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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: 22 Dec 2009, 15:16 
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Joined: 26 Oct 2008, 13:48
Posts: 70
Location: Central California coast
Hi Gio,

Hybrid is acceptable except getting the bias can be a pain. My priorities would be simplicity first, cost second. Simplicity implies p-t-p wiring as opposed to PCBs, minimal parts count and no exotic or hard to find parts - typical amatuer DIYer!

I have a PSU that will give me 160VDC unloaded after the FWR and cap input. I would probably follow that with a small LC filter. Also, since the current is not much, I should be able to double it if the circuit calls for a higher B+. I have 5751s, 5814s, 12AX7s, 12AU7s, plus some oddball tubes like 6AU6, 12BH7,,,wish I had some 5687s, I have no 6DJ8/6922. I prefer using 9-pin tubes for this amp to keep the foot print small (although I do have one 6BX7). I haven't decided whether to use the Ipod attenuator or run a volume control.

Thanks for your help,
Mike 8>)


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PostPosted: 22 Dec 2009, 23:33 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
Hi Mike,
How much current can you provide? I'm assuming that a tube design that requires audio output transformers is out.

There are some good OTL (output transformer less) designs at headwize: http://gilmore2.chem.northwestern.edu/p ... /index.htm to look at.

If you go Hybrid you will need a low voltage supply as well. Or you could go all low voltage like Rogers' DIY 12AU7 Tube / IRF612 MOSFET Headphone Amplifier. Or you could go with a tube voltage gain stage and then a opamp buffer. An opamp should do a pretty good job driving a 140 ohm load.

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: 23 Dec 2009, 11:44 
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Joined: 26 Oct 2008, 13:48
Posts: 70
Location: Central California coast
Hi Gio,

Correct, OTL is preferred. I've been to Headwize, and there are some good designs there which are definitely worth considering. My PSU is around 50VA, so I'm fat there, and it could be tapped for 15V single rail for a hybrid bias supply. I'll have to study the alternatives and generate a block diagram to post.

Happy Holidays to Everybody Image


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PostPosted: 24 Dec 2009, 17:43 
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Joined: 26 Oct 2008, 13:48
Posts: 70
Location: Central California coast
Hi All:

Well, I decided to build Roggom's high voltage version of the DIY 12AU7/IRF612 headphone amp. :headphones:

I have a couple IRF630s and I'll use a pair of 6C4s in place of the 12AU7. I am a little concerned about the THUMP on/off, but the amb.org e12 or maybe Velleman's speaker protector are possibilities. The added complexity [+ & - 12V supply] and real estate is my concern because I want the foot print to remain small. Any one have some more suggestions for slow-turn-on/off??

May your holidays be upbeat -
Mike 8>)


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PostPosted: 25 Dec 2009, 12:22 
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Location: Winnipeg, CANADA
What I eventually did to eliminate the turn on thump was to use a switch to mute the amp.

Also, here is my DIY Class-A Mosfet Headphone Amplifier. Basically the same as Rogers', but without the voltage gain stage.
Cheers

_________________
[ 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: 29 Dec 2009, 00:18 
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Joined: 26 Oct 2008, 13:48
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Location: Central California coast
A "mute" switch is certainly simple! I guess I could just always unplug the phones before turning it off, and plugging in after i turn on the amp...the mute switch is better!

Have an upbeat New Year everyone,

Mike 8>)


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PostPosted: 11 Jan 2010, 16:25 
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Joined: 02 Dec 2009, 16:02
Posts: 5
I finished building this little guy and used a 12AX7 instead because I am using this for a guitar preamp. I have a couple of problems, the first is that I don't seem to have any voltage negative or otherwise on the grid. The plates are very strong at 140 vdc and 118 vdc. The other problem is that the impedance of an electric guitar is between 7 and 9 K Ohms and since this preamp is designed for an Ipod headphone out, could my problems be because of the impedance mismatch?
After reading my own post I realized I didn't mention the problem, it has little or no gain and the sound is very distorted and scratchy. Thanks in advance for the help. :eek:


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PostPosted: 12 Jan 2010, 21:35 
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Joined: 14 Oct 2008, 17:35
Posts: 901
Location: Dartmouth, Nova Scotia
I have not yet tried a guitar on the preamp to see how it performs, but I think I may have recommended the use of this circuit at the input for use with a guitar...

http://www.till.com/articles/GuitarPreamp/

I have not yet tried this circuit either but it is very simple and can probably use just about any basic N-channel FET. It could be made small enough to fit in with the tube preamp with the use of an optional input switch. :idea:

I have said that I am going to make an updated preamp that will have different input options, like the Guitar or mic, or the RIAA equalizer to be used as a phono preamp as this project seems to be fairly popular. It is just difficult to find time to work on projects during the school year. ;)

I have a Bass guitar now so I can do some fun experimenting. ;) :xmass:

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


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PostPosted: 13 Jan 2010, 18:31 
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Joined: 02 Dec 2009, 16:02
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Seems like an easy build. One more quick question, should I ground the center tap on the PT? I am getting 60 hz hum even with the volume pot in the lowest position. Filament wires are twisted and I have only one ground lug. Everything else is pretty well shielded. Thanks so much for the help so far.


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PostPosted: 14 Jan 2010, 20:18 
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Location: Dartmouth, Nova Scotia
60Hz hum is usually caused by a grounding problem or bad placing of noise sensitive components, check your wiring cairfully and make sure of no ground loops.

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


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