RJM Audio Sapphire Desktop Headphone Amplifier

[rjm]

I don't think JFETs could be substituted for the input devices here. I don't think the circuit would be stable without the fixed voltages set up by the base-emitter diode drop present in the BJTs.

 

[joensd]

The schematic on your webpage shows an output stage with multiple To-92 devices whereas the PCB shows single bd139 or similar in the output stage.
I believe one of them is wrong or at least another version.
What are these versions called/referred to?
Thanks!

 

[joensd]

Excuse me, mixed them pages up!
Anybody built both and care to comment on sound?

 

[joensd]

One more excuse as I realize there is uh so many versions!
Slowly digested the whole thread.

Anybody having leftover PCBs from the last versions?
Especially interested in withmatt´s mini version.
Otherwise I´ll make batch of the mini´s.

 

[rjm]

Probably not, and I only have the 4.1z and 4.2b boards myself.

As you note, though, there are Gerber/.brd files floating around so you can get older versions made if you prefer.

Having listened to all the revision history, the "4" (all discrete) is superior to all previous versions of the Sapphire using op amp input stage.

-Richard

 

[joensd]

Thanks Richard.
I´ll take my time to think about what I need.

I´d love to do a tiny SMD-version but don´t understand hfe-variations enough to proceed with it.
If I take the simulation file that was attached earlier (sapphire_41m_thd.asc),
the BC327-25-model has a hfe of 385.7 and the BC337-25-model of 292.4.

Simulation of DC-offset looks fine. Even with a hfe-variation of +-5.
But let that variation get bigger or change the absolute values of the models and DC-offset quickly can become >100mV.

See attachment with "original" hfe-values with variation of +-20.
If I make the hfe of npn and pnp the same it still doesn´t work out to 0V offset.

Probably need some time to digest that.

 

[rjm]

The trim pot. is there to zero the DC offset. There is a little fluctuation as the circuit warms up, but nothing to worry about. I would not recommend making it without the trimmer.

 

[joensd]

Thanks again, Richard.
I´ll send you an email regarding the boards.

 

[fmmech_24]

..for those, who do.

 

[rjm]

Neato! It's like the same ... but different!

 

[MRBond]

I would like some considerations if possible.

1- Could anyone say how this amp performs with HE400i sound stage, bass etc?

2- How does this amp compare to the L30 or A50 topping etc?

3- This project seems similar to the Little Dot MK V amp does anyone know which one is better?

 

[rjm]

I am unfamiliar with the amps you list so I can't comment there.

For the hifiman headphones, they are 35 ohm models so may benefit from the high current build of the Sapphire.

 

[IPV]

Hello,
I want to make a variant of this amplifier without the components of the power supply. I will use another scheme for this. In this case can I give up capacitors C6-7-8-9-10-11?

 

[rjm]

Anything to the left of Q15-16 can be omitted. The cap numbering (and number) depends on which board revision, so I prefer to describe it that way..

 

[IPV]

I mean this variant. I will use a Denoiser power supply.

 

[rjm]

There, you would keep the capacitors you indicated by the white arrows.

 

[IPV]

Okay, I'll keep them, if that's the indication.
Thank you.

 

[IPV]

This would be the PCB version I want to make. I hope it's not a mistake ...

 

[rjm]

Looks good - I think. If it was me I would add a couple more caps in the extra board space.

 

[MRBond]

Hello.
Could someone help?
I'm looking to mount this Sapphire amp, but I need to know if it is possible to make a small change to the final assembly.

I have a hearing impairment heard on the right side hears less than the left, so I think of mounting the sapphire with two audio outputs and two volume controls so that I can adjust the sound on each side of the phone so that there is no imbalance in the ear canal.

Would it be possible and how would you do it?

Thanks.