Why 7805 is better than LM1085?

fmak · 2003-05-26 7:28 pm

However, when I replace the two 7805s in the CD player with LM1085s, the sound become worst. In summary:

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I have only just come across this post. The LT1085 is not a good regulator, the noise level measures at about 150 uV rms as per spec.

Good 7805s come in at around 40 uV.

I posted measurements over 1 MHz bandwidth some days ago and I have come to the conclusion that I shall in future select 3 terminal regs before insertion.

PMiczek · 2003-05-26 7:49 pm

What would you consider "good" v. "bad" for the 7805, select by manufacturer, or select/measure individual parts? Does this apply to the rest of the 78xx line?

PM

Elso Kwak · 2003-05-26 8:03 pm

Re: Component values

PMiczek said:
Was there something earlier in this thread about additional caps in parallel with C10, or am I confused? What kind of regulation do you expect with this circuit as shown?

And, thank you very much for posting it.

PM

Hi PMiczek,
Yes I added two 4700µF caps in parallel with C10. And I used a inductor with DC-resistance smaller than 1 Ohm. A loudspeaker crossover ferrite cored coil is suitable.

To answer your question about the kind of regulation:
Quite frankly I did not bother! I just did put some parts together with a glimpse at Guido Tents circuit that was borrowed from Audionote. The schematic is only intended for the TDA1543 and sounds better in my opinion than a MC7805, LM1086 and Jung Like regulator in this application. (In that order).
My circuit has poor load regulation but good line regulation as there is no feedback from the output.
:bigeyes:

PMiczek · 2003-05-26 8:33 pm

Elso,

you wrote,

My circuit has poor load regulation but good line regulation as there is no feedback from the output.

OK, I finally get it...

(I was wondering why this seemed so simple) Thank you again, I will try this out, at least in the lab.

PM

fmak · 2003-05-26 8:43 pm

PMiczek said:
What would you consider "good" v. "bad" for the 7805, select by manufacturer, or select/measure individual parts? Does this apply to the rest of the 78xx line?

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Measure noise voltage at intended load ; can't measure output impedance easily myself. Verify in service if low noise is needed, particularly for digital circuits. Look at specs before purchase; they can be different. NJM seems consistent. The new LT1963s are very good for noise and are well protected. The fixed voltage LT1085/6s are rather noisy.

PMiczek · 2003-05-26 8:49 pm

Thanks,

PM

fedde · 2003-05-31 5:22 pm

I am thinking about upgrading my 78xx regulators in my Nonoz II DAC project. Now, I use these:
- L7812CV (ST) (pre-regulation)
- MC7808C (F???) (DAC)
- 7805CT (Onsemi) (receiver)

I've heard that Motorola makes some nice regs. At least, the specs look quite ok (83 dB RR!).

I consider these options:
- MC78xxC (e 0,69 ex.)
- MC78xxAC (e 1,59 ex.)
- MC78TxxCT (e 2,91 ex.)

Anyone tried these (maybe also in a TDA1543 DAC?) ? Would the 3A versions (MC78Txx) be the best/worth the money !? I saw in an other thread they were supposed to sound better, but the RR is slightly lower.

Fedde

fmak · 2003-06-02 11:53 am

fedde said:
I am thinking about upgrading my 78xx regulators in my Nonoz II DAC project. Now, I use these:
- L7812CV (ST) (pre-regulation)
- MC7808C (F???) (DAC)
- 7805CT (Onsemi) (receiver)

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Of the many posts on 3 terminal regs, none seems to have drawn attention to the importance of the pcb or the way in which they are connected.

Grounding and layout seem to have an udue influence on the noise coming out of these regs; a clean ground and output layout provoke differnt kinds of rude bahaviour from different regs ie 7805, 1086, 323, LM340, Lt1963 etc. by way of spikes and even oscillations when loaded with resistors even. These can be of the order of several hundred uVs. I am talking here about an order of 10 cm of wire or track.

Cure these problems in situ and you end up with much less aggressive sounding digital.

fedde · 2003-06-02 12:46 pm

fmak said:
Grounding and layout seem to have an udue influence on the noise coming out of these regs; a clean ground and output layout provoke differnt kinds of rude bahaviour from different regs ie 7805, 1086, 323, LM340, Lt1963 etc. by way of spikes and even oscillations when loaded with resistors even. These can be of the order of several hundred uVs. I am talking here about an order of 10 cm of wire or track.

Cure these problems in situ and you end up with much less aggressive sounding digital.

Ok. I use a quite compact PCB for my DAC made by Jean-Paul. I think that the PCB is well made. The distance from the regulators to the IC's is <5 cm.

I understand that the correct decoupling and layout is more important than the actual regulator type.

Fedde

Elso Kwak · 2003-06-02 5:26 pm

NJM7805

Hi Fedde, I believe it was Fred who suggested to use the NJM7805 from JRC corporation Japan. I wouldn't disregard a hint like that! :bigeyes:

fedde · 2003-06-02 5:37 pm

Too bad that that part is not available from Farnell

I thought he recommended Motorola parts, probably some damaged brain cells again here

Fedde

Raj1 · 2003-06-02 6:02 pm

lm317

Hi,

How about the lm317T's, how do these compare to the 78** series etc?

Thanks
Raja

Elso Kwak · 2003-06-02 6:54 pm

Njm7805

fedde said:
Too bad that that part is not available from Farnell

I thought he recommended Motorola parts, probably some damaged brain cells again here

Fedde

Hi Fedde,
No brain damage over here!
Found back the post. It is # 12 in this thread!(end of point 7)
http://www.diyaudio.com/forums/showthread.php?postid=77078#post77078
Good luck, :idea:

Bricolo · 2003-06-02 7:48 pm

Re: lm317

Raj1 said:
Hi,

How about the lm317T's, how do these compare to the 78** series etc?

Thanks
Raja

that's a good question!

fmak · 2003-06-02 8:45 pm

fedde said:
Too bad that that part is not available from Farnell

I thought he recommended Motorola parts, probably some damaged brain cells again here

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You can get the NJMs from rswww.com

fedde · 2003-06-03 12:37 am

I could not find the NJM parts at rswww.com

Anyway, it would be to costly to get them to the Netherlands. Probably I would end up paying >50$ for a couple of regs.

Fedde

fmak · 2003-06-03 8:01 am

fedde said:
I could not find the NJM parts at rswww.com

Anyway, it would be to costly to get them to the Netherlands. Probably I would end up paying >50$ for a couple of regs.

Fedde

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It's in their paper catalogue. Tell me what you need and I shall see if I can get them for you.

fedde · 2003-06-03 11:12 am

fmak said:
It's in their paper catalogue. Tell me what you need and I shall see if I can get them for you.

That's cool! I sent you a private mail regarding this...

Fedde

Happy Ears · 2003-11-02 12:53 pm

Re: Re: Elso

Elso Kwak said:
Hi Andy,
I am not sure but I suspect the TDA1543 is spitting HF-garbage back into the powersupply. And second with all these clocks running in the same enclosure, Latch, Bitclock, etc. these might couple into the powersuply too, upsetting the regulator.

Elso , I was reading this former post cq disscussion about your 1543 power supply circuit ... interesting debate !
If there is any suspect that the 1543 dac is reversing HF garbage
back into the circuit ... why not using a coil to avoid this ?
perhaps interesting for Fabian too !

Why 7805 is better than LM1085?

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