, depending on recording. It's really annoying, as the overall sound is significantly better than my 2017 Macbook's audio out (one of the best for any computer out there), but those blistering highs make it hard to enjoy on 50% of the recordings.

Does anyone have an idea for a tweak here?

 

[HiGHFLYiN9]

You can try adding some speaker grill cloth between the headphone driver and your ear. https://www.parts-express.com/parts-express-speaker-grill-cloth-black-yard-70-wide--260-335

 

[CatalinM]

That doesn't sound very... exact. Plus the fact that I would have to change that grill when listening to other amps.

 

[pmillett]

After some 50hrs of almost continuous music playback through the amp I feel it has gotten slightly better, but it's still too bright. With the Samson SR850, it's just a little too glassy, but with the Audio Technica it gets some really searing highs, depending on recording. It's really annoying, as the overall sound is significantly better than my 2017 Macbook's audio out (one of the best for any computer out there), but those blistering highs make it hard to enjoy on 50% of the recordings.

Does anyone have an idea for a tweak here?

Try moving the bias point off center a bit - set it for maybe 9V or 8V instead of 11V, This will introduce more 2nd harmonic which tends to smooth out the highs...

Pete