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Old 27th July 2008, 05:40 PM   #11
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It also occurs to me that it may be helpful to summarize my listening habits and music tastes. I live in a loft apartment--it's actually a renovated nineteenth century elementary school classroom. The ceiling is about eighteen (18) feet tall. I'm sure that my speakers are not adequate for the room but it is an apartment and I do have concerns about offending my downstairs neighbor. The Klipsch's I run are on stands. The lack of bass in them kind of works to my advantage in that regard.

Adam,

That info. is very important. Comparatively speaking, your listening space is a cavern. Paul Joppa's 102 dB. rule does not apply to your situation. You need 30+ WPC in combination with the Klipsch speakers. SE amps at that level of power O/P are HIDEOUSLY expensive. Go push/pull.

It is definitely excellent that you have experience with electronics and that you understand the importance of safety, when working with electricity. Don't worry about sourcing parts for a project built from a schematic. The guys here will get you "connected" to sources for parts.

I suggest you build an "integrated" stereoblock using Mullard style topology. I recommend a 12AT7, 2X ECC99s, and 4X EL34s, as the tube complement.

Believe it or not, your "local" WalMart is a source for a chassis. Buy a large, deep, plain Aluminum, baking pan. If being "purty" matters, you'll get finishing tips galore, from the DIY "crew".
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Old 27th July 2008, 08:19 PM   #12
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I've never been afraid of having too much gain. That is why there is a volume control that can be adjusted up or down. The preamp from Doc will work fine however I personally believe an Aikido would be much better. If your worried about your ability to put one together rest assured there are people here only to happy to be able to give you instructions.

The amplifier should be able to provide for your modest needs and for this I would suggest a Dynaco Stereo 70 or something along this line. The reason is it will provide a lot of bang for the buck. You will be able to enjoy it and then promptly send it down the road at a hefty profit.

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Old 27th July 2008, 08:58 PM   #13
rhing is offline rhing  United States
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Default Try the Bottlehead Forum

Have you tried the Bottlehead forum at http://www.audioasylum.com/forums/bottlehead/bbs.html? If you are serious about Bottlehead gear, most of the Bottlehead users are accommodating if you post for a listening session at their home around your area.

I can appreciate everyone's input on this thread in terms of alternatves to Bottlehead amps. You might also consider some of the diyTube push-pull amp kits for power amps (http://www.diytube.com/phpBB2/index.php). These kits are largely based on Dynaco amplifier designs. The diyTube kits are basically boards that you need to populate. Most of their instruction manuals include Bill of Materials (BOMs) for guidance on purchasing components including transformers, coupling caps, resistors, etc.

For a preamp, I would consider John Broskie's Aikido linestage amp kits (http://glass-ware.stores.yahoo.net/index.html). You'll have to add your own power supply and power transformer. The Aikido kits are flexible enough for you to configure it to your needs. The nice thing about the PCB-only kits is that you can get creative on enclosures and still have the relative simplicity of working with a PCB to keep things organized. For a complete kit, the Transcendent Sound Grounded Grid is a nice linestage to consider.
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Old 28th July 2008, 12:42 AM   #14
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Guys,

Adam's budget is $500. Unless considerable care is exercised, the magnetics alone will consume the available cash.

The $62.27 Edcor CXPP60-8-4.2K seems quite suitable as the O/P trafo.



AnTek is a source for affordable toroidal power trafos. The $50.00 AnTek model AN-4T360 will provide for all needs, except the C- bias supply. The $10.00 model AN-0124 takes care of that need.

I envisage the 2X rectifier windings of the AN-4T360 being connected in parallel and SS bridge rectification being employed. 600 PIV diodes will be quite safe in this regime. Snubbed General Semi PN junction parts go on the ground side and Cree SiC Schottky parts go on the B+ side. IIRC, Jim McShane carries the rectifying diodes, along with all the tubes needed.

A CLC filter using a 4.7 μF. 'lytic in the 1st position keeps the power trafo cool, reduces "hash", and holds the B+ rail voltage down a bit. a Hammond 193M would be the choke.

As the B+ rail voltage will still come in on the high side for an EL34 amp, let's turn a liability into an asset by employing combination bias. A shared RC bias network under each pair of EL34s "eats" the extra B+ Volts and allows the use of a single bias trim pot. in each channel.

My earlier suggestion that a 12AT7 section be used as the voltage amplifier was anything but accidental. The 'T7 sounds TERRIFIC in PP amps and its low Miller capacitance allows the use of 510 KOhm grid leak resistors, without incident. That in turn allows 50 KOhm volume controls to be cap. coupled to the 'T7 sections. A 12 nF. coupling cap. puts the 3 dB. down point at 26 Hz., which should be FINE. Remember, Adam's Klipsch speakers don't go there. Does anybody know where a good deal can be had on 12 nF. PIO capacitors? Obviously, 15 nF. parts would work too.
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Old 28th July 2008, 02:35 AM   #15
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There are lots of kits out there that are done on boards, seem cheap, and become very tempting. What you have to remember is that there is a lot more to doing this than just mounting the parts. The Bottlehead kit will teach you a little about general grounding and layout, and because you are not reliant on board traces, you will make all the connections yourself. There is also an upgrade path, and a few curious projects where people have put alternate double triodes/directlt heated single triodes in place of the 12AU7's.

As for the Klipsch speakers, a 300B might keep you happy, but I wouldn't bet on 2A3's. I think you could do some investigation over on their forum about using type 50's in the Paramour with the upgraded iron to possibly get some more power. If you keep your eyes open on your local Craig's List, you will likely be able to find a pair of 95+db Klipsch speakers cheaply. I found some 102db efficient Klipsch CF-4's for $500, and they have been quite nice for me.
-Paul
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Old 28th July 2008, 05:02 AM   #16
w5jag is offline w5jag  United States
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I would look hard at Tubelab's Simple SE as a first project.

It sounds excellent, is easily driven by the line output of a CD / DVD player, can meet your power requirements, can be inexpensive or expensive as you wish, is well documented, and a lot of people on here run them.

Can't help you with the Arkansas Bar, it's been a couple of decades since I took it, but you should do fine. I thought the multistate was the hardest part.

I'm in Fort Smith, btw.

Win W5JAG
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Old 30th July 2008, 06:23 PM   #17
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I think Eli's got the best idea. Remember, $500.00 budgets and 30 watt SE amps don't go together well.

The topology Eli mentioned is going to make a very nice sounding amp with enough power to take care of his large room, and work within the budget too.

The lowest bass may be somewhat lacking, but that's probably the optimum tradeoff in this set of circumstances.
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Old 30th July 2008, 06:50 PM   #18
GordonW is offline GordonW  United States
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Are we worried about the output transformers saturating on low bass? Otherwise, I would, from experience, probably be inclined to hedge the f3 point a bit lower... I hesitate to spec anything above 20 Hz, for a rolloff point. Probably something like a 22nf (.022uf) coupling cap... for an f3 of around 16 Hz, or so... that would still do a good job of not passing "turntable rumble" or other LF hash/trash... but would not EXACERBATE the rolloff of the speakers (remember, rolloffs are CUMULATIVE... you add the rolloff of an amp to the rolloff of the speaker, and you FURTHER lean out the bass, along with exacerbating the group delay below 40 Hz).

I agree with the idea of limiting the amount of LF current through the OT's... but IMHO, it needs to be a little less "intrusive" into the audible range...

Just speaking as a speaker designer, as well as a tube amp tweaker...

BTW: I'm also a big 12AT7 fan... in fact, one of the next amps I'm planning to build is a clone of an early Stu Hegeman design... the HK A250 amp section. 12AT7 in a neat positive-feedback (to the phase splitter) configuration. I've got the same design amp (the Award A300) using a 12AX7, a 12AU7 and 6V6 output tubes... the amps I'm planning on will be monoblocks, with a 12AT7 and PP 6L6 outputs, for about 25w/ch. I'm thinking the amp with the 12AT7 may actually have more "magic" than even the one with the 12AX7 and 12AU7...

Regards,
Gordon.
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Old 30th July 2008, 11:52 PM   #19
agweeks is offline agweeks  United States
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Thanks everyone for the input and ideas. I'll be finished with the bar exam at 11 a.m. tomorrow. Until then, don't take my lack of participation as a lack of interest. I look forward to reading all of your posts and exploring the ideas and putting together my project.

Thanks again,

AGW
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Old 31st July 2008, 02:05 AM   #20
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Are we worried about the output transformers saturating on low bass?
Gordon, I always worry about core saturation in circuits that employ loop NFB around the O/P trafo. My level of concern is increased, when the O/P "iron" is not "top notch". By all accounts, Edcor O/P trafos are an excellent value, but I prefer to avoid an attempt at squeezing blood from a stone.

510 KOhms combines with 18 nF. to "corner" at 17.3 Hz. I don't think we should press our luck any further.

Can any member suggest a source for low WVDC 18 nF. PIO capacitors?
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