The BEST way to build a GSG for headphones only?

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The BEST way to build a GSG for headphones only?

Postby MidSentry54 » Mon Jul 09, 2012 9:11 am

First and foremost- is this a good idea? I'm hoping the overall SNR is decent enough for this application.

I know a lot of people just fashion a series resistor on the output terminals, but I was wondering if there was a better way.

I have a populated GSG board with no iron (yet). Could I simply put a pair of output transformers spec'd to my headphones and call it done?

What other changes would you make to get the best performance out of the GSG for this dedicated purpose?

My main headphones are Audeze LCD2's. Here are the specs:

• Impedance: 60 Ohms, nominal
• Maximum diaphragm excursion: 2.5mm p-p
• Efficiency: 91 dB/1mW
• Maximum output: 133dB, 15W
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Postby highflyin9 » Mon Jul 09, 2012 12:37 pm

I've thought about this myself, for none other than the Audeze. I think the impedance is 50ohms unless the design changed. I'll bet ElectraPrint would be able to make the transformers. I know it's also important to space the output and power transformers further apart, as sensitive headphones will pick up on hum from flux interaction more easily than speakers will.
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Postby MidSentry54 » Mon Jul 09, 2012 12:58 pm

It seems a bit overkill to use this amp to power headphones but I'm thinking the Audeze might perhaps benefit from it.

So are most people using 3.5K primaries?

A 3.5k/50 ohm transformer would be your suggestion?
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Postby highflyin9 » Mon Jul 09, 2012 1:59 pm

MidSentry54 wrote:It seems a bit overkill to use this amp to power headphones but I'm thinking the Audeze might perhaps benefit from it.

Not at all imho. Headphones like Audeze and HiFiMan would benefit from the wattage.

So are most people using 3.5K primaries?

I'd say the lion's share of GSG builds use 3.5K outputs. There are a few that use 5K.

A 3.5k/50 ohm transformer would be your suggestion?

That would be my assumption, but there are others on this board that are more knowledgeable than me, I would wait for their input.
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Postby MidSentry54 » Mon Jul 09, 2012 9:31 pm

Highflyin-

I saw your GSG build on Head-Fi; I noticed what looked like a yet-to-be connected balanced headphone jack. Did you add series resistors and connect it? Curious... beautiful build, btw.
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Postby highflyin9 » Tue Jul 10, 2012 10:35 am

MidSentry - that build is solely for some Frugel horns. What you saw was a pilot light ;) I would say that currently it is a bit bass light and ideally listened to with a sub. It may be the tubes, I need to get another set of 6B4Gs to roll, it's just they're so pricey for a matched pair. As it is, I don't think the bass would be satisfying through a set of headphones.
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Postby MidSentry54 » Tue Jul 10, 2012 3:26 pm

Ah...OK. Pilot light....gotcha.

Remember when 6B4G's used to be dirt cheap? You couldn't give them away. I scored a batch because a friend of mine tried to sell them on eBay back before amps like the GSG called a lot of attention to them...he concluded they were worthless (as a financial venture) and stashed them away. He was happy to take my slightly-less-than-current-market-value offer for them. They're mostly JAN...Sylvanias...but I'm fine with that.

Regarding subs: Some people listen to headphones with subwoofers (myself included). I do it more for the visceral impact in the <70hz region where things are more felt than heard. John Broskie talks about the very same thing on his site...somewhere...

In fact, I think there is a slight advantage to listening with headphones/subwoofers. It's the same thing when dealing with in-room acoustics and loudspeakers; we all know how the low frequencies have a tendency to screw up the other frequencies (including other low frequencies!) hence the popularity of bass traps. In my opinion, it's worse with headphones. Listening to a bass-shy headphone amp, with an output for a subwoofer that can EQ and (gasp!) enhance the lowest frequencies to suit (outside of the ear space) is often ideal for me. I feel it results in a purer midrange, and a Much more satisfactory listening experience overall. You should try it!
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Postby highflyin9 » Tue Jul 10, 2012 7:53 pm

Yeah, things have changed quite a bit. The Sovteks tripled in price and everything else followed suit. I have listened to headphones with a subwoofer before, it's not a bad way to go. I tend to prefer bass heavy headphones like the Denon series, Beyerdynamic DT990, I'd say the Audeze have plentiful bass too. I've always felt that headphones like the HD800, Qualia and K701s needed more heft and body, but I never tried them with a subwoofer. I guess it might be strange to show up at a headphone meet with a sub while trying headphones (lol)
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Postby Shannon Parks » Wed Jul 11, 2012 6:46 am

I've thought an awful lot about this, and I still think something like the 20/20 is the way to go for higher efficiency headphones:
http://www.diytube.com/phpBB2/viewtopic.php?t=5239

With a SET amp attached to speakers, we want the absolute max voltage swing we can get because the SET amp will only manage a few watts output and the speakers can usually handle loads more. Many headphones on the other hand may be rated at 1W or less, and we want the max output limited to maybe 500mW. Something like a dual 50 ohm linear pot could be used in this 20/20 arrangement for adjusting the level sweet spot. The lower parallel resistance tames the screwy headphone impedance characteristic under control, emulating a low amplifier output impedance. I don't understand with this method isn't used on every single headphone output that exists, to tell you the truth. The performance trumps the single dropping resistor method by a mile.

But your Audeze LCD2 headphones are a different beast and can handle up to 15W. So a direct transformer connection appears best. A 3.5K to 60 ohm output will work well, but we can still be a little less worried about max power output and we can have a higher reflected impedance (at the transformer primary). First, let's look at what turns ratio a 3.5K:60 ohms tranny would be. The formula is square of primary divided by secondary. Here's a handy calculator:
http://www.maxmcarter.com/classecalcs/tratiocalc.html

So we want a 7.64:1 turns ratio. About the closest we come is the GXSE10-16-1.7K (or the GXSE15). That would be 10.3:1. It would behave as a 6.4k:60 ohm transformer. The reflected load would be a touch more linear and lost max output would be minimal. A volume control on the input would still be advisable for max level control.

Here's some tips for lowest noise performance:
http://www.diytube.com/phpBB2/viewtopic.php?t=5236
My GSG was super quiet. I think with the efficiency rating of the Audeze, noise won't be a problem.

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Postby highflyin9 » Wed Jul 11, 2012 9:23 am

Great information Shannon! Do you happen to have any suggestions for increasing bass quantity in the G*S*G (e.g. tweaks to the circuit)? I'd love to build a version for headphones, but that's the only thing getting in the way.
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Postby 20to20 » Wed Jul 11, 2012 9:51 am

highflyin9 wrote:Do you happen to have any suggestions for increasing bass quantity in the G*S*G (e.g. tweaks to the circuit)? I'd love to build a version for headphones, but that's the only thing getting in the way.


I think you are focusing on the wrong end for tweaking your bass...

If you have an amp and headphones with a flat FR you need to do the frequency customization at the preamp. What are your typical source materials and player system?

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Postby highflyin9 » Wed Jul 11, 2012 9:54 am

Hello 20, If this is being built as a headphone amplifier then there will be a potentiometer / attenuator in the unit and no preamp. Signal would be coming straight from a CD player.
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Postby 20to20 » Wed Jul 11, 2012 11:03 am

highflyin9 wrote:Hello 20, If this is being built as a headphone amplifier then there will be a potentiometer / attenuator in the unit and no preamp. Signal would be coming straight from a CD player.


OK, I can appreciate trying to do it all in a self contained unit. Perhaps Shannon could comment on this approach to the bass boost. You could set an 80Hz low pass filter (80Hz crossover for whoofers) with your attentuator to provide some positive feedback signal to the driver or output limited by a series resistor so the amp doesn't puke it all up.

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Postby Shannon Parks » Wed Jul 11, 2012 11:55 am

I may lose all credibility with this post, but I think an Alps pot with the loudness tap can be a solution, apart from a full preamp. We Americans in particular love our bass, and the loudness circuit (aka bass boost) accomplishes our needs and can be defeatable.

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Postby 20to20 » Wed Jul 11, 2012 12:36 pm

separks wrote:I may lose all credibility with this post,

Shannon


(lol) (lol)

I bought a nice 12 band equalizer for $10 at a flea market last summer. It was new in the box from circa 1980 and all I had to do to freshen it up was hit the sliders with some tuner cleaner. It has Master Volume and other goodies like expansion and the monitor/tape outs. Just gotta keep an eye out and be willing to buy that kind of stuff when you don't need it but knowing that some day you will. I have a ton of stuff in my DNIBIW closet.

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