Lepai LP-2020A+ DC offset survey

[lorriman]

Folks, I'm slightly disappointed to find my spanking new amp has an offset of 70mv on one channel (respectable 20mv on the other).

I'm pretty new to electronics, and pretty clueless, and would rather start modding one of these with no offset issues (the bias pot stuff here is beyond me, though I would like to do it, nd it's not part of the diyaudio lepai 2020A+ mod guide).

So I'm wondering if a replacement is likely to be as bad or worse.

Please do vote to give a polled idea of the spread of max DC offsets when you first got your amp. Answer the poll with whichever is the higher of the two channels.

I'm following the format on AudioKarma of 0-15mv=good, 16-50=ok, 51-85mv=audible distortion/something wrong, 86-100= bad, 100+mv=danger.

I've also added poll options for the 2nd version of the amp just for curiosity, and because there are ten possible poll options.

 

[lorriman]

I've made the poll open to choosing more than one option for those with more than one 2020.

 

[Pano]

Interesting poll. I'll measure the 2 or 3 I have when I get home - all 1st generation, I think.
You have to be careful with these measurements, with some DVMs the leftover RF in the output can skew the DC measurement making it read higher than it really is.

 

[lorriman]

Do you mean by 1st Gen a LP-2020A rather than 2020A+?

I seem to have missed that trick. Are they significantly different that I should consider adjusting the poll?

I'm perfectly willing to drop the B version.

 

[lorriman]

"You have to be careful with these measurements, with some DVMs the leftover RF in the output can skew the DC measurement making it read higher than it really is."

Hmmm, what advice do you suggest for that? Leave the amp on for a few minutes doing nothing?

 

[lorriman]

Well, I can barely believe it but a second Lepai has a DC offset of 110mv on one channel with a single digit offset in the other. I've also noticed that both amp produce large voltages after the relay switches: up to 700mv in one instance.

I have a third coming tomorrow (I've intentions for these things; I haven't gone Lepai nuts).

 

[Bare]

Three Lepais in a row have failed on me.
All three have lost their left channel while in use. Bungler? perhaps.. but I've also been 'fooling' with Audio since '71 .
Over the decades I've learned to avoid at least the more obvious mistakes.
First one I "thought" I caused this by tripping on the speaker wires.
After 2! more did the Exact same thing I now wonder about the first 'death' as well.
Clearly these are substandard Imitation Chips .. period.
Buy / use a Lepai at your own risk.

 

[radiosmuck]

Three Lepais in a row have failed on me.
All three have lost their left channel while in use. Bungler? perhaps.. but I've also been 'fooling' with Audio since '71 .
Over the decades I've learned to avoid at least the more obvious mistakes.
First one I "thought" I caused this by tripping on the speaker wires.
After 2! more did the Exact same thing I now wonder about the first 'death' as well.
Clearly these are substandard Imitation Chips .. period.
Buy / use a Lepai at your own risk.

Have you tried the tda7297F board? Less than $6 on ebay and sounds better to me.

 

[Redshift187]

The Lepai have been known to die if you pull the speaker cables out while they're running.

For measuring the DC offset, are you making sure to use "direct" (bypass tone controls) and shorting the inputs to ground? We need some consistency here for this data to mean anything.

 

[Switters]

@Bare

I thought I had the same problem with a channel of my Lepai, then I discovered was the tone control switch, I bypassed it and both channel now are ok.

 

[lorriman]

I didn't know about shorting inputs to ground, but in anycase it seems to make no difference to my readings. All three Lepais have at least one channel above 50mv and one of the three has 110mv.

 

[Bare]

Erm.. Who Cares? there is so much 'extra' junk not found on the Tripath suggested circuit on that thing that Offset is inevitable.
Yet they didn't even bother with DC offset/ variable resistors.
Even the Cheaper YJ t2020 amp has those.. Buy one

 

[lorriman]

Erm.. Who Cares? there is so much 'extra' junk not found on the Tripath suggested circuit on that thing that Offset is inevitable.
Yet they didn't even bother with DC offset/ variable resistors.
Even the Cheaper YJ t2020 amp has those.. Buy one

Sounds interesting!!! Thanks for the tip. I can't find this amp anywhere, however.

 

[THUMP LUMP]

2020 A+....... 22mv Left & 40mv Right.