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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

View Poll Results: a kit amplifier or home-brew amplifier
A kit amplifier 3 10.71%
Home-brew amplifier 18 64.29%
Both are equally good 6 21.43%
No opinion… 1 3.57%
Voters: 28. You may not vote on this poll

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Old 13th Jan 2012, 7:14 pm   #81
Don_Zalmrol
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Default Re: I want to build a stereo headset valve amplifier

Yes, the design and circuits that I'm using is based on a project from somebody on HeadWize.
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Old 13th Jan 2012, 7:20 pm   #82
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Default Re: I want to build a stereo headset valve amplifier

Quote:
Originally Posted by Don_Zalmrol View Post
Yes, the design and circuits that I'm using is based on a project from somebody on HeadWize.
Check. The good forum for things headphone is head-case.org

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Old 19th Jan 2012, 12:05 pm   #83
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Default Re: I want to build a stereo headset valve amplifier

Thx for the advice on head-case.org.

Everything of my parts has arrived and I have begun to drill the holes in the casing.
Tonight I will up some photos to my site about the project.

Just a quick question about the volume control.
I'm using an ALPS 100KAX2 log pot for controlling the volume.

But which way do I mount it?
With the small pinout to the left side or to the right?

Otherwise if I place wrong, the volume will go up instead of down when turning it…
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Old 20th Jan 2012, 1:37 pm   #84
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Default Re: I want to build a stereo headset valve amplifier

However the pinout on the pot is arranged, you need the terminal at the clockwise end of the track as signal input, and anticlockwise end as ground. Output between the wiper and anticlockwise end.

If the pot construction makes this unclear, use a meter to measure resistance between wiper and ends at each limit of wiper travel.
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Old 20th Jan 2012, 6:17 pm   #85
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Default Re: I want to build a stereo headset valve amplifier

Thx, I will do that.

Meanwhile the housing is almost completed, I just need to drill two more holes for a 8 pin bridge (or how you call it in English…) to easily mount the rectifiers and other cables from the HT and LT windings.

In the link you can found some picture I've took of my progress so far:
http://www.don-zalmrol.be/index.php?...=Headphonesamp

It's my own website, sorry it's in Dutch…
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Old 20th Jan 2012, 6:49 pm   #86
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Default Re: I want to build a stereo headset valve amplifier

That is very nice looking - let us know what it sounds like!

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Old 23rd Jan 2012, 10:00 pm   #87
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Default Re: I want to build a stereo headset valve amplifier

Having a problem with my transformer.
I've installed the transformer to the casing and connected my wires according to the Hammond circuit design for 240V and soldered the HT and LT (with CT) to my 8P bridge connector.
The HT nor LT are NOT connected to the GND. I've measured it to be sure with my multimeter.

And when I power up the transformer, the fuse blows…

I connected the circuit as such:
From the mains socket -> switch -> fuse -> transformer -> mains socket

Any ideas?
The transformer is not using any resistor ballast or isn't connected to anything else…

(Edit)

False alarm, the fuse I've used was 0,5A and the startup rush current from the transformer was higher then the fuse. I've put now a 1A fuse in it, but will change it to 2.5A because this is the maximum amperage of the HT winding

Last edited by Brian R Pateman; 23rd Jan 2012 at 10:51 pm. Reason: Colour fault repaired.
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Old 24th Jan 2012, 9:58 pm   #88
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Default Re: I want to build a stereo headset valve amplifier

I've finished installing the power connections to the HT and LT side of the valve sockets.

As you can see in the pictures, I've twisted the cables to cancel out the noise.
And connected the LT connections to the caps (left & right) channel.

Is this done well or can it be done better?
Just curious, because like you all know this is the first time I undertake such a project…
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Old 25th Jan 2012, 12:06 am   #89
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Default Re: I want to build a stereo headset valve amplifier

Looking at that second picture, I think you are counting the valve pins wrongly. With the gap at the bottom, you count clockwise so pin 1 is the first on the left and counting round, pin 9 is the other side of the gap. The heater pins are pins 4,5 and 9. It looks like you have counted round the wrong way so you have pins 1,5 and 6 as heater which won't work!

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Old 25th Jan 2012, 10:12 am   #90
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Default Re: I want to build a stereo headset valve amplifier

Damned, I will correct my mistake tonight…
Luckily I've asked, otherwise my amplifier would have probably given a nice little fireworks show…

Thx!
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Old 25th Jan 2012, 10:43 am   #91
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Default Re: I want to build a stereo headset valve amplifier

Better to have asked now rather than discover the error when it's all neatly wired up......


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Old 25th Jan 2012, 11:23 am   #92
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Default Re: I want to build a stereo headset valve amplifier

^ idd!

Is the wiring otherwise done properly?
I mean with the twisting pair, the cable is a bit difficult to twist properly…
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Old 25th Jan 2012, 1:27 pm   #93
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Default Re: I want to build a stereo headset valve amplifier

It looks pretty good although I would have done the link across (what should be) pins 4-5 with just a short length of bare tinned wire rather than the red loop you used. It's just a cosmetic point, entirely up to you.


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Old 25th Jan 2012, 10:11 pm   #94
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Default Re: I want to build a stereo headset valve amplifier

Allright, I'm done connecting everything.
Here a some pictures of the end result.

If there is anything that you guys notice, tell me where there is room for improvement or something that needs to be done else!

If everything is in order, I will test the amp with the valves connected.
The audio input will come for testing from my laptop and an old Panasonic RP-HFT600 headphones (56 Ohms)
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Old 25th Jan 2012, 11:00 pm   #95
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Default Re: I want to build a stereo headset valve amplifier

I've redone the green audio output wires and put nicely tucked away on the side.

I have also some microphone lead cable lying around, if necessary I can always change it to that cable and connect the masse to the ground of the chassis on both sides…
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Old 25th Jan 2012, 11:17 pm   #96
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Default Re: I want to build a stereo headset valve amplifier

There are some rather long leads which may cause some hum problems. I suggest you carefully check all your connections, make sure there are no shorts from the HT supply to chassis then when you are happy, check it again! (hint) after the first check, go away and do something else for an hour, then come back and check it again. When you are really satisfied that all is well, time for a trial run. Hopefully you can report here tomorrow that all is well.


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Old 26th Jan 2012, 12:50 pm   #97
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Default Re: I want to build a stereo headset valve amplifier

There is a short from the HT supply to chassis. But that is the result of 2 resistors on the beginning of the HT supply to dissipate the startup rush current to the valves…

I'm going to recheck the valve circuit and connections.
If everything seems to be in order, I will test the amp and report what happens.

Just a small question, what would happen if the valves (both the 12AU7's and 6CG7's) receive more than 330VDC on their plates?
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Old 26th Jan 2012, 5:34 pm   #98
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Default Re: I want to build a stereo headset valve amplifier

The amp works!
Just some problems…

Excessive hum…
When I touch the input cable from the ALPS meter the hum seems to be lesser, I will change the cabling to a piece of shielded audio cable.

And also probably change the audio output cable to the shielded mic cable.

The right channel seems to be louder than the left channel…

The HT plate voltage is stable around +-300VDC (to 305VDC).

Any other tips or problems with my setup that would cancel out the hum problems?
Just noticed something, when I put my hands between the 12AU7's and the 6CG7's the hum is almost gone.

Also noticed a small error with the volume control, it goes the wrong way up ><

Last edited by Don_Zalmrol; 26th Jan 2012 at 5:55 pm. Reason: Noticed something…
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Old 26th Jan 2012, 7:24 pm   #99
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Default Re: I want to build a stereo headset valve amplifier

Cables for the in- and output are changed to shielded cables.
Problems seem to solved.

I've also grounded the shields and tucked the cable nicely away.
Redone some of the other cabling and shortened some of them.

Should I measure anything else, or check something else?

If not and everything seems to be in order, I can finish up the project by creating the bottom plate and feet.

Then this concludes this project for now!

Thank you all for your help!!!
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Old 26th Jan 2012, 8:01 pm   #100
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Default Re: I want to build a stereo headset valve amplifier

I've measured the voltages of the LT heater supply voltage on all four sockets and the range from 6,231VAC ~ 6,789VAC.

At the beginning of the LT winding the voltage is around 6,231VAC.

The voltages between the elco caps are:
Main (center) = +- 303VDC
Left = +- 209 ~ 301VDC
Right = +- 300 ~ 301VDC


The sound is quite clear and sounds very good.
Also the gain is quite high with the volume control!
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