StereoHead - reviews of headphones, amplifiers, sound cards. DIY preamplifier in class A (clone Lehmann BCL) PCB fabrication

Lehmann Audio Black Cube Linear USB

• Manufacturer Lehmanaudio Vertribes Gmbh (Germany)
• Made in Germany
• www.lehmanaudio.com
• Inputs Phones 3.5 mm, RCA, USB,
• Outputs 2 Phones 6.5 mm, RCA
• Input resistance, kOhm 47
• Reproducible range, Hz
• — by linear input 10 - 35000
• — by USB input 10 - 20000
• With unevenness, dB -1.5
• Distortion, % 0.001
• Signal-to-noise ratio, dB 95
• Dimensions, mm 280 x 110 x 44
• Weight, kg 1.5
• price, rub. 44500

This device is already well known to our regular readers, because the Black Cube Linear, as well as its USB version (which is what appears in today's review), have already participated in the tests of the AV Salon. True, both times these were tests of external DACs. But on board this miniature component is not only a high-end Burr-Brown converter, but also a perfect pre-amplification section with a volume control and a quite decent, according to numerous audiophile reviews, telephone amplifier. Because of this, we decided for the third time to "provide a podium" to a product from Lehmann Audio.

It was made with typical German quality - if you want, you won't dig. Strong, beautiful and functional. The rear panel has USB input(type A) and four expensive gold-plated RCA sockets without any markings. An explanatory label is located on the front of the component. There you will also find a DIP switch, which can also be set by the gain in steps of 0, +10, +20 dB, and this immediately gives out a studio-class thing in the Black Cube Linear USB. After all, the analog path here works with a signal of a higher voltage than is accepted in household appliances. There is nothing unusual on the front panel. A volume knob and two stereo phone jacks that appear to be in parallel. Each can include both low- and high-impedance headphone models. The input selector is not provided - the device automatically switches from an analog source to a digital one when a signal appears in the latter.

1. Audez'e LCD-2

With the isodynamic phones Black Cube Linear USB forms a rather melodious duet. The sound is not fair, but ordered, the dynamics are fresh, realistic. And the resolution is top notch. But the more you happen, the more it seems that for such money it is not best amplifier. Bass almost lacks hardness, space - scope. The sound is unemotional, as if constrained by something, limited - it will not give you goosebumps, like others. And switching to the USB input finally convinces that the Black Cube Linear USB is, first of all, a good DAC. Expressiveness appears, articulation improves, nuances are much more delicate. Those. exactly what was "lost" in the analog path from the very input. And such a wording, you know, is a sentence for the “telephone operator” ...

2. Sennheiser HD 800

Failed to rehabilitate Black Cube Linear USB and in tandem with German phones. Liveliness of sound, detailing, scene - all this is a solid four, but no more. Bass is not impressive. In addition, with high-impedance phones, the amplifier has a low volume margin - don’t rely on super dynamics. There are also advantages: linearity is impeccable, informative, decent localization ... But this is not enough to defeat real telephone amplifiers.

Greetings! After buying the headphones, the question of high-quality amplification for them began to brew and I began to choose the appropriate options, I immediately discarded the factory solutions, due to the overpriced and fairly cheap element base. The choice fell on DIY options. Then a preamplifier for the power amplifier became necessary and I set to work on the assembly. My choice was a Lehmann BCL clone, the original version is quite well known, has a decent sound, a large number of people on foreign forums have repeated this design. But the amplifier is very sensitive to the quality of the element base, so the best components were used, which I could reach. The whole amplifier is assembled from parts bought on ebay. I beg your pardon, but some photos are a little outdated, under them I will write what has changed today, let's start!

Some technical specifications

• Frequency response: 10-35000Hz
• Input impedance: 47 kOhm
• Signal to noise ratio: 95dB @ 0dB gain (Gain switchable: 0dB +10dB +18dB +20dB)
• Output power: 200mW/300Ω 400mW/60Ω
• Distortion:<0.001% при 6 мВт на 300 Ом
• Headphone impedance: 32 to 600 ohms

Assembly, setup

In the photos, the line output is not yet connected, it is connected from the headphone output, through 48 ohm resistors.

The design cost 12-13 thousand rubles, which is quite inexpensive when compared with factory options. Now it makes me happy with its sound. Works with Technics sl-pg480a and sennheiser hd280, I plan to replace the headphones with something more serious soon. Now it works as an amplifier for headphones and as a preamplifier for the power (If necessary, I will also write about it in more detail)

Finished product :)

If I missed something important, ask in the comments, I will supplement the article.

At the request of commenters

Listings on ebay will not exist for a long time, I indicated the names on the links, then it will be possible to find in the search.

UPD: 02/16/2016

Now paired with Maverick Audio D2 + Sennheiser HD650.

Since 2011, the amplifier has undergone a number of upgrades and improvements:

• The internal power wiring was replaced from the Chinese wire to PuGv, the signal ones were also replaced from noname to clotz.
• The U-shaped transformer has been replaced by a cast transformer, mounted on a circuit board directly behind the main toroidal transformer. Printed circuit board for transformer era 220V primary, 9V secondary: pcb_transformer
• The samwha capacitors swelled up and were replaced with simple jamicons, maybe later I'll get confused and change to something from audio-grade.
• Raised the opamp current to 5mA. lovelycubeclassabiasmod
• Changed the RCA connectors to decent ones.
• I packed all the amplifier wiring in tesa heat resistant tape.
• I connected the line output and actively use the amplifier as a preamplifier.
• I changed the indication from blue to a pleasant green (eyes became less tired at night).

I bought simple ears so that I could gamble at night and sometimes listen to music, I took inexpensive, but large KOSS UR20. Having connected to the receiver, I was somewhat dumbfounded, the sound is very, very pleasant, jazz and classics just go with a bang. In terms of low frequencies, of course, they lose a lot to Koss the plugs, and KOSS Porta Pro are noticeable, which I have been carrying as portable for a year now. I was very surprised when I decided to listen to Koss Porta Pro after listening to the songs on the KOSS UR20 - from the pro port it was as if cotton wool had been pushed into my ears. And I thought they were very "decent" in terms of sound. Although maybe this time and the atmosphere could spoil them so much? What is all this for? Yes, I decided to assemble an amp for the ears, the amp will be home, never portable.
I decided to start building a clone of Lehmann Audio Black Cube Linear doctorhead.ru/catalogue/?i=523
Here is the result:

All together it took about 3 evenings and less than 1000 rubles of money.
Who cares, welcome under the cat, there will be a lot of photos with a detailed description.

Scheme and design

Nutrition

I was thinking how to make a signet, I found a scanned printed circuit board on some Polish forum

And circled it in my favorite Sprint Layout

Here's what happened

True, I slightly redrawn it, because I found a couple of errors and resized it to fit my detail sizes. Then it turned out that the foil textolite in the store is only 10x15 in size, and the board was larger, I had to redraw it again and reduce its overall dimensions.

PCB manufacturing

LUT or Laser Ironing Technology is our everything) I have been using glossy magazines as a transfer material for a long time, the main thing is that there are not many dark areas and fills on the magazine sheets.
We print 2 sides.

After that, the most fun - you need to somehow combine them. I made LUT from both sides at once, put a piece of textolite into sheets and carefully wrapped them, then ironed well first one side then the other with an iron. In principle, it turned out well, one side ran away by a few tenths of a millimeter.
After ironing, you need to place the board in water and carefully remove the soaked paper, I do it with my fingertips under water, like this

After laundering from paper, such a board is obtained

We carefully study it for the presence of jambs, if there are any, we correct it with a scalpel with a ruler and a marker. If everything is fine, we throw the board into a bath with a solution of ferric chloride (the recipe is on the bank). The main thing in this business is to stir the solution and regularly turn the board over for uniform etching.

I stick toothpicks around the edges to keep the pickling bath edges from touching the board.
After etching, it is necessary to rinse the board well from the solution

Toner, from the finished board, is washed off with acetone.

For ease of assembly, I like to apply the designations of the elements

Then all holes are drilled using a collet chuck engine

I tinned the lower part of the board using a braid with flux and a small amount of solder.


All the following pictures are mostly with the board not yet washed from the flux.

Assembly

And we check them. The power supply did not start the first time, it turned out that the LM337 was completely Chinese and simply did not work. Therefore, the first test of the amplifier in the kitchen at night was from 2 laboratory sources (the lower one, by the way, is also homemade).

The check showed that the radiator is required. The pay looks like this.

I took an old radiator from the motherboard and drilled it


Cut, bevelled

Mica and KPT, radiator in place. The circuit consumes about 150 mA on each power arm. Reminds me of a class A amplifier.


I took the transformer ready from an old decommissioned Hungarian amplifier.

Test listening did on the following ears TDS-5M and 3 pairs of KOSS))) all average.

Frame

From old stocks, we lift sheet aluminum and cut the overlay to fit the front panel of the CDROM

Without thinking for a long time, I screwed this panel with two screws, chose the cutest ones))))

We drill and try on, it has already become better.

.

Painting and decoration

Assembled board in the case


I had to change the power capacities in front of the stabilizers from 4700 to 10,000 near OPA2134 from 470 to 4700 uF, as there was a small hum that could be heard at night in complete silence. I also added radiators for integral stabilizers, since their temperature regime in a closed case is not the best.

Here is such a nice, in my opinion, turned out to be an amplifier

Outcome

What's left to do:
1. Cover with a second coat of paint
2. Cover the front panel and body with varnish to protect the coating (lacquer will be available only next week).
3. Cut out the back panel and put in normal RCA connectors (no time for this yet). If all goes well, I'll do it this weekend.
4. Try on the amplifier at least RMAA. I looked with an oscilloscope, gave a rectangle at the input, saw exactly the same at the output.
UPD Items 1,2 and 3 completed

Bonus
And this daughter is doing a test audition)))

After buying the headphones, the question of high-quality amplification for them began to brew, and I began to choose the appropriate options, I immediately discarded the factory solutions, due to the inflated price and rather cheap element base. The choice fell on DIY options. Then a preamplifier for the power amplifier became necessary and I set to work on the assembly. My choice was a Lehmann BCL clone, the original version is quite well known, has a decent sound, a large number of people on foreign forums have repeated this design. But the amplifier is very sensitive to the quality of the element base, so the best components were used, which I could reach. The whole amplifier is assembled from parts bought on ebay.

original amplifier:

A few technical specifications:

Frequency range: 10 - 35000 Hz

Input impedance: 47 kOhm

Signal-to-noise ratio at 0 dB gain: 95 dB

Gain switchable: 0dB; +10dB; +18dB; +20dB

Output Power: 200mW/300Ω (400mW/60Ω)

Distortion at 6 mW into 300 ohms:<0.001%

Headphone impedance: 32 to 600 ohms

Assembly, setup

First, I bought a factory amplifier board, they sell bundles on ebay from the Chinese, I didn’t poison my own, the amplifier is very sensitive to wiring, and if the topology of the board is wrong, it starts to glow, and this board is multilayer, double-sided, with gold-plated holes. The output transistors are selected in pairs.

Capacitors Samwha, elna, rubycon, epcos, wima. 1% accuracy resistors are used. The potentiometer is Japanese Alps, I chose it because it has an almost perfect channel balance for potentiometers, the discrepancy between the channels is not distinguishable by ear, I may eventually change to DACT, but it will cost like half an amplifier :)

As an alarm relay in protection, a relay from Takamisawa with gold-plated contacts is used. The protection provides both load disconnection when a constant voltage appears at the output, and a five-second turn-on delay. The protection is switched on from a separate stabilized power supply, which excludes its influence on the power supply of the amplifier and guarantees the operation of the protection in the event of a power failure of the amplifier.

Transformer of the Czech company Talema. The second, U-shaped, has already been replaced with a quality one in the fill. The operational amplifier opa 2134, transferred to class A, loaded with resistors, it would be more correct to use a jfet cascade, but for now, I will do it as I have time and desire. Brought down switching gains (0dB; +10dB; +18dB; +20dB) can be adjusted clearly to your headphones to avoid sharp and very smooth volume additions.

In the photos, the line output is not yet connected, it is connected from the headphone output, through 48 ohm resistors.

The design cost 12-13 thousand rubles, which is quite inexpensive when compared with factory options. Now it makes me happy with its sound. Works with Technics sl-pg480a and sennheiser hd280, I plan to replace the headphones with something more serious soon. Now it works as a headphone amplifier and as a power preamplifier.

Finished product :)

Board: Headphone Amplifier kit Diy Base on Lehmann AMP Circuit

Case: DIY Aluminum Headphone Amplifier Case Amp Enclosure

Transformer: 220V/115v 30W R-Core Transformer for preamp 9V*2 15V*2

Now paired with Maverick Audio D2 + Sennheiser HD650.

Since 2011, the amplifier has undergone a number of upgrades and improvements:

1. The internal power wiring was replaced from the Chinese wire to PuGv, the signal ones were also replaced from noname to clotz.
2. The U-shaped transformer has been replaced by a cast transformer, mounted on a circuit board directly behind the main toroidal transformer. Printed circuit board under the transformer era 220V primary, 9V secondary.
3. The samwha capacitors swelled up and were replaced with simple jamicons, maybe later I'll get confused and change to something from audio-grade.
4. Raised the opamp current to 5mA.
5. Changed the RCA connectors to decent ones.
6. I packed all the amplifier wiring in tesa heat resistant tape.
7. I connected the line output and actively use the amplifier as a preamplifier.
8. I changed the indication from blue to a pleasant green (eyes became less tired at night).

I bought simple ears so that I could gamble at night and sometimes listen to music, I took inexpensive, but large KOSS UR20. Having connected to the receiver, I was somewhat dumbfounded, the sound is very, very pleasant, jazz and classics just go with a bang. In terms of low frequencies, of course, they lose a lot to Koss the plugs, and KOSS Porta Pro are noticeable, which I have been carrying as portable for a year now. I was very surprised when I decided to listen to Koss Porta Pro after listening to the songs on the KOSS UR20 - from the pro port it was as if cotton wool had been pushed into my ears. And I thought they were very "decent" in terms of sound. Although maybe this time and the atmosphere could spoil them so much? What is all this for? Yes, I decided to assemble an amp for the ears, the amp will be home, never portable.
I decided to start building a clone of Lehmann Audio Black Cube Linear doctorhead.ru/catalogue/?i=523
Here is the result:

All together it took about 3 evenings and less than 1000 rubles of money.
Who cares, welcome under the cat, there will be a lot of photos with a detailed description.

Scheme and design

Nutrition

I was thinking how to make a signet, I found a scanned printed circuit board on some Polish forum

And circled it in my favorite Sprint Layout

Here's what happened

True, I slightly redrawn it, because I found a couple of errors and resized it to fit my detail sizes. Then it turned out that the foil textolite in the store is only 10x15 in size, and the board was larger, I had to redraw it again and reduce its overall dimensions.

PCB manufacturing

LUT or Laser Ironing Technology is our everything) I have been using glossy magazines as a transfer material for a long time, the main thing is that there are not many dark areas and fills on the magazine sheets.
We print 2 sides.

After that, the most fun - you need to somehow combine them. I made LUT from both sides at once, put a piece of textolite into sheets and carefully wrapped them, then ironed well first one side then the other with an iron. In principle, it turned out well, one side ran away by a few tenths of a millimeter.
After ironing, you need to place the board in water and carefully remove the soaked paper, I do it with my fingertips under water, like this

After laundering from paper, such a board is obtained

We carefully study it for the presence of jambs, if there are any, we correct it with a scalpel with a ruler and a marker. If everything is fine, we throw the board into a bath with a solution of ferric chloride (the recipe is on the bank). The main thing in this business is to stir the solution and regularly turn the board over for uniform etching.

I stick toothpicks around the edges to keep the pickling bath edges from touching the board.
After etching, it is necessary to rinse the board well from the solution

Toner, from the finished board, is washed off with acetone.

For ease of assembly, I like to apply the designations of the elements

Then all holes are drilled using a collet chuck engine

I tinned the lower part of the board using a braid with flux and a small amount of solder.


All the following pictures are mostly with the board not yet washed from the flux.

Assembly

And we check them. The power supply did not start the first time, it turned out that the LM337 was completely Chinese and simply did not work. Therefore, the first test of the amplifier in the kitchen at night was from 2 laboratory sources (the lower one, by the way, is also homemade).

The check showed that the radiator is required. The pay looks like this.

I took an old radiator from the motherboard and drilled it


Cut, bevelled

Mica and KPT, radiator in place. The circuit consumes about 150 mA on each power arm. Reminds me of a class A amplifier.


I took the transformer ready from an old decommissioned Hungarian amplifier.

Test listening did on the following ears TDS-5M and 3 pairs of KOSS))) all average.

Frame

From old stocks, we lift sheet aluminum and cut the overlay to fit the front panel of the CDROM

Without thinking for a long time, I screwed this panel with two screws, chose the cutest ones))))

We drill and try on, it has already become better.

.

Painting and decoration

Assembled board in the case


I had to change the power capacities in front of the stabilizers from 4700 to 10,000 near OPA2134 from 470 to 4700 uF, as there was a small hum that could be heard at night in complete silence. I also added radiators for integral stabilizers, since their temperature regime in a closed case is not the best.

Here is such a nice, in my opinion, turned out to be an amplifier

Outcome

What's left to do:
1. Cover with a second coat of paint
2. Cover the front panel and body with varnish to protect the coating (lacquer will be available only next week).
3. Cut out the back panel and put in normal RCA connectors (no time for this yet). If all goes well, I'll do it this weekend.
4. Try on the amplifier at least RMAA. I looked with an oscilloscope, gave a rectangle at the input, saw exactly the same at the output.
UPD Items 1,2 and 3 completed

Bonus
And this daughter is doing a test audition)))