Show us your flea-watts amps!

[Genov]

Decware SE84UFO’s. I ran just one for about 5 years. Love it, but got interested in running a fully-balanced monobloc setup. So I got a second amp, and had special Y-RCA cables made to accomplish this.

It took 22 months to get the second amp from Decware, but worth the wait, cause the sound is great!

Each amp is 2.3 watts. My drivers are 99db efficient, so plenty of volume.

 

[ceylon]

Decware SE84UFO’s. I ran just one for about 5 years. Love it, but got interested in running a fully-balanced monobloc setup. So I got a second amp, and had special Y-RCA cables made to accomplish this.

It took 22 months to get the second amp from Decware, but worth the wait, cause the sound is great!

Each amp is 2.3 watts. My drivers are 99db efficient, so plenty of volume.

View attachment 2963088

sweet glassware, my man

 

[kurorin]

 

[jcmusic]

So what is the power tube and wattage rating?

 

[kurorin]

So what is the power tube and wattage rating?

Power tube: Arcturus 012A.
0.2 watts power, SET mode.

 

[FlaCharlie]

Power tube: Arcturus 012A.
0.2 watts power, SET mode.

Interesting . . . I've built some low power amps but nothing that low. I guess it just goes to show that extremely little wattage is needed in some situations.

Is this your amp / video or just something you came across online?

The video is somewhat confusing - apparently the "soundtrack" was previously recorded since he pulls one the 12A output tubes out and there is no change in the sound. The amp is then turned on after it has been replaced.

Do you have any more info on this amp? Schematics?

I'm interested in what the other tubes are and how they're used. It looks like there are four 9-pin miniature tubes in the front end which seems odd. More and more I find that input tubes contribute more to the sound than output tubes.

I recently completed a build which uses the 12A as a driver tube. I'll add a post with a pic or two.

 

[FlaCharlie]

Here's my latest build, the GloTone Cockeyed Monkey. Details, including schematics, are here:

GloTone Cockeyed Monkey - A Directly Coupled SET

So here's my latest DIY amp, the Cockeyed Monkey . . . I always like to try some things that are "new to me" in my builds and this one has several elements that I've been meaning to try for a while. I had never built a directly coupled amp so I figured it was time. I decided on using this...

www.audiokarma.org

 

[TriodeLuvr]

Interesting . . . I've built some low power amps but nothing that low. I guess it just goes to show that extremely little wattage is needed in some situations.

I have an idea in mind for a very low power headphone amplifier using RK-34 tubes. They'll be configured as cathode follower outputs with a 5K:8 output transformer at each cathode. Instead of B+, the exposed anode connections will be grounded and a negative supply voltage will be applied to the cathodes through the transformers. Output power will probably be something on the order of 100mW or so.




Jack

 

[TriodeLuvr]

Here's a tentative schematic of the concept:

The transformer is 5K:8Ω only because that's what I have on hand. It's nearly impossible to find output transformers now that are made for the power and impedance(s) of headphones. However, I recently tested the frequency response of several small toroidal power transformers, and the performance with no DC current was excellent. This means a 1:2 voltage ratio toroid can probably be cascaded to step up the 8Ω output Z of the above circuit and match the 32Ω Z of Grado phones more efficiently. It has since also occurred to me that the input stage above might not even be required.

Jack

 

[Lavane]

Neat design. Nice and simple.
I haven't opened it up yet, but the headphone amp I'm using now is all tube with output transformers. It also has a 16 ohm to 600 ohm impedance selector. I've been curious how this circuit it setup. It defenetly makes a difference switching the impedance with the 50 ohm AKG's I listen with.
Switching up or down on the selector either makes the headphones too bass heavy, or weak bass. There seems to be a high end roll off also when switching to an impedance that's more bass heavy.

 

[TriodeLuvr]

I'd be interested to see the schematic. AFAIK, Magnequest was the only company to ever make a decent multi-tap headphone OPT, and Mikey priced them commensurate with performance. The Grado SR60i phones are extremely sensitive. I tested them recently and found that anything above 20mV RMS is very loud. That represents less than 1mW at 32Ω. This opens the door for many configurations of amplifiers to drive them successfully. I've been wanting to use the RK34 for several years, and this looks like a good opportunity.

Jack

 

[Lavane]

I'm guessing these small OPT's on the amp I have don't have multiple taps.
That's why I was curious how the impedance was selected.
I haven't been able to find a schematic. The headphone amp came from a limited run of various single ended amplifiers using EL84's, 6L6's etc. labeled Nob Sound sold by Douk Audio. I took a chance on the headphone amp and have been pretty happy with it. All of them use switch mode power supplies.
So how would you be able to have a selection of impedances without multiple OPT taps?

 

[tubelectron]

Flea-Watt and most of all Flea-Size... At least compared to the last Flea-Watt but Large-Size amp build by @FlaCharlie, presented a few posts above !

OK : only the one in the center is finished and operational today...
The two others waits their turn !

T

 

[TriodeLuvr]

So how would you be able to have a selection of impedances without multiple OPT taps?

If a "universal" headphone amplifier is desired, something that can accommodate anything from 8Ω to 600Ω, that's tough. I think a moderate range of impedances can be accomplished using a standard 8Ω output transformer to drive another step-up. For hi-fi quality response, that's probably limited to loads of 100Ω or less. Driving 300Ω or 600Ω requires higher voltage for equal power delivery, so the cathode follower approach might be unworkable without a 5K:600Ω OPT. Edcor makes one, but it's guitar amp grade. I'm not a fan of capacitor coupling at output power levels, but maybe this genre is an exception. If that's acceptable, a parafeed topology with a very low Rp output stage could be used to drive high Z phones. Of course, that's an entirely different amplifier. Maybe a higher power amplifier with a set of various resistive networks could be used. If it's permissible to throw away a fair amount of output power, a wider range of loads could probably be accommodated without violating the optimum loading of the output stage. Just thinking out loud here...

Jack

 

[Lavane]

That may it in my case. It may have a resistive network.
I would have to look up the data sheet for the output tubes to see what the max output could be. They're pentode RF tubes if I remember right, with the single 12AX7 driving both Channels. I know if set to 16 ohms, it puts out 1.2wpc.

 

[Musictubes]

I'd be interested to see the schematic. AFAIK, Magnequest was the only company to ever make a decent multi-tap headphone OPT, and Mikey priced them commensurate with performance. The Grado SR60i phones are extremely sensitive. I tested them recently and found that anything above 20mV RMS is very loud. That represents less than 1mW at 32Ω. This opens the door for many configurations of amplifiers to drive them successfully. I've been wanting to use the RK34 for several years, and this looks like a good opportunity.

Jack

Thermionic Labs has a series of headphone transformers with multiple taps. https://www.thermioniclab.com/en/headphone-transformers/

 

[TriodeLuvr]

Thermionic Labs has a series of headphone transformers with multiple taps.

Wow, they sure do! Thanks for that info!

Jack

 

[kurorin]

Interesting . . . I've built some low power amps but nothing that low. I guess it just goes to show that extremely little wattage is needed in some situations.

Is this your amp / video or just something you came across online?

The video is somewhat confusing - apparently the "soundtrack" was previously recorded since he pulls one the 12A output tubes out and there is no change in the sound. The amp is then turned on after it has been replaced.

Do you have any more info on this amp? Schematics?

I'm interested in what the other tubes are and how they're used. It looks like there are four 9-pin miniature tubes in the front end which seems odd. More and more I find that input tubes contribute more to the sound than output tubes.

I recently completed a build which uses the 12A as a driver tube. I'll add a post with a pic or two.

It's my video and my system.
The video was recorded with iPhone direct, just have an insert in between (without sound) to show the valves.
Amplifier was made by Kenji Mizushima in Japan. He has all the schematics in his website (single-ended.com) just sometimes the website is not working, I don't know why.
The amplifier is 71A Single Ended Triode with the option to use 12A as well. I love both tubes just 12A is something even more special.

 

[FlaCharlie]

Flea-Watt and most of all Flea-Size... At least compared to the last Flea-Watt but Large-Size amp build by @FlaCharlie, presented a few posts above !

OK : only the one in the center is finished and operational today...
The two others waits their turn !

T

You're the master of compact design!

I'm used to working in tight spaces when restoring vintage amps or modding a circuit in an existing chassis but when I build things myself from scratch I like to have plenty of room.

 

[FlaCharlie]

It's my video and my system.
The video was recorded with iPhone direct, just have an insert in between (without sound) to show the valves.
Amplifier was made by Kenji Mizushima in Japan. He has all the schematics in his website (single-ended.com) just sometimes the website is not working, I don't know why.
The amplifier is 71A Single Ended Triode with the option to use 12A as well. I love both tubes just 12A is something even more special.

Thanks, I found the website. The schematic was somewhat hidden but I also found it so I'm posting it in case others are also curious. The whole design seems rather complex.

I'm not very technically oriented but it seems like it shouldn't take so much to drive a 71A or 12A. These tubes are normally used as an input tube with a line level source going directly to the grid.