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Old 3rd June 2009, 01:21 PM   #331
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Default Re: 100nF monolithic bypass on the opamp rails

I've upgraded the power cap to a 25v 6800uF cap, and I was wondering if I could bypass it with a 100nF Polyester cap as I don't have any film ones?
Quote:
Originally posted by col
It must have been too hard to implement the overshoot diodes on a one-sided PCB, so they left them out. I don't see the logic behind it being a cost cutting measure when it obviously puts the chip at risk operating at voltages above 13.5v especially, if they have disabled the over voltage feature :|

I think the LM338T 5A regulator circuit before the power input is the way to go. That way you can connect it to any DC voltage from 32v down. Just remember that it requires the voltage to be at least 1.5v above what you want to operate at for regulation to work.

here is the data sheet:

http://pdf1.alldatasheet.net/datashe...SC/LM338T.html

I based my circuit on "FIGURE 3. Regulator with Protection Diodes". The caps I'm using are much bigger than the diagram and the one after the regulator is low ESR. The power is very clean.

http://pix.minirig.org.au/main.php?g2_itemId=1057

With the trimmer you can adjust the output voltage to what ever is desired. Iv'e got mine set on 13.3v.

col.
Thanks for the info, it does look some sort of regulator would be the best solution. I just this minute managed to fix my lepai, I replaced the TA2020 and it's not making music again.

Right now I've got a diode in series (where the inductor was) which drops 0.5v and I've also removed the zener diode that joins the fault pin to the mute pin so the overcurrent protection is now enabled.

I'll see how it goes, I bought 2 TA2020 IC's so if I cook this one I've still got a spare...

Also, I think overshoot diodes could be added, but it would be a bit messy as the heatsink would be in the way...
Quote:
Originally posted by col
For those that have kept their opamp in the circuit a minor mod but well worth doing is bypassing the opamp power rails.

http://pix.minirig.org.au/main.php?g2_itemId=1063

Best caps for this purpose are 50V 100nF monolithic, these are designed for bypass applications. Polyester caps can be used for bypassing but they are not as effective at very high frequencies.

col.
I'll give this a go, I've only got Polyester caps at the moment but I guess they will be better no caps at all?
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Old 3rd June 2009, 05:33 PM   #332
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Hello Mike, your polyester caps will work fine.
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Old 3rd June 2009, 06:58 PM   #333
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col: What section are the toroids on the 41Hz.com site? I can't find them anywhere.
Quote:
Originally posted by Calamaro
Hello Mike, your polyester caps will work fine.
Cheers, i'll give it a go,
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Old 3rd June 2009, 11:30 PM   #334
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Quote:
col: What section are the toroids on the 41Hz.com site? I can't find them anywhere.
I think it might be in the "members only items for sale" section. You have to be logged in to access it. They are changing the site though and its a bit hard to navigate at the moment.

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Old 3rd June 2009, 11:33 PM   #335
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Default Most Important Mods

I think the two most important mods that still need to be worked out are:

1. Implementing the overshoot diodes
2. Tone control detent switch

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Old 3rd June 2009, 11:49 PM   #336
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Default Empty section of board

Does anyone have any idea to what the empty section of the board is?

If you look in between where the output filter inductors and the power input inductor is you can see "1k*4" and 4 empty positions for resistors, under that there is a "0.47u" and the place for a cap.

Next to the power stiffener cap there is the place for a diode marked "5v". Also, down by the power switch there is a place marked "A733" and a couple of wire links that are empty.

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Old 4th June 2009, 12:52 AM   #337
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Default Re: Empty section of board

I've been listening to it all day today now I've fixed it, it sounds lovely.
Quote:
Originally posted by col


I think it might be in the "members only items for sale" section. You have to be logged in to access it. They are changing the site though and its a bit hard to navigate at the moment.

col.
I can't login right now, I went to get some build instructions for my amp9 yesterday and it says my password is wrong. I then asked them to e-mail me my password and it sent me a blank password!

I've posted this on their forum so with any luck they should get it sorted soon.

Would these work if they physically fit on the board?

http://uk.farnell.com/jsp/search/pro...sp?sku=1612716

It's rated for 3 amps but I'm not sure if it would give off more EMI compared to a toroid?
Quote:
Originally posted by col
I think the two most important mods that still need to be worked out are:

1. Implementing the overshoot diodes
2. Tone control detent switch

col.
For number 1, would there be enough room under the board for 4 more diodes of the same sort? They just need to be wired in a similar way to amp6...

For number 2, you could short the mute pin to ground, then replace the power/mute switch with a DPDT one that is the same shape so it would fit in the hole. With a dual gang switch you could then switch the audio input pins on the TA2020 between a direct feed from the RCA ins or a feed from the op-amp (with tone controls). Would this work?

If you don't mind drilling you could use a round toggle type switch and this way you could keep the mute/power switch as it is...

Quote:
Originally posted by col
Does anyone have any idea to what the empty section of the board is?

If you look in between where the output filter inductors and the power input inductor is you can see "1k*4" and 4 empty positions for resistors, under that there is a "0.47u" and the place for a cap.

Next to the power stiffener cap there is the place for a diode marked "5v". Also, down by the power switch there is a place marked "A733" and a couple of wire links that are empty.

col.
I haven't a clue, but that extra piece of PCB could come in handy if you wanted to short it to the +ve power input, then you could have the overshoot diodes coming from that extra piece on PCB...
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Old 4th June 2009, 09:34 AM   #338
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i think my lepai just broke. when its on there just comes a soft ticking sound and the tripath chip gets very hot. what might be wrong? some of the solderings of the chip are shorted? i just changed the pre amp to LM4562, but worked fine with it. after a night of sleep the amp was dead.
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Old 4th June 2009, 10:23 AM   #339
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Would the volume pot still work OK if I used a 50k log POT?

I've managed to break the volume pot trying to get thr front panel off!
Quote:
Originally posted by whelibob
i think my lepai just broke. when its on there just comes a soft ticking sound and the tripath chip gets very hot. what might be wrong? some of the solderings of the chip are shorted? i just changed the pre amp to LM4562, but worked fine with it. after a night of sleep the amp was dead.
Mine did exactly the same thing, constant ticking sound when unmuted?

Try removing the zener diode between pin 18 (fault pin) and pin 11 (I think), and see if you still get ticking.

With the zener gone, try connecting an LED and 2k resistor between pin 18 (fault pin) and GND and see if the LED lights up.

Your TA2020 could be dead, but it may just be a short in the outputs...
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Old 4th June 2009, 10:25 AM   #340
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Quote:
i think my lepai just broke. when its on there just comes a soft ticking sound and the tripath chip gets very hot. what might be wrong? some of the solderings of the chip are shorted? i just changed the pre amp to LM4562, but worked fine with it. after a night of sleep the amp was dead.
whelibob, sounds like one of your outputs has shorted. What voltage were you using? My suspicion is that the output inductors can't handle much current and fail, this then takes out the channel on the TA2020 chip. It happened on one of mine, luckily I had not modded it and only had it turned on for 20 mins. I was able to return it and get a replacement.

Mike has just had a similar failure, he was able to replace his chip.


I just put some more capacitance on the power cap:

http://pix.minirig.org.au/main.php?g2_itemId=1066

I might take out the zener too! Mike, did you replace it with a wire link or just remove it?

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