Welcome! Need support, you got it. Or share you ideas and experiences.
173.28.169.173
Last night, I put together my long-awaited Quickie kit. The chassis plate was MIA in the first shipment, so "Queen" Eileen sent one out via USPS Priority Mail, which was very nice. I ended up with a black plate, which is great, since I had asked a few questions in another thread about what it would take to paint one of these. Now I won't have to worry about that.
Some early impressions:
a) They weren't lying when they named this thing the "Quickie" - it went together so fast that I was just starting to enjoy myself (or, perhaps the solder fumes were starting to get to me) when the next thing I knew, the amp was done! Like all of my Bottlehead gear, it fired up the first time with no problems or debugging needed.
b) The dinky 3S4 pentode tubes draw so little current that the heaters are nearly invisible when on - you can just make out a tiny, dim sliver of orange if you look close enough. An indicator LED might be a good idea for a modification.
c) The transformer mod mentioned in another thread is very easy and seems to work well. Where to put the headphone jack is another story. Can I drill through this plate without cracking or shattering it? The only other option, I suppose, would be to whittle out some of the wooden base down to about 1/8" thickness, then drill a hole through that. The headphone jack I have doesn't have a very long "neck" (it's a non-shorting leftover from my SEX amp) and I'm using a Seduction base, which is at least 1/2" thick. I don't have any fancy woodworking tools, unfortunately.
d) I'd guesstimate that I'm getting somewhere from 6 and 8dB of gain with a fresh set of Energizers.
e) Sound is very good, though perceptibly different than my C4S'ed SEX amp. The Quickie seems fresh, lively and perhaps a little less refined....but the biggest difference is that the SEX seems to have an enormous soundstage, whereas the Quickie's is noticeably "closer" to the listener. The SEX has a magic to it, a cohesiveness and refinement, if you will, that the Quickie doesn't seem to have - maybe it's the beefier tubes, two stages, higher gain, or C4S boards. But, for $99, the Quickie is an incredible deal! Just don't expect it to be a $99 SEX amp "knockoff" with headphones - they do sound a bit different.
f) Using Specos wired as 8000/500ohm autoformers, taken off of the coupling caps (i.e., parafeed), I get enough juice to drive a pair of Beyerdynamic DT880 Pro (250ohm) quite loudly with about 2V input. A pair of Grado SR60's also can be driven loudly (even though they are only 32ohms, they seem quite sensitive), but they sound honky and have flabby bass due to the impedance mismatch. I don't like how Grado's sound on my SEX amp, either - they seem to be better for coaxing good sound from not-so-good sources like iPods.
g) Here's a thought - what if I were to get a pair of transformers with ultra-linear taps? Could I connect them to the screens of the pentodes? Or would I lose too much quality by going away from a no NFB design?
I'll post some photos once I stain and seal the base, as well as stuff a headphone jack somewhere. I'd appreciate some advice about whether or not the plate is a bad idea to be drilling through....
Follow Ups:
Im done too! I'm using Beyer-Dynamic dt880 Premium (250ohm). At Maximum volume I have comfortable volume, well balanced sound. Im wondering if you used the brown leads from the Spectos? Should I use a different tap with these? Just looking to get maybe just a bit more volume.
I used the brown leads, per the instructions given in another thread. I think the output impedance off the plate is something like 4000 ohms, so the Specos wired as 8000/500 gets you 250 ohms, which is a light load on the tubes. I don't remember if the Specos have 1k taps, but I'm assuming that if you used a higher impedance tap, the distortion would be higher and the damping factor poor, whereas using something like the 8 ohm taps would yield a good damping factor and lower distortion (since the tubes would see a higher "reflected impedance") but the output would likely be very low. Remember, these little tubes are putting out WAY less than a watt, probably like 50mW or something. I don't know the exact current or voltage output from this thing, so that's just a wild guess....
Again, with resource-hungry cans, I think the SEX amp is superior for critical listening - which is both a testament to Bottlehead's impeccable design (and reflected by the justifiably higher price). Where the Quickie really shines is in its cheapness, ability to be modified, and ability to be used as a tube buffer or preamp with line-level equipment. I like to think of the headphone output as a "bonus."
I'm using mine in my music room/study, coming off an a new aluminum iMac. I may end up building a Stereomour once they come out, put it in the living room in place of my SEX amp, and use the SEX amp in the study with the Quickie as an output buffer. The iMac's audio output is rather low from the headphone jack, and I just can't bring myself to remove my DAC from my "good" system in the living room just to feed the Quickie (though I did try it).
Great post - thanks!
"f) ...Grado SR60's... sound honky and have flabby bass due to the impedance mismatch. I don't like how Grado's sound on my SEX amp, either"
I am guessing that the Grados are not designed for the IHF standard 120 ohm impedance, and want to see a much lower source impedance. You might try them on the SEX amp speaker outputs - probably too loud, but the bass might get less flabby. You can short the 120 ohm resistors with clipleads to try it.
"g) Here's a thought - what if I were to get a pair of transformers with ultra-linear taps? Could I connect them to the screens of the pentodes? ..."
I've posted about using the Speco in series feed. The 4K and 2K taps (labelled 1.25 and 2.5 watts respectively) will provide 35% and 50% ultralinear taps if you want to try it. Remember this puts the +36 volts on the headphones unless you use the 8 ohm output as a plain (not autoformer) transformer, and the effective output impedance will be increased. A fairly easy experiment though.
I received my two Quickie kits on Oct 8th (the name "quickie" also applies very well to its delivery).
One green plate, one white plate. The white one had two of the 9V battery lead holes undrilled, so I used the peel-off paper from the other plate as a template, and used a small hand drill, and appropriately sized drill bit, and had no problems doing so.
The green plate closely matches my Paramounts and FPIII, so it should fit in with them very nicely.
If you want to add a phone jack hole, just drill slowly & carefully, and keep the RPMs low (that's why I used a small hand drill), and don't use too much pressure. I'd also advise using a series of increasing diameter drill bits, rather than only using a 3/8 drill bit. It's a lot easier than drilling aluminum or even wood.
I did all of the basic chassis assembly in one sitting (OK, I took a short pee break between the two of them), and with the assistance a couple of mild adult beverages (though this isn't an absolutely necessary part of the process). No missing parts, and nothing left over ;-)
Next comes the wiring, soldering, testing and listening, as time allows (the next rainy day or two). No need to rush things...
Stay tuned...
/ed B in NC
real radios glow in the dark
Well, it turned out to be a less than stellar day outside, so I proceeded with the wiring, soldering, testing and listening with both units.
Everything went smoothly, no problems, and I am really pleased with the good sound!
Once again, got it all done in basically one session, with another short pee break, and popping the cap off a second mild adult beverage, to celebrate the completion ;-)
With fresh Panasonic batteries, I get around 2.9 mA cathode current per channel (B+ is around 38VDC with the new batts). The two NOS Sylvania tubes were nearly matched, the two NOS GEs were about 5% different between the two of them.
I teested it with a SEX amp, into "SEXY" speakers sans the powered woofs, fed with a Sony "car man" CD player which has been my reliable test bench audio signal source for several years.
Very nice clear sound, though the 3S4s tend to be somewhat microphonic, which only happens when I flip the input switch, or tap the chassis plate, otherwise these line stages are dead quiet with no signal input..
I had the Quickie under test sitting on a standard BH 10X6 inch wood base which I temporarily borrowed from my Seduction phono stage.
I'd imagine that the filament or grids in those tubes tends to be just a little bit "springy".
Thanks for a neat and fun audio project! I'll add a photo or two later...
/ed B in NC
real radios glow in the dark
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: