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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old 16th April 2012, 02:37 PM   #22271
Edmond Stuart is offline Edmond Stuart  Netherlands
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Hi Jan,
The other way around.
Cheers,
E.
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Old 16th April 2012, 02:52 PM   #22272
jan.didden is offline jan.didden  Europe
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OK thanks Magnoman and Edmond.

jan
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Old 16th April 2012, 03:25 PM   #22273
ThorstenL is offline ThorstenL  Germany
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Hi,

Quote:
Originally Posted by EUVL View Post
So even for a power amp, rather less total capacitance then to have caps in parallel ?
You can use other methods to have multiple capacitors that do not share the problem of multiple parallel capacitors.

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Originally Posted by EUVL View Post
Any reason why (e.g. ringing between caps) ?
Multiple capacitors plus parasitics create interesting resonances.

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Originally Posted by EUVL View Post
How does that manifest itself sonically ?
Some will call it "glare" or "harshness".

Ciao T
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Old 16th April 2012, 03:59 PM   #22274
magnoman is offline magnoman  United States
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Isnt PS by-passing a design implementation to achieve a minimum required impendance over the desired range of frequency? I dont see how this rules out parallel capacitances if done properly.
I see the bigger issue (or at least more subjective) determinining the minimum required impendance over frequency.

-Antonio
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Old 16th April 2012, 04:12 PM   #22275
ThorstenL is offline ThorstenL  Germany
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Hi,

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Originally Posted by magnoman View Post
Isnt PS by-passing a design implementation to achieve a minimum required impendance over the desired range of frequency?
IF (and that big IF) it is designed accordingly, it may do so indeed.

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Originally Posted by magnoman View Post
I dont see how this rules out parallel capacitances if done properly.
Please re-read my original post:

"Usually, but not always, you see several capacitors in parallel..."

I do not rule it out, however in most cases a lot of parallel resonant circuits means a lot problems.

I can see sense if for example we see several smaller value film cap's paralleled to generate a low ESR that matches that of the big electrolytic cap and VERY LOW ESL and we see in parallel a much larger value capacitor with medium ESR, which essentially acts as snubber, but to be honest, I have yet to see such a use published.

Ciao T
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Old 16th April 2012, 04:13 PM   #22276
PMA is offline PMA  Europe
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John Curl's Blowtorch preamplifier part II
The biggest issue is always to dampen transients that result from switching of rectifier diodes. Almost no one cares, though it is well measurable. If not damped, very short spikes get through the amplifier and occur at speaker terminals. On can find them by a fast digital scope in a single shot trigger setting.
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Old 16th April 2012, 04:22 PM   #22277
ThorstenL is offline ThorstenL  Germany
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Hi,

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Originally Posted by PMA View Post
The biggest issue is always to dampen transients that result from switching of rectifier diodes. Almost no one cares, though it is well measurable. If not damped, very short spikes get through the amplifier and occur at speaker terminals. On can find them by a fast digital scope in a single shot trigger setting.
And if someone has carelessly "bypassed" the power supply, instead of removing these transients, they set off extensive tails of resonant energy.

If only instead the designer had elected to soft switching rectifiers (or schottky ones) place a smidgen of inductance and resistance between multiple cap's of the same type, snub the mains transformer and had carefully considered and snubbed the bypass network...

Shame I almost never see this kind of design.

Ciao T
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Old 16th April 2012, 04:51 PM   #22278
john curl is offline john curl  United States
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All my 'A' rated products have high speed, soft recovery diodes throughout.
AS DOES the modified HCA 3500 under discussion, once changed.
Subtlety in adding snubbers and RFI proofing are not completely worked out in this example.
The best reason that I can determine for using a minimum of paralleled power supply capacitors of similar value, is that the capacitors are poorly placed relative to what they are actually supposed to do, and essentially generally do nothing, but create secondary resonances that can easily be simulated with a transient analysis of a similar network with the inductance of the caps and wiring added. Of course, you need a low impedance at the circuit itself, and there I usually use a REALLY GOOD polystyrene or polypropylene cap, that I now to be well internally damped, and generally well behaved.
While this may be obvious to some, is was NOT obvious to me for about 5 years, when I allowed these extra caps to be added to the design. When we removed them, the sound got better for the HCA-3500. End of story.
When we get finished with these details, you might be interested in what else we did.
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Old 16th April 2012, 05:25 PM   #22279
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by magnoman View Post
Isnt PS by-passing a design implementation to achieve a minimum required impendance over the desired range of frequency? I dont see how this rules out parallel capacitances if done properly.
I see the bigger issue (or at least more subjective) determinining the minimum required impendance over frequency.

-Antonio
Yes, a single cap may have a specific resonance peak (in fact all caps have that).

The purpose of the additional parallel cap is to lower the first resonance peak, and replace it with a lower one (at higher freq). Then you use another parallel cap to lower THAT resonance and replace it with a lower and higher freq one etc.
But you must know what you do, you must know the parasitic resistance and inductance of the various cap types of course.
If you are interested in this, there a set of very nice articles with graphs on my website by Kendall Castor-Perry (aka the Filter Wizzard).

jan
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Last edited by jan.didden; 16th April 2012 at 05:28 PM.
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Old 16th April 2012, 05:31 PM   #22280
john curl is offline john curl  United States
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Without the hi speed diodes, we are now in 'B' territory, and I am reasonably sure that if just the circuit board mods were implemented, we would have a pretty good product, much like the HCA-2200, but more powerful, that would satisfy most customers.
Now, to go for the 'gold'! How can we make this into an 'A' rated product?
With the hi speed diodes we get a step closer, but there is more to do.
First, every input and output wire has to be of a certain quality, usually subjectively determined, and usually not from the hardware store, yet not very expensive, like some wires tend to be. Connectors, both input and output, have to be noted VERY CAREFULLY as to what material they are made of, despite their external appearance. We normally use a magnet to test for steel, etc.
At this level, we might be an 'A-' or a 'B+' . Close, but not near perfect. more later
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