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Old 6th November 2008, 03:59 AM   #1
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Default Need help making some choices on what to build

Hi,
I want to build an amp but I'm not quite sure what road to take in regards to wattage, operating class, tube type, fixed vs cathode bias, etc... Any insight would be greatly appreciated.

As for operating class, I've heard SE is way better for spacious, full, airy sounding music. I can see how this might be great for things like classical music, solo guitar/piano, etc. My musical tastes are a bit harder edged though to what it seems most people say SE are best at. My interests range from acoustic blues and light folk to slightly heavier stuff like The Beatles/Grateful Dead/Neil Young et cetera to stuff like Pink Floyd and Led Zeppelin. I've heard that fixed bias and push pull are two things that can give music some more kick and bass volume. What would you guys recommend I look towards?

As for wattage, what do I really need? I have a home built guitar 18 watt amp (2x 6V6) and I tried running my iPod through it and it was plenty loud and sounded pretty nice, actually. I ran it through a 2x12" guitar cabinet which was 8 ohms, despite the amp output being 4, so it should be even louder with the proper load. But yeah, I don't have much of an idea quite how loud different wattages are, so it's hard for me to decide what I want. I basically want an amp loud enough so that you can really feel the kick of the music if you turn it up. I really don't know quite how to quantify that, hah.

Also, my budget is 400 bucks. Is this reasonable? What's a good project within this price range based on what I described above?

Thanks alot everybody
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Old 6th November 2008, 12:40 PM   #2
cjkpkg is offline cjkpkg  United States
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I lurked here for a while researching which power amp to build. After weighing full kits, partial kits, and schematic only with point to point construction I decided on the SimpleSE from tubelab.com. This is a board only from tubelab but George has a thorough walkthrough and bill of materials to stuff the board. He posts here often and answers any question related to the build along the way - as well as other people who have built one.

Chassis was homemade - $15
PCB - $35
Resistors/capacitors - $50
Tubes/sockets - $50 5AU4, 12AT7, 6L6GC
PT - $50 - Allied 6K7VG
OPT's - $50 - Edcor XSE 15W 8K
Misc stuff - $50

With inexpensive iron I kept it around $300. Of course you could spend that on iron alone with boutique type stuff. The only upgrade I did was to the coupling caps - I went with the 715p orange drops - very inexpensive compared to Auricap or similar.

This was a really fun project - so much in fact that I am now in the process of building an Aikido based preamp.

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Old 6th November 2008, 04:03 PM   #3
kevinkr is offline kevinkr  United States
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I think it is a bit more complicated than this, in addition to choosing a topology you also need to think about what sort of speakers you are going to use this amplifier with, their efficiency, the size of your room, and your preferred listening levels.

Musical preferences are important too, that said I frequently listen to very bass heavy techno with a 300B SE amplifier and very efficient, large and complex diy Onkens with horns on top.

Next you need to think about what you are actually capable of building and debugging. If you are a total newbie something simple would increase the chances of success.

SE amplifiers can be built that exhibit excellent performance even in the deep bass, but many don't, and smaller SE amplifiers often struggle with multi-way speakers with complex X-O, while some larger ones will drive just about anything. High performance SE amplifiers are expensive and it is difficult to design and build really good ones. Simpler designs like George's (tubelabs) SE amplifier offer good performance and a relatively easy build and are suitable for efficient speaker designs.

Push pull amplifiers offer much more power, and output transformers of comparable quality are lighter and less expensive for a given output power because they do not have to handle much dc magnetic flux unlike SE opts which unless parafeed, do.

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Old 6th November 2008, 08:10 PM   #4
Jeb-D. is offline Jeb-D.  United States
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$400 is reasonable.

What kind of speakers do you have?(if any) If you don't have any yet, are you planning to build those too, or buy some.

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Old 7th November 2008, 12:47 AM   #5
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Hi, thanks for the responses:
I have no speakers yet. I'm planning to pick up a set of old sturdies from Goodwill or so for 40 bucks until I have more money.

I'm pretty experienced with building stuff. I've built a Fender 5e3 guitar amp (albeit with single channel), and modified/serviced my '68 Fender Bassman. On the non-tube side I've built many pedals and other electronic doodads. I'm going to be getting a scope so with that I feel pretty confident at debugging.

One thing I'm really aiming to do is to learn how stuff works and how to tweak junk myself instead of just building a schematic. So the only thing I'd ask for in terms of circuit is that it's not really crazy with all sorts of obscure biasing techniques or feedbacks or current feeding setups or whatnot. I just really want to understand what I'm building.

How might I go about stating how loud I listen to music? I have no idea how to put that in writing...
Thanks!
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Old 7th November 2008, 12:59 AM   #6
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As other posters have indicated, amps must be discussed in combination with speakers. The desire to "bang heads", strongly (IMO) suggests a PP amp of substantial power O/P.

"Iron" is always the biggest expense, when amp building. Really top notch stuff could easily eat the entire budgeted $400. Edcor offers trafos which have acquired a reputation for decent performance at comparatively modest expense. $62.27 buys their model CXPP60-8-6.6K. That trafo mates well with PP 6L6GC "finals". Because the 6L6 can safely enter a positive control grid current regime, the greatest bang for the power buck may be in that type. Somewhere in the neighborhood of 50 W. should be available from a PP pair of 6L6GCs operating in Class "AB2".

A Mullard circuit variation employing Tubelab's "Power Drive" can be built around 6FQ7, 12AT7, and IRFBC20 small signal devices, along with 6L6GC O/P tubes, that would not require a line stage with gain, when a CDP is the signal source.
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Old 7th November 2008, 01:04 AM   #7
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Hmmm, I'd guess that 50 watts would be too much. I have a 50w guitar amp and that thing is pretty loud. My 18 watt 2x 6V6 amp got plenty loud for me, I'd say. I think I'm more stuck between something in that wattage rage or something more like 8.

Cheers
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Old 7th November 2008, 01:06 AM   #8
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How loud?

Hum,Well...
Is it soft,background kind of music,the kind you could carry on a conversation over? (my style,most of the time.)
Or,
Do you like to have it LOUD,so that you can feel the beat in the floor,and make the whole house rock? (me,the other half of the time.)


I started out with a tube amp from an old Sears Silvertone console,and rebuilt it. This amp is a pretty simple example of a Push-Pull amp,using a 12AX7 and 2x 6V6GT's per channel,with a 5U4 rectifier. It turned out *MUCH* better than I expected. I dare say that it is still my favorite amp,in my collection.

Here's some info:
http://s199.photobucket.com/albums/a...uff/PP-6V6Amp/
and
http://www.users.qwest.net/~ptaylor/...V6amppage.html

The amp makes approx 8W per channel,before any visible clipping/distortion is seen on the O'scope. The sound is great,and considering the small output transformers the bass is very good.
My speakers aren't all that efficient,but in my small room,it can get up to "concert level" volume fairly easily.
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Old 7th November 2008, 01:11 AM   #9
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Quote:
I think I'm more stuck between something in that wattage rage or something more like 8.

Then build an "El Cheapo" using 6V6 O/P tubes and DynaClone Z565 O/P trafos. You'll get 6 WPC in triode mode and 12 WPC in UL mode. The $400 budget should cover a pair of very nice PEC hot molded Carbon volume controls. Heck, you might end up with a few bucks for "software".
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Old 7th November 2008, 01:13 AM   #10
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I want it go to loud enough that you can't hold a conversation easily through it. Just enough so you can feel a bit of the bass in the drywall.
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