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Old 2nd March 2012, 02:06 PM   #1111
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Thx for the tips, I'm a complete noob in the DIY audio so I figured after days of reading just to give it a go and see how it works out....
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Old 13th March 2012, 12:25 PM   #1112
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i just got a lepai Lp-ta2020a+ but im not getting any sound out of it. any suggestions?
it powers on and i can hear the relay kick in, but there is no sound.
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Old 13th March 2012, 10:47 PM   #1113
jjne is offline jjne  United Kingdom
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Just received my uber-cheap ebay Lepai LP2020.

Despite the cheap price, and a few faults I've noticed, the sound has whetted my appetite for T-class amps enough to seriously consider putting together a multi-channel monoblock using Arjen's TK2050 monoblock modules. I have bought a TEAC 2050-based Tripath amp which I'm looking forward to.

Few things I've noticed about this unit.

1) The volume control is a bit odd. Room-filling sound only really starts to be achieved with the volume around the 2pm mark, more than I would have liked. Is this normal, and what levels are likely to damage the unit?

2) There is a slight noise coming from the right output -- it's there even without the input connected and does not increase as the volume is turned up. I'd imagine this is power related -- it does sound like a clipped rendition of a 50Hz sine wave.

3) What is the score with the tone controls? I get a reasonably flat response with the pots around half-way, but it isn't quite there. I've noticed that some people replace these, however I'd like to be able to bypass them completely (this particular unit lacks a bypass control). Is there an instruction anywhere on how to achieve this?

Despite all this, this is a cracking little amp for the money. Although it seems to be a little lacking in dynamic range, the detail does definitely have something of the valve sound about it. I've only tried it with a cheap set of budget bookshelf speakers so far, but it's already apparent that this amp has my old AMC 3000-series beaten in some respects. Not bad for 12 delivered from China, and that included what claims to be a 12V/5A PSU as well (hmmm, I'll need to check that as well as it also calls itself a "Toshiba", made by "Delta", and I'm not convinced lol).
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Old 14th March 2012, 02:06 AM   #1114
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No output? Check your signal source on another amp, if possible. Also, try a different 12V power supply. There is no output relay on this unit...what you may be hearing is the protection kicking in because the power supply has lost regulation.

Noise in 1 channel could indeed be the power supply, which sounds from the labeling like a cheap knock off. More than 3A is not needed. Radio Shack has a 12V 2.5A wall wart that in my experience has good regulation. Try that.
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Old 14th March 2012, 07:34 PM   #1115
jjne is offline jjne  United Kingdom
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Thanks Stu for that, and the heads-up that a 2.5A supply will be sufficient (at least for testing).

I swapped the supply for one intended for a small Juniper Networks firewall (2.5A) and the amp is now deathly quiet. Seems to have further improved the sound slightly as well, the bass seems more extended than before. So win-win

So yeah, the cheap knock-off power supply isn't that great, although it'll have its uses for something else I'm sure (monitor power etc).
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Old 15th March 2012, 12:52 PM   #1116
arvesen is offline arvesen  Sweden
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I bought a 14v 4a power supply on ebay, but when it was delivered it was labelled 15v 4a. will this damage my t-amp?
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Old 15th March 2012, 01:07 PM   #1117
Franfj is offline Franfj  Spain
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Quote:
Originally Posted by jjne View Post
1) The volume control is a bit odd. Room-filling sound only really starts to be achieved with the volume around the 2pm mark, more than I would have liked. Is this normal, and what levels are likely to damage the unit?
I would worry first for damaging the speakers, when the unit overloads the Tamp output at high freq is unstable and could damage the speakers. Anyway, you will notice a very bad sound when the amp starts clipping, in that case turn down the volume.

There is a pin to drive an overload indicator, but isn't used on the Lepai, I have tried to add a LED, but as said before, is really easy to recognize when the amp stars overloading because of the bad sound that outputs.
Quote:
Originally Posted by jjne View Post
3) What is the score with the tone controls? I get a reasonably flat response with the pots around half-way, but it isn't quite there. I've noticed that some people replace these, however I'd like to be able to bypass them completely (this particular unit lacks a bypass control). Is there an instruction anywhere on how to achieve this?
Is explained in the thread, but you could try to have a look at the wiki Amplifier:Lepai T Amp - diyAudio and when you know what version of the board you have we can help you with bypass.


Quote:
Originally Posted by arvesen View Post
I bought a 14v 4a power supply on ebay, but when it was delivered it was labelled 15v 4a. will this damage my t-amp?
Don't think so, but it is not the best option, the Lepai has a built in protection that drops the voltage to 13.5v but people say that with an input higher than that 13.5v the sound is worse because of the protection. I would try to get a lower voltage psu (try first yours with a volt meter, because often, the output differs slightly from specs).
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Old 17th March 2012, 03:01 PM   #1118
jjne is offline jjne  United Kingdom
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Thanks -- I've not noticed any hard-clipping from the amplifier (the speakers I'm using are 8R so should in theory be easier to drive anyway).

I think my unit is a 2020B (it has a speaker relay but no tone bypass switch) although it's labelled as a 2020A+ so I'll pull it to bits today and see what the score is, and hopefully follow those instructions.
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Old 17th March 2012, 03:47 PM   #1119
jjne is offline jjne  United Kingdom
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2020B it is... and I've traced the board and understand now what needs to be done, just need to get hold of a decent pair of 2.2uF unpolarised caps now I have some good quality 2200uF Panasonic caps as well so I'll replace the power cap while I'm on.
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Old 26th March 2012, 07:52 PM   #1120
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Having examined the schematic, as well as the TA2020 datasheet, it is clear that the power supply quality is important in terms of the ultimate results. Also, I observe that the power supply provided with the Lepai amp varies from vendor to vendor. The supply provided by Parts Express appears to be of better quality than most. However, it is still 12V at 2A, slightly limiting the power output of the amp.

The TA2020 datasheet states that 14.5VDC is the highest recommended PS voltage for the chip. Since the amplifier can produce up to 20W RMS into 4 ohms per channel, in order to get the most from both channels driven, a linear regulated PS of 12-13VDC capable of 4A would yield maximum sustainable results from this design. This could be achieved using a 12-0-12V 3-4A power transformer, connecting the 12V leads together and the center tap as ground, into a bridge rectifier and linear regulator circuit. There are several simple linear regulator circuits for 3-5A output, including 3-5 7812 regulator chips in parallel with their outputs connected via 0.1 ohm ballast resistors, or a single 7812 with a parallel bypass transistor. I suspect a computer switching power supply would work nicely, also, since these provide up to 20 or so A output on the 12V rail with pretty good regulation (usually output voltage between 11.8 and 12.2V measured under varying load). As used computer power supply is likely the least expensive option, since these change hands for $15 or so. However, older ATX supplies can have high frequency switching noise in the DC, so some sort of outboard filter might be needed for good results. Worthy of experimentation; I will do some if I can get up the energy....
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