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 Post subject: Class D 100W power amp
PostPosted: 30 Oct 2014, 00:21 
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Dave, a DIY buddy, another member of the Melblourne Audio Club, hobbled together a Class D amp from a $30 Sure Electronics (STA508) module purchased on ebay. These are rated at 100W pc. First he tried it with a SMPS but later a linear PS for my he better results. I have heard the amp and thought it OK?

What have I to lose by trying one? Mine I will use the same module and a 27V linear PS. This PS will have a 10A rec. bridge and 30,000uf of filtering. The module, about the side of you hand, has ferrite chokes on the speaker lines to stop ultrasonic noise getting out. Dave replaced the input caps with better polies. Not sure ( no pun intended) I'd bother. There is a lot of surface mount on the multilayer brd. and Sure have gone to a lot of trouble to make it easy to use the brd. E.g. By mounting RCAs on the brd. plus the ability to remotely add RCAs.

I will have two inputs; one with a pot and one direct. This will allow the amp to by used by itself or with a preamp with no pot in the way. The enclosure is a 2U 19" rack mount.

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Website: retro-thermionic


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PostPosted: 30 Oct 2014, 18:44 
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Here is a link to the Class D module: http://store.sure-electronics.com/audio/audio-amplifier-board/medium-power

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
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PostPosted: 01 Nov 2014, 06:45 
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Got the amp finished after a long day. It worked first time. Had a click when the 4oz brass knob was touched so I brought the front plate to the PS ground potential. All good now. Tomorrow I should get a good listen. Max Vcc is 32V for max power . My PS delivers 25V under load. Not sure how much power I can drag from it.
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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
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PostPosted: 01 Nov 2014, 20:32 
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Hi Mark, all the class D amps I have heard recently (not in HT systems) have been pretty good. Powerful, quiet and low distortion as long as you don't overdrive them. Really nice efficiency as well. Next best things to tubes.

Good listening
Bruce

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PostPosted: 01 Nov 2014, 23:32 
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gofar99 wrote:
Hi Mark, all the class D amps I have heard recently (not in HT systems) have been pretty good. Powerful, quiet and low distortion as long as you don't overdrive them. Really nice efficiency as well. Next best things to tubes.

Good listening
Bruce

Bruce, "Great snapp'n duck's bums", I would never expect you to say "next best things to tubes". Now I can't wait to have a serious listen. I liked what I hear quietly and "yes" did find it sounded strained up loud.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
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PostPosted: 04 Nov 2014, 06:09 
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Had a chance to spend a little more time listening to Mr. "D". Here is my subjective banta;

Before I get too far into this I must add that the normal preamp I use, a 6N7 preamp designed by Suncalc, could not be used with an input impedance of only 22K to the Class D module. A new hybrid tube and Pass B1 preamp, (Parley) had to be used. I have not found Parley bright in the past but the music I was hearing today was very bright. Not only bring but a hard edge to the sound.

Imaging was razor sharp but sound stage was thin. Bass was full bodied, I really do didn't need my stereo subwoofers. Lots of gain and plenty of volume. Im jumping from a big heavy 300B to a $30 Class D amp. A big change. I still fell into the music. So not all bad. Tomorrow I will tone down the tweeters by 3db to see if that takes the bright edge off the sound. I named the amp "Mirage" because it doesn't really amplify the signal coming in. It produces a pulsed copy of the music, what may appear as a Mirage.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
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PostPosted: 09 Nov 2014, 07:18 
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I have been trying to get a balanced sound from my Class D amp "Mirage". I now have gone back to earlier Xovers on the speakers I was using to get sound brightness and glassiness out of the music. The old Xovers cross higher than the new ones. It has worked in part but maybe the tweeters could be dampened about 6db.

Also when the volume is up Mirage 'tends to distort to early.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 09 Nov 2014, 19:32 
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mwhouston wrote:
I have been trying to get a balanced sound from my Class D amp "Mirage". I now have gone back to earlier Xovers on the speakers I was using to get sound brightness and glassiness out of the music. The old Xovers cross higher than the new ones. It has worked in part but maybe the tweeters could be dampened about 6db.

Also when the volume is up Mirage 'tends to distort to early.

I have now dropped the tweeters by 3db and finally the sound is good and balanced. Time to enjoy. But soon back to the Silver Dragon (300B).

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 10 Nov 2014, 18:01 
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Nice work Mark. With the right setup, class-d amps can sound real good.

Cheers

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PostPosted: 14 Nov 2014, 01:47 
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Not to sure what is going on but the Class D amp was all distorted and awful the other day after a few hours of reasonable play. I have played it all day with my bigger 2-ways (VoXDeuX65) and it has not faulted. It may not like something in my other system.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
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