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Class D Switching Power Amplifiers and Power D/A conversion

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Old 8th January 2013, 09:22 PM   #621
vdij is offline vdij  Moldova
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U+-50V, Rout-8 Om, F-1kHz, bridge. P.S. Bridge preamp.
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Last edited by vdij; 8th January 2013 at 09:48 PM.
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Old 10th January 2013, 10:34 AM   #622
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Quote:
Originally Posted by peterhenk View Post
Hi Rens,

Clear, will use a "star" for V+ / V- too.

Once ready I will post a picture ;-)

Thanks
Peter
Hi Peter,

I built my amp with a wiring quite similar to your sketch. I showed some pictures of it in the pictures-thread.

Class D Amp Photo Gallery

I have no hum and no problem with ground loops.
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Old 16th January 2013, 08:24 AM   #623
4real is offline 4real  Netherlands
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Yesterday, I build a test setup with A1000SMPS and 2x L-15D-PRO (see Class D Amp Photo Gallery post 606, connected to a miniDSP 4x10 HD. All is working fine, sound is good, but bass is lacking a lot. My old UcD400, and even cheap *** T-amp had a much fuller bass.

It might be the DC blocking cap, but I guess that only part of the story. Could it be that the miniDSP is not comfortable driving the low imput impedance of the amp? If so, I'll try adding a unity gain buffer in front of the amp to improve things. Are there any other people that noticed this?
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Old 16th January 2013, 08:14 PM   #624
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Originally Posted by 4real View Post
Yesterday, I build a test setup with A1000SMPS and 2x L-15D-PRO (see Class D Amp Photo Gallery post 606, connected to a miniDSP 4x10 HD. All is working fine, sound is good, but bass is lacking a lot. My old UcD400, and even cheap *** T-amp had a much fuller bass.

It might be the DC blocking cap, but I guess that only part of the story. Could it be that the miniDSP is not comfortable driving the low imput impedance of the amp? If so, I'll try adding a unity gain buffer in front of the amp to improve things. Are there any other people that noticed this?
Hi 4Real

Must be your miniDSP not liking the L15D , the input cap of 22 micro's has an impedance of 390 ohms at 20 Hz , that gives a - 1 dB at 20 Hz with the 3k23 input impedance ( Unsuitable for "Passive" Preamplifiers post #390) of the amp . My system improved slightly in the Bass region after I added two 12000 uF buffer caps on the A1000SMPS.But even before that Bass was very good .

Cheers ,

Rens
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Last edited by doctordata; 16th January 2013 at 08:32 PM. Reason: Typo
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Old 17th January 2013, 07:26 AM   #625
4real is offline 4real  Netherlands
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Thought so. I'll try connecting my iPad and see if that works better bass wize. If it can drive a headphone, is can surely drive the amp. If so, I'll be adding a LM4562 buffer with unity gain in front of the amps, giving in 100k input impedance. I have aux power on my PSU, so this sould be an easy fix. I just hope that it will all still fit in the case I have in mind.

About the extra buffer caps. That also crossed my mind. The A1000SMPS only has 10.000uF. I read somewhere that adding a lot more might destabalize the SMPS because it is tuned to the capacitance. I'll ask Cristy about it.
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Old 17th January 2013, 03:49 PM   #626
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Quote:
Originally Posted by doctordata View Post
Good remark Jan ,

You made me thinking , I have no audible problems with this and read allot about it . So I measured my carrier frequencies today and they are well within 25 kHz of each other . LF and RF are just 4 kHz apart and the rest of the channels within 10 kHz . If I use the amp in Stereo mode ( 2 channel RF and LF ) the sound stage is very precise and dolby digital is just stunning , enjoy it every day .
What I understand from the papers is that the THD is about 10 times higher at low power and the AM intermodulation and EMI are much higher if you synchronise the clocks . I have noticed that the new CxD250-HP from Christi at Connexelectronic has the ability to synchronise the clocks , so lets have some discussion here
It's quite easy to ad an external clock to my 5 L15D's just 5 resistors and 5 capacitors and a clock . Does it make sense ???

Cheers ,

Rens

And I'm drinking a nice Chardonnay
Hi,

I think the hassle of putting an external module to synchronize the clock is not worth for the small improvement on distortion.
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Old 17th January 2013, 04:12 PM   #627
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I am currently using this one as a subwoofer amp for my 4 ohms JBL GT5-12, because my IRS900 died after I accidentally shorted the output while there's an input signal. I connected it to the sub pre-out of my receiver, it has good and detailed bass but lean and not so powerful, also cone movement is kinda loose. Unlike my the previous IRS900 that makes my subwoofer sounded like an 18 incher, bass is much fuller and the cone movement is well controlled. ( both are using the same power supply ). There must be some cause why the L25d is not delivering full sounding bass.

I also noticed that the inductor is hot even when the amp is idle, I think it needs ram heatsink like the one attached.

Also when I tested it on full range, sound of the highs is a bit dry and sibilant compared to my other class ab amps, does anyone noticed this too?

I'll increase the self osc frequency to 450khz to check if the highs will improve.
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Last edited by jlester87; 17th January 2013 at 04:19 PM.
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Old 17th January 2013, 08:35 PM   #628
4real is offline 4real  Netherlands
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I just tested my ipad with the l15d-pro. Bass is just fine. Looks like the minidsp is indeed the probel here. It just can't drive the low imedance of the amp. So now I have two options:

- make a buffer
- replace the opamps of the minDSP for one that can drive lower loads, for example LM4562
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Old 17th January 2013, 09:50 PM   #629
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Originally Posted by jlester87 View Post
I also noticed that the inductor is hot even when the amp is idle, I think it needs ram heatsink like the one attached.
The ram heatsink might alter your inductor's ferromagnetic properties .

Cheers ,

Rens
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Old 17th January 2013, 09:59 PM   #630
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Your inductor shouldn't get hot, I have a 750 watt amp that runs slightly warm all the time.
Which core did you use ?
I use a t106-2.
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