Modifying a Lepai LP-2020A+ (Blue PCB Type)

[chrism]

Just wondered if anyone is interested in posting modifications to the newer style Lepai amp? Lots of postings over on DIY Audio for the older red board ones but not so much on the newer style PCB ones.

I have done the volume control / tone control bypass mod and it basically turns it into a power amp. Sounds very good and certainly to my ears betters the stock unit. I use a Beresford DAC as a preamp into it. I can post what I did (pinched from DIY Audio) if anyone wishes to try it.

Regards

Chris

[Saber]

Sounds interesting, wonder if t would work as a Power amp with the 6lj valve pre a few of us have on order. Was it tricky to do?

[chrism]

Fairly easy to do.

All I did was remove the surface mounted resistors at C30 and C31.
Remove the bipolar capacitors at C20 and C21 - carefully as I reused them below.

Add flying bypass cables as follows:
194711947219473
Connect C30 positive side to C20 positive side and add a bipolar capacitor into the lead.
Connect C31 positive side to C21 positive side and add a bipolar capacitor into the lead.

Make sure nothing touches the cap legs (tape up the soldered leads etc)- you will see what I did from the photos - its a temp lash up but I like it and will tidy it up before I close the case.

The volume pot, tone controls and tone switch are all disabled so it runs as a power amp only.

[chrism]

Ok not much interest but here goes.

Next mod done last night and tested.

Taken out pot, tone switch and tone controls - quite tricky and need to go slowly. Make sure that the tiny casing earth wire to the front panel is not damaged. Sound is a little "cleaner" than before so I may take both op amps out next to cut the power to the redundant parts of the board. I have added a few poor quality photos of the sad looking Lepai and its Maplins bench supply. I am proposing to make a new face plate next as the holes don't look too good! and also tidy the wires.

I had added a 10,000uf smoothing cap in leau of the standard 3300uf but don't think it made much difference (possibly due to the linear supply having smoothing caps in it).

[Puffin]

I have made and modded several Class D amps. The original modding frenzy on Diyaudio was centred around the TA2024 chip amps. Sometime later the Lepai amps entered the fray and some threads emerged. I suspect that as with most of these cheaply built amps the Lepai was (allegedly) felt to be the poorest quality of those around at the time (2006 - 7 from memory) and suffered reliability issues. If the manufacturers followed the Tripath data sheet then the things should work as expected. However the modders found that by substituting better quality parts in key areas there was an advantage to be gained. Those with more technical knowledge also made changed to the circuit which others could copy.

The thing to always remember about these BTL amps is not to bridge the outputs, if you do...it is goodbye amp. I wasted a couple of TA2024 amps this way.

These days I think there are better quality boards around from the likes of Sure Electronics. I have one of their TK2050 boards which is pretty good. Of course you have to provide all the ancillary parts to make the amp and a case, if you want it to look pretty.

If you are getting into DIY stuff I would suggest you try a Gainclone or a Mosfet amp to compare with the Lepai.

[Saber]

Thanks for posting that chris, I think id need to practice my soldering. :)

[chrism]

Thanks for posting that chris, I think id need to practice my soldering. :)

Considering that the amp was around £20.00 and usually collecting dust on a shelf well worth ago. If you only want a power amp the first mod - op-amp bypass mod gives the biggest improvement and very easy to do. It is also easy to reverse as well and costs nothing except a bit of thin solid core hook up wire (bit easier to solder into the board.

Go for it as its fun but I would sort it for you if you are anywhere near Sheffield.

Regards

Chris

[chrism]

Can anyone help with a quick query please.

I have a 10uF cap on the output of my Beresford Caiman that I use as a pre-amp and just wondered if I need another cap on the input of the Lepai power amp that I am modding. I have a 2.2uf film cap on it and am tempted to remove it and just have a wired bypass.

Any thoughts?

Regards

Chris

[RothwellAudio]

All I did was remove the surface mounted resistors at C30 and C31.
Remove the bipolar capacitors at C20 and C21 - carefully as I reused them below.
It would be very unusual for resistors to be given the designator C anything. Seems to me you might have removed some capacitors. You really need to see a circuit diagram to know what you're doing - just pulling out components because someone on a forum says so doesn't sound like a great idea to me.

[RothwellAudio]

Can anyone help with a quick query please.

I have a 10uF cap on the output of my Beresford Caiman that I use as a pre-amp and just wondered if I need another cap on the input of the Lepai power amp that I am modding. I have a 2.2uf film cap on it and am tempted to remove it and just have a wired bypass.

Any thoughts?

In theory you wouldn't need two DC blocking caps. Again, seeing a circuit diagram would make me feel safer about making any specific recommendations though.

[chrism]

It would be very unusual for resistors to be given the designator C anything. Seems to me you might have removed some capacitors. You really need to see a circuit diagram to know what you're doing - just pulling out components because someone on a forum says so doesn't sound like a great idea to me.

Thanks for this but I don't have any issue removing the preamp stage from the Lepai and the bypass works a treat (the mod is well documented elsewhere). I was actually asking a more specific question about doubling up on output / input decoupling benefits.

Regards

Chris

[RothwellAudio]

Sorry, I didn't intend to offend, but alarm bells ring when I hear someone say they have removed some resistors and they're actually capacitors.
BTW, I did answer your specific question.

[chrism]

Hi Andrew, You didn't although I was a bit confused by the reply.

The datasheet for the TA2020 does not go into this sort of detail.

I am looking at the signal decoupling and am aware that lots of products have output decoupling capacitor and again another capacitor on the input. I could just remove the Lepai input ones and see how it sounds but thought that I would call on others that may already have experience with this before I did.

Regards

Chris

[RothwellAudio]

You would need to know what the circuit is to be sure, but as long as the input to the power amp has no DC resistance to ground you would be ok to remove the capacitor. However, is there a resistor at the pre-amp's outputs? It wouldn't be unusual if there were, and it that case it could make a real mess of the power amp's input biasing arrangement, which might make a real mess of your loudspeakers. Or maybe not.

[chrism]

Not sure about the Lepai's power amp input being affected in this way as the Beresford DAC Pre-amp out works well with a range of different power amps.

Anyone else?

[RothwellAudio]

Depends what the circuit is. Certainly a conventional power amp with a long tail pair at the input needs to be DC blocked to prevent DC offsets at the output. Many single rail circuits need to be DC blocked at the input to prevent the circuit's bias voltage from being affected by DC paths at the input.

[Firebottle]

Andrew's right, it looks like there is a bias voltage on the TA2020 input pins, so you do need a capacitor as a dc block.

:)

[chrism]

Thanks Alan, I will leave the 2.2uf film caps that I put in it.

Regards Chris

[chrism]

Just thought that I should post how far I have now got with the Lepai Power Amp project. 2.2uf Input decoupling caps now in place and .47uf output caps - Vishay MKT1822 caps on the output. Tidied the cabling up a bit as well.

Next job is to address the DC at the output being different on each channel - was like this before I started though (appears to be a common problem on the Lepai).

Sounds great and a far cry from the original Lepai - very clear and smooth sound and the metallic edge on highs now gone.

A picture of the mods so far.

Regards

Chris

[danilo]

I just a couple of weeks ago .. Finally.. put into my trash bin 3 Lepais that I modded.
Far more extensively than yours actually. Hey, you haven't done the Coils.. yet.
First Lepai; lived 1 week, Second one; 2 days. Third one close to a month. Wasn't willing to try a 4th one.
Typically they lose a channel, go intermittant. Inevitably going completely dead... Yippeee!
Fully addicted, a year or so into the adventure, I even built a Tripath evaluation circuit /amp from scratch.
Complete failure, as the chip, despite vendors vociferous claims, was a bad copy Fake.
As I inevitably realised, were ALL the others.
My Lepais and accumulation of 'spare' ta 2020 chips were Chinese Fakes.
Not much Sherlock required to realise that the Decade + dead Tripath firm was no longer producing chips.
Sadly Genuine Ta chips were pretty good music makers. The Fakes are decidedly not.

Try and get a hold of a 41hz.com Amp 6 gizmo ? As these featured Genuine Tripath chips.
Damned things worked really quite well TBH. Well worth owning.
Rare as hens teeth Now though.

Failing that I suggest an Lm3886 chip amp.
Say a Neurochrome or My Ref circuit.
LM 3886 chips when bought from a Genuine supplier are Good.. far better than the tripath designs,
AND still in current production.

Anyways you are clearly having fun.
Hell, I spent almost 2 years fooling about with the 2020's.
G 'luck.

[chrism]

Hi Danilo,

I was very lucky as the Lepai that I bought for £18.99 a few years back has a genuine TA2020 in it. You can still buy the chip from a European distributor for about £9.00, well until stocks run out!

Really enjoyed modding the little amp and have spent £12.00 to date on it so not bad. The sound quality has really amazed me and it still works well. Not sure what else to try now as I've run out of ideas but have removed the resistors at R42 and R43 since.

Hope that it lasts as I really like the smooth detailed sound it produces - the pre-amp bypass mod giving the biggest effect and I found the others quite small by comparison.

Regards

Chris

[chrism]

Hi Danilo,

Struggling to find any 10UH toroidal inductors to fit in the Lepai. I was very kindly sent some by Alan but I need to go for a bigger case to fit them in (perhaps the next bit of my project). If you have that will fit that are surplus I would do a deal for them!!

Regards

Chris

[chrism]

Just thought that I should post a summary of where I have got to in case anyone else gives the conversion ago.

1. Bypass Mod. Realised that the numbering on the Lepai boards can be all over the place and that C20 & C21 can be switched on some boards. I have now soldered onto the back of the inputs through a 2.2uf film cap to the C20 and C21 positive sides. On my board the upper red input goes to C20 and the lower black to C21. The sound pulls to one side if you get this the wrong way round. This mod gives the biggest improvement in my opinion. You remove the surface mounted capacitors at C30 and C31 as well (I also removed the resistors R34 to R37).

2. Input Cap. I removed the supplied cap and replaced it with a 10,000uf electrolytic cap. I also added a small film cap as a bypass. This gives a bit more weight to the sound and worth doing.

3. Output Caps. I swapped out the six output caps with .47uf Vishay film caps. I used MKT 1822 but wish I had gone for ones with 5mm leg spacing as the 1822 are just too wide. Worth doing but does depend on how good the stock caps are in the first place.

4.Redundant Component Strip Out. Removed the opamps and all caps and resistors close in Removed vol pot, tone pots and tone switch. Removed all caps and resistors around them. Removed resistors R42 and R43. I think that this just reduces the power drain to the unused parts. I did notice that this mod corrected the DC offset imbalance that I originally had on the outputs.

5. Capacitor Swap. Replaced the remaining electrostatic caps as follows. C4 & C10 - Nichicon FG 1uf 50v. C13 & C15 - Panasonic FC 220uf 25v. The big one next to C4 - Panasonic FC 470uf 35v. I used what I already had and replaced with like for like capacitance.

Next up will be the inductors as I managed to locate some 10uh toroidal ones for a few quid and I may also replace the surface mounted differential output caps at C34 and C37 with 0.01uf film caps.

I have attached a few photos of how it looks - luckily the lid still goes on!.

I have a datasheet for the TA2020 as well if anyone would like a copy.

Regards

Chris