HPS 4.0 phono stage

[syn08]

Here's the HPS4.1 current noise plot. Unfortunately the RIAA correction is already installed, so the increase of the current noise with frequency is masked by the RIAA gain drop at high frequencies.

Anyway, the equivalent input current noise @1KHz is about 5pA/rtHz. This maps to a negligible current noise contribution to the total noise, for a 10-20ohm MC.

However, for a MM cartridge having 500ohm, the current noise contribution is 2.5nV/rtHz, which adds to the 0.3nV/rtHz input voltage noise and the 2.8nV/rtHz cartridge noise. This clearly shows that HPS4.1 is not recommended for MM cartridges. OTOH, using something of the HPS4.1 complexity for a MM cartridge doesn't make much sense anyway. A simple, low noise JFET construction with a gain of 40dB (like HPS2.0) will do just fine.

[Joachim Gerhard]

I agree and when i find the time i will do a stage for the grados.

[scott wurcer]

Thanks, I was looking at the new 2 Ohm 2 mH Grados and it would seem difficult to take complete advantage of its noise floor. Your Benz at 12 Ohms and .4mH puts the trade off far out in frequency.

[syn08]

Originally Posted by scott wurcer

Thanks, I was looking at the new 2 Ohm 2 mH Grados and it would seem difficult to take complete advantage of its noise floor. Your Benz at 12 Ohms and .4mH puts the trade off far out in frequency.

Yep, the new Grado is quite a strange MM animal. Can't imagine how they got to 2ohm and 2mH, that sounds pretty odd to me.

[syn08]

I have decided to do a PCB for the raw power supply (rather than using perf board and wiring). See the attached pictures.

Testing went very well, 0.28-0.3nV/rtHz and 0.008% distortions at all frequencies and output levels up to 40Vpp. I also got only 25uV output hum (input shorted), before even throwing everything in the steel case. This is an excellent level, equivalent to 2.5nV input hum. It's actually a little better than HPS3.1 in the same stage (before case), probably because of a better layout of the input stage. But the key to low hum is the dual mono construction and the ground loop(s) handling, as described on my web site under "wiring".

[syn08]

Before closing the lid:



The new box installed in the phono stack, ready for listening tests.



All I can tell so far: after 108dB of gain at 60Hz, zero hum, ear on grille on my 97dB horns. And also zero hiss.

[syn08]

http://www.synaesthesia.ca the Low Noise Designs part was updated with HPS4.1 schematics, Gerbers, comments, etc... Measurements to follow ASAP (they were mostly posted here, anyway).

Comments welcomed, as usual.

[syn08]

http://www.synaesthesia.ca the Low Noise Measurements page was updated with the HPS 4.1 measurements.

Currently, continuing the listening tests. So far, I was able to identify two significant differences to HPS 3.1: low level resolution/imaging and the vinyl noise handling.

Compared to HPS 3.1, I like better HPS 4.1 at low listening levels. It seems to have better resolution/imaging. With HPS 3.1 I can't resist turning up the volume

Pops are, to me, better handled by HPS 3.1. The entire vinyl noise appears more distinctly in HPS 4.1. HPS 3.1 has a more "soothing" effect on the vinyl noise. I guess it's related to the head amp pulse response (less overshooting in HPS 3.1) because this changes with the MC capacitive loading. 47Kohm/220pF is HPS 3.1 is audibly equivalent to 47Kohm/470pF in HPS 4.1. But also switching both to 100ohm input impedance levels the field?!

I'll invite a few friends to capture their opinions as well, then I'll draw the conclusions of this exercise. HPS 5.0 will be a new generation of Peltier cooled devices...

[Joachim Gerhard]

exiting ! You start to listen ! can´t wait to see the "cool" one. I look if i can find some gallium transistors.

[syn08]

Originally Posted by Joachim Gerhard

exiting ! You start to listen ! can´t wait to see the "cool" one. I look if i can find some gallium transistors.

HPS 5.0 is going to use BF862 in SMD. Probably the best low noise JFET available today, so sorry a P-channel equivalent doesn't exist...