RJM Audio Sapphire Desktop Headphone Amplifier

This was one hell of a ride. I started to have random noise and both boards slowly get silent then return to normal. Did everything, replaced the regulator, problem went away then came back, rebuilt the board completely and the same thing. At the end it was my old transformer randomly dropping voltage or cutting out. Both board draws 51ma on + and - rails which seems a bit low to me but it works fine. Gonna see if i can get away with a 10W trafo for both boards.
 
Hi, So i thought of designing a pcb with (ngl many downgrades over the original design) to suit my particular case and availability of parts ), My pcb design skills are still pretty fresh. Though i would like to know what do you all think (i did take some even to me pretty risky shortcuts, do tell me if they are a total no go)
Kind Regards.
 

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Thought i would do a redesign for myself (IMO its an improvement, but not sure if i am missing something). Instead of a old power supply. i swapped it with a capacitance multiplier and a lm7xxx power supply.
Thanks
Regards
 

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Hello Richard,
After searching for a suitable headphone amplifier, I finally decided on your Sapphire.

My question is about the power supply. I read that it is possible to power sapphire with stabilized voltage. Which of these 3 options would you recommend as the best?

1, Rectified AC voltage + Z-reg
2, VRDN (Ommited Z-reg)
3, VRDN + Z-reg

Thank a lot!
 

rjm

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@HRDSTL
The VRDN is a textbook application of the LM317/337 3-terminal adjustable voltage regulator, with an optional "de-noiser" that injects inverted output noise back into the reference terminal of the regulator to - how best to describe this? - boost the effective feedback of the regulator IC? The principle seems sound, but, as always, instabilities become an increasing concern when you try to dial up feedback loops past their original design point. Presumably, Bob Dobkin knew the limits when he developed the LM317 back in 1976. The cost of going beyond the original design is unclear.

So your options are VRDN with Z-reg omitted, or Rectified AC + Z-reg. There is no value in using the Z-reg after the VRDN, which has significantly higher performance.

The guiding philosophy with the Z-reg is that a headphone amp is somewhere intermediate between a line stage and a power amplifier. Generally, line stages use regulated supplies, but unregulated supplies are used in power amplifiers. A relatively common opinion is that voltage regulation doesn't improve the sound of power amplifiers. (In addition to the cost/difficulty/inefficiency involved.) I have found headphone amps to be very sensitive to the power supply, and that both noise and dynamics are affected. Too little and too much regulation both have a negative impact, so I opted for a middle path - simple Zener-based reference with a single transistor pass element.
 
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Hello Richard,
The board is already at home. I'm surprised how fast it came, ...from Japan to Slovakia 12 days.

The boards are very high quality, matte black. I'm curious what the sound is like, hopefully sapphire will be ready by summer. If I like the sound I will build a preamp from sapphire, of course on the original boards and I will support Richard again!

Richard, I have enough bc550c/560c, ...can I also use these or better buy bc327-40/337-40.

Thank You!
 

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I have enough bc550c/560c, ...can I also use these or better buy bc327-40/337-40.
They are both CBE pinout in TO-92 packages so yes, you should be able to substitute the BC550/560 for the BC327/337 no problem.
(If there was a reason I originally chose the BC327/337 set over the BC550/560, I have forgotten it now. Maybe someone told me they sounded better. It was on that level, anyway.)
 
Hi friends, has anyone built the sapphire that you use as a preamp? I'm mainly interested in the sound if it will be as good as a headphone amplifier.

Since I need a quality preamplifier more than a headphone amp, I started with a line stage first. I decided to go with a fixed gain of 10db (3x). So far I've fitted what I've found at home, the rest ordered today in the mouser. I decided to go for dual mono (2x toroid, 2x psu)

Incl. Sapphire preamp:
  • dc blocker
  • on/off module H9KPXG
  • VRDN: bipolar regulator (2x psu)
  • Sapphire (2x)
If you use only one signal source, a streamer with adjustable output is sufficient. In my case I will use two signal sources (streamer + phono).
 

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@HRDSTL

I'm not sure if I count, but I did.

Brief comment - I'm not sure what your DC blocker is, but you probably don't need it. Also, you don't need that fancy soft start relay. Just use a power switch for the mains directly, the Sapphire Z-regs are soft-on by design, there are no clicks or pops audible even if you accidentally leave the volume up when turning on/off. You also don't need the regulator... just a transformer and rectifier diodes is sufficient, but I won't insist on it - you can if you want.
 
Today the Sapphire in line stage configuration finally finished, ready to be built into the box. I set the supply voltage to 13V and set the DC offset close to 0 mv. I'm just curious about the sound, ...but I'm sure it will sound better than a preamp with modern integrated circuits (opa1611, ...)
 

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