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Old 25th September 2005, 02:39 PM   #1
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Default Valve headphone amp

I guess I just became an Audiophile!

I've been listening to hours of music everyday for as long as I can remember but have never owned anything better than cheap head band / inner ear phones, the one ninety nine kind from Walmart (ASDA).

I decided to bid on some decent headphones thinking I'd maybe go insane and spend thirty or fourty pounds. I kept getting out bid a few pounds from their new price.

After that happened a few times I started getting anrgy and figured "Forget it, just buy some new!". A few days later and I now have a pair of ultra sexy Sennheiser HD650's!

I don't have any kind of system. My system is my computer's sound card at the moment. Suprisingly, considering it's a cheap computer to start with, it can actually drive the headphones reasonably well. Loud enough that I'm bothered about the cones distorting, as that was usually the end of the cheaper headphones (Is this also true of more expensive phones?).

But the one thing I've read as a constant for headphones like this is that they usually benefit from having a dedicated driver.

I've looked at the solid state amps but thought it might be nice to try for a valve driver. Information on this is quite limited on the net. There also seems to be an equally limited source of reasonable quality transformers.

I know Sowter produces a Mu-Metal headphone transformer that has a tap at 300 ohms. The headphones are 300 ohms so that would seem to be a possible option. But they're not particularly cheap transformers, over a hundred each. And they're driving relatively low powers.

I'd hoped with headphones I'd be able to keep the cost reasonable since I'm starting with a massively reduced power rating compared to normal speakers. I guess I just want to be careful that I don't end up paying hundreds more for something that doesn't quite shine as brightly as it should for it's cost.

Then with Mu-Metal I have to start thinking about inductors / constant current sinks etc since I think the Sowter transformers are for single ended use.

I'd like to ask for some advice on possible amp topologies, noteworthy valves for headphones or where I can find reasonably priced quality transformers that would do these headphones justice without then exceeding their capability.

Ideally I'd like to follow the Audionote theory on design of keeping it simple and just using higher quality parts, rather than having lots complex tweaking points and options all over.

I'm willing to go for things like the Sowter Mu-Metal transformers but it's like I say, whether or not I'm going to notice that much of a difference.

Please hit with some ideas, particularly if you've tried them yourself!
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Old 25th September 2005, 03:38 PM   #2
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There are a few here http://headwize.com/projects/index.htm
and here http://www6.head-fi.org/forums/forum...p?s=&forumid=6
look out for the OTT 6C33 and 6AS7 creations by kevin gilmore.
And there is this http://www.tubecad.com/2004/blog0011.htm
Improving the Aikido line stage...
Poll..anyone interested in an Aikido linestage PCB group buy?
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Old 25th September 2005, 03:58 PM   #3
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Hi there,
I am at the moment working on a simple headphone amp using ECL82's. Do a search on the forum under ECL82 and Headphone, it should bring it up. This will be a very simple headphone amp, and by no means will it be high spec but th great advantage will be that been parafeed,I can use cheap 12VA toroidals as output transformers. All in all I expect the project to cost no more than ?100.00
Otherwise do a google search under "Headwize projects" which should bring up a whole section on valve headphone amps.

Good luck

Shoog
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Old 25th September 2005, 10:19 PM   #4
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Old 27th September 2005, 10:03 PM   #5
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Thanks everyone!

I've been having a read and look around and think I'm going to try a single stage, single ended amp by Andrea Ciuffoli; SESS Headphone Amp

The amp is nice and simple with only a few components, which means I have more money available to spend on each.

However, the power supply for the amp is something I'm not totally sure about.

Click the image to open in full size.

This is pretty much exactly the same as a design from Lundahl; Hybrid Power Supply

This will be my first audiophile amp, but for guitar amps I've found I usually prefer the more upfront and defined sound of solid state rectification. So I think I may get rid of the valve rectifier and replace it with some high quality, soft switching diodes, perhaps Schottkys. Otherwise, I think I'd be concerned I might end up with something a bit too smooth sounding for my liking.

Something that bothers me about the supply is the use of three 20H chokes, which seems like quite a lot. Again, I'm more used to guitar amps where a single 10 / 20H choke will be the only inductor in the supply, resulting in a noticeable amount of hum.

It also appears that he's using 350V capacitors on the left and right channels to account for any transients to 350V as the supply fluctuates. Since the channels are only meant to be ~179V each, could I force the channels to be better balanced so's that I could use 200 / 250V capacitors here instead?

I'm tempted to just split the two channels totally to get a true monoblock form. Since I'll probably using solid state rectification I wouldn't have to worry about another valve heater winding, valve socket, valve, and having higher voltage windings to begin with for the valve rectifiers. I'd also get rid of the need for using 350V capacitors.
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Old 27th September 2005, 10:20 PM   #6
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It's overkill for a headphone amp that needs 20 mA or so per channel... what DOES matter is supply ripple. Single-ended stage has little rejection of power supply noise, and headphones are very sensitive. But no reason you can't achieve the same hum level with CRCRC filtering... you WILL need bigger caps. And you MUST take care with grounding.

I'd probably look at Brodie's transformerless circuit myself...
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Old 3rd November 2005, 06:51 PM   #7
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just been looking for brodies transformerless circuit and cant find it. Can you help. ta
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Old 3rd November 2005, 06:58 PM   #8
dhaen is offline dhaen  Europe
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Quote:
Originally posted by eeka chu
snip..

Something that bothers me about the supply is the use of three 20H chokes, which seems like quite a lot. ...snip
His projects always have lots of Lundahl chokes and transformers. He sells them.
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Old 3rd November 2005, 07:45 PM   #9
alk is offline alk  Europe
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He must also sell Elna Cerafines.
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Old 3rd November 2005, 07:58 PM   #10
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eeka chu,

To answer your original (parenthetical) question:

"I don't have any kind of system. My system is my computer's sound card at the moment. Suprisingly, considering it's a cheap computer to start with, it can actually drive the headphones reasonably well. Loud enough that I'm bothered about the cones distorting, as that was usually the end of the cheaper headphones (Is this also true of more expensive phones?)."

The cones of Sennheiser HD650s just won't distort, at least not until
it's so loud that you go deaf or get a brain haemorrage!
The reason for the distortion is no doubt that the sound card can't
swing enough voltage or current (probably voltage in the case of
the 300-ohm Sennheisers). So what you get is amplifier clipping.
Any decent dedicated headphone amp should solve that problem.

Morgan
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