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Obviously, the "Stereomour" we've all been talking about is not out yet, but it's almost guaranteed that it will become the 4th Bottlehead kit I build, after the C4S'ed S.E.X., Seduction, and Quickie (which I'll be using as a headphone amp). A few questions (if these can even be answered yet):
a) I see that it will be designed to use 2A3 tubes. What about 300B's? Will it be "adaptable" through a few circuit changes like the Paramounts? The extra 5 or so watts from a 300B (as opposed to the 2A3) puts a whole other class of options on the table for speakers. It seems like 95dB+ speakers tend to be horn-loaded or single driver, which I'm finding I don't like so much (too limited at the extremes in the case of single-drivers (not to mention that annoying Lowther "shout"), and too bright in the case of horn tweeters like Klipsch).
b) I'm assuming this will be AC heated, correct? Have the prototypes been quiet enough (i.e., hum/noise of < 1mV or so) for headphones if one decided to add a jack? (The S.E.X. seems dead quiet, but that's a) at a lower wattage/power, b) using DC on the filaments, and c) using indirectly-heated cathodes.
c) Any ideas in terms of cost? Will it be similar to the cost of two monobocks, or slightly less due to needing one chassis, one power supply, etc.?
Thanks in advance...I realize these questions may not be answerable at this stage, but the anticipation is hard to control.....
Follow Ups:
Thanks for the info. I had a feeling that the transformer would be a limiting factor in any potential 300B conversion. While the hum might not be great for headphones, I think 2 or 3mV probably wouldn't even be noticeable on my current speakers - though that's a lot higher than my S.E.X. build, which has an inky black silence, even turned op all the way on 99dB/W/m Klipsch RF-5's. The S.E.X. amp spoiled me with its dead silent background - my solid state stuff wasn't even that quiet!
Since I've not heard DHT's and am not sure of the difference in sound quality between them and indirectly-heated tubes (though the Quickie might give me a taste of that, albeit using DC), I may be better off in the long run sinking $700-900 into more sensitive speakers, 6EM7's, and the MQ irons for my S.E.X. amp. I'd love to build some Voigt pipes, Zigmahornets, or another TQWP variant, but with no woodworking tools and no place to put any (1 car garage + SUV = no workshop) I may have to stick with pre-made stuff. The late Terry Cain's "Abby" looks incredibly cool, but at $2k/pair with shipping, they're way beyond a comfortable price point. Luckily, no wife = no WAF to worry about, so size/practicality are not the stumbling blocks here.
The open-baffle speakers Coca linked to are interesting as well, though I've never heard any OB speakers to know what they might sound like.
To get more power, you must supply more power. More volts and more current from the power supply, that is. Since Paramour in all its iterations has aimed to be the least expensive directly-heated power amp we could manage, there is not enough power supply to spare for an 8-watt 300B amp. It will adapt to a 45, of course - that requires less power and is less demanding.
It is AC heated of course. That means 2-3mV of hum with a good 2A3, and I do not recommend it with headphones. A 300B will usually make at least 5mV and 8mV is not as uncommon as you would hope, if it has AC filament power. I just think that's too much, so I can't see an AC-heated 300B. There may be a 300B integrated eventually - I'm certainly thinking about it - but I don't see a good enough design yet.
Incidentally, CB is right about the iron. I will be making small modifications to the design of all the iron shortly (including the power transformer). The audio iron re-designs are pretty much complete as of last Friday, but the power transformer might take another week.
Thanks for talking about your design process.
How cool is it to be able to read about a product that you're deeply interested in as it is coming to life?
God I love this place!
The Stereomour will be AC heated, and thus a 300B conversion will be very difficult.
The AC heating makes for a circuit that is not quite quiet enough for headphone use.
As for price... Well, I would expect with the amount and size of the iron that 700-900 seems like a likely range, but I don't believe the iron has been 100 percent nailed down.
For a different spin on speaker choices for flea power amps, check out this web sight.
www.hawthorneaudio.com
Bernie.
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