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Old 20th May 2009, 10:44 PM   #241
col is offline col  Australia
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hmm, my ghettoblaster project didnt start out that well. i connected my 12v motorbike battery to my lepai t-amp with the powercord supplied and the cord started to overheat. probably shortcircuited the damn thing, due bad isolation of the cord :|
Mine didn't come with a power cord. whelibob, what voltage is your battery putting out? I noticed that the Lepai design does not have the overshoot diodes implemented. I'm wondering if that causes problems at voltages around 13.5v.

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Old 20th May 2009, 10:55 PM   #242
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I haven't found LM4562. I replace JRC4558 with OPA2134PA. The sound became crystal clear. I shall LM4562 once I found.
Panda, OPA2134 is a great sounding opamp, you probably don't need to try another. There is more to be gained in cleaning up the tone controls.

if you change the 3 pairs of capacitors with either green caps or MKTs and match the resistors, then change the pots (the supplied pots are REALLY bad) you will get the biggest sound improvement. The values for the Capacitors are 4 x 10nF, 2 x 39nF and 2 x 47nF. The resistor values are on the PCB.

http://pix.minirig.org.au/main.php?g2_itemId=976

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Old 21st May 2009, 08:31 AM   #243
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Originally posted by col


Mine didn't come with a power cord. whelibob, what voltage is your battery putting out? I noticed that the Lepai design does not have the overshoot diodes implemented. I'm wondering if that causes problems at voltages around 13.5v.

col.
the powercord vas faulty, it shortcircuited. i took a powercord from an old transformer and now it works fine. im probably also going to get a new op-amp, but im doubting about the capacitors and resistors, since i havent done alot soldering. if i change the op-amp and the pots, will it improve the sound alot? or do the capacitors and resistors make a big difference? should i get linear or logaritmic pots? same kinda pots for every slot? and how do i get the pot knobs off? tried to twist them out counterclockwise, but didnt twist that hard, so that the pots dont brake.
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Old 21st May 2009, 09:23 AM   #244
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don't take the knobs off until you have replacement pots, they break! The pots are standard B100k log pots. Any electronics shop will have them. The replacements I got are Taiwan Alpha and are much better. I wouldn't bother changing the opamp unless you do the tone controls. If you haven't done much soldering there is plenty of advice in this forum. Get yourself a temperature controlled soldering iron and a solder sucker (some prefer braid) first off.
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Old 21st May 2009, 12:00 PM   #245
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allright, how do these pots look like:
http://www.partco.biz/verkkokauppa/p...oducts_id=5430
manufacturer is Radiohm. it says 100kA on the pic :S
couldnt find same pots as you on ebay, all of them where mono pots.
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Old 21st May 2009, 12:24 PM   #246
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those pots (A100K) are linear. you need dual ganged B100K log pots. These are the ones I got:

http://jaycar.com.au/productView.asp...T&SUBCATID=773

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Old 21st May 2009, 12:41 PM   #247
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allright, how do these pots look like: http://www.partco.biz/verkkokauppa/...roducts_id=5430 manufacturer is Radiohm. it says 100kA on the pic :S couldnt find same pots as you on ebay, all of them where mono pots.
just clicked on the "english" version. says they are log pots. just the photo is a linear one. They should be fine, actually they look like even better quality

A friend has taken my first modded Lepai off me for a few bucks extra. Will have some photos up of the second one I'm doing soon. Have used matched MKT's in the tone control and replaced all the ceremics with monolythic caps.

One thing I noticed on the second one is that the heatsink mounting holes are not close enough to the chip, had to enlarge them so that the chip contacted properly. Also, the power switch has been re-wired and turns the led out now.

I'm going to have a go at replacing the inductors on this one.


photo of the board stripped down:

http://pix.minirig.org.au/main.php?g2_itemId=1030


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Old 21st May 2009, 01:39 PM   #248
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Quote:
Originally posted by col


Panda, OPA2134 is a great sounding opamp, you probably don't need to try another. There is more to be gained in cleaning up the tone controls.

if you change the 3 pairs of capacitors with either green caps or MKTs and match the resistors, then change the pots (the supplied pots are REALLY bad) you will get the biggest sound improvement. The values for the Capacitors are 4 x 10nF, 2 x 39nF and 2 x 47nF. The resistor values are on the PCB.

http://pix.minirig.org.au/main.php?g2_itemId=976

col.

Great. I can go to 2nd step next week.

Thanks a lot.
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Old 21st May 2009, 01:53 PM   #249
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Quote:
Originally posted by Gmorris
Panda360:

So did you try by-passing the input cap on your Lepai? If so, how was the end result?


I'm about to construct a portable "boom-box" using aluminum angles and some old Polk Audio bookshelf speakers. I'll post some pics once I'm done.

Gmorris,


I am not quite sure which one is input cap. Is it the largest one?
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Old 22nd May 2009, 10:21 AM   #250
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a photo of my new Lepai:

http://pix.minirig.org.au/main.php?g2_itemId=1036

I'm waiting on some new inductors and 2.2uF MKTs.

Gmorris, I swapped out all the 10uF caps for 2.2uf electros and it made no difference to the start up pop.

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