OPA637/627 for sulzer instead of AD817/AD797? - diyAudio
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Old 20th January 2003, 11:25 PM   #1
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Question OPA637/627 for sulzer instead of AD817/AD797?

Im now in the asembling fase of my sulzer regulators and have some thoughts.

I have around a few opa627BP and opa637AP which i thought i might use for the sulzer regulators?

Perhaps any advantages/disadvantages between opa627/637 vs. AD797/AD817(ADs recomended by Jang/Didden)?


/kasra
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Old 21st January 2003, 06:15 PM   #2
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I know there are people out there who know this!!!

What parameters of an opamp should one look if its going to be used for a sulzer regulator?

/kasra
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Old 21st January 2003, 06:26 PM   #3
joensd is offline joensd  Germany
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Hi kasra,
there have been numerous threads about the Jung and Sulzer regulators on Headwize .
There are also loads of links to the articles of Walt Jung.
Sorry I donīt have them to hand.

Regards
Jens
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Old 21st January 2003, 09:52 PM   #4
Nicke is offline Nicke  Sweden
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Default Re: OPA637/627 for sulzer instead of AD817/AD797?

Quote:
Originally posted by kasra
Im now in the asembling fase of my sulzer regulators and have some thoughts.

I have around a few opa627BP and opa637AP which i thought i might use for the sulzer regulators?

Perhaps any advantages/disadvantages between opa627/637 vs. AD797/AD817(ADs recomended by Jang/Didden)?


/kasra
I donīt have the answer,but be careful with the OPA637.
It is not stable with gain less than 5.
I use AD817 in my Jung regulators and it works great...

Nicke
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Old 21st January 2003, 11:06 PM   #5
ALW is offline ALW  United Kingdom
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Default What to look for?

Ok, here's a potted summary from my experience having built about 30 of the Jung / Didden types, in my order of importance, and assuming bootstrapped op-amp supply...

1. Sonics

2. Open loop bandwidth / response shape / gain

3. Dynamic behaviour (speed, settling times etc.)

4. PSRR

5. Noise

6. Stability

The only thing that ultimately matters is the sonic performance, the AD817 and AD825 are, IIRC, quite similar in many regards, but sound totally different.

The AD817 looks slightly better on paper - it slews faster, has better settling times, wider bandwidth, open loop gain is higher, ol b/w is similar to the AD825, but in my opinion and that of many others who've tried it the AD825 sounds better, and is what I use primarily.

I've got some samples lined up that look potentially better than the AD825, but that's a secret for a select few for the moment

Andy.

P.S. The stability of the AD825 equipped reg's is wonderful too - I've not had a single unit oscillate, ever.

I couldn't say that for the AD797, which could be a total bitch to get stable!

P.P.S. Your choice of device could also depend upon application...
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Old 22nd January 2003, 12:34 AM   #6
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I use the AD797 in the Jung regulators installed in my Hafler SE-100 preamp with no stability problems observed. It's the
quietest voltage regulator I've ever seen.
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Old 22nd January 2003, 07:49 AM   #7
ALW is offline ALW  United Kingdom
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Default Stability

One thing to remember for non-unity gain stable op-amps is it's the noise gain of the circuit that's relevant for stability, not the DC gain.

As for the AD797, the load presented to it has a big impact upon stability - powering digital circuits often leads to instability, without further measures (lowering feedback bandwidth for example).

Steady-state noise is rarely, if ever, the most important PSU characterstic sonically.

Andy.
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Old 22nd January 2003, 11:20 AM   #8
lohk is offline lohk  Europe
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Andy, as a start, would a Jung type (or sulzer) regulator with a TL081 make sense ? These have low offset, compared to TL071s as I have learned just recently, but maybe slightly more noise. Does it make sense to make a Sulzer like regulator with 4 outputs using a single TL084 (for a NAC42.5 f.e.)?

Klaus
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Old 22nd January 2003, 12:30 PM   #9
ALW is offline ALW  United Kingdom
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Default Lohk

I've used TL071's in both Sulzer and Jung types, and they worked fine.

Impedance performance will be better than most 3-terminal reg's, but nowhere near as good as AD817 / AD825, can't remember the noise figure for the TL071, but worth a go, and they are cheap.

Andy.
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Old 22nd January 2003, 12:49 PM   #10
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Default sulzer etc

If you use a quad TL084 for a 4-channel reg you cannot use the bootstrap because there is only one supply pin for the 4 opamps. You can, if the output voltages are in the right range, use the supply of just one reg for the whole opamp. It would be interesting to see if there is any cross-coupling between reg outputs because of this.

To play it safe, I would use just a single 081 for each channel. Or, since we are talking cheap opamps, why not the original 5534? The sulzer was very good with that one, and they are less than a dollar apiece nowadays.

As already noted by other posters as well, I would not recommend the 797 unless you are really good at fighting oscillations or ringing.

Jan Didden
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