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Old 17th July 2012, 12:51 PM   #1
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Default Newbie plan

Hey,
I'm new to this forum, so i'm sorry if i posted this in the wrong section, but here goes.
I want to build a tube amp for music. The source will be my pc, and the amp with the speakers will replace my creative inspire 2.1 system. I'm not new to tube amps, i have built a guitar amp for myself (a Carvin Legacy clone) and one for my friend(Bogner XTC clone), but i've never built an amp intended for music before. So this is where the questions begin:

1) I have no idea what speaker system to use. I guess ~5-6 inch full range speakers will do(i intend to build a cab for them myself too), but i don't know if they'll provide enough bass. So i guess i'll have to build and add a crossover and a woofer? Oh, and since the speakers will be placed on top of my computer desk(except for the woofer), i can't use those tower-like speaker systems you see in an audio-purist's living room. Not that they have to be small, but i'd like to keep the speaker cabs under 40x25x20cm(HxWxD). So what'll be best for me?

2) I don't have much of an idea for an amp either. I guess 2 12ax7 gain stages with a volume control somewhere and no eq will be the preamp. As for the power amp i don't know if i want it cathode biased or fixed bias, i don't know if i want it with a PI or without one, i don't know if i want it triode/pentode/ultra-linear. Heck, i don't even know what tubes to use But i do have some el84's with an OPT laying around so i'd want to use those. Also i won't be playing music loud. Any schematics you would recommend and any music amp tips for beginners?

Oh, i forgot to add that i listen to jazz-fusion, smooth jazz and instrumental rock mostly, and a bit of 80's hard rock and metalcore.
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Old 17th July 2012, 03:24 PM   #2
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Default Here are a few designs....

Do you have a pair of output transformers or just one? Is it for SE or PP use? Do you have UL taps on the transformer?

For SE EL84's do a search here for RH84

For PP EL84's search for Baby Huey (UL design), Red Light District (Pentode), and El Cheapo.

If you need to source output transformers Edcor is a great value BTW.......
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Old 17th July 2012, 04:17 PM   #3
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It's one push pull transformer without ul taps. What's the difference in sound between se and pp el84 designs? I also can't find any el cheapo schematics.
Well if the amp's more or less decided, then what do i do with speakers? What's the best speaker configuration for my needs?
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Old 17th July 2012, 04:48 PM   #4
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Old 17th July 2012, 05:00 PM   #5
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Quote:
Originally Posted by xtreme2ya View Post
It's one push pull transformer without ul taps. What's the difference in sound between se and pp el84 designs? I also can't find any el cheapo schematics.
Well if the amp's more or less decided, then what do i do with speakers? What's the best speaker configuration for my needs?
What's the budget?

An SE EL84 is going to be about 2-5 watts or so, depending on triode or UL config. A PP EL84 is going to be about 4-5W triode, about 12W UL, and about 15W pentode.

Here is an el-cheapo builder's thread:

El Cheapo, builders thread

There is also an El-cheapo Grande variant, although I'm not too familiar with it.

IIRC, this can be easily built with EL84's........This is Eli Duttman's design, the RLD is SY's project, and the BH is Gingertube's.

Try a search using a hyphen el-cheapo.

There are lots of choices for full range drivers, search the FR forum; there are lots of threads for small, desktop, tube-friendly designs.

Sounds like you'll need some transformers; Edcor offers output transformers at three different price points, the X series, the GX series, and the CX series.

EDIT: Planet10 just posted the schemo above; Dave should also be able to answer the EL84 variant question as well as give you some direction on the FR drivers.

Last edited by boywonder; 17th July 2012 at 05:02 PM.
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Old 17th July 2012, 05:23 PM   #6
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Dave, thanks for the schematic!
Boywonder, the budget is rather small and i don't intend to buy expensive speakers just yet, this is gonna be my first, and thus experimental, music amp build, so i'll keep things cheap and simple. The plan is to use random soviet speakers that i can get for dirt cheap. Then, when i'll understand the basics of the sound, i'll look into more expensive and better components(speakers included).
What i meant was what speaker configuration is best for my purposes, i.e. the 2 FR drivers with a cab or a crossover system into 2 mid-high range drivers and 1 subwoofer?
And is power tube saturation(at least some of it) sought after in music amps as it is in guitar amps?

Btw these Edcors look really nice, but they're expensive if you include shipping to Latvia.
Also, looking at the Red Light District and the El Cheapo, one has a constant current source and the other has a regulated screen voltage. What is the purpose of this? Is it to make the amp less dynamic and to even out the signal level?

Last edited by xtreme2ya; 17th July 2012 at 05:30 PM.
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Old 17th July 2012, 05:36 PM   #7
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Xtreme: I didn't notice that you are in Latvia.....

Tube amps like a nice, flat impedance curve over the entire freq range, so that is something to consider when choosing speakers. For a moderate volume desktop setup, sensitivity is also important but if you use small enclosures you'll most likely have to live with less than 90db sens (which will probably be fine if you don't need to rock the house).

You don't want any saturation in a hifi amp; quite different than a guitar amp. A guitar amp is typically designed to produce sound; a hifi amp is designed to reproduce sound. This means that you want a robust/stiff power supply and a carefully designed driver section, etc to minimize distortion.
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Old 17th July 2012, 05:43 PM   #8
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Quote:
Originally Posted by xtreme2ya View Post


Also, looking at the Red Light District and the El Cheapo, one has a constant current source and the other has a regulated screen voltage. What is the purpose of this? Is it to make the amp less dynamic and to even out the signal level?

The El Cheapo uses a CCS in the tail of the LTP to optimize the performance of the phase splitter; it approximates an infinite tail R. I'm not too familiar with regulated screen supplies, but I imagine that it's covered in the RLD thread. It's not there to make the amp less dynamic...........

The BH also uses a CCS in the tail of the LTP for the same reason as the El Cheapo.

FR speakers work great augmented by powered subs...........search for FAST over at the FR forum.

Last edited by boywonder; 17th July 2012 at 05:45 PM.
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Old 17th July 2012, 06:32 PM   #9
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Ok, i'm pretty much decided on an amp now, so i'm off to the fr forum. Thanks for the help!
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Old 18th July 2012, 09:20 AM   #10
amilaw is offline amilaw  Australia
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Hello

If you are looking for a low cost amplifier look at my 6p3s schematic its easy to construct and very stable. All tubes are very easy to find. Its on here just search for 6p3s.

Cheers.
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