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Class D Switching Power Amplifiers and Power D/A conversion

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Old 1st February 2007, 01:47 AM   #111
Fin is offline Fin
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Quote:
Originally posted by sashmo
I tried sending you an email but as I'm still under moderation I'm not able to. I do want a Lepai so could you email me the details?
I don't imagine the moderation thing is 2 way.
BTW I've just ordered 6 more NAN40s, 1 for me and 5 for a tech friend who is quite impressed with them.
I appreciate your taking the time and offering advice.
I'm trying to think of a safe way to get an email to you. I don't like posting email addresses on a public forum.

Yeah - I'm tempted to get a few more of the NAN40's myself.


Quote:
Originally posted by Lostcause
Hey Fin, thanks for the reply...
LM108's......The words 'rocking horse' and 'rare' spring to mind!
They do look good though!
I have found similar spec'ed regs but none at the corner shop that's for sure.
Looks like the good old LM317 for me! or wait until I've got a nice shopping list before doing an on-line order.
You should be fine with LM317. It's rated up to 1.5A so it should be OK. The main reason I mentioned LM1085 was becuase it is "Low Dropout".......so it only needs an input voltage that is 1.5V above the desired output voltage. Sashmo could use one with his 13.5V supply to bring the voltage down to 12V. However, if you are using that 20V supply - then LM317 will do. It needs the input to be at least 3V above the output. Sashmo could use one with his older AC/DC converter (probably).


Quote:
Originally posted by Lostcause
It's those caps that confuse me as well...some say no cap after the reg...some say two...some say...whatever!
I think it's going to be a switchable input as well, so I can do a quick A/B on the effect of more power...
TTFN
I would think that a large cap before the reg...and a smaller one after the reg would work well. It also depends how far things are away from each other. If the reg can be placed very close to the circuit it is feeding - and that circuit already has a power supply cap or decoupling cap - then you might not need to place a specific cap after the reg. However, if the reg is further away - like on another board - then a cap after the reg is required. This is where you end up with 2 caps between the reg and the device it is powering.

And....there is another cap.........that can be placed on the adjustment pin of an adjustable reg like LM317. This cap helps lower the noise of the reg and is normally in the order of 10-100uF.

Please not that I have not tried the following and it is only a suggestion. Proceed at your own risk.........
My initial feeling is that someting like this would be appropriate:
Power supply output (13.5V - 20V DC)........10,000uF cap........LM317 (set at 12V or 13.5V).......150uF cap...........DC input of T-amp PCB (with 330uf/470uf/560uf/680uf cap onboard).
The 150uF cap might need to be bigger.....but not bigger than the 10,000uF cap. It would be good to experiment with this value.
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Old 1st February 2007, 08:01 AM   #112
sashmo is offline sashmo  Australia
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Default Lepai

That's OK. I'll wait until the moderation period ends and play it from there. BTW they are $5 each plus p & p.
They seem to run pretty hot so I'm in the process of fitting a bigger heatsink.
Cheers
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Old 1st February 2007, 11:35 PM   #113
Fin is offline Fin
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Hey Sashmo

I just tried to send you an email through this forum...but you have not enabled the option to receive emails.

Go to your member profile...to edit options....and enable your email.....then I'll try again.
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Old 2nd February 2007, 12:48 AM   #114
sashmo is offline sashmo  Australia
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Turning into a saga isn't it.
I checked and I was set up to receive emails so it must be that way while I am under moderation.
Oh well if I keep posting, my time in the bin may be shortened.
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Old 2nd February 2007, 12:50 AM   #115
sashmo is offline sashmo  Australia
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Hey...
I just got out of the bin.....Thankyou moderators
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Old 2nd February 2007, 01:06 AM   #116
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Sashmo - try sending me an email......or got to "User CP - Edit Options - Hide Email Address" and select "No". An "email" button will appear below all of your posts............
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Old 11th February 2007, 08:01 AM   #117
zBuff is offline zBuff  New Zealand
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just a little update, I've removed the ground wire that was ontop the treble pot now. Removed some of the power links to the opamp that would have been a little parasitic on the power rail, haven't removed the ground lines to it yet though.

I would remove the blue LED is I could get rid of my DC offset.

Everything is just a little bit cleaner and sweeter now.

Does anyone think there would be any advantage is separating the power/digital ground and the analog ground?

Sorry still haven't got around to putting the schematic of the preamp portion into a computer yet, but I think I remember someone mentioning that a Tamp doesn't really gain much from a separate preamp stage, I don't think you'll be able to use the preamp on that board for anything like impedance matching anyway, I should have measured it for any DC offset before I distconnect the power to it.
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Old 11th February 2007, 10:04 AM   #118
Pano is offline Pano  United States
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Hi all, I was working on a Lepai yesterday - it's not all that easy to mod. Some tight spots in there near the chip board.

Anyhow, the signal flow is basically like this:

RCA -- Volume Pot -- DC blocking caps (says 3.3uF on PCB, nice were 10uF) -- Opamp (gain 6dB) -- blocking caps --- tone section --- blocking caps --- sub board -- chip.

I think that's it.


The input signal connects to the chip board right at one end. I cut the traces there. You could use that as a new input point, if you wanted to. Will post a photos here in a minute.

I had a 1st planned to use the opamp as an active low pass filter, as this is going to be a bass amp. Then for various practical reasons I decided to keep the LP filter in another box.

Sooo... I replaced the cheap 10uF caps that come after the pot with some nice Panasonic FC 3.3uF that came from an AMP6. From there I jumped to the edge of the chip board. Now my signal flow is: RCA -- pot -- blocking caps -- chip board. A much reduced signal path.

I know this is almost impossible to follow without photos and arrows, but I will post those ASAP.

Also replaced was the power stiffener cap. The stock was a 2200uF 25V of dubious quality. It's rather small for its value - not a good sign. I squeezed a big Panasonic 2200uF 25V in. That's my trademark cap, the Panny FM.

Also replaced the two little electrolytics on the chip board with 1200uF pannies. A very tight fit.

So now it's a Super Lepai. It will be renamed "Cafe de laPaix." If it were for full range use, I would use film caps on the inputs, not the 3.3uF electrolytics that I did. Soon I may swap them out. Just wanted to get it up and running, you know?
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Old 11th February 2007, 10:18 AM   #119
zBuff is offline zBuff  New Zealand
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I was wrong to remove the earth wire from the board to the top of the treble pot. Removing will cause hum when you touch the case or the volume pots with your hand.

I did something stupid, I tried pulling up one of the legs of the resistor to the blue LED, I must have had it shorted against something because when I turned the amp on there was spark and a little smoke. Now my amp is dead, the red LED just blinks. I think I might have fried the chip.

Should have double checked everything before turning it back on.
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Old 11th February 2007, 10:38 AM   #120
Pano is offline Pano  United States
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Oh dear, that's bad news. What could you have shorted to kill the amp? The outputs are pretty robust.

Check again, maybe you can save it.
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