sic NPN (SAND) upgrade for D1B1??

[qusp]

Hi Guys, i'm a SS fan, but I do have to admit to knowing very little about possible mosfet upgrades and what effect if any they have on sound quality. I can understand why they would help to make an amp more efficient or switch faster and at higher current, but arent we already past what we need there? i'm not so much skeptical, just curious and not at all beyond tweaks some might call dubious, so thats not my angle

now if I havent scared you off with the above question, I want to get some advice on how to test this for myself, im building the D1B1 symmetric buffer for my sabre dac (ackodac) and I would like to get some suggestions about how to best burn a couple hundred dollars on 8 fets (or less if anyone has any great suggestions), possibly even more like 40 a piece on the ones driving the cables and only 10-15 a piece for the other 4. the schematic calls for IRF610's, all are NPN for those not familiar with the schematic. I tried to PM Papa to see if he knew how I could upgrade the sand, but I guess due to overwhelming demand for his time, he has had to chose not to accept PMs, (which I totally understand) so thought i'd ask you guys.

I figure although this is a fairly low current application, I know the sabre sound very well and since there are only a few active devices in this design it might be a good opportunity to get my head around the 'sound' of different fets.

if you mods feel this thread might be best in the parts forum I apologize, feel free to move it, but since its fairly specific to this design at the moment I thought it might be a good place to ask. plus of course there is the possibility of Mr Pass himself popping his head in. thanks for putting the original design out there Nelson , I look forward to getting it running on all cylinders

thanks for reading

[qusp]

oh I should probably mention I have been looking at the sic devices from IXY and some schottkey from cree and IXY for the power supply, but wondered how this performance increase for power conversion translates into the audio band. also read good things about GaN, but same story

[Nelson Pass]

I have been playing with a number of new exotic parts, and
I can tell you that the interesting thing about them is not
the speed or low Rds, rather it is the transfer curves as
reflected in the distortion characteristic.

Some of these parts do not represent an improvement in this
regard, but a few exhibit much lower distortion. So far, the
lowest figures are about 20 dB better than the IRFP240.

[qusp]

aha ICIC and am I on track with the manufacturers above Papa? IXY in particular? come on gimme some sugar!!..ermm sand. I already enjoy the IRFP240, so those numbers are quite exciting to me, especially when trying to match the 140db DNR of the sabre. very excellent! now to go check out some transfer curves. thanks for the heads-up mate!!

[zhoufang]

Dear Nelson,

Have you tried Semisouth R550 in that position?
I'm interested to know how will it perform in the place of IRF610 in D1, but lacks the proper setup and equipment to do the measurement.
If you have interest to test R550 and have yet to do so, I can sent you a pair or a quad of R550.

Regards,
Zhou Fang

[Nelson Pass]

I spent some time with the R550 last weekend. As an output
device it has more bandwidth than the other power parts such
as the R100's or IRFP240's, and this is due to lower capacitance.
With that comes greater distortion at lower frequencies. For
this it would be natural if your source impedance was high or
you were building a tweeter amp.

The IRF610 still has lower capacitance, but also much lower
transconductance, about 1/5 as much.

I don't know what a D1B1 is, but if it's the IV for a DAC, then
you are better off with JFETs like the 2SK170's, maybe a
few in parallel.

[EUVL]

> you are better off with JFETs like the 2SK170's, maybe a few in parallel.

Or just use one 2SK372V (available e.g. from ampslab).
(Almost) equivalent to 2.5x 2SK170 in parallel.
Just need to watch your thermal management.



Patrick

[zhoufang]

Nelson

Thank you for sharing!

Originally Posted by EUVL

>
Or just use one 2SK372V (available e.g. from ampslab).
(Almost) equivalent to 2.5x 2SK170 in parallel.
Just need to watch your thermal management.



Patrick

Or I guess 2SK369 will do well too.

[qusp]

Originally Posted by Nelson Pass

I spent some time with the R550 last weekend. As an output
device it has more bandwidth than the other power parts such
as the R100's or IRFP240's, and this is due to lower capacitance.
With that comes greater distortion at lower frequencies. For
this it would be natural if your source impedance was high or
you were building a tweeter amp.

The IRF610 still has lower capacitance, but also much lower
transconductance, about 1/5 as much.

I don't know what a D1B1 is, but if it's the IV for a DAC, then
you are better off with JFETs like the 2SK170's, maybe a
few in parallel.

Hi Nelson, thanks yes it is indeed the D1 I/V but amputated and used as I/V and buffer for any current out dac. the circuit was taken from the D1 and there is soon to be an SMD version as well. check the latest revision by owen which is SMD and omits the buffer, but I have the PCB pictured on this page

thanks for the heads up though, I will grab some 2SK170 as well to try

[qusp]

yes the problem with them is heat though, I think I will grab some, but not sure if it will work with this PCB very well. this PCB is pretty much exactly the D1 I/V and buffer, which I am using until either Owen puts out a PCB or I get off my *** and do it on perf. as you know it uses 610's is it just learning that makes you choose Jfets here now or something else?