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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

AD797 Preamp based on stolen trademark
AD797 Preamp based on stolen trademark
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Old 6th July 2020, 04:54 AM   #111
gigigirl is offline gigigirl
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Join Date: Oct 2016
Hi Keilau, Great suggestion, Yes same board on Alliexpress without fake op-amps, (which I do not need_ for $36. I do not need balanced, so single ended is fine for me.

Lusya HIFI MBL6010D Preamp Tone audio Board Pre signal Buffer Amplifier Board T0047|Amplifier| - AliExpress

Cheers
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Old 6th July 2020, 11:20 AM   #112
keilau is offline keilau  United States
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Join Date: Mar 2013
Location: Windy City, US
Quote:
Originally Posted by gigigirl View Post
Hi Keilau, Great suggestion, Yes same board on Alliexpress without fake op-amps, (which I do not need_ for $36. I do not need balanced, so single ended is fine for me.

Lusya HIFI MBL6010D Preamp Tone audio Board Pre signal Buffer Amplifier Board T0047|Amplifier| - AliExpress

Cheers
Quote:
Originally Posted by Lusya
The board is suitable for the NE5532, NE5534 and OPA series op amps.
The AD797 cannot be placed in the front position. You can use the reverse output at the back to replace the different op amps. The sounds have different changes. OPA series op amps to adjust the sounds you like. The three-stage balance, the density of the sound is good, the treble is strong, the vocals are sweet, and the low frequency is deep.
When it cannot use the AD797 opamp, how does it relate to the MBL6010D? It must have a different circuit topology than the MLB6010D. However, I do realize that AD797 is not the optimal choice for line level preamp. The confusion just deepens.
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Old 9th July 2020, 05:32 AM   #113
gigigirl is offline gigigirl
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Join Date: Oct 2016
Hi, Well as far as I know from their blurb the 1st pair of op-amps are an input buffer!! Whatever that means.

Anyway I received my Chinese AD797 op-amps today. Yes I know they are fake, but have used them before for testing my phono amp, then I replaced them with genuine one. The genuine ones definitely sounded better, but it was not night & day, they were very close.
So how did they sound, well initially very good, better that the 55 series, definitely brighter. I have left the playing on repeat in my 2nd system. I will do a more serious listen in a couple more days.
Also it occurred to me that the from pair of dual op-amps could be replaced with one of the many available, any suggestions.

Cheers
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Old 11th July 2020, 06:09 AM   #114
Berlusconi is offline Berlusconi
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Join Date: Sep 2019
AD797 Preamp based on stolen trademark
@keilau @gigigirl

Thanks guys for useful information

Meanwhile, my package has arrived too and I have tested the board. The board sounds good but as it is almost certain that components are all fake I have initially decided to desolder everything and rebuild it with genuine components.

However, I've found a better solution: bare boards of the same 1.2 version (shown on image 1 below) are also available <HERE> and I will build it from the stratch as the board itself seems to be proprtly designed.

I also have stumbled upon the schematics of the board (shown on image 2). below.

I wish you a pleasant weekend
Attached Images
File Type: jpg 6010D-Bare Board.jpg (117.5 KB, 464 views)
File Type: jpg 6010D-Schematics.JPG (62.7 KB, 472 views)
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Old 17th September 2020, 07:30 AM   #115
gigigirl is offline gigigirl
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Join Date: Oct 2016
Default Changed input voltage to +/-17 VDC

Hi, Have not looked at my pre for a while as although I was happy with the sound I was not happy that I was getting some hum coming through. I know I could move the trans to a separate case, but that means extra complications & as it is for my lab workshop 2nd system I decided not to.

Hovever I have just upgraded the P/S to mt phono amp in my main system & the old unit, still very quite became available. It is a Omishra P/S brough through the A/K site.

So last week I had read a blog, again on another site suggesting yjat you can use a DC +/- P/S to replace a trans, you just need to step the DC voltage up a bit. So I set the Omishra P/S to +/- 17VDC & hooked it up to the Pre amp AC input putting the + voltage on the R/H side (as you face the board) the - voltage on the L/H. The what I would call netral (yes I no it's not, but I do not know what to call it) in the center.

Turned it on & no smoke & to my delight it worked very nicely indeed, Through my AKG 701 H/Phones, no hint of hum & a definite sound improvement.

So now I will go a little further & get a couple of genuine NE5534 op-amp & change the Vol pot for something of better quality.

Hopefully I can live with it in my main system while I upgrade my Korg B1.

Cheers
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Old 17th September 2020, 10:55 PM   #116
egellings is offline egellings  United States
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That AD797 is one sweet jelly bean!
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Old 18th September 2020, 07:07 AM   #117
Berlusconi is offline Berlusconi
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Join Date: Sep 2019
AD797 Preamp based on stolen trademark
Hi gigigirl,

Thanks for the info. I have suspected that there will be some fake parts in the "finisher board" but my original plan was not just to replace the ICs with the original AD979. What I plan to do is to build the preamp from the scratch, with components purchased from Farnell. First I had to wait because AD979 was not on stock.

Now I have purchased two bare boards and everything else will arrive today by UPS from the UK. At least I will know that I have done everything right.
Meanwhile, I have inspected the "completed board" purchased from Aliexpress.

ICs look different just like they have recycled them from used equipment, capacitors have slightly different color from the original Wima, electrolytic capacitors resemble the original, and yet I am suspicious. (Please, read the PS below, regarding these capacitors)

I was astonished to find out that the values of resistors differ from these on the schematics and on the silkscreen: 2K49 instead of 2K2, 12K1 instead of 10K, 205R instead of 220R... It seems like they used resistors with the closest values they could find in the workshop. I simply could not let it be that way.

Now, only components for the preamp cost me about EUR200, without VAT included + costs of the chassis. At least, I know that there will be no junk in my chassis.

Regards

EDIT: Even if you change the thoroidal with the external +/-17 VDC power supply, voltage in the circuits will remain the same: there are two voltage regulators LM317 and LM337 on the board which will keep the same voltage approaching the rest of the circuit. Essentially, you have provided smoother source of power at the input of the existing power supply on the board. This indicates that these "ELNA" capacitors likely are fake.

Last edited by Berlusconi; 18th September 2020 at 07:29 AM.
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Old 22nd September 2020, 08:56 AM   #118
Berlusconi is offline Berlusconi
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Join Date: Sep 2019
AD797 Preamp based on stolen trademark
Quote:
Originally Posted by gigigirl View Post
....So I set the Omishra P/S to +/- 17VDC & ...
Cheers
There is no need to use an external power supply since the existing on-board power supply is adequate, you just have to make proper adjustment. Originally, the board is set to +/- 15.00 VDC. I have adjusted voltage on two 5K potentiometers that are located behind the heat sinks. Now, it measures +/- 17.5VDC. You can measure the positive rail voltage on the IC pin #7. Similarly, the negative rail voltage can be measured in the IC pin #4. Adjust the voltage slowly because response to changes at potentiometers is slow.

Furthermore, it is necessary to set voltage drift to zero at all four ICS. As usual, the Chinese instructions are wrong.

Here is how to adjust voltage:

Before you start, observe the board: there are four rectangular areas: the lower two are for the left channel and the upper two rectangles correspond to the right channel.
Also there are two small holes on the PCB between these two 220 uF axial capacitors. You can use them for the ground probe during measurements.
1.
First set the input potentiometer to max volume to have good response to subsequent changes. Otherwise you might see no changes at all if the input potentiometer is set to zero.
2.
Start with 20K potentiometer LR4 which is located in the lower right rectangular area at the board See the attached schematics. Adjust voltage at IC pin #6 to zero. I have measured that voltage at the left side of 220R resistor located in the lower left rectangle on the board.
3.
Proceed with the 20K potentiometer in the lower left rectangle and measure the voltage at + output of the left channel and G. Now the left channel is adjusted.
4. Repeat the same procedure for the right channel.

Now, the device is ready for use.

I have made some measurements which indicate that the preamp is virtually "a wire with gain" over a very wide range of frequencies. It has entirely flat response between 5Hz and 200KHz.

Cheers
Attached Images
File Type: jpg Schematics-AD797.jpg (44.2 KB, 251 views)

Last edited by Berlusconi; 22nd September 2020 at 09:06 AM.
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Old 22nd September 2020, 11:06 AM   #119
ginetto61 is offline ginetto61  Italy
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Join Date: Sep 2009
Location: Milano
AD797 Preamp based on stolen trademark
Quote:
Originally Posted by Berlusconi View Post
There is no need to use an external power supply since the existing on-board power supply is adequate, ...
It is a field where opinions differ

Explain the advantages of an external power supply - YouTube

Many totl preamps have external mains transformers at least
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“And is it any wonder That the monkey's confused” ― Roger Waters
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Old 22nd September 2020, 02:37 PM   #120
Berlusconi is offline Berlusconi
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Join Date: Sep 2019
AD797 Preamp based on stolen trademark
Thanks Ginetto,
Very kind of you. I do appreciate that... but that guy from youtube has another target audience: "audiophiles".

Here, in this particular case, we have at hands more than adequate power supply built into this preamp. Furthermore, this power supply is linear, regulated, and adjusted to +/- 15.00 VDC by default, but fortunately, still adjustable. If we connect it in series with another power supply with higher voltage, we will end up again with 15 VDC because that 220R along with the 5K pot define the output from LM317 / LM337 pair to +/- 15.00 VDC. The only "benefit" from this is dissipation of heat needed to drop the extra voltage through the heat sink. Nothing else. If one can hear any difference it is, unfortunately, audiophile placebo effect.

Hence the only way to change the voltage at the IC in this circuit is to select another value at the potentiometer. May I suggest you to read reliable technical document linked below at TI, not youtube Fake News.

No offense meant, this is strictly technical matter.

https://www.ti.com/lit/ds/symlink/lm317.pdf

Last edited by Berlusconi; 22nd September 2020 at 02:39 PM.
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