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OB FAST with tube + SS amplifier ?
OB FAST with tube + SS amplifier ?
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Old 27th November 2015, 01:53 PM   #1
Bigun is offline Bigun  Canada
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OB FAST with tube + SS amplifier ?
Default OB FAST with tube + SS amplifier ?

I am collecting parts to build a 2A3 SET amplifier for my Audio Nirvana 15" OB speaker. I'd like to 'future proof' my amplifier build by including an optional line-level cross-over. The idea would be that I could in the future use the same amplifier for a FAST OB set-up. This would mean driving a full-range speaker with the SET amplifier and a supporting woofer with something else, likely solid state.

To get the most out of my investment in the 2A3 amplifier I'd like to cross-over low - hence why a FAST approach and not the traditional 2-way with woofer and tweeter.

There are some obvious constraints - the full range driver needs to be of high sensitivity, at least 90dB. The woofer does not need to be sensitive because it can be driven by a powerful SS amplifier. To keep the size reasonable multiple woofers could be used, e.g. 2 x 12" (e.g. Linkwitz Orion).

This will be a mono speaker for general listening from multiple room locations, so I'd like to have good dispersion characteristics.

Out of interest - which speaker drivers would you consider for such a FAST speaker ?
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Old 27th November 2015, 02:44 PM   #2
xrk971 is offline xrk971  United States
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OB FAST with tube + SS amplifier ?
The 90dB requirement limits it to just a handful of units.

The ones I have personally tested and can recommend are:

1. Radio Shack 40-1197 (FE-103). Very smooth great sound. 90.5dB at 2.83v. You can still get these on line.

2. Faital Pro 3FE25-8, also very smooth and great balance. 91dB. Very inexpensive but great sounding.

3. Faital Pro 3FE22-16, 16ohm good for tubes? Also 91dB and great sounding.

4. If you like high SPL and lots of dynamic reserve but don't mind if upper end is 15kHz only then PRV 5MR450-ndy 8ohm. 95dB.

All of these I would run a 270Hz to 350Hz XO.

Of course there are Lowthers, Fostex EN's etc., Lcao, AN, etc. I have not tried them but some have ragged frequency responses or a big 8dB peak somewhere in 5k to 7k range.

Last edited by xrk971; 27th November 2015 at 02:46 PM.
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Old 27th November 2015, 03:19 PM   #3
Bigun is offline Bigun  Canada
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OB FAST with tube + SS amplifier ?
Thanks XRK971 - these are drivers I would not have thought of so you have opened my eyes - I must be honest, I like the description of the last one in particular but it looks like a boom-boom car audio thingy not hi-fi. Am I wrong - did I become a 'snob' for so-called hi-fi drivers ?
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Old 27th November 2015, 04:06 PM   #4
xrk971 is offline xrk971  United States
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OB FAST with tube + SS amplifier ?
It's not boom boom - it's pro audio and mid and up only. No bass so has to be used with woofers in FAST. Very detailed ultra low distortion sound. Here is what it sounds like in an OB FAST with a slot loaded woofer complement.

Measurements and sound clips in this thread:
http://www.diyaudio.com/forums/attac...d-thd-meas.png

Last edited by xrk971; 27th November 2015 at 04:08 PM.
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Old 28th November 2015, 07:01 AM   #5
Godzilla is offline Godzilla  United States
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This should be fun!
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Old 28th November 2015, 12:15 PM   #6
guangui is offline guangui  Puerto Rico
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Quote:
Originally Posted by xrk971 View Post
The 90dB requirement limits it to just a handful of units.

The ones I have personally tested and can recommend are:

1. Radio Shack 40-1197 (FE-103). Very smooth great sound. 90.5dB at 2.83v. You can still get these on line.

2. Faital Pro 3FE25-8, also very smooth and great balance. 91dB. Very inexpensive but great sounding.

3. Faital Pro 3FE22-16, 16ohm good for tubes? Also 91dB and great sounding.

4. If you like high SPL and lots of dynamic reserve but don't mind if upper end is 15kHz only then PRV 5MR450-ndy 8ohm. 95dB.

All of these I would run a 270Hz to 350Hz XO.

Of course there are Lowthers, Fostex EN's etc., Lcao, AN, etc. I have not tried them but some have ragged frequency responses or a big 8dB peak somewhere in 5k to 7k range.
XRK971 knows his stuff...But, the RS 40-1197 is very difficult to source these days and the ones that come up for sale are around $25.00 each. Personally I am convert to Faital and PRV, very good products at inexpensive prices.
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Old 28th November 2015, 12:28 PM   #7
xrk971 is offline xrk971  United States
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OB FAST with tube + SS amplifier ?
1197's: There was a German speaker website that has them in stock. They are ridiculously expensive at $70 - but maybe not compared to some modern drivers that don't perform as well in smoothness or sensitivity costing $85 and up. I can't find that link at present.

This is emphemeral just saw eBay listing for qnty 4 1197's for $95.

Radio Shack 40-1197 4" Speakers NOS FE-103 Quantity 4

That's a great deal of they are in good condition. They have fabric surrounds so no need to worry about foam rot.
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Old 28th November 2015, 05:22 PM   #8
Bigun is offline Bigun  Canada
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OB FAST with tube + SS amplifier ?
It's encouraging that there's a choice of drivers.

I was recently reading about some 4-way OB designs, LX251(?) and NaO-II. I wonder how much a 2-way FAST OB gives up to the more sophisticated 4-way design?
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Old 28th November 2015, 05:54 PM   #9
xrk971 is offline xrk971  United States
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OB FAST with tube + SS amplifier ?
I have done a 3 way open baffle with two 12in woofers and a pair of full range TG9FD's for mids and a dome tweeter. It sounds great with a lot of depth and dynamic head room and crystal clear highs. But the complexity and size is a lot more to handle. I found the 2 way FAST OB just as good on most material for a lot less effort. One thing that is nice with a single full range on top is the coherence of the telephone band so imaging and transients are very good as they are phase coherent and a point source.
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Old 28th November 2015, 06:39 PM   #10
freddi is offline freddi  United States
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my five to six watt 2a3 amp built `1993 has sat for over a decade - sounded pretty good with some tube era lps and good lp dubs of 78 - built so whomever wanted to steal stuff might not take. Faital 4fe32 seem a lot more detailed than say pa130. I can have fun now with a pocket sized tpa3116. I need to re-reference the ground buss in this clunker.

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