Tone control bypass switch implemented
Iv'e done the tone control bypass switch
a few photos, the last one shows the front panel with the fault led too.
http://pix.minirig.org.au/main.php?g2_itemId=1120
The sound difference is not so pronounced with mine. When the tone controls are set half way and then I switch to bypass there is only a slight difference.
thanks for the mod Mike!
col.
Iv'e done the tone control bypass switch
a few photos, the last one shows the front panel with the fault led too.
http://pix.minirig.org.au/main.php?g2_itemId=1120
The sound difference is not so pronounced with mine. When the tone controls are set half way and then I switch to bypass there is only a slight difference.
thanks for the mod Mike!
col.
had to wind back the tone bypass switch mod
The right channel kept dropping out, even though all connections were good. Mike, when you connected the wires from the switch to the volume pot center terminals did you disconnect the pot center terminals from where they were previously? My volume pot is still in the PCB. Could the PCB tracks be causing the problem? It's either that or all the additional bits of wire have caused more resistance and a drop in signal/power or something.
col.
The right channel kept dropping out, even though all connections were good. Mike, when you connected the wires from the switch to the volume pot center terminals did you disconnect the pot center terminals from where they were previously? My volume pot is still in the PCB. Could the PCB tracks be causing the problem? It's either that or all the additional bits of wire have caused more resistance and a drop in signal/power or something.
col.
That's strange... I left my wires from the volume pot still connected to the PCB, otherwise I would get no sound when I'm using the tone controls...col said:had to wind back the tone bypass switch mod
The right channel kept dropping out, even though all connections were good. Mike, when you connected the wires from the switch to the volume pot center terminals did you disconnect the pot center terminals from where they were previously? My volume pot is still in the PCB. Could the PCB tracks be causing the problem? It's either that or all the additional bits of wire have caused more resistance and a drop in signal/power or something.
col.
All I can suggest it to double check the connections, and also check no PCB traces have lifted as they tend to lift quite easily on this PCB I've found...
Also, are you sure you wired up the channel the correct way around? When I first done this mod L&R used to swap over when I flipped the switch.
I connected them up one channel at a time, so I know they are correct. If I have the switch selecting the opamp/tone controls signal only the left channel plays. When i switch to the bypassed side of the switch it starts with only the left side playing and then after a couple of minutes the right channel comes back in. Is very weird, like there is too much loss over the additional wiring. Iv'e put it back to how it was for now. I still have the switch, caps and wires so easy to try again if I can think what might be the problem.
col.
col.
I think it might be related to the amount of current that the LM4562 op amp I'm using requires. Perhaps the JRC4558 needs less power so isn't as sensitive to the additional wiring. In other circuits I power these opamps with +/- 15v rails. If I measure the voltage going to the opamp on the Lepai it's only around 5v on the positive rail and 4v on the negative rail. Would be good to boost the voltage to the opamp 
col.
col.
need help on lepai
hello
I just change the first cap to 2200 uf 16v near the power supply connector and also change the 2x10uf @ the top of volume pot with the value of 4.7uf 250v poly(dayton brand).now here the prob. when I switch the power on, there is a big humming noise coming from my speaker. If I raise the amps a little bit on the air the hum reduced it self.but even though if u put your ears on each speakers u'll still hear it........ I want to have my bass,treble control working if ur thinking to bypass it.
Pls help me on this. uh by the way I also changed the op-amps to lm4562 and it works great!!!!!!
Ann
hello
I just change the first cap to 2200 uf 16v near the power supply connector and also change the 2x10uf @ the top of volume pot with the value of 4.7uf 250v poly(dayton brand).now here the prob. when I switch the power on, there is a big humming noise coming from my speaker. If I raise the amps a little bit on the air the hum reduced it self.but even though if u put your ears on each speakers u'll still hear it........ I want to have my bass,treble control working if ur thinking to bypass it.
Pls help me on this. uh by the way I also changed the op-amps to lm4562 and it works great!!!!!!
Ann
Re: need help on lepai
I had one of these some time ago and the case didn't like being earthed i.e. when I placed it on top of my CD player (outer case tied to earth - UK 3rd pin) it hummed like crazy and produced large amounts of DC through the output. Not good for the speakers
I did post it earlier on in the thread....
Hope it helps
Lee
msj965 said:hello
when I switch the power on, there is a big humming noise coming from my speaker.
Ann
I had one of these some time ago and the case didn't like being earthed i.e. when I placed it on top of my CD player (outer case tied to earth - UK 3rd pin) it hummed like crazy and produced large amounts of DC through the output. Not good for the speakers
I did post it earlier on in the thread....
Hope it helps
Lee
aszu said:I ordered this amp from export-genie, it arrived some time ago.
Second (much more important) thing: I hooked this amp to a pretty generic laptop psu (12V, 4A) and to my modest speakers set (Mission 560i). And.. WOW! This sounded really good! It was so clean and transparent. Not thinking much, I instantly replaced this inferior op-amp with LM4562, powered it up and.. was completely stunned..
I hope my mini-review will help someone. I am getting back to rediscovering my whole library
which board are u referring to?
1) http://cgi.ebay.com/New-Ver-PCB-25w...ICS%2BUFI%2BUA%2BIA%2BUCI&otn=15&po=LVI&ps=54
or
2) http://cgi.ebay.com/Lepai-TA2020-Cl...4f997f1b&_trksid=p3286.c0.m14&_trkparms=65:12|66:2|39:1|72:1205|240:1318|301:1|293:1|294:50#ebayphotohosting
thanks,
gychang
Yep, after trawling thru the LM4562 datasheet, it does perform better with voltage power rails above +-10v...col said:I think it might be related to the amount of current that the LM4562 op amp I'm using requires. Perhaps the JRC4558 needs less power so isn't as sensitive to the additional wiring. In other circuits I power these opamps with +/- 15v rails. If I measure the voltage going to the opamp on the Lepai it's only around 5v on the positive rail and 4v on the negative rail. Would be good to boost the voltage to the opamp
col.
I think a PSU based on a MAX775 IC could give -12v at around 100ma, would this be enough juice for a LM4562?
The tone controls on my modded Lepai are untouched. I'm thinking because the Lepai's are so cheap, you could have one with tone controls on all the time, and another with the tone controls bypassed.
I always use mine with the tone controls bypassed now, but plan to just mod the tone controls on my other one (to go in the car).
I finally got those RS inductors today, soldered them in and the bass it definitely better. It sounds like there is more dynamic range now, it almost seems like it was quite a compressed sound before, in terms of the bass at least.
Piccy:
An externally hosted image should be here but it was not working when we last tested it.
I may have been able to squeeze inductors that are the next size up, but these sound great so I'm happy.
Hi Mike, glad those inductors worked for you and a lot less hassle then having to wind them yourself.
I just bought a pair of Hemp Acoustics FR8C 8" full range drivers. These are 95db efficient and are perfect for the Lepai. It pays to have tone controls powering these though, especially in a non-optimal enclosure, so I probably won't bother with the tone bypass on this Lepai.
I do have a spare Lepai waiting for modification though..........
col.
I just bought a pair of Hemp Acoustics FR8C 8" full range drivers. These are 95db efficient and are perfect for the Lepai. It pays to have tone controls powering these though, especially in a non-optimal enclosure, so I probably won't bother with the tone bypass on this Lepai.
I do have a spare Lepai waiting for modification though..........
col.
code: 233-5134 £0.44 ELC coil inductor,10uH 2.3ABone said:
Col found it, so credit goes to him.
The same manufacturer does produce a 3A (I think) inductor also, which should also be stocked by RS. I can't look it up tho as the RS site appears to be down!
The 3A inductors do have a larger diameter, so I'm not sure if they'd fit the Lepai, but it may be worth a go.
I've never wound any inductors yet, but I have done a few transformer toroids and I know how much of a pain they can be!col said:
I think as you've improved (or should I say fixed!
) your tone control I think there isn't really much need for you to bypass your tone control anyway. I'm lucky I'm just using my Lepai with commercial bookshelf speakers that sound nice with no EQ, but having the tone controls can be a real bonus with DIY cabs. 
i worked out the opamp and power circuit for the Lepai amps...
I have a few... all running the same opamp and similar tone control (Only resistors different for different chip's input impedance)
Any software which can sketch it out?
Realised the opamps are there just to create a low impedance output to the tone controls so it will not affect tone control. (correct me if i am wrong)
There are 3 sets of signal coupling caps.
They are are
(1) 2x 10uf after volume pot before op amp,
(2) 2x 10uf after op amp to tone control,
(3) 2x 10uf or 1uf after tone control to chip.
Set 1 removed DC before Opamp, but another circuit adds in DC again.
Set 2 remove DC before tone control.
Set 3 remove DC before the Amp
They are all labeled as 2.2uf on the board.
Shouldn't we change the (3rd) set just before the chip instead of the one before the op amp?
I have a few... all running the same opamp and similar tone control (Only resistors different for different chip's input impedance)
Any software which can sketch it out?
Realised the opamps are there just to create a low impedance output to the tone controls so it will not affect tone control. (correct me if i am wrong)
There are 3 sets of signal coupling caps.
They are are
(1) 2x 10uf after volume pot before op amp,
(2) 2x 10uf after op amp to tone control,
(3) 2x 10uf or 1uf after tone control to chip.
Set 1 removed DC before Opamp, but another circuit adds in DC again.
Set 2 remove DC before tone control.
Set 3 remove DC before the Amp
They are all labeled as 2.2uf on the board.
Shouldn't we change the (3rd) set just before the chip instead of the one before the op amp?
Magixz,
I changed all of the signal coupling caps on my Lepai using 2.2uF polyester. I also used 2.2uF polypropylene on the first set, mainly because there was space to squeeze them in. The 2nd and 3rd sets are a bit more confined. 2.2uF polyester can be hard to find and expensive though. It may be worth experimenting with 1uF polyester and seeing how it sounds, hopefully it won't impact on the bass too much. I kinda of feel the inductors are doing that anyway.
http://pix.minirig.org.au/main.php?g2_itemId=1060
anachoret, 92db speakers will be fine and the amp sounds good straight out of the box. I wouldn't worry too much about the start up pop just stick your fingers in your ears when you turn it on
col.
I changed all of the signal coupling caps on my Lepai using 2.2uF polyester. I also used 2.2uF polypropylene on the first set, mainly because there was space to squeeze them in. The 2nd and 3rd sets are a bit more confined. 2.2uF polyester can be hard to find and expensive though. It may be worth experimenting with 1uF polyester and seeing how it sounds, hopefully it won't impact on the bass too much. I kinda of feel the inductors are doing that anyway.
http://pix.minirig.org.au/main.php?g2_itemId=1060
anachoret, 92db speakers will be fine and the amp sounds good straight out of the box. I wouldn't worry too much about the start up pop just stick your fingers in your ears when you turn it on
col.
anachoret said:
Hi,
I'm still using the original capacitors, and the pop idn't very bad when powering from SMPS. It only really seems bad when power it from a battery. Maybe because a battery can give more current?
Anyway, as has already been said, changing caps will almost eliminate the pop, and it is quite and easy job even if you're a beginner when it comes to soldering.
My 2.2uF caps arrived today, once I've fitted them hopefully I will have less turn on pop.
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