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Class D Switching Power Amplifiers and Power D/A conversion

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Old 28th January 2006, 07:47 AM   #1
Bgt is offline Bgt  Netherlands
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Just build the amp. in a housing. Still busy investigating why the crosstalk is so bad, 55Db@15khz. It is the same housing used for an UCD amp. and I had no probs there with crosstalk. Same PSU, protection pcb and wiring layout..well almost. Will post a pic later.
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Old 28th January 2006, 10:11 AM   #2
t. is offline t.  United Kingdom
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Look forward to reading what you think Bert when its up and running
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Old 28th January 2006, 05:40 PM   #3
Bgt is offline Bgt  Netherlands
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After routing the wires a bit different the crosstalk is much better(I am still busy finding out the crosstalk dependency of wiring layout). Tested the amp. with music and the sound is very nice.
Will do an A/B test later. Also found out that when using an output relay you have to put a resitor over the relay contacts otherwise it wont switch on. If it does not see a load there is some offset, 1.8V, which stops the relay from closing. Input impedance is a bit on the low side, 10k, it works with a passive pre but att. the volume a bit. Will keep you informed.
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Old 28th January 2006, 06:23 PM   #4
Pierre is offline Pierre  France
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Hello, _another user of coldamp_ !

I found a similar issue with starting. I asked them and told me that there is a slight offset when you start with no load (that's something not very recommendable with any Class-D amp, specially if you inject signal, anyway)

In your case, presumably that small 1.8V (no load) offset is detected by your DC protection circuit and, as you have your relays after the output (correct me if I'm wrong), it won't never switch on properly. They told me to add a 1K-2K resistor in parallel to avoid any problems, also in bridge mode setup (that is on the app.notes, I think).

So that seems to be not an issue at all.

Nor the input impedance, I think that it is even good in order to reduce noise and anyway almost every pre-amp (even passive) can drive it with no problems. I have used it even directly connected to my CD player.

I didn't have any problems with crosstalk, and I must say that I like the sound of my coldamps veeery much. What kind of speakers are you using, Bgt?

BTW: are they being so helpful as they were with me? I think that support is simply excellent.

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Pierre
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Old 28th January 2006, 07:23 PM   #5
Bgt is offline Bgt  Netherlands
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Pierre,
The relay is after the output, but it works. Speakers are Driade, the hex shaped towers...well actually more like pillars. The sound is nice, no doubt about it...but different. It is fuller in a way, sounds very powerfull. The UCD is leaner.
Sergio from coldamp is very helpfull.
Pierre, maybe you dont have a crosstalk issue because you perhaps use 2 monoblocs. I use 1 transformer driving 2 rectifier circuits, 1 for every amp. For me it is of utmost importance to have a low crosstalk value and a small amp. Don't like big cases. Low crosstalk gives space/direction/subtlety to the music(if recorded properly).
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Old 28th January 2006, 07:31 PM   #6
Pierre is offline Pierre  France
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Well, in fact I use a single supply.

Sorry, I don't know that speakers. What is the exact model (it's just that you have awake my curiosity ;-))

Just didn't pay attention to the crosstalk problem because it is totally unnoticeable while listening to music. It is more a purist issue, isn't it?
However, keep us updated on how it goes with your experimentation.
Do you have any other measures?

They told me that they were preparing a custom access for users with forum for direct technical support. I don't know if it is ready by now, they promised to give me a username and password.

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Pierre
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Old 28th January 2006, 07:36 PM   #7
Bgt is offline Bgt  Netherlands
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they already have a service forum. Got a username and password. And having low crosstalk values is normal I think. If there is high freq. crosstalk the sound becomes dull, borring. And how I love good sounding amps. so the music can make you feel very comfortable/emotional(if recorded properly). You get spoiled by beautifull sound...well........more addicted.




This is the only pic. of the speaker I could find.
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Old 29th January 2006, 12:16 AM   #8
Pierre is offline Pierre  France
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Where are the speakers? I can't see any speakers?
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Old 29th January 2006, 12:31 AM   #9
SY is offline SY  United States
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I hated to pull that pic, but....
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Old 29th January 2006, 11:07 AM   #10
Pierre is offline Pierre  France
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Wow! Bgt, I have also received an username and password: I am now able to communicacte with them directly at a secure personal page, with forums directly attended by technical support. They also offer a folder where we (users) will be able to see the latest documents.

Great value, I think. I hadn't seen something like this before from a supplier.
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