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Old 8th June 2009, 09:49 PM   #361
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Quote:
Originally posted by Calamaro


Please check both boards under the switch: just a different wiring.
Congratulations for your hard work!
Cheers, I had a bit of spare time over the weekend, ideal soldering time.

I've checked the bottom of both boards, and the boards themselves appear to be identical, there are only changes around the switch area where a trace is cut and another connection bridged with wire on my original (modded) amp.
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Old 8th June 2009, 10:38 PM   #362
qingcai is offline qingcai  United States
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I just bid this one, ebay item: 400053344046

the seller ask for 25$ , I bid this for 23$.

looks it has better component. not received yet.
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File Type: jpg tamp-20w-01.jpg (92.4 KB, 983 views)
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Old 8th June 2009, 11:49 PM   #363
col is offline col  Australia
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Nice mods Mike. Not sure about the 2p coin though. I think it's illegal to drill holes in coins of the Queens realm

What did you end up doing with the Inductors? Can't see them from your photos.Can you upload a shot of the rear panel?

I think your new Lepai is similar to the last two that have arrived here. I notice that yours have polyester/MKT output filter caps. Looking at the MK1, I think that is how they started off. I thought all the MK2-3s had Mylar though.

The power switch / Mute switch has been re-routed. It now turns off the power. The start up pop happens on both versions. Iv'e reduced mine a lot by replacing all the 10uF caps for 2.2uF but there is still a small "pop".

Any joy with the tone controls detent switch? I'm waiting on you leading the way with that one.

col.
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Old 9th June 2009, 12:47 AM   #364
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Quote:
Originally posted by col
Nice mods Mike. Not sure about the 2p coin though. I think it's illegal to drill holes in coins of the Queens realm
I hope I don't get busted for treason!
Quote:
Originally posted by col
What did you end up doing with the Inductors? Can't see them from your photos.Can you upload a shot of the rear panel?
I'm still using the stock inductors right now, I've put an order in at RS and am waiting for some higher current ones to arrive.

Here's a shot of the back panel:
Click the image to open in full size.
It's not a work of art but I was happy to have something better than the stock connectors...
Quote:
Originally posted by col
I think your new Lepai is similar to the last two that have arrived here. I notice that yours have polyester/MKT output filter caps. Looking at the MK1, I think that is how they started off. I thought all the MK2-3s had Mylar though.

The power switch / Mute switch has been re-routed. It now turns off the power. The start up pop happens on both versions. Iv'e reduced mine a lot by replacing all the 10uF caps for 2.2uF but there is still a small "pop".

Any joy with the tone controls detent switch? I'm waiting on you leading the way with that one.

col.
I'm glad I've got one of each version, at least I now know the differences... I think I'll try swapping out the 10uF caps as when the amp is turned on it really makes my speaker cones move a lot.

As for the tone overrride switch, I thought I had a DPDT switch but it turned out to be SPDT so I've now ordered a DPDT and am waiting for it to arrive. It shouldn't be too hard tho, I'm thinking I may be able to use wires straight from the volume pot, as my volume pot is already hovering above the PCB...

I plan to have the 2 wires from the middle volume pot pins go to to the center 2 wires on the DPDT switch.

I'll then have out 2 wires on the switch go to the PCB were the volume pot wires should go, so when the switch is in one position it well work as normal, but I will have 2 more wires going after the op-amp but before the cap and resistor before the audio in pins on the Tripath chip... This way the switch in the other position should put the output from the volume pot straight to the TA2020 (cap and resistor)...

I'm not 100% sure if this will work but it should do in theory... As soon as I make some progress I'll be sure to post my findings.
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Old 10th June 2009, 02:52 AM   #365
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Quote:
Originally posted by qingcai
I just bid this one, ebay item: 400053344046

the seller ask for 25$ , I bid this for 23$.

looks it has better component. not received yet.

Qingcai,

There are many fake components in China. Have you seen the ceramic capacitor with MKT casing?

Anyway, listening is believing.
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Old 11th June 2009, 07:09 PM   #366
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Default tone control bypass mod

tone control bypass mod works

you need to follow along from pins 10 and 13, they should lead to a 20k resistor. Follow the 20 resistor, this should lead to a to a 2.2uF cap.

Unsolder the 2.2uF cap, and solder some wires in the PCB holes the cap came from.

Now, the shaded side is the signal from the op-amp, and the non-shaded side goes to the TA2020 input pins.

solder the wire from the shaded side to one of your switch terminals, so that then the switch is in this position, you will hear the signal from the op-amp.

Now, for the other wire, you need to solder this to the centre (switched) pin on your switch, and you still meed to have the 2.2uF cap inline also, I soldered the cap straight to the switch, then ran a wire from the cap to the PCB:

Click the image to open in full size.

Now, you should have one last pin on your switch, wire this up to the centre pin on the volume pot.

I did one channel at a time, this way you can make sure L & R do not get swapped over then you switch.

Here's both channels modded:
Click the image to open in full size.

Sorry for the out of focus pics, I only had a camera phone to hand...

Thoughts, sounds nice, I tried to match the bass and treble with the knobs to the bypassed signal, and you can definitely hear that the JRC4558 is not a nice op-amp!

EDIT: Feel free to replace the 2.2uF electrolytic caps with something a little nicer if you have it to hand. I stuck with the electrolytics as this was all I had!
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Old 11th June 2009, 11:38 PM   #367
col is offline col  Australia
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Quote:
tone control bypass mod works
excellent! Will have a go at it on mine when i get a chance and find a suitable switch.

Quote:
Thoughts, sounds nice, I tried to match the bass and treble with the knobs to the bypassed signal, and you can definitely hear that the JRC4558 is not a nice op-amp!
The opamp is the least of your worries. The resistors in the tone control are not matched and they feed into bad quality dual-gang pots that are inaccurate, the capacitors are not matched either and are the wrong values and of the cheap ceramic variety. This leads to the 2 channels going all out of sync as they pass through the tone control section. What a mess!

There is a lot to be gained by cleaning all this up, more than just simply swaping out the opamp. You need to match up the resistor pairs with 1% 1/2W metal film, then change the pots for something better and match up some MKTs of the right value. If you do this and get the stereo signal passing through the tone control in sync then swap out the opamp it will sing! (mine does


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Old 12th June 2009, 12:23 AM   #368
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Quote:
Originally posted by col
excellent! Will have a go at it on mine when i get a chance and find a suitable switch.
I'll try and grab some better pics of mine next time I have it apart, once you find the 2 caps to de-solder it's pretty easy from that point on. It works just like a source selector switch really, with only 2 sources (volume pot and op-amp).


EDIT: I hope you don't mind, I couldn't find a decent pic of the top of the amp so I pinched one from your minirig page! I've circled the caps that need removing:

Click the image to open in full size.
Quote:
Originally posted by col
The opamp is the least of your worries. The resistors in the tone control are not matched and they feed into bad quality dual-gang pots that are inaccurate, the capacitors are not matched either and are the wrong values and of the cheap ceramic variety. This leads to the 2 channels going all out of sync as they pass through the tone control section. What a mess!

There is a lot to be gained by cleaning all this up, more than just simply swaping out the opamp. You need to match up the resistor pairs with 1% 1/2W metal film, then change the pots for something better and match up some MKTs of the right value. If you do this and get the stereo signal passing through the tone control in sync then swap out the opamp it will sing! (mine does


col.
Well that does explain why I can hear such a difference when using that bypass switch!

I'll do these mods to fix the tone controls on my 2nd Lepai. I'm planning to use it in the car so I'll be having the tone controls in use all the time, so it will be nice to have it sounding good.
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Old 12th June 2009, 02:28 AM   #369
col is offline col  Australia
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Quote:
I hope you don't mind, I couldn't find a decent pic of the top of the amp so I pinched one from your minirig page!
no worries. What was the switch that you used to bypass the tone controls?

this is the minimum mods to clean up the tone control:

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

It uses 1/2W metal film 1% resistors and matched green caps (cheap better than ceremics though) and taiwan alpha pots.

If you want to do something even better, this one uses matched resistors and matched MKT caps, with the same taiwan alpha pots:

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

col.
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Old 12th June 2009, 01:59 PM   #370
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Quote:
Originally posted by col
What was the switch that you used to bypass the tone controls?
This is the switch I used:
http://www.mcmelectronics.com/product/58-10230

Any DPDT switch should work tho.
Quote:
Originally posted by col
this is the minimum mods to clean up the tone control:

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

It uses 1/2W metal film 1% resistors and matched green caps (cheap better than ceremics though) and taiwan alpha pots.

If you want to do something even better, this one uses matched resistors and matched MKT caps, with the same taiwan alpha pots:

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

col.
Thanks, I'll have to order a few more bits, the only thing I have right now is resistors but they are only rated for 1/8W.

I couldn't find anyone in the UK selling taiwan alpha pots, any other 100k log pot would work I imagine, are they a standard size? EG 20mm?
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