New Headphone Amp

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izzy wizzy
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New Headphone Amp

Post by izzy wizzy » Fri Dec 29, 2017 5:04 pm

I got Sennheiser HD650s for Xmas so needed an amplifier to drive them. Had to start somewhere so cobbled together the amp below with parts I had lying round. It has things in it I wouldn't normally do like a 317 current source and a glow tube; it was the easiest way to get it going.

It's driven by the phono stage and RPi streamer via my passive source selector/TVC box. It's totally silent at loud listening volume which is pleasing. I'm sure with a bit of fiddling around it could be better but for now, it's pleasing to be reaquainted with my records after many years of having to be quiet.

cheers,

Stephen
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6n6headphone.JPG
6n6headphoneamp.JPG
Last edited by izzy wizzy on Fri Dec 29, 2017 5:24 pm, edited 1 time in total.

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pre65
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Re: New Headphone Amp

Post by pre65 » Fri Dec 29, 2017 5:15 pm

I'ts nice to be able to build something from bits to hand. :)

At least you now have a standard to compare with if (when) you build something else.
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simon
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Re: New Headphone Amp

Post by simon » Fri Dec 29, 2017 10:11 pm

Proper amp :-)

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andrew Ivimey
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Re: New Headphone Amp

Post by andrew Ivimey » Fri Dec 29, 2017 10:58 pm

What a clever little circuit; ingenious even!
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izzy wizzy
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Re: New Headphone Amp

Post by izzy wizzy » Sat Dec 30, 2017 12:45 pm

I can't take much credit for the circuit. It was going to be a Raven type thing http://www.nutshellhifi.com/Raven-MarkII.gif but first up, I didn't want an input transformer; can try later.

It all started with the ouput transformer, the Lundahl 1671, which I already had. The HD650s are 300 ohm so that makes a 4.8k load for the valves. In LTSPICE that gave me about the right gain for 6N6 valves.

To get balance, I would need a CCS in the tail and a LM317 was at hand. Not ideal but any other option for now would be too hard. So that's the audio circuit.

The power supply started with a transformer I have with mulitple taps. I got some 6AX4 from Billingtons (theonly thing I had to buy) as I had no rectifiers other than mercury vapour or silicon. I could have gone for multiple LC sections but thought a glow tube would look nice and be very easy.

Of course it's on a piece of wood. Quite where I go with it is up for grabs.

Is a lower drive Z advantageous? To do that would require more step down so a different output transformer. That would mean less stage gain and so another stage so something along these lines http://kandkaudio.com/images/PP%206H30% ... %20amp.pdf,

After trying for years to get a properly working 813 amp, it's nice to put together something that works first time and is completely silent. I admire those that can get a design straight away into a nice box acceptable to management :)

cheers,

Stephen

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Re: New Headphone Amp

Post by Cressy Snr » Sat Dec 30, 2017 1:37 pm

Great stuff.
We need more projects. :lol:
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izzy wizzy
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Re: New Headphone Amp

Post by izzy wizzy » Tue Jan 02, 2018 11:12 am

I just found this http://www.hifisentralen.no/forumet/diy ... erker.html which is someone who did the same thing as me (beforehand) but differently and in a proper box.

cheers,

Stephen

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andrew Ivimey
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Re: New Headphone Amp

Post by andrew Ivimey » Tue Jan 02, 2018 1:09 pm

Looks like he did it in Danish too - Respect!
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.

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Mike H
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Re: New Headphone Amp

Post by Mike H » Tue Jan 02, 2018 1:47 pm

simon wrote:
Fri Dec 29, 2017 10:11 pm
Proper amp :-)
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DSJR
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Re: New Headphone Amp

Post by DSJR » Sat Jan 06, 2018 3:54 pm

I do have huge respect at you lot for 'cobbling together' a good working item out of bits from a parts box and adapting what you have to suit :D I get much pleasure when I first switch on one of the amps I assemble for a living, but the main work is done with pre-assembled boards and a given specified supply design config and I can only imagine the huge pleasure when all but unknown-outcome projects such as this work and work so well to your satisfaction :D

izzy wizzy
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Re: New Headphone Amp

Post by izzy wizzy » Sun Jan 07, 2018 8:30 pm

I tried a few things with the amp over the weekend. Upping the current from 15mA to 20mA per side improved things a bit.

I also tried comparing the original vs a modded channel with the CCS replaced by a resistor and an input transformer added. By monoing the headphones and swapping the source and phones back and forth, I could compare the two topologies. I preferred the transformer input vs the CCS for all kinds of reasons but mainly as it didn't have that typical solid state halo/haze over the sound field.

I used the Sowter 3575 for starters as it has flying leads so easy to wire in. I have a Lundahl 1544a which I can try as well.

Updated schematic
6n6headphoneamp-a.JPG
Cheers,

Stephen

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Re: New Headphone Amp

Post by IslandPink » Mon Jan 08, 2018 10:03 am

Good effort. The 317 doesn't have a great reputation in that application - I remember the sound of Allen Wright's 300B PP amp !
Always liked the 3575's though, very transparent and natural-sounding.
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izzy wizzy
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Re: New Headphone Amp

Post by izzy wizzy » Mon Jan 08, 2018 1:23 pm

IslandPink wrote:
Mon Jan 08, 2018 10:03 am
Good effort. The 317 doesn't have a great reputation in that application - I remember the sound of Allen Wright's 300B PP amp !
Always liked the 3575's though, very transparent and natural-sounding.
I'm not sure the 317 has a great reputation at all but it is versatile ;)

Will be interesting to try the Lundahl 1544a vs the 3575. You are right about the 3575 sound. They seem to be very nice and natural.

In the end though, all I've got now is Lynn Olson's Raven so no new ground but it seems to work well.

cheers,

Stephen

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