DIYHiFi.org

If you see ( or have) a good Chip amp based regulator please point me to it. I have missed it. I have built several with the LM1875. I have heard the idea proposed but haven't seen a finished example on the web.

http://cache.national.com/ds/LM/LM1875.pdf

I proposed the idea in the other forum on the blowtorch thread, but unfortunately I didn't have much time to work on it since, I suspected that you had worked on it (chip amps regs) when I read the thread where you proposed some very interesting circuits to improve the LM317/337 regs.

The Idea is to get a low noise reference (a few leds then an RC filter and a fet buffer for this purpose then the chip amp (LM3875/LM3886) with a gain from 5 to 10 ? soon I will have more time and I will probably work on it.

"Yes there is nothing like the inductive kick back from a smoothly running turntable motor with the constant load of a heavy high inertia flywheel running at constant speed."

You mean like on our ill-fated SOTA motor regulator project?

I guess "smoothly running" does not apply to something with so much cogging, right?

I'm pulling for you too, because I know you can't change even if you had to. [joke]

Jocko

Quite a while ago (like 1990 or so) I used an LM675 in a regulator design for a laser transmitter used in a broadband RF application. I also tried it for audio use - in the name of understanding the subtleties of such a regulator for my day job, of course. No, it was never published.

I think the LM675 is similar to the LM1875.

http://cache.national.com/ds/LM/LM675.pdf

An LM675 worked fine as a turntable supply, too. I ran the '675 at about 5 Vrms output into a toroid power transformer connected in reverse - the normal primary supplied the motor. Actually, there were two of these circuits used to supply in-phase and quadrature voltages to the motor. The signals were generated by using a crystal oscillator at several MHz, into a '4059 divider. The output of that was fed to a discrete DAC that was a variation of something found in the "Art of Electronics" - it was set up to give the I and Q sine waves. The output of the low pass filters fed the LM675's.

I also tried an LT1210 as a regulator. Using the internal compensation network allowed for a modest bypass cap to be used, even though it's a current feedback amplifer.

http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1009,C1028,P1329,D2461

It was so long ago, I don't remember what it sounded like and why I moved away from it. I think that was around the time I took a vacation from audio.

I am a little bit confused, so forgive me if it is a silly question.

Aren't you not worry about bandwidth ?

If I am correct, the LM1875 is rated at 70kHz bandwidth.
So how would it response to noise at frequencies higher than 70kHz at the output / feedback path ?


Patrick

What all this "our" stuff anyway?

I ran mine off of a Sultzer regulator with a big improment over the stock three terminal regulator. changing the regulator on the motor board was the key instead of the outboard preregulator "Electronic Flywheel" aproach. A certain person who we we will call "Mr. T "made some money selling modified SOTA Electronic Flywheels to the unwary. Three different value PP and PS bypass caps on each electrolytic for a preregulator for a three terminal IC (fixed voltage) motor power supply anyone? I could never keep a straight face and take someones money for dubious mods like Mikey could. Parts farms with very expensive parts. If they can't hear it make sure they can see it anyway....

Just a little?

The gain bandwidth for a chip amp is over 2 or three times that of a typical three terminal regulator which allows for lower output impedance. The distortion, noise. and PSRR at high frequencies are orders of magnitude better. High frequency response is controlled by the output cap which will by much large than zobel cap values show on the data sheet for USE AS AN AUDIO AMPLIFIER. You are not trying to swing any voltage on the output of a voltage regulator. You can run low closed loop gains for lower noise and output Z.

This is lost cause and I leave it to someone else to teach how to build racing motocycles to the training wheels set.

I'd go a bit beyond that. You are trying not to swing any voltage on the output of a voltage regulator.

I seem to recall standing right next to you when you tried to convince Rodney Hermann that we could.

Jocko

Hi Fred,



I've got a blue LED mod that really sounds great.

Works on regs, amps, preamps, empty boxes...

I swear.... wanna hear me?

Cheers,
greg

I sure don't remember it. I remember pestering a lot audio pesonalities but I don't remember ever meeting Rodney Hermann......

One or both of our memories are going........ I can't believe I would forget another Hun.

Speaking of Shunt regs - I've just set up these new arrivals for testing. Anyone recognise them?

Cheers,
Greg

They're set to 12V and I've loaded them with 4//1K for 48mA.
No visible hum.
Took a pic of the noise on 1mV/cm grid.

Have you a 7A22 plug-in for that scope? One of the best pieces of test equipment I ever bought. Great for zooming in on this type of stuff. I believe it goes to 10uV/cm. Probes are differential so it helps to get a more pure reading. What is the sweep speed?

jh

Hi Jim,

Sorry, didn't record the time scale - a few clicks over from a ripple sawtooth, probably 1mS/cm.

Plan is to hook the output up to Juli@ (balanced) for analysis through RMAA - as soon as I can get the new soundcard sorted.

Cheers,
Greg