Bottlehead Fantasy Products/Wish List

[xcortes]

Come on Grainger. What side are you on?

Besides I was gonna buy three kits so it was four, not two!

Seriously in the long term that's something I want to try.

Following a friend's advice my next system won't have iron or CFs, Right now I have to concentrate on my WOT 437A preamp.

[Doc B.]

I think that would be a WAF 437A amp (with auto former) ;^)>

[ssssly]

1. DAC (have been eagerly waiting a few years on this one)
2. KT88 or similar based amp 25-50ish WPC (not holding my breath)
3. Tube crossover
4. A TT kit would be fun
5. An active step up for phono stages would be nice as well
6. New speakers. I'm working on a slot loaded, semi open baffle line array and a 3 way, front loaded PPSL. So if you would just do the engineering for me it would free me up for more scuba diving and weekend track days. Not to mention the GAF on the pile of speakers sitting around is getting lower by the second.

And I would really like PJ to get on the flux capacitor thing. Would make it way easier to buy nice tubes if we could just go back in time and buy them new.

[Doc B.]

I'm chipping away this weekend at repackaging our prototype DAC for RMAF. It's not what the final one will be, but it should have a lot of the same nutritional goodness. I am indeed glad that I won't be responsible for your suffocation regarding the making of yet another PP 6550 amp in a saturated market. But we do continue to think about higher powered amps.
I think the active step up is about 80% worked out, with a prototype or two in operation. Tube crossover may happen depending upon some upcoming research and results thereof. TT kit would be fun. Unfortunately it's a tough one to do well, inexpensively. Speakers - talk to me in a bit. Working with Mr. Blumenstein on some ideas.

Re the flux capacitor, I'm selling them on ebay.

http://www.ebay.com/itm/120780999047?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1586.l2649

[Dr. Toobz]

I am indeed glad that I won't be responsible for your suffocation regarding the making of yet another PP 6550 amp in a saturated market. But we do continue to think about higher powered amps.

What about a single-ended 6550/KT88? What would be really cool is to do an integrated SEP/SET amp that not only straps the pentode to triode with the flip of a switch, but includes typical Bottlehead goodies like active loads, carefully-chosen components, high-quality irons, a shorting headphone jack, etc. to help the amp sound better than it normally might in pentode mode. (I've actually heard that KT88's sound good in a SEP configuration, if done properly, but I've never heard one wired that way, only PP). That would give builders a nice-sounding, 4 or 5W SET amp with the option of flipping a switch to SEP mode to double the wattage and/or get a different type of sound, depending upon one's speakers.

Ditto for an EL84-based amp, which I do know sound very good single-ended.

[johnsonad]

Another for an EL84 based guitar headamp with an optional headphone output.

[Grainger49]

ssssly,

Your numbers 1, 3 and 5 are either in the works or talked about.  Number 4 has been done and was abandoned a few years back.  It was a very nice looking table and it might still be marketed.  Doc would know.

[ssssly]

Re the flux capacitor, I'm selling them on ebay.

http://www.ebay.com/itm/120780999047?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1586.l2649

Could be interesting in a Pmour or FPIII power supply.

ssssly,

Your numbers 1, 3 and 5 are either in the works or talked about.  Number 4 has been done and was abandoned a few years back.  It was a very nice looking table and it might still be marketed.  Doc would know.

Indeed, and I am eagerly following the progress.
How's the Eros coming along?

And the breath holding is an overused scuba phrase. More concerned about exploding than suffocating. But you can rest easy on either account. The market is very saturated. Just prefer to spend my hard earned money in the Bottlehead camp.

A Bottlehead Blumenstein combo would be very interesting indeed.

A plasma tweeter kit would be nice. Never got my attempt working properly and abandoned it for other things.

Any take on active interconnects?

[Grainger49]

I'm going slow with the Eros.

I made a pair of unshielded interconnect, KACG, active shielded interconnects using "Zippertubing."  All it took was a 6V wall wart, two short pieces of shielded Zippertubing and a 6k resistor for each tube to limit the current to 1mA.  It worked but was awfully awkward.  I did change the current in steps up to 7 or 8mA and higher current shielded better.

http://www.zippertubing.com/

[Paul Joppa]

Here's a little more brainstorming on the OTL power amp.

As the Bottlehead reference system has gotten more refined we have been finding limitations with transformers, but also with cathode followers. And we have long felt that paralleled tubes have limitations when pursuing the highest degree of resolution, and so does feedback in general. OTLs keep coming up, to get around the transformer problem. However, the fact is that no tube has a low enough impedance to drive an 8-ohm speaker with a reasonable damping factor, without resorting to heavy feedback or massively parallel tubes. And I mean heavy; a cathode follower is not good enough. In addition, in order to get more than a watt you need more current than any practical tube can supply.

Both problems can be addressed with parallel tubes. Here's an example:

The 6AS7 or 6080 can have a plate resistance as low as 280 ohms according to the specification. Since cathode followers and other feedback approaches are out, that would be the output impedance. An 8 ohm output impedance would give a damping factor of 2 into a 16-ohm speaker, and would require 35 triodes in parallel. A stereo pair would be 35 tubes, drawing 8.75 amps at 135 volts, for a total dissipation of 1181 watts. Heater power would be another 87.5 amps at 6.3 volts, or 551.25 watts. Of course, if you are avoiding transformers you probably don't want to use plate chokes, so figure another 350 watts or so for the current source plate loads. For this, you'll get ideally 150 watts out; in practice due to the inability to find a set of 35 matched 6080 tubes you might get 100 watts - of parallel tube sound. The chassis plate could be as small as 20 square feet. You'll need a separate 20- or 25-amp circuit just for the amp.

This does not sound to me like a Bottlehead amp at a Bottlehead price. If anyone has a spare $10k-$15k to build one as an experiment, it would be interesting to find out whether it sounds OK or not.

At lower power, you need feedback to get the output impedance down. I must have been thinking of that when I suggested a single 6C33 for a 1-watt amp. That could be much easier to build - but, again, with heavy feedback it will not reach the highest level of resolution. I suppose we should try it; at least it won't be as expensive as the massively parallel approach.

[xcortes]

Thanks Paul,

Your original post mentioned zero feedback and that's what got me excited. Massive feedback cools me down a little bit. Sounded too good to be true. At least in paper!