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Old 25th May 2004, 06:39 PM   #21
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Quote:
Originally posted by sss
[snip]lets say u got a power amp with a gain of 20 and u are measuring the thd at 1Khz freq and the thd at that freq is 1%
now u are doing the same test but under load conditions and the thd is still 1%

if the gain of that amp under load is only 10 the thd metter wount show nothing!! the thd remains 1% even if the signal is attenuated

hope that helps u to understand things better
No I don't. If the no-load THD is 1%, how can it also be 1% at load? All amps I have ever seen get worse under load. I also have no idea what is meant with the statement that at a gain of 10 the meter would not indicate anything? I realise this may be a language problem?

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Old 25th May 2004, 07:46 PM   #22
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Quote:
Originally posted by CRFX
I am interested to know what effect "better" caps have in the PS. When they are in the signel path "better" caps should have a noticible effect. But in a PS what differnence does it make? Do they make a smother dc voltage?

If you think about it, the PS caps are in the signal path, at least in a class B amplifier. If you draw arrows indicating the momentaneous flow of current through the output transistors and the loudspeaker when the rectifier diodes aren't conducting, you'll see the current going through the PS caps!

To what extent that affects sound is another issue, for those inclined to debate such things...

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Old 25th May 2004, 10:07 PM   #23
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Hi,

Quote:
To what extent that affects sound is another issue, for those inclined to debate such things...
And he asked himself...What is an amplifier?

A modulated powersupply perhaps? Must be....
So you'll be in part listening to that too, so.....

Does it matter what class the amp is running in for the powersupply caps to matter?
Not really, they're always there those nasty electrolytics, aren't they?
So yes, it would matter more in a class B or class AB amp than in a pure class A design but it matters nonetheless.

Nobody ever built an amp with nothing but polyprops in the PSU?
Guess not.

I'll be the first to admit it's easier to do with tubes due to the much higher rail voltages used but the difference is easily heard...

Thankfully electrolytics have much improved over the years but filmcaps haven't exactly been sitting still either.

Give it a try guys,
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Old 25th May 2004, 10:07 PM   #24
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Quote:
Originally posted by janneman
I also have no idea what is meant with the statement that at a gain of 10 the meter would not indicate anything?
what i'm trying to say is the gain can change with the load impedance or frequency and the thd metter wount show more distortion
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Old 25th May 2004, 10:53 PM   #25
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Quote:
Originally posted by fdegrove


Nobody ever built an amp with nothing but polyprops in the PSU?
Guess not.

There is some company making enormeous film caps to replace
lytics in PSUs and I think Jonathan Carr has used them, or
maybe he just talked about trying them. Not sure if they are
polyprop. though. Probably costs you an arm and a leg anyway.
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Old 25th May 2004, 11:08 PM   #26
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isnt it a proble with polypropylene caps they are large? for decouplin of DACs i need small caps to decouple as near as possible at the IC pins. MKS is avaiable in 2,5mm. Also multilayer ceramics X7R are very small. MKP10 is huge.
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Old 25th May 2004, 11:11 PM   #27
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Hi,

Quote:
There is some company making enormeous film caps to replace
No idea these even existed...

When using tubes most people use something like these caps:

SCR

Lowest available voltage is 250VDC which low for tubes yet too high for most thing SS.

Still the difference is easily heard when upgrading loudspeaker x-over series caps, for instance.

Quote:
Probably costs you an arm and a leg anyway.
Not cheap but still worth every penny.

Cheers,
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Old 25th May 2004, 11:15 PM   #28
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Hi,

Quote:
isnt it a proble with polypropylene caps they are large?
They're often not larger than their polyester equivalents except when you go down to very low voltage such as 63VDC perhaps.

Either way, shouldn't one design the PCB around what's one planning to use on it?
Pitch of robotic insertion components is always stated in the leaflets.

Cheers,
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Old 25th May 2004, 11:18 PM   #29
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Quote:
Originally posted by fdegrove


No idea these even existed...
Can't for my life remember brand or any links unfortunately.

Quote:

When using tubes most people use something like these caps:

SCR

Yes, the SCRs are available locally here. Not cheap if you need
larger values, but reasonable for smaller ones. We also have
ICEL. Didn't you speak well of them once?
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Old 25th May 2004, 11:28 PM   #30
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Hi,

Quote:
ICEL. Didn't you speak well of them once?
Indeed, I did.
For non-boutique caps they're among the best you can get in MKP.
Jadis uses them and I'm sure other branders have wound their wrappers around them too.

Unfortunately I can only get them in small values (~0.100F) and high voltages (~1000VDC+).

For SS PSU use I'm sure there are alternatives by means of the excellent BG caps, for instance or if all alse seems impossible, just bypass elcos with decreasing values of MKP in //.

100F elco + 10F MPK + 1F + 0.100F + 0.10F + 0.010F...

Knowing where to put them so they can work their best is just as important though...

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