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Old 6th March 2019, 11:55 PM   #101
jaycee is offline jaycee  United Kingdom
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If you left out R1, R2 and C6, that is why it is picking up RF. You'll also likely end up with quite a bit of DC offset. R2 and C6 specifically form a low pass filter to prevent RF pickup. This is used on pretty much any opamp input.
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Old 7th March 2019, 02:19 AM   #102
prasi is offline prasi  India
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hello spacehead,
I have built it too and is currently housed in an aluminium case since a year. Works just fine. Use the PCB . If I remember correctly, xrk had issues when built point to point/breadboard, but when he used my PCB, it was ok.
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Old 13th March 2019, 02:41 PM   #103
Spacehead is offline Spacehead  Finland
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Hi

The PCB has arrived. It is high quality. Thank you. Next I will gather the components. It looks like I need to visit a component shop. Is there a BOM somewhere? What type of inductor you need?

Click the image to open in full size.

Last edited by Spacehead; 13th March 2019 at 03:02 PM.
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Old 13th March 2019, 03:23 PM   #104
xrk971 is offline xrk971  United States
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Hi Spacehead,
Glad you got the board. No need for a BOM - I never made one as you can just just go by the schematic and the silkscreen even to populate this board. All resistors are usual 1/4w axial 1% metal thin film. For the inductor, take 18ga or 16ga magnet wire and wind it around a 6mm drill bit - about 10-12 windings - not critical. Remove the varnish off the ends with a match and sand it down, then tin it with solder and install. Make sure all your caps are rated at least 25v for electrolytics. For the film caps, 100v is the typical, even 50v can work. You will need some BD139/BD140's though - get real ones as there are fakes floating around from China that go pop when you put any current through them. You can also use other opamps of your choice as long as pinouts are the same. Don't delete or skip any parts - they are all needed for this to work correctly!
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Last edited by xrk971; 13th March 2019 at 03:25 PM.
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Old 13th March 2019, 03:36 PM   #105
Spacehead is offline Spacehead  Finland
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Quote:
Originally Posted by xrk971 View Post
Hi Spacehead,
Glad you got the board. No need for a BOM - I never made one as you can just just go by the schematic and the silkscreen even to populate this board. All resistors are usual 1/4w axial 1% metal thin film. For the inductor, take 18ga or 16ga magnet wire and wind it around a 6mm drill bit - about 10-12 windings - not critical. Remove the varnish off the ends with a match and sand it down, then tin it with solder and install. Make sure all your caps are rated at least 25v for electrolytics. For the film caps, 100v is the typical, even 50v can work. You will need some BD139/BD140's though - get real ones as there are fakes floating around from China that go pop when you put any current through them. You can also use other opamps of your choice as long as pinouts are the same. Don't delete or skip any parts - they are all needed for this to work correctly!

I have gathered the shopping cart. I think I can buy real inductor, I wonder how many H is a good value?


I have real BD139/BD140 and separate heat sinks for them, that can dissipate around 1W each.



Is the value of RG freely chosen according to the desired gain?

Last edited by Spacehead; 13th March 2019 at 03:38 PM.
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Old 13th March 2019, 04:01 PM   #106
prasi is offline prasi  India
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Inductor is not critical anywhere from 0.5uH to 1 uH or any value near about.
I used a 0.8mm enameled wire to make one. It doesnt pass lot of current.
RG doesnt set the gain. Its a ground lift resistor and can be 4.7 to 10 Ohms.
R3 and R4 set the gain and is currently configured at 15.
You could reduce the gain by decreasing R4.
With default values, I found that with a mobile as the source, very high volume is reached with 40% volume pot position.
regards
Prasi

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Old 14th March 2019, 07:58 PM   #107
Spacehead is offline Spacehead  Finland
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I got the components today for a pocket change.

Click the image to open in full size.

I have only 1.04k in my stock, which are close enough. I will complete the PCB at some other time. Gain will be adjustable with sockets for R4. For my headphones R4 will be 2.2K. I will try it with NE5532 and TL072. Inductor is 1 uH.

Last edited by Spacehead; 14th March 2019 at 08:12 PM.
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Old 15th March 2019, 01:28 PM   #108
Spacehead is offline Spacehead  Finland
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PCB has been completed. It worked right away. With NE5532 DC offset is 27 mV and with TL072 it is 4 mV and 7 mV. The sound quality is good.



R4 2.2k, R3 1k, R2 1k.


Click the image to open in full size.


How much DC offset did you get and which op amp did you use? Did you measure the distortion with different op amps?

Last edited by Spacehead; 15th March 2019 at 01:34 PM.
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Old 15th March 2019, 02:53 PM   #109
prasi is offline prasi  India
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Nice work! Congrats!
I used TL072 and DC offset was too low to remember.
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Old 15th March 2019, 06:47 PM   #110
Spacehead is offline Spacehead  Finland
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Originally Posted by prasi View Post
Nice work! Congrats!
I used TL072 and DC offset was too low to remember.
Thank you.

Unfortunately it is not silent while source is connected and nothing is played.
There is some white noise with NE5532 and with TL072. It is audible. That is with 16 ohm sensitive earbuds, that I use to test for noise. With 32 ohm headphones it is better but not hifi level.
The source is quiet. Is this supposed to have pitch black noiseless background?

I don't have volume pot because I use the source's digital volume control. Does that matter?


Maybe the noise comes from the output filter network?


I tested the amplifier with speakers too, because ESP has rated it for 8 ohms.

As a 2W speaker amplifier it is excellent.

Last edited by Spacehead; 15th March 2019 at 06:57 PM.
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