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Class D Switching Power Amplifiers and Power D/A conversion

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Old 21st June 2007, 06:24 PM   #511
schumpe is offline schumpe  Canada
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Default can i use 10k pot?

Hello,
I have a 10K Alps Blue Velvet audio pot. Can I use that as a replacement for the stock one in a SI T-Amp? Or do I have to get a 50K or 100K one?
Thanks
Dominik
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Old 21st June 2007, 07:44 PM   #512
Pano is offline Pano  United States
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That depends more on your source than anything.

Can your source (preamp, CD, DVD, TV, Tuner etc.) drive a 10K load? Most likely, yes.

Modern sources can usually drive 600 ohms without too much trouble, so 10K is not a worry at all. Pro equipment is normally 10K input impedance.

So if you have a modern solid state source, you'll be fine. If you are using a tube source, it would be happier with 50K or 100K.

Lower input impedances have the advantage of lower noise, that's why they are used. But I have had no noise problems with 50K.

A long answer to a short question.
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Old 21st June 2007, 08:22 PM   #513
schumpe is offline schumpe  Canada
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Long answer, yes, but also good!
So I can use my nice pot, that's sweet.

I guess I'm building pro-equipment here

Thanks a bunch.
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Old 5th July 2007, 01:06 PM   #514
schumpe is offline schumpe  Canada
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Default a couple more questions...

I have a couple more questions.

1) I added a 12000 microF power supply cap to my T-amp. I had one lying around, that's why it's such a large one. Is there any problem with using the switch connection on the T-amp board, rather than adding a switch to the power line before the new supply capacitor? I am using an external power supply, which doesn't have its own switch.

2) I haven't replaced the input caps, yet. I saw this picture in a gallery:

http://forum.stereophile.com/photopo...cat/505/page/2

Is it ok to leave the surface mount capacitor on the board and bridge it like in the picture? I would assume this is easier to accomplish, since I'm not that skilled with the soldering iron and I don't want to ruin something that sounds really nice now.


Thanks
-
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Old 5th July 2007, 01:35 PM   #515
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Yes, you can use the existing power switch holes. However, the traces on the board are very thin and I wonder about their ability to deliver appropriate power to the chip. They're so thin they can actually act as a fuse if you hook up the power backwards.

As for the capacitor, the quality (low ESR) of the cap seems to be more important that the amount of capacitance. Also having the high-quality cap close to the chip seems to be very important. Some steady-handed people solder the cap directly to the chip pins. So, you may get indifferent performance depending on what type of cap you're using and how far from the chip it is. One of the most important mods is to replace the cap (C10) in between all those inductors wih a higher value, low-ESR type. You can get a 680uf of the same diameter. Mouser sells a Nichicon that works fine in my experience. Others recommend panasonic FM series (Digi-Key).

Yes, just bridge the cap. It's easy enough to remove, but bridging the pads on the board is a pain. Just take a single strand of very thin wire. Just hold it in the corner where the existing cap joins the board, and just touch it with a hot iron, and it should melt. Then, curl the other end of the wire around the cap and repeat, then trim off any excess.

--Buckapound
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Old 5th July 2007, 01:49 PM   #516
schumpe is offline schumpe  Canada
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Thanks for the quick response!
I actually replaced C10 already. I used a 1000 microF Jameco cap. Sound is better than original. No idea about the quality of the cap, but I'm kind of reluctant to put too much money into upgrading a 30 dollar amp.
The big cap I was talking about is for the power supply.

I'll try bridging the input caps. Just trying to find some metallized film caps locally. Most websites have a minimum order of some 20 dollars or so. For the time being I'll probably go with the 2.2 microF electrolytics which I already have.

Cheers
-
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Old 5th July 2007, 02:05 PM   #517
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Try this. I've used these with good results:

http://cgi.ebay.com/Finest-Polypropy...QQcmdZViewItem

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Old 5th July 2007, 07:01 PM   #518
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I rewired my T-amp per Pano's diagram. It worked as a charm. I then decided to put it in a different box and do a better job soldering. I haven't changed anything except removing the original LED from the grid. I DIDN'T BRIDGE the LED connections. Now there's no sound. Should I have bridged the connections or the problem is elsewhere?
Thanks!
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Old 5th July 2007, 08:45 PM   #519
schumpe is offline schumpe  Canada
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I think it should work without the LED as well. I suppose bridging it is a bad idea.
You could always try to put the LED back in place. That's also an easy way to see if your amp still gets power or if there's something wrong with the supply.
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Old 21st July 2007, 08:52 PM   #520
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Hi all,

As a constant sceptic I went to try out the T-amp.
I modified it to get full bandwith and better powersupply decopling.

I must say I am amased, I had a friend over for a lisening session and he is as pretty much amased as I am. We both agreed that something that small donít have the privlige to sound as good.

The bass is tight, the top is nice. It a very nice amplifier and my friend is going to order two, we are going to give another common friend a listen since he also is looking for a upgrade.
Iím not gonna give the classic audiophile critic, it is a very nice amplifier worth much more than it's list price.

If anyone is on a small budget, buy the t-amp. Thats all.

Best regards from the tube-o-phile,

Mags
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