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"Millett Hybrid" redux: NuHybrid headphone amp, using the Korg Nutube - Page 5

post #61 of 65
Thread Starter 

OK, I made a discovery - the microphonic "ping" at power-up has nothing to do with the relay engagement.  It is noise induced from flipping the power switch.

 

I tried leaving the power switch turned on, and instead turned the amp on and off by switching the AC to the adapter.  The relay pulls in after 10 seconds. No "ping" noise (well, none in HD600s - I'm sure there is still some noise in efficient headphones or IEMs).

 

I also tried moving the power switch very slowly... also no ping sound.

 

It is true that if the delay is lengthened, you won't hear it as much when you flip the power switch.  But I guess I don't quite understand why it matters.  Let's say it takes 20 seconds (from the time you hit the power switch) for the ringing to calm down.  You can make the power on delay more than 20 seconds and you won't hear it.  Or you leave the power on delay at 10 seconds (which is where it is now) and you hear a decaying ringing for 10 seconds.  It's not that loud...

 

Pete

post #62 of 65

Hey Pete,

 

I bought your board+nutube and am waiting to receive the parts from Mouser. Looking forward to build it. I am a new builder, so i decided i would use this build to try my hand at customizing the case. Having positive experiences with the cases from Hifi2000 (an italian vendor) who supplied the case for a recent diyaudio amp build, i bought a relatively large economy case from them, which i can play around with. One of the things i was thinking was to mount the nutube on the outside top of the case, since it looks so nice, and connect it through holes in the top via wires insulated with heatshrink tubing. I wonder if this would affect the performance to any great extent? My feeling says probably not, but i am a novice in this area so i would rather take the word of someone who actually knows what hes talking about :) Apart from the leads connecting it to the PCB, are there any exposed parts that carry voltages in the nutube?

 

Best,

Silas

post #63 of 65

Any changes to the NuTube buffer based on discoveries with the headphone amp? I know most implementations will not have a volume knob, but there would still be the on-off switch.

post #64 of 65
Thread Starter 
Quote:
Originally Posted by smellor View Post
 

Hey Pete,

 

I bought your board+nutube and am waiting to receive the parts from Mouser. Looking forward to build it. I am a new builder, so i decided i would use this build to try my hand at customizing the case. Having positive experiences with the cases from Hifi2000 (an italian vendor) who supplied the case for a recent diyaudio amp build, i bought a relatively large economy case from them, which i can play around with. One of the things i was thinking was to mount the nutube on the outside top of the case, since it looks so nice, and connect it through holes in the top via wires insulated with heatshrink tubing. I wonder if this would affect the performance to any great extent? My feeling says probably not, but i am a novice in this area so i would rather take the word of someone who actually knows what hes talking about :) Apart from the leads connecting it to the PCB, are there any exposed parts that carry voltages in the nutube?

 

Best,

Silas

 

I think the biggest risk would be noise pickup.  Try and keep the wires as short as you can.

 

There is no exposed metal on the Nutube package other than the pins, so they are all that needs to be insulated.

 

Pete

post #65 of 65
Thread Starter 
Quote:
Originally Posted by HiGHFLYiN9 View Post
 

Any changes to the NuTube buffer based on discoveries with the headphone amp? I know most implementations will not have a volume knob, but there would still be the on-off switch.

 

I haven't tried to get the buffer to oscillate, but it might be unstable with very low DC resistance across the inputs.  This would apply only to the input buffers - the output buffers have a high resistance on the gate (the Rp of the Nutube is pretty large) so they should be fine.

 

To be safe, you can either change to 10k resistors on the source terminals of the 2N7000s - that seems to lower the gm enough that there's no oscillation - or change to 2N3904 + 10k like on the headphone amp.

 

Pete

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