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Old 14th September 2005, 09:53 PM   #11
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Quote:
Originally posted by BWRX


Are you sure? It says it's available in TO-220 and PFM (surface mount) on ti's site.
The only product currently available in the U.S. is the TL783TER (the TL783CKC was the TO-220 version.) It shouldn't be difficult to utilize the TL783TER -- save for the fact that it has to be heatsinked with copper area.

You can "scale" the POOGE 5.51 regulator and avoid using an opamp by changing the transistors, resistor values etc.
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Old 15th September 2005, 04:23 PM   #12
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Default tl783

Hi Beppe,

Yes, you should have a capacitor to ground from the output of the TL783 anyway. The inductor is then connected to the output of the regulator (junction between regular and capacitor) with another capacitor to ground after the inductor. All it is basically doing is adding a low pass filter after your standard TL783 regulator circuit. If it is Class A there will no change in current, so you could probably use even more value of inductance than I originally suggested without worrying about loss of regulation. With all power supply decoupling, it is good practice to use a quality Tantalum capacitor as smoothing, in addition to the normal electrolytic. Tantalums work better at surpressing higher frequencies. You can also add a couple of ceramic capacitors to get rid of RF noise if you wish. As far as I am aware the TL783 is still available in TO220 in the U.K, as I have only recently used one in a 100v constant current source circuit.

If you need any more advice please ask.

regards,

Steve
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Old 15th September 2005, 06:45 PM   #13
beppe61 is offline beppe61  Italy
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Quote:
Originally posted by Dark Harroth


> 250? For that?

Dear Mr. Harroth,

thank you for your kind and valuable reply.
Unfortunately here in Italy is not very common to find good deal on electronic equipments, even refurbished.
Yes. The list price is 250 euro (maybe I can get some small discount but I don't know).
I am tempted because it is variable from 0V up to 60V and it could be fine for powering some DIY prototype of preamps that I have in mind.

> Are you sure you don't want to try the schematic in the datasheet?

I am really interested in the TL783.
It is very convenient and it seems easy to use.
I am just doubtful about the residual ripple, that should be the minimal possible.

> A 44000 uF capacitor bank will not cost you more than 40 euros,

WOW. 44000 uF ! I thought that something like 2200 uF /100 V were enough. The circuit draws about 0,1 A at 60V maximum.

> the IC costs itself about 5-6 euros and the transformer+rectifiers - 50 euros.
In total from 100 to 120 euros.

The price is very tempting indeed.
But the Sorensen appears a lab grade power supply.
Anyway I have not the specs.

> Why waste so much on a PSU, that in fact may not perform as equally as the IC?

Are you telling me that the TL783 based PS could be better performing that a lab grade PS?
I am doubtful about this.

> I'd try to understand you if it were a brand new PSU, but it's
second-hand.

But maybe built to very high standards.
I really don't know anyway.

> A preamp doesn't even need a PSU with current/voltage adjustment if you've tested it already and it works.

I agree completely. The circuit worked fine with a rudimental PS but the output was not the last word in noise etc.

> P.S.: if I were you, I'd buy a transformer, some Schottky rectifiers and the left over money from those 250 euros I'd spend on capacitors.
I have some problem in selecting the best parts for the PS (diodes and caps above all other things).
Caps, for instance, had an unbelievable influence on the sound.
I had a very old Mallory cap on hand and I liked it immensely.
As I said before, here in Italy is very difficult to find the best components and the price are insanely high.
Any suggestion will be very welcome and appreciated here.

Thank you very much again.
Kind regards,

beppe61




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Old 15th September 2005, 06:54 PM   #14
beppe61 is offline beppe61  Italy
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Default Re: tl783

Quote:
Originally posted by steve hawkins
Hi Beppe,

> Yes, you should have a capacitor to ground from the output of the TL783 anyway. The inductor is then connected to the output of the regulator (junction between regular and capacitor) with another capacitor to ground after the inductor. All it is basically doing is adding a low pass filter after your standard TL783 regulator circuit.
If it is Class A there will no change in current, so you could probably use even more value of inductance than I originally suggested without worrying about loss of regulation.

Inductors are indeed very often present in audio preamp (expecially tubed ones).
I think that their effects could be very remarkable in lowering residual ripple but they are more complicated than a R-C filter.
Are very much more performant than simpler R-C filters?

> With all power supply decoupling, it is good practice to use a quality Tantalum capacitor as smoothing, in addition to the normal electrolytic. Tantalums work better at surpressing higher frequencies. You can also add a couple of ceramic capacitors to get rid of RF noise if you wish.

Good to hear that. No experience with tantalum caps.

> As far as I am aware the TL783 is still available in TO220 in the U.K, as I have only recently used one in a 100v constant current source circuit.

It seems also available here from RS Components.


If you need any more advice please ask.
regards,
Steve
Dear Mr. Hawkins,

thank you sincerely for your extremely kind and valuable help.
I will try to do my best.

Kind regards,

beppe61
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Old 16th September 2005, 12:00 PM   #15
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I use a very large capacitance bank when powering my preamp. Nothing else. I've tested several types of capacitors from different manufacturers, and the worst imho (it also appears to be the most available) is Jamicon. Never buy those Btw, you can use a capacitance amplifier, that was discussed here.

And also I don't trust everything that's not bought new, especially after I bought a used kepco psu. A few hours after I had turned it on to test a self-made battery charger it sparked a few times inside it and the electricity got shut down in the whole apartment. So I lost 150 dollars.

And, tantalum caps produce noise and are used mainly in digital (i.e. PC) power supplies.
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Old 16th September 2005, 12:13 PM   #16
beppe61 is offline beppe61  Italy
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Quote:
Originally posted by Dark Harroth
I use a very large capacitance bank when powering my preamp. Nothing else.

You mean that you don't use any kind of regulation?
I think the at YBA they do the same.
Why don't you like voltage regulators?
Do you think they influence the sound in a negative way?
That is very importnat to me.

> I've tested several types of capacitors from different manufacturers, and the worst imho (it also appears to be the most available) is Jamicon. Never buy those

I record your precious suggestion.
Thank you. Actually Jamicon caps ar not that common in high-end products. This must say something.

> Btw, you can use a capacitance amplifier, that was discussed here.

I think it is a little too complicate for my taste.
I would like to stay simplest as possible.

> And also I don't trust everything that's not bought new, especially after I bought a used kepco psu. A few hours after I had turned it on to test a self-made battery charger it sparked a few times inside it and the electricity got shut down in the whole apartment. So I lost 150 dollars.

That is a very important point.
I sometimes go to electronic fairs and there is surplus material.
I don't know what to do beacuse it is difficult to assess the real quality of the components.
Once I bought a lot of dried out caps.
It is my personal experience that capacitors are maybe the most important parts of a power supply.
They also influence the resulting sound of audio equipment in an unbelievable way.
Actually I did not believe it until I heard it.

> And, tantalum caps produce noise and are used mainly in digital (i.e. PC) power supplies.
Thank you for your extremely kind and helpful suggestions.
Kind regards,

beppe61
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Old 16th September 2005, 12:42 PM   #17
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Quote:
Originally posted by Dark Harroth

And also I don't trust everything that's not bought new, especially after I bought a used kepco psu. A few hours after I had turned it on to test a self-made battery charger it sparked a few times inside it and the electricity got shut down in the whole apartment. So I lost 150 dollars.
Used test equipment doesn't go to Heaven, it goes to EBay. Quite frankly, some of the stuff on EBay at the moment is "stems and seeds".
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Old 16th September 2005, 04:05 PM   #18
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Quote:
You mean that you don't use any kind of regulation?
I think the at YBA they do the same.
Why don't you like voltage regulators?
Do you think they influence the sound in a negative way?
That is very importnat to me.
I don't trust single-chip regulators, because they add audible noise when I use a low-level signal source and have to turn the volume to the highest level. And making a hi-performance discrete design is a very time/nerve-costing idea.

In my two preamp projects I use capacitors, because preamps usually don't consume more than 100mA, and with a 88mF bank at each rail I don't hear any noise. Of course, this depends actually on the schematic used, but my ones perform well.
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