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Class D Switching Power Amplifiers and Power D/A conversion

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Old 6th February 2010, 10:09 AM   #991
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Join Date: Feb 2010
Hi there, just registered to this very interesting forum.

I'm currently modding both my Lepai TA-2020 aswell as my Sure TK2050 2x100W. I've come to the point where I replace the filter inductors, but stumbled upon an issue I hope you can help me with.

Background:

I bought a lot of 10pcs 10uH toroids, and seeing as newbie-ish I still am with class D-amps I bought cheap ones. What I realised now afterwards was that I see people all over using red iron powder toroids, while the ones I bought seem to be light green ( #12 material according to iron powder material properties ).

Now with background in place, to my question: Will the TK2050 or TA2020 work well with these inductors or is it like asking for trouble? My knowledge in inductors is very limited and I don't wish to ruin neither my amps nor my speakers.

Link to the item I bought: Inductor 10uH 10 uH +/- 10% 5 pcs - eBay (item 260512722675 end time Feb-23-10 01:11:57 PST)

I'm thinking of keeping the original output filter capacitors, for the TK2050 that should give me at least an extra 20kHz to the output I suppose just by replacing the original inductors.

Thanks in advance, I don't dare solder these toroids to the boards before I know it's a harmless procedure.
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Old 7th February 2010, 12:55 AM   #992
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Originally Posted by sendler View Post
You may want to try the output filter swap before you give up on it as it is not any harder to do than what you have done already and will make a bigger improvement. The stock coils are much too high in value and too whimpy in current.
Okay, I finally swapped out the output filters as you suggested, Sendler. The first thing I noticed was that perceived loudness is greater than before. I have to turn down the volume pot on my preamp quite a bit compared to pre-swap.

For several weeks I have been listening exclusively to my ST-70 rewired in triode mode, and I have been really liking what I have been hearing. I've been spinning vinyl 95% of the time. So that's been my frame of reference. I'm chastened and pleased to admit that I'm liking the Sure amp more at first blush. But as I've found with all things hi-fi, it's best to live with the sound for a while before passing judgment, as sometimes an impressive initial hearing later reveals previously overlooked deficiencies.

That said, this f'in amp is knocking my socks off! Delicate, powerful, refined, smooth, musical, it's got it all as I sit here listening.

That is all for now. Thanks to all of you who blazed the trail.
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Old 7th February 2010, 04:58 AM   #993
wwenze is offline wwenze  Singapore
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Default Strange hiss and failed soft-start

Double whammy, oh well...

I shorted the 1uF input capacitors via bare wires under the PCB, yet this gives me a hiss both times I tried. The hiss is there even without anything else connected to the input - just the shorting of the input capacitor, and goes away after I remove the short. What could go wrong here?

Also, I made a manual soft-start with a 270 ohm resistor (the only high-power value I had) between the PSU and the amp, it seems to take forever to charge - the voltage across the amp terminals never goes past 5.3V - with or without extra capacitors. Likely too high a resistance. I'm going to tackle this another way with a DPDT switch disconnecting the amp from the PSU and the capacitor in off position so there's nothing to disturb the capacitor's charging.

But is there any math to tell what value should be used just in case? I'm guessing ard 20~ish for 15000uF considering the PSU trips with over 4400uF normally.

Or I should just heck and just use 4400uF.
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Old 7th February 2010, 09:50 AM   #994
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wwenze, I suppose that your hiss is due to the bare wire acting as an antenna picking up RF. Why are you shorting the 1uf input cap and just not remove it instead?
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Old 7th February 2010, 12:14 PM   #995
sendler is offline sendler  United States
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Default Short

Quote:
Originally Posted by wwenze View Post
Double whammy, oh well...

I shorted the 1uF input capacitors via bare wires under the PCB, yet this gives me a hiss both times I tried. The hiss is there even without anything else connected to the input - just the shorting of the input capacitor, and goes away after I remove the short. What could go wrong here?
You are shorting the amp's 2.5v off set trimming circuit to ground through R14. You can remove R14 if you plan to remove the spike suppressor that is under the RCA connector but it still might short back through your volume control depending on it's layout. Because of the single rail power supply and the 2.5v trimming voltage, I think these amps will always need an input cap.
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Old 7th February 2010, 12:57 PM   #996
sendler is offline sendler  United States
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Default New favorite coil

I have a new favorite coil and I think my search is over. The 7443310390 from Wurth. I was very happy with the 7447709003 but then checked their web site before ordering a bulk quantity and found that they had a new coil on offer. It is their newest design and does sound a bit better than the 7447709004 or 7447709003 that I was using and they come in the perfect value right in between those two at 3.9uH. They don't look shielded but Wurth says it is a shielded bobbin and they measure with good shielding. They sound very transparent and holographic, and are the perfect size to drop right in.
Digi-Key - 732-2125-1-ND (Manufacturer - 7443310390)
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Old 7th February 2010, 02:03 PM   #997
wwenze is offline wwenze  Singapore
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Quote:
Originally Posted by sendler View Post
You are shorting the amp's 2.5v off set trimming circuit to ground through R14. You can remove R14 if you plan to remove the spike suppressor that is under the RCA connector but it still might short back through your volume control depending on it's layout. Because of the single rail power supply and the 2.5v trimming voltage, I think these amps will always need an input cap.
Thanks a lot. I see, I missed this when reading the schematics. Didn't spend much time reading it though.
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Old 7th February 2010, 02:21 PM   #998
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Quote:
Originally Posted by sendler View Post
They sound very transparent and holographic, and are the perfect size to drop right in.
"Drop in," eh? You mentioned how easy I'd find swapping out the coils, but I found replacing the coils difficult, since they're surface mount and the PCB isn't a through-hole design. I ended up soldering up some short lengths of wire to connect the coils to the board. Is this standard practice or am I missing something?

My music sounds good, so I'm happy for now.
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Old 7th February 2010, 04:17 PM   #999
sendler is offline sendler  United States
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Default All of the 12X12 Wurth coils drop in

Quote:
Originally Posted by soldersmoker View Post
"Drop in," eh? You mentioned how easy I'd find swapping out the coils, but I found replacing the coils difficult, since they're surface mount and the PCB isn't a through-hole design. I ended up soldering up some short lengths of wire to connect the coils to the board. Is this standard practice or am I missing something?

My music sounds good, so I'm happy for now.
Are you using the Wurth coils? They are 12X12mm the same as the ones you are taking out. They are easy to fit right back in. Getting the old ones out can be tough. I think I am going to buy another cheap soldering iron and have someone help me desolder both side at once. Otherwise the stock coils can be desoldered on one side while prying up which breaks the housing on the other side allowing the first contact to rise clear of the pad. Then the other side can be desoldered normally.
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Old 7th February 2010, 04:25 PM   #1000
sendler is offline sendler  United States
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Default Redo on favorite coil

Quote:
Originally Posted by sendler View Post
I have a new favorite coil and I think my search is over. The 7443310390 from Wurth. I was very happy with the 7447709003 but then checked their web site before ordering a bulk quantity and found that they had a new coil on offer. It is their newest design and does sound a bit better than the 7447709004 or 7447709003 that I was using and they come in the perfect value right in between those two at 3.9uH. They don't look shielded but Wurth says it is a shielded bobbin and they measure with good shielding. They sound very transparent and holographic, and are the perfect size to drop right in.
Digi-Key - 732-2125-1-ND (Manufacturer - 7443310390)
These three coils are all pretty close. I had another chance to really crank it up and am reversing my preference back to the 7447709003. It is a little more aggressive sounding and is therefore fussier about nailing the Zobel but also a bit more spacious. They are all about the same price.
Digi-Key - 732-1238-1-ND (Manufacturer - 7447709003)
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