Considerations for using monoblock speaker tube amps with headphones.
May 21, 2020 at 6:18 PM Thread Starter Post #1 of 9

Three

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Hi folks, it’s been a while. I was here on the forums for a little while back in 2007-8 and pieced together my first real headphone setup based on all the good info here - Sennheiser HD650 with an Original Master amp. It was a nice little setup and I got a lot of use out of it. Fast forward to the present day and a lot has changed in my pursuit of audio nirvana. I sold off my headphone setup some years ago and focused solely on my stereo, which is now at what I would call a very advanced state of stability and providing much joy.

BUT, my wife’s new cat is terrorizing my life. The cat tends to be restless in the evenings and just will not keep away from the speakers if music is playing. So now I’m back on the forums looking for the best way to incorporate a pair of headphones into my arsenal while we weather the storm.

I’d like to utilize as much of my current equipment as possible (see profile About section), which leads me to my question about using my tube amps to power the headphones. The amps are Audio Note Quest monoblocks:
- 8wpc into 4 or 8 ohms, pure Class A
- Each amp has one 300B, one 6SN7, and one 5U4G rectifier
- Zero negative feedback
- Single ended output
- Directly heated triode

I have my eye on the Audeze LCD-2 at the moment, but of course I’d be open to hear about other options in the $1-1.5k price range. I believe this budget should get me a halfway decent pair of ‘phones with lots of room to grow if I find myself putting in a lot of headtime. Note: I am not a treble junky; in fact I am very sensitive to high frequencies and quickly find things irritating if tilted up at all. I like tone, body, texture, and musicality; I value these qualities over pin sharp imaging.

So if I want to avoid buying a separate headphone amp, what are the considerations that need to be made?

1. Safely connecting headphones to speaker terminals: I’ve seen the Hifiman HE-Adapter but I’m not sure about the parts quality or whether it can even be used with monoblock tube amps (something about the amp’s negative terminals not sharing a common ground?). Are there other pre-made options like this or is DIY the best route via something like the simplest RobinetteBox?

2. In general I am much more concerned about hurting the amps given the relative cost to repair or replace. Would this approach put any extra strain on the amps? I assume not since the amp sees a constant ~8 ohm load with the adapter.

3. Are there other headphones that would be better suited to this type of arrangement? AKG K1000? Based on my searching it seems like the older LCD-2 was commonly used with speaker amps, but I lose the trail a bit with the current model.

4. Anything else I need to be concerned with before plugging these into my amps? I am already aware that tube amps need to have a load connected to them before you power them up, so I shan’t be unplugging the speakers while the amps are on, etc.

Plan B: My preamp (Audio Note M5) does not have a headphone jack but it does have a second set of pre-outs that I could feed to a dedicated headphone amp if the Quests won’t work. This would at least give me access to the front end of my system. The problem here is, I would want the headamp to be tube based...and down the rabbit hole we’d go.

Thanks a lot,
Jon

RSyPQRv.jpg
 
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May 22, 2020 at 12:08 PM Post #2 of 9

ProtegeManiac

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So if I want to avoid buying a separate headphone amp, what are the considerations that need to be made?

1. Safely connecting headphones to speaker terminals: I’ve seen the Hifiman HE-Adapter but I’m not sure about the parts quality or whether it can even be used with monoblock tube amps (something about the amp’s negative terminals not sharing a common ground?). Are there other pre-made options like this or is DIY the best route via something like the simplest RobinetteBox?

Can't find anything else, the RobinetteBox is your best bet. If you can't build it yourself there are DIYers who might be able to build it for you.


2. In general I am much more concerned about hurting the amps given the relative cost to repair or replace. Would this approach put any extra strain on the amps? I assume not since the amp sees a constant ~8 ohm load with the adapter.

As long as the adapter doesn't mess up the ground nor cross each amp's own + and - I don't really see a problem.


3. Are there other headphones that would be better suited to this type of arrangement? AKG K1000?

Yes but

1. Good luck finding one

2. If the cat jumps at the speakers due to the sound, and not something particular about the sound like very low frequencies, the cat might jump at the K1000s. (then there's the question of whether it might still happen with any open headphones, but the K1000 is still basically like making an electrostat for desktop computer speakers and then hanging them on your head)

3. Despite the lower sensitivity it might still need a gain attenuator to reduce the noise out of a speaker amp.


Based on my searching it seems like the older LCD-2 was commonly used with speaker amps, but I lose the trail a bit with the current model.

That's because in the time since the LCD-2 came out amps with 1000mW per channel cropped up to the point that now a $99 Schiit Magni3 Heresy has 3000mW per channel and before that the $399 Lyr had 6watts per channel. This isn't even just one brand - AudioGD went from 1000mW to 3000mW in the entry level amps.


Plan B: My preamp (Audio Note M5) does not have a headphone jack but it does have a second set of pre-outs that I could feed to a dedicated headphone amp if the Quests won’t work. This would at least give me access to the front end of my system. The problem here is, I would want the headamp to be tube based...and down the rabbit hole we’d go.

All tube transformer-coupled : WooAudio WA6
 
May 22, 2020 at 2:23 PM Post #3 of 9

Three

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Can't find anything else, the RobinetteBox is your best bet. If you can't build it yourself there are DIYers who might be able to build it for you.




As long as the adapter doesn't mess up the ground nor cross each amp's own + and - I don't really see a problem.




Yes but

1. Good luck finding one

2. If the cat jumps at the speakers due to the sound, and not something particular about the sound like very low frequencies, the cat might jump at the K1000s. (then there's the question of whether it might still happen with any open headphones, but the K1000 is still basically like making an electrostat for desktop computer speakers and then hanging them on your head)

3. Despite the lower sensitivity it might still need a gain attenuator to reduce the noise out of a speaker amp.




That's because in the time since the LCD-2 came out amps with 1000mW per channel cropped up to the point that now a $99 Schiit Magni3 Heresy has 3000mW per channel and before that the $399 Lyr had 6watts per channel. This isn't even just one brand - AudioGD went from 1000mW to 3000mW in the entry level amps.




All tube transformer-coupled : WooAudio WA6

Thank you for the input!
 
May 23, 2020 at 1:59 PM Post #4 of 9

jimbop54

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I am running my HiFiMan HE-560’s directly from my 2A3 mono amps. About 3.5 watts of Class A power. I made a simple adapter to connect the headphone cable to the amp’s output terminals (with no resistors).
the amps have a similar tube arrangement: 5Y3, 6SN7, 2A3.
Glorious sound!
 

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May 23, 2020 at 2:34 PM Post #5 of 9

Three

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I am running my HiFiMan HE-560’s directly from my 2A3 mono amps. About 3.5 watts of Class A power. I made a simple adapter to connect the headphone cable to the amp’s output terminals (with no resistors).
the amps have a similar tube arrangement: 5Y3, 6SN7, 2A3.
Glorious sound!

Nice. Are those vintage amps? I’ve never owned a 2A3 amp, but I know some folks prefer them over 300B.
 
May 23, 2020 at 4:04 PM Post #6 of 9

jimbop54

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Nice. Are those vintage amps? I’ve never owned a 2A3 amp, but I know some folks prefer them over 300B.
Not sure what you mean by “vintage”. The originated as George Wright WPA-3.5 amps (probably from the early 2000’s).

I have done many component upgrades and some circuit tweaks, so I built them into a larger chassis to house the larger caps and such.

D4A4A352-1385-4A18-B09F-AAA06E18407D.jpeg
 
May 24, 2020 at 9:49 AM Post #8 of 9

audiobomber

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Once upon a time I had Stax SR44 earspeakers, which connected to my amp output terminals and the speakers. I was never happy with that compromise, I could hear the slight degradation from the extra parts.

The M5 preamp can be configured many different ways, not sure what features yours has. I don't suppose there's "tape out" that you could use for a headphone amp? If the M5 has balanced and unbalanced outputs, you could connect a headphone amp to the balanced output terminals. Neither would compromise your main system.

A cat can do a lot of damage. I have a suggestion for you; get a water pistol or squirt bottle. Squirt him every time he looks at a speaker. Don't let him see that you are doing it. Of course, praise and pet him when he's behaving.

I've had several cats. One was a wire chewer, not sure how he didn't get electrocuted. A few sat quietly on or beside me while I listened, some were indifferent, one hated music, would give me a dirty look and leave in a huff whenever I played the stereo too loud. The one I have now parks on me for hours but gets a worried look on his face and leaves whenever I play music with a muted trumpet.
 
May 24, 2020 at 10:29 AM Post #9 of 9

Three

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Once upon a time I had Stax SR44 earspeakers, which connected to my amp output terminals and the speakers. I was never happy with that compromise, I could hear the slight degradation from the extra parts.

The M5 preamp can be configured many different ways, not sure what features yours has. I don't suppose there's "tape out" that you could use for a headphone amp? If the M5 has balanced and unbalanced outputs, you could connect a headphone amp to the balanced output terminals. Neither would compromise your main system.

A cat can do a lot of damage. I have a suggestion for you; get a water pistol or squirt bottle. Squirt him every time he looks at a speaker. Don't let him see that you are doing it. Of course, praise and pet him when he's behaving.

I've had several cats. One was a wire chewer, not sure how he didn't get electrocuted. A few sat quietly on or beside me while I listened, some were indifferent, one hated music, would give me a dirty look and leave in a huff whenever I played the stereo too loud. The one I have now parks on me for hours but gets a worried look on his face and leaves whenever I play music with a muted trumpet.

Thanks a lot for the feedback.

My M5 is the current Phono version with no tape loop. It does have balanced outputs as well as a second pair of single ended outputs, so either of those would be a fine Plan B. I don’t know that the Quests would be a compromise as they are a pretty simple design with very high quality parts, but I suppose I don’t have any first hand experience to weigh that opinion against.

Water can also do damage if the aim isn’t on! But I get your point. I’ve been using a little handheld vacuum to try and condition her into not going near the speakers, but I swear she just doesn’t care for more than a moment. She’ll run away and two seconds later she’s right back over there looking at me like I’m an asshole for spoiling her day. She was actually pretty good for a while, but her renewed interest is quite intense.
 

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