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 NEW  Bruce Heran outlines the details and construction of his simple DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project.

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PostPosted: 19 Jul 2010, 19:55 
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Joined: 03 Aug 2008, 20:22
Posts: 386
Location: Denver, Colorado
Sorry to hear you are having issues with battery sources. Some D cel batteries are nothing more than a AA in a plastic shell. http://www.naturalnews.com/phototour_en ... ies_2.html

The amp draws about 400ma constantly, so there may be an issue with capacity. The best thing would be to find a small UPS battery either 12v 3Ah or 12v 7ah. They are rather common in use in computer ups systems and hallway emergency lighting.

Hope this helps


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PostPosted: 20 Jul 2010, 10:20 
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Joined: 17 Jul 2010, 15:46
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Voltage is now 13.3 under load.


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PostPosted: 20 Jul 2010, 11:38 
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Joined: 17 Jul 2010, 15:46
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Out of curiosity I hooked up the amp to a 19V, 3A power supply, and while conditions got better, there is still a little bit of clipping (though now it seems very slight). Also the sine wave is negatively offset from zero. Is this a problem? I'm not measuring much DC offset at the output (and it is positive in both channels).
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Amp clipping2.PNG


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PostPosted: 20 Jul 2010, 11:54 
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Location: Denver, Colorado
Looks much better, just be careful that you reduce the heater voltage to between 12 and 13 volts. 12.6 would be ideal, this can be accomplished by an LM7812 and a heatsink. Also there may be a few millivolts of dc offset, just make sure to unplug you headphones as you power up and down (to prevent in rush)

Rogers


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PostPosted: 20 Jul 2010, 20:34 
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Joined: 14 Oct 2008, 17:35
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Location: Dartmouth, Nova Scotia
Hello, I built a similar amplifier to this, well basically the same just different values, but would like to know how I could improve it.

I am using an IRF640 mosfet, LM317 CCS with 4.7 ohm bias resistor (half the value used for the project in this thread), The 12AU7 has 2.2K cathode bias resistor and a 50K bias pot. Input cap is 2.2uF, output is 2200uF 16V, and to prevent DC "pop" on power up I have a 5 second delay relay. I also plan to run the circuit off 24 volts so I want to optimise the circuit for that, there is a peace of thick aluminum with the LM317 and IRF640 mounted to it that will be mounted to the aluminum chassis the amplifier is going in.

It all works, that is as of the last time I tried it....

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My Mini 12AU7 Tube Preamp, Pioneer SX-D7000, JVC XL-V221BK, JBL L80T, DCM TF700


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PostPosted: 21 Jul 2010, 08:12 
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Joined: 08 May 2009, 08:20
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Location: Duesseldorf, Germany
Hey Crazzy,

just a simple question: is there any reason why you are using the IRF640?
The Datasheet shows a C_iss of 1140pf (input capacitance). Man, thats a bunch...
I haven't measured anything, but i would mind that the input capacitance is way too high.
The IRF510 and IRF610 is 140pF / 180pF and much easier to drive.

It could be a improvement to change the 640s with one of the other types.

One more suggestion is to change the output cap with a 35VDC type.
If a short occurs (IRF shorting internally), you'll have a "safety" in the back.

Just only my :2c:.

Have fun ;-).

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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 21 Jul 2010, 11:57 
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Joined: 14 Oct 2008, 17:35
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Location: Dartmouth, Nova Scotia
I read about the use of IRF530/40/630/40, on the project and found out that the highs might not sound right, or something like that. I used IRF640 because that is what I have and it seemed to work just fine the last time I used the amplifier. :worried: I was cheap with the output capacitor. :?

What do you recommend I change if I still use the IRF640? I will see if I can find IRF610/510 but I don't come across those all that often.

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My Mini 12AU7 Tube Preamp, Pioneer SX-D7000, JVC XL-V221BK, JBL L80T, DCM TF700


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PostPosted: 21 Jul 2010, 18:56 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
Hi Alan, for sure - replace that mosfet as it is not suitable. If you can't find any I'm sure I have a couple of IRF510 or IRF610 that I can mail you.
Cheers

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[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


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PostPosted: 22 Jul 2010, 20:31 
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Joined: 14 Oct 2008, 17:35
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Location: Dartmouth, Nova Scotia
Well that would be be great Gio, you don't really have to though, before you send me some I will see if I can find some in my parts piles, and at the TV shop, I may be able to get some at the local electronics store too, I appreciate the offer though. :up:

I will post some picture of what I am putting together.

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My Mini 12AU7 Tube Preamp, Pioneer SX-D7000, JVC XL-V221BK, JBL L80T, DCM TF700


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PostPosted: 24 Jul 2010, 17:38 
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Joined: 24 Jul 2010, 17:33
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hi, I'm wondering if I should build this, or the original version ( http://diyaudioprojects.com/Solid/Tube- ... phone-Amp/ ).
is it true that the older variant has twice as much gain? what are its disadvantages? I have enough parts around that I could make both versions.
I'm afraid I don't really understand what I'm doing, so please forgive me if this is very silly.


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