Well I found a spare hour today.... and instead of concentrating on my new amp I thought I would bypass the input on my Lepai...why not....quick job I thougt...
Now bypassed and it has absolutely nothing there...pin drops....nothing!
This is very strange! I completely bypassed everything by running the RCA inputs through shielded wire to two of the pots ( giving me a balance control!) and then onto a set of Slimic caps (left over from a Charize mod)... then to a new pair of 20K input resistors to repace the 8K2's in there (must be because of some upstream series resistance on the old tone controls...
But when I power up there absolutely nothin...not a bean..the speakers are silent...not even a turn on thump?
I have completely bypassed the entire input section with no connections to the board what so ever... is there somethimng else I need to sever on the tracks other than the input channels?
There are no bad conections/solder joints as I have DMM'ed the lot and there is no logical reason for the lack of sound...what gives?
Now bypassed and it has absolutely nothing there...pin drops....nothing!
This is very strange! I completely bypassed everything by running the RCA inputs through shielded wire to two of the pots ( giving me a balance control!) and then onto a set of Slimic caps (left over from a Charize mod)... then to a new pair of 20K input resistors to repace the 8K2's in there (must be because of some upstream series resistance on the old tone controls...
But when I power up there absolutely nothin...not a bean..the speakers are silent...not even a turn on thump?
I have completely bypassed the entire input section with no connections to the board what so ever... is there somethimng else I need to sever on the tracks other than the input channels?
There are no bad conections/solder joints as I have DMM'ed the lot and there is no logical reason for the lack of sound...what gives?
Fin said:
hey fin,
When I say balance control, I just mean that I use one channel of each dual pot.
I also completely removed them from the board and rotated them to be isolated.
You can see from the pic that there is nothing untoward...wonder what happened? Pardon the Phone/camera quality...
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What does the brown wire do in the twisted pair that hops off the balance contols to the caps?
I see that the white wire comes from the wiper - good. And the brown wire from ground - OK, but where does it go?
Where does the signal go after the cap and resistor? Right to the sub board? Did you break the traces from the sub board to the main PCB?
Put a finger tip on the connections of the new input caps. Got hum?
I see that the white wire comes from the wiper - good. And the brown wire from ground - OK, but where does it go?
Where does the signal go after the cap and resistor? Right to the sub board? Did you break the traces from the sub board to the main PCB?
Put a finger tip on the connections of the new input caps. Got hum?
Hey Captain,
That brown wire is not connected at the other end, I just left the cat5 as a twisted pair and connect one end to ground to give it a semi shielded effect.... would have used the shielded wire but it got rather fiddly in there
The resistor is connected to the board where the other one was removed so it enters the signal path in exactly the same place but creates a break from the original traces.
No hum no nothing I'm afraid sir, even when you turn her on you don't even get the customary thump!... not even a click... but the power is definately there at the pins, I measured that as well.
It's really strange!
That brown wire is not connected at the other end, I just left the cat5 as a twisted pair and connect one end to ground to give it a semi shielded effect.... would have used the shielded wire but it got rather fiddly in there
The resistor is connected to the board where the other one was removed so it enters the signal path in exactly the same place but creates a break from the original traces.
No hum no nothing I'm afraid sir, even when you turn her on you don't even get the customary thump!... not even a click... but the power is definately there at the pins, I measured that as well.
It's really strange!
Hmmmm.... OK.
I have a modded Lepai that refuses to run on one of my SMPS - a 15V job. The LED lights, but no sound at all.
Go back to the standard 12V SMPS and all is good.
Don't know why it's that way. Bad contact at the power plug? Electric voodoo? Don't know. I put it on the shelf for the moment - might have to bring it back down.
I have a modded Lepai that refuses to run on one of my SMPS - a 15V job. The LED lights, but no sound at all.
Go back to the standard 12V SMPS and all is good.
Don't know why it's that way. Bad contact at the power plug? Electric voodoo? Don't know. I put it on the shelf for the moment - might have to bring it back down.
I wonder if there is some kind of signal detection on the input that mutes it when there is nothing going through that elaborate input section? That's pretty much whats happening really, it seems like it is muted.
Now that I've completely bypassed the input it may be thinking there is no signal there?
Just a thought... I'll have a closer look at the mute pins later...
Now that I've completely bypassed the input it may be thinking there is no signal there?
Just a thought... I'll have a closer look at the mute pins later...
Did I say a lot of offset? No, it's the same but now there is no turn on mute circuit so I get a BIG thump with those 10uf Cerafines.
Not that I care at all...
Before boxing her back up I put some copper shielding over the inputs and caps etc...
This is now the amp it should always have been
Excellent! as good as an amp6 once you have done all that I have
Now for my main amp to finish... come on Lee get a shuffle on
Not that I care at all...
Before boxing her back up I put some copper shielding over the inputs and caps etc...
This is now the amp it should always have been
Excellent! as good as an amp6 once you have done all that I have
Now for my main amp to finish... come on Lee get a shuffle on
Fin said:
Hi Fin, don't ask me to explain how the mute circuit works, it also appears to have an overvoltage aspect to it so that's probably why Pano's amp doesn't like 15V.
As far as removal is concerned you just need to remove the wire from the board to break the connection, it draws voltage on one of the wires and returns it to pin 11 on the other depending on the conditions.
I also removed the grounding resistor and the little inductor and just put a bridging wire in there to permanently connect it directly to ground. You leave them in I suppose and just remove the wire.
It really does sing now so I'm listening to it on my main system whilst I get my new amp finished. It's amazing how more 'open' the sound is with far better seperation and staging. I recommend shielding the inductors from the rest of the circuit, I think this also made a big difference, especially in such a small box.
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Good find on the mute circuit, Lee. I'll have a look at it.
Wanted to run the chip on 15V for a while to see how it does. Shouldn't be a problem, as the AMP6 runs on 14.5V all day without breaking a sweat. The diode at the input of the Lepai is going to drop the voltage a bit, so I may bypass it.
Wanted to run the chip on 15V for a while to see how it does. Shouldn't be a problem, as the AMP6 runs on 14.5V all day without breaking a sweat. The diode at the input of the Lepai is going to drop the voltage a bit, so I may bypass it.
panomaniac said:
Hi Michael, just wondering if you can do that without some extra diodes in there? Maybe that's why it has a protection circuit?
TA2020 datasheet..........
"Diodes (DO and DH) are Motorola MBRS130T3 (the DH diodes are required for VDD>13.5V)"
I changed out the diodes to the recommended ones when two of them failed after being left on for a couple of weeks.
About half way down the page there is a modded Lepai T-amp.......but the Google translation is not great.......
http://www.maurarte.com/T-AMP.htm
http://www.maurarte.com/T-AMP.htm
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gychang said:
I modded mine to the point were most of the board became redundant
, to that end, its quite a big box for a small amp!There are quite a few pictures and diagrams of what to do further back in the thread but not one collectively.
I would recommend bypassing the entire input section and wiring it in (in-air) through new resistors and caps, replace the power caps and use either a new quality pot or one for each channel.
IF you can find one for the right price that is... an amp6 is better and cheaper in the long run otherwise......
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