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PostPosted: 16 Apr 2017, 19:02 
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Hi everyone,I would like to build a Headphone tube amp using Hammond Transformer,6AS7G and 6SN7/12SN7 for my Beyer Dynamic DT880-600R and Sennheiser HD-650 I just don't know which schematics is suitable for my application their are a lot in the web it can get overwhelming.I did build two tube headphone amp KIT that uses 6AS7g/6080,12A#7,6CG7 and 6DN7 they do sound really good to my ears but for the price i think i can build one with you guys help for cheaper judging by the components was used for these kits i think they are over price i know that transformers are not cheap.Eventually i will build a tube amplifier for speakers but for now i would like to do something small to begin with, Preferably using HAMMOND TRANSFORMER because it's locally available for me and maybe incorporating a Tube Rectifier whatever you guys think will works best for my application.

Thanks You in advanced,
Alex Q


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PostPosted: 16 Apr 2017, 19:57 
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Ok. Here is a schematic for a 6AS7 HP amp I designed, but it uses a 12A*7 driver tube, not the 6SN7 driver. But that is easy to change.
Attachment:
Schematic - Amp.jpg

I prototyped the output stage with just my signal generator on the input. I tested it driving a 65Ω load (for Sony V6s) and it performed flawlessly.
Attachment:
CF Prototype.jpg

Here is the FFT.
Attachment:
Output FFT.jpg

This is driving about 377mV rms into the 65Ω load; so about 2mW. This is the equivalent of 108dB SPL (per ear) with the Sony V6s. They have a sensitivity of 106dB/mW. The 2nd harmonic distortion at this level is only about 1.8% and 3rd harmonic about 1%. This gives a THD just about 2%. And at this SPL you couldn't hear it anyway. This stage actually performs pretty well.

Your Sennheiser HD-650s are 300Ω with a sensitivity of 103dB/Vrms (which is 3.3mW@300Ω so about 98dB/mW; weird specification by the way, dB/V) so this output stage should drive them just fine. The same 377mV rms signal (≈0.5mW@300Ω) would produce about 95dB SPL per ear in your HD-650s. And the output stage can do way better than this; especially into 300Ω. A modest vacuum tube power supply to supply about 300v@85mA should be no big deal.

So now you have one option. Lets see with what others chime in.


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PostPosted: 17 Apr 2017, 20:02 
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Hi Matt,
I found a HAMMOND 272JX transformer will this work((It's the only one in stock from my local dealer).Sorry i prefer to use the 6SN7 because i have more of these than the 12A*7 Is it possible for you to rework the schematic for 6SN7 instead and if you can tell me what type/wattage ratings for all of the resistors and if you can make a schematic for the POWER SUPPLY? Thank you for taking the time to response and sorry for being a noob,Thanks again!

Alex


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PostPosted: 18 Apr 2017, 19:13 
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Well, here is the 6SN7 version. Redesign was no big deal.
Attachment:
Schematic-6SN7_Version.jpg
I still think you should go with the 4S driver as it allows you to roll tubes to select sensitivity, but that's up to you.

As for the power supply, the Hammond 272JX is SERIOUS overkill. The voltage is high so you'll have to use large dropping resistors and it's a 287mA transformer for a little 86mA draw. The filament windings are also overkill. The 6AS7 filament draws 2.5A@6.3v and the 6SN7 only 600mA. That a total of 3.1A@6.3V plus whatever you need for the rectifier. The 272JX is 6.3v@8A and 5v@4A. The problem is, drawing 3.1A on an 8A filament winding is going to result in an over voltage condition that shortens the life of your tubes. And finally, that's a $100+ USD transformer here in the states. You could order a suitable one for import and still pay less even with shipping and duty. I strongly suggest you try and find a more suitable transformer.


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PostPosted: 19 Apr 2017, 17:36 
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Suncalc wrote:
Well, here is the 6SN7 version. Redesign was no big deal.
Attachment:
Schematic-6SN7_Version.jpg
I still think you should go with the 4S driver as it allows you to roll tubes to select sensitivity, but that's up to you.

As for the power supply, the Hammond 272JX is SERIOUS overkill. The voltage is high so you'll have to use large dropping resistors and it's a 287mA transformer for a little 86mA draw. The filament windings are also overkill. The 6AS7 filament draws 2.5A@6.3v and the 6SN7 only 600mA. That a total of 3.1A@6.3V plus whatever you need for the rectifier. The 272JX is 6.3v@8A and 5v@4A. The problem is, drawing 3.1A on an 8A filament winding is going to result in an over voltage condition that shortens the life of your tubes. And finally, that's a $100+ USD transformer here in the states. You could order a suitable one for import and still pay less even with shipping and duty. I strongly suggest you try and find a more suitable transformer.



Hi Matt,
Thanks you for your response!I take your suggestion building it with the 4S.Thanks again


Alex


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PostPosted: 24 Apr 2017, 18:16 
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Alex;

Here is the PS schematic using the 5U4 rectifier and the transformer we discussed.
Attachment:
Schematic_PS_5U4GB.jpg

Ignore where it says 12A*7 by the 6.3v filament. You can go ahead and use the 6SN7. The same filters apply to both. The voltage numbers are based on the published Hammond DCR and Vo specs for the transformer.

If when you build it, the final B+ voltages are abve about 310V (with everything drawing appropriate current), then insert a series resistance in front of the main filter choke to tame the voltage. At 85mA you'll drop about 21v per 250Ω. This would be about a 1.8W. I would recommend that you order a 250Ω 5W wire-wound resistor just in case (5W due to derating). They're cheap and good to have around.

Let me know if you have any questions.


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PostPosted: 25 Apr 2017, 19:02 
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Matt,
Thank you very much!

Alex


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PostPosted: 13 May 2017, 21:21 
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I would like to thank MATT for the schematics and all the help/guide he've given me,I finished the headphone amp and i'am pleased how it turned out it sound good specially with the HD650 and Q701,It sounds a lot smoother than the kit that i paid twice the amount of how much i spend for Matt's designed.Again Thank You MATT!

Alex Q


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PostPosted: 15 May 2017, 18:36 
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Here are some pics.The slight HUM sounds like 120hz to my ears.


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PostPosted: 15 May 2017, 20:36 
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Hi Matt,
Here are more pics,you mentioned acting like an antenna in the pic those resistors are upright.

Alex


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