Regulator for phono amp - vrefs, transistors, etc.

[davemar73]

I'm planning on making myself a phono preamp, probably op-amp based. So I'm going to start with the voltage regulator design for it. It will need to deliver +/-15v or 18v at up to a couple of 100mA or so max current (probably require a lot less). The main requirement will be very low noise. I'm also rather preferring a series regulator rather than a shunt job; and to use op-amps with pass transistors, possibly with the -ve side tracking the +ve. It'll be nice to have a design that's reasonably scalable for different applications.

OK, I know there's Jung's super regulator, but I do like to design my own stuff sometimes. So what I'm trying to decide upon is the various building blocks of the design. First part is the voltage reference, it will have to be low noise. What do you guys reckon achieves this? A TL431, a fixed voltage reference IC, a zener diode (maybe with constant current source)?

How about pass transistors? Most design seem to use bipolar, but what about MOSFETs? If bipolar any particular parts that stand out? The same goes with the op-amp choice?

Throw some suggestions at me!

Cheers, Dave.

[h_a]

Hi Dave,

it appears a bit awkward to me to start a phono amp by designing the regulator first

Especially since you want to go for opamps which have tons of PSRR at low frequencies.

Concerning your parts choice you have already all popular choices as I see it, so you're ready to start. I do not know any reason why you shouldn't use mosfets if that's what you want; the usual drawback is of course the large variation in VGS, so individual trimming is necessary. I guess that's one of the reasons they're seldom used.

However for 100mA the mosfets do not have much advantage compared to bjts, so it's a matter of taste.

A very nice regulator is the POOGE regulator, which you can also find in this forum. It's all discrete and performs excellent - though not that outstanding as the Jung. Of course such extreme levels need also proper pcb-layout and quite some testing to get the maximum.

Have fun, Hannes

[Gordy]

Although I have not used it I am told that the Analog Devices REF02 is a decent voltage reference component.

Kevin Gilmore used it in his dual-tracking supply, here: http://headwize.com/projects/showfil...lmore3_prj.htm


G.

[davemar73]

it appears a bit awkward to me to start a phono amp by designing the regulator first

I've got a pretty good idea in my mind what I'm aiming for the amp design. Something based around 2 gain stages using AD797s or something similar. I think the regulator design should be pretty much the same for any tweaks on that basic amp design.

How does the REF02 compared with the TL431?

Looking at this page http://www.tnt-audio.com/clinica/regulators_noise3_e.html it seems a simple zener-emitter follower gives very low noise. Could this be considered for use as a voltage reference (i.e emitter output going into regulator's error amp)?

[peranders]

I'm a bit skeptical to those measurements since you don't have a calibrated level. I real spectrum analyzer would propably given different results.

A good way to start is to inverstigate the noise performance in the datasheets. Remember though that the PS have to be more performing if the amp itself is made by discrete parts compared to opamp. Is it MM or MC amp you are going to design? Since you plan to use AD797 you don't have to have an extreme PS altough it doesn't hurt.

Have you checked National's new ultra low noise opamps?

[jackinnj]

Originally posted by peranders
Have you checked National's new ultra low noise opamps?

Actually, as well, check out National's new buffer the LME49600 -- the product folder at National describes its use in a power supply regulator.

The easy thing about the Jung super-reg is that PCB's are available from Old Colony Sound. Janneman of this forum did the noise and impedance testing for the 1995 articles. I use a surface mount version of the boards in one preamplifier, and the through-hole boards from OCS in another.

Jack

[AndrewT]

have you read W.Jung's paper on low noise voltage references?

[jackinnj]

Which Jung paper? The one in AX? I thought there was to be a follow-up to the article on current sources.

[jackinnj]

Originally posted by h_a
Hi Dave,

it appears a bit awkward to me to start a phono amp by designing the regulator first

I think you have to view the power supply as the engine, the preamp stuff as the transmission.

[AndrewT]

http://waltjung.org/PDFs/Getting_the...References.pdf