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PostPosted: 24 May 2010, 16:03 
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Joined: 08 May 2009, 08:20
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Location: Duesseldorf, Germany
Usually MKP caps (metalized polypropylene) are used in the signal path or as DC blocking caps.
A typical value is 1uF. Some good caps are from Wima, Audyn, Vishay, Mundorf, Solen and so on...
You may find them nearly everywhere for a good price..

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 24 May 2010, 16:46 
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That is good , because I ordered some 1Uf Polypropylene caps from DigiKey today!

Thanks!


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PostPosted: 26 May 2010, 12:13 
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fotomaticon wrote:
Ok, If I do go with a DC blocking cap what is the best type of cap and what value should be used.

You can find an example on Tom's DIY TDA2050 Hi-Fi Chip Amplifier build.
Cheers

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PostPosted: 17 Jun 2010, 02:07 
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Joined: 15 Dec 2009, 20:16
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Read my post on this forum : HIGH POWER ZCA vs GAINCLONE.

Using an input cap and resistor is up to you, but many serious Gainclone builders have omitted them due to detrimental sound influences.

Also, the Gainclone does not perform it's magic with 10,000UF per rail................that's totally over the top and serves no benefit as found by many builders...........in fact it stuffs up the sound.
You will only need the best quality 1,000uf caps on the rails and no bypass caps are required (I use BLACK GATES)


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PostPosted: 17 Jun 2010, 15:49 
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Hey ziggy,

once u use a GC for driving big speakers at higher volume you'll know what 10.000uF are good for.
I've also tested the GC with several supplies and different designs.

My experience still is that more capacitance makes the output capability more stable and accurate.
Each tone sits where it should be. Even at high power. With less capacitance the amp starts to
slow down or soften / distort, when long deep bass sequences run into the caps.
The supply must be able to follow the signal, and that's not the case when a small capacitance runs empty.

There is one simple, true and only fact about amplifiers:
They are nothing others than modulated power supplies and the
quality of sound rises and falls with the power supply quality.
If you want a fast and accurate amp - build a fast and accurate supply!.

What is a 300VA transformer good for, if the caps can't follow the current?!?
What will the caps deliver if their capacitance isn't enough to supply the circuit?!?

:idea: - just omit the caps and you'll have the best GC ever?!?

I'm also using 10.000uF per rail on the TDA2050. I've tried it with 4700uF, with 2200uF and MosFet regulators
(Cap multiplier and IRF840 discrete inline regulator). 2200uF was definately not enough. 4700uF was OK,
4700uF and MosFet filtered was way better... WTF - the best design was and is the simple 10.000 snubbered
supply from CarlosFM (ok - meanwhile a bit pimped up). Yep - a straight and unregulated high cap supply...

The difference between all the supplies was somewhat amazing!.

Gio took the TDA2050 as an example for the input cap. It has a reason why i (personal) use input caps.

The input caps i use are some good MKP types and i can say, that the sonic difference between cap / no cap
is very marginal. If not nearly NULL. I agree with the statements that caps can sound good or less good.
Once you've fried a CD-Player or a porta device or your speakers you'll really love input caps.
Good input caps i mean. And there are enough good and cheap input caps available -
reproducing good and accurate sonic results...

Do you really think that you're able to hear the difference between cap / no cap??? (That's not a question to annoy you!).

My favorite way to build amps is using accurate supplies and I/O protection (the simplest way - input cap).
May sound unusual to you. But, the amps sound very well, very satisfying (even the little TDA amp).
Isn't that what we all want? And i don't have to be afraid of frying my NAD player, PC-soundcard, mp3 player or my speakers.
Yep - that will be the case once the LM / TDA has shortened out...

Have fun ;-).

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 18 Jun 2010, 01:14 
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Joined: 15 Dec 2009, 20:16
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Hey Tom, I'll try some larger caps (10,000uf) at each rail and report my findings.I'll try this again as the last time I did this I think I had some bad caps which probably affected the sound?


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PostPosted: 18 Jun 2010, 05:59 
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Joined: 18 May 2010, 09:33
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On the input cap issue, I will be using a completely recapped (well all the electros) David Hafler preamp for everything going into the amp. So I guess I wont need the input caps afterall?

Alan


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PostPosted: 18 Jun 2010, 19:36 
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Hi Alan,

i would say - it dependes...

A proper preamp should have an DC blocking output cap or a well balanced
output with no DC at the end. I have no idea about the Hafler pre output - sorry.

Should be easy to check it (Schematic, DMM or so).

If the preamp provides a DC free output, it shouldn't be a problem to omit the input cap.
So - it's your choice. Simply be sure, that the preamp is really free of DC.

Ziggy,

i think if your last set of caps were that bad, the circuit wouldn't work at all.
We made out the bad experience that a capacitor failure
blows up the IC's or fries the speakers.
That's the same problem with using unbalanced rail fuses.

The LM chips provide a very good PSRR (rejection ratio). Nothing can happen here,
if you decide to use bigger caps. The only thing that could happen is current flowing back
into the caps, while the PS rejection jumps in. That makes the difference, but that wouldn't happen,
if the transformer isn't too big. That's discussed in several articles on the GC Webs.

Just test it out which capacitance you like best.

I'll surely stick with my 2 * 10.000 per rail.
A lot of other builders recommend 2 * 10.000 for the LM3886.

The LM 3875's (and kits) usually use 1500uF. They are mounted very(!) close to the chips.
The kits also come with the suggestion to use transformers at about 220VA - better more (300VA - Stereo setup).
With this transformers the caps charge and recharge very fast. But you really need "fast" caps then.
Maybe that does the magical trick... At the end, the real trick is what you like ;-).

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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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