LJM Audio

[maty tinman]

I would like to see measurements like vzaichenko did with the L12-2.

L12-2 CFP Output amp 120W*2 8R

​

Old L20.5, from eBay

Signal to noise ratio > 98DB

How much the new at 1 watt? "A weighted".

 

[ljm_ljm]

I would like to see measurements like vzaichenko did with the L12-2.

L12-2 CFP Output amp 120W*2 8R

​

Old L20.5, from eBay



How much the new at 1 watt? "A weighted".

Do you want to see a FFT test figure is.

When I find time to test.

 

[ljm_ljm]

I would like to see measurements like vzaichenko did with the L12-2.

L12-2 CFP Output amp 120W*2 8R

​

Old L20.5, from eBay



How much the new at 1 watt? "A weighted".

Your photos, not my test. Maybe is a test of other people do.
But I can take time measure FFT.

 

[maty tinman]

They was made by vzaichenko.

I think is more important to know the harmonic profile. Systems with H2 predominant sound different than H3 predominant. More "natural", "credible" vs detailed.

 

[ljm_ljm]

They was made by vzaichenko.

I think is more important to know the harmonic profile. Systems with H2 predominant sound different than H3 predominant. More "natural", "credible" vs detailed.

I had a time measurement.
15 db is 0 db 18 db, respectively. Detail please look at the pictures. I didn't also too.
And I save the past QUAD405 FFT on the same tests were compared.
You can see the size of the distortion.


In addition. SNR main relationship and transformer, filter capacitor has much to do.
I am very, very poor capacitor tested. 80 v1000 UF * 4.

If you use a better filter capacitor, capacitor. There will be a better noise ratio.
So the numerical only used as a reference.

 

[maty tinman]

Very good graph in a class AB poweramp.

And yes, the PSU usually is a bottleneck in almost hard. Commercial or not. More diyers do not want to spend more money in the PSU. An even more resounding error in those who are class A amp/preamp.

LJM L20.5 + preamp with H2 predominance would be a very good idea I think.

You have this: CLASS A Single-ended Preamp 9

​

and the new design:

NEW Preamp Board Pure Class A Single Ended Transistor Preamplifier 20Hz-20KHz | eBay

​

By the way, you have new logo in the 2018 boards.

PD: the preamp with better potentiometer... And L20.5 amplifier board with heatsinks like L12.2
​

 

[ljm_ljm]

Very good graph in a class AB poweramp.

And yes, the PSU usually is a bottleneck in almost hard. Commercial or not. More diyers do not want to spend more money in the PSU. An even more resounding error in those who are class A amp/preamp.

LJM L20.5 + preamp with H2 predominance would be a very good idea I think.

You have this: CLASS A Single-ended Preamp 9

​

and the new design:

NEW Preamp Board Pure Class A Single Ended Transistor Preamplifier 20Hz-20KHz | eBay

​

By the way, you have new logo in the 2018 boards.

PD: the preamp with better potentiometer... And L20.5 amplifier board with heatsinks like L12.2
​

In fact L20.5 amplifier distortion can be reduced by 30%.

You should know. L20.5 GAIN is 31, it may not need a preamp, and get a sufficient volume, at least 30 square meters of space.

If reduce the GAIN of 18. The THD + N can reduce at least 30%.

Only need to put 330 ohm resistance, to 510 ohms. An increase in the number of feedback. Is to reduce the distortion and noise is proportional.

Is estimated to be about 0.0008%.

If you use the preamp, consider such operations.


In fact I in use. Does not use the preamp.
This kind of situation it can get very accurate low distortion effect. The sound is great, I think.

Of course. Join the influence of other amplifier, may lead to distortion, or voice change.

This is related to personal preferences. PREAMP9 is a relatively good amplifier.

But I suggest PREAMP9 installed in a separate case. And away from the interference of transformer.

Single-ended amplifier are easy to be interference.

 

[ljm_ljm]

Very good graph in a class AB poweramp.

And yes, the PSU usually is a bottleneck in almost hard. Commercial or not. More diyers do not want to spend more money in the PSU. An even more resounding error in those who are class A amp/preamp.

LJM L20.5 + preamp with H2 predominance would be a very good idea I think.

You have this: CLASS A Single-ended Preamp 9

​

and the new design:

NEW Preamp Board Pure Class A Single Ended Transistor Preamplifier 20Hz-20KHz | eBay

​

By the way, you have new logo in the 2018 boards.

PD: the preamp with better potentiometer... And L20.5 amplifier board with heatsinks like L12.2
​

B: yes. I have a new LOGO. Is the panda.

Because I live in chengdu, sichuan province. Here is the hometown of panda.

L20.5 has two versions, the earliest version of power tube after installation is wide. There are about 9 cm.

Then I reduced the width, only 7 cm. In addition to this point. Voice and no difference.

7 cm, is for the sake of easy to install in ordinary aluminum chassis.

In a CLASS B L20.5 can think it work. Because it is only a small, static current.

At the time of test + - 35 v voltage, almost no temperature.

I fixed it in a little box, aluminum plate is enough.

Maybe I will increase the radiator version later. There will be about 7 to 8 CM * 20 CM size.

Use a small weight of radiator. About 200-300 grams.

 

[Pemo]

Hello lLiu. I found in the ljm2_ljm2 store in Taobao this amplifier for 980 yuan. Is this a complete amplifier or just the boards. Do you have a 110 AC version? Thanks. Best regards. PEMO

 

[ljm_ljm]

Hello lLiu. I found in the ljm2_ljm2 store in Taobao this amplifier for 980 yuan. Is this a complete amplifier or just the boards. Do you have a 110 AC version? Thanks. Best regards. PEMO

Can be customized. But this is not including postage charges abroad.
Do you want to consulting agency business. About 8 kg

 

[maty tinman]

Only I find:

LJM shop

??-ljm ?????????-???

L20.5 assembled board

L20.5 ????? HIEND ???? 0.0015% AP ????-???

Speaker protection (Black version)

????? ??-???


here!

L20.5 ????? ???-???

980,00 CNY = 128,49 EUR + shipping + customs

with Google Translate:

20.5 Finished Products

Customer-made products.

Output power 60W *2 8 Ohms, 120W *2 4 Ohms

Use customized high quality 300VA transformer

Each channel is powered separately. 2-way power board, 2-way speaker protection board.

I think that a 80 watts / 8 Ohms at THD 0.1% should be a bestseller.

 

[maty tinman]

With more big case and with a 1 mm steel sheet separating the transformer from the circuits.

With an optional RF/EMI filter inlet. This has the best specs: Schaffner FN 9244B 1A (230 Vac) or 3A (115 Vac).

[PDF] FN 9244

[URL]http://maty.galeon.com/WP-imagenes/hard/IEC-inlet-filter-Schaffner-FN_9244-typical-filter-attenuation.png[/URL]
[B]
[COLOR=SeaGreen]B[/COLOR][/B]: medical

 

[Pemo]

Can be customized. But this is not including postage charges abroad.
Do you want to consulting agency business. About 8 kg

My agent in China is Taobao Focus, they will contact you and ask for a 110 V AC input. Thanks

Regards

PEMO

 

[ljm_ljm]

I measured Between -57 and Ground. Same behavior. Quite quick rising of the voltage when connected to the amp boards.

Resoldering all the PSU points did not make any difference.
The PSU measures fine without any load (between +-57 and +-58V)

<60V is No problem.

 

[jvhb]

Hi, I was curious enough to order a set of L20.5 via Aliexpres. Unfortunately the seller has sent complete assembled boards and not DIY kits as ordered, but that is besides the point really:

However, it turns out that the Input/VAS section has two SOT26 components, which I hadn't noticed in the photos!
But these have been covered in some type of paint, so I can't read any type code on them :/

But my guess is, that they are dual DMMT5401 PNP. This also explains the strangely low number of small transistor visible in the pictures.

LJM, can you please confirm that you are using two DMMT5401?
- If not, what are these devices?

Selling amplifier kits with "secret" components is no good - how will I be able to fault find or repair, if I can't see what components are used..

Edit: I received the "old" style PCB, where the output transistors are clear of the board. That is fine by me though.

 

[Pemo]

Hello jvhb. I know the quality of LJM amps is ok. But the most important issue here is: "Does it sound as expected?" Is this ultra low THD is significant? Thanks and regards. PEMO

 

[jvhb]

Hello Pemo, sorry I can't give you any subjective opinion on how it "sounds". But I would imagine that it is exactly like other very low THD amplifiers: Completely clean and transparent. So for me, there is no point in trying to make listening tests.

My interest is mainly scientific/objective, and I want to have a look at the topology used, and make some tests and measurements. At the moment I am trying to ascertain what these SOT26 are.

If I go further, and build a complete L20.5 amplifer, I will open a thread in Solid State forum.
Cheers,
Jonas

 

[ljm_ljm]

Hello Pemo, sorry I can't give you any subjective opinion on how it "sounds". But I would imagine that it is exactly like other very low THD amplifiers: Completely clean and transparent. So for me, there is no point in trying to make listening tests.

My interest is mainly scientific/objective, and I want to have a look at the topology used, and make some tests and measurements. At the moment I am trying to ascertain what these SOT26 are.

If I go further, and build a complete L20.5 amplifer, I will open a thread in Solid State forum.
Cheers,
Jonas

 

[Mortenhoe]

How do I lower gain on these bad boys?

 

[XPZMIePKdFlkA]

How do I lower gain on these bad boys?

Maybe by reducing the static current, as noted by LJM?
See LJM comment on that here: [wiki=http://www.diyaudio.com/forums/solid-state/199093-l20-amp-njw0302g-post3841646.html]%[/wiki]