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Neurochrome HP-1: Ultra-High End Headphone Amp

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#30
#31
Congratulations on the new amp Tom. Very nice review there and very informative too. I Wish I could hear one on my DT880-250's. Will one be making the rounds anywhere the Metro Wash DC area?

I have been playing around over past couple of weeks with stupid simple SE Class A head amps using 2, 4, and 10 qnty BF862 JFETs and loving it. Not ultra-low HD by any means but, I compare it to the sound of an OPA1688 on the same phones with same 18v (two 9v batteries) and I like the sound of the discrete class A amp better. Will the HP-1 be an even cleaner, drier, sounding version of the IC opamp headamp?
 
#32
The HP-1 runs on ±18 V (--> VCC-VEE = 36 V), so you'll have much more power available than you will from a pair of 9 V batteries. It beats any amp I'm aware of on noise floor and THD, so if you're into clean "nothing added" sound it'll be a good fit for you.

There's a loaner floating around in the US via the SBAF. I'll likely continue the loaner tour via Head-Fi as well. Toss me a PM or email if you're interested in joining.

Tom
 
#34
The power into 600 Ω is approx. 225 mW. Considering that the Beyerdynamic T1 headphones are 102 dB @ 1 mW efficient, 200 mW is enough to produce an SPL of 125 dB before clipping. How much do you value your hearing? 😉 Please be careful. The HP-1 is quite powerful.

The amp runs on ±18 V (nominal) rails and the LME49600 has an output drop of about 1.5-2 V when driving a 600 Ω load.

Tom
 
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#35
Tom,

Thanks for the quick response. I do value my hearing very much!
Looks like your HP1 will do the trick rather nicely!

I have built several head amps in the last few years, mostly AGDR designs and have enjoyed the build efforts.

I have to convince my better half to fund this journey!!

Alex
 
#36
Now in blue. Enclosures are in stock and the documentation is almost done. Yay.

All components are provided by Mouser Electronics. The volume knob, RCA connectors, chassis, hardware, and feet you can get from me. Bam! Done!

Tom
 

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#37
tomchr - very nice headamp! I can see that a great deal of work went into designing & testing the unit.

A question - what is the output impedance? I just looked through the specification listing on your site and I didn't find it. I'm just curious if you have a series (output) resistor after the looped OPA1611 + LME49600 pair or not. I'm guessing not, since it sounds like you have designed to maintain phase margin for the expected headphone/cable capacitive loads. Probably no need for the resistor to isolate load capacitance.
 
#39
Whoops - didn't know it was parallel. 🙂 Yep, agreed, I have 1R on the output of each op-amp half in my parallel ODA amp (3 dual NJM4556AL on each channel) for the same reason. 0.5R is just fine, IMHO, insignificant damping factor effects. Thanks for the reply!

Also - while on Tom's site I noticed that he is offering AP testing services to the DIY community for what I would say is a very reasonable price. I have been searching for for years for someone doing that. Another good resource for the bunch of us DIY'ers to know about. 🙂
 
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