Bi-amplification and Fostex 168e Sigma - diyAudio
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Old 2nd January 2011, 02:08 AM   #1
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Default Bi-amplification and Fostex 168e Sigma

I am wondering if this set-up will be fubar or really sweet:

First, I have a pair of Fostex 168e Sigmas in the following recommended cabinets:

https://www.madisound.com/pdf/fostex...ez_enclrev.pdf

I run these with an Acurus A150 (150 wpc), which I know is not a great match. So I've ordered a T-amp through Sure Electronics (15wpc):

2*15W @4? TA2024C Tripath Digital Class-D Audio Amplifier with Case & 12V PSU Free Shipping (AA-AB341)_Audio Amplifier and other Audio Boards_RF and Audio, Video Equipments_Sure Electronics' Webstore

Now, I have a pre-amp with two outputs (Melos MA111, which I love, esp. for its phono stage), so I was thinking I could run the T-amp and the Fostexes from one output and the Acurus and a pair of woofers from the other output. For woofers, I was thinking of these, perhaps in the corresponding open baffle kit:

Silver Iris OB 15 Augie [SI-OBA-15] - $165.00 : Zen Cart!, The Art of E-commerce

My worries:

1. Mismatches due to the amp differences and/or the vastly different efficiencies of the speaker drivers (Fostexes-- 94.5, Augies-- 88.7).

2. Crossover issues (do I want crossovers for both the Fostexes and the woofers here, or just one or the other, or neither?)

3. Aural dissatisfaction. I like 1950s and '60s jazz. I like bass "snap"-- plucking of the string bass, bass drum thumps, etc-- but I don't care for the earth-shaking-but-muddy sound of most subwoofers. I like "presence." I feel like I'm missing some of that since the Fostexes just do not have much bottom.

Thanks for any suggestions or advice.

Jay
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Old 2nd January 2011, 03:08 AM   #2
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SS amps usually have too much damping for things such as Sfullrange drivers on horns. I say try a tubed amp and see whether that missing bass returns. I myself have a 208Sigma based horns that had not given me too much pleasure until I put a SET amp to drive it.

I did read somewhere in the LansingHeritageSite that a member had decided to put a component in the amp end (SS) when driving vintage (1950s-60s) JBL amps due to what I have had described.
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Old 2nd January 2011, 05:40 AM   #3
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by Bemopti123 View Post
SS amps usually have too much damping for things such as Sfullrange drivers on horns. I say try a tubed amp and see whether that missing bass returns. I myself have a 208Sigma based horns that had not given me too much pleasure until I put a SET amp to drive it.

I did read somewhere in the LansingHeritageSite that a member had decided to put a component in the amp end (SS) when driving vintage (1950s-60s) JBL amps due to what I have had described.

Since you're already thinking about changing the amp, I second the vote on trying at least a couple of tube amps with almost any Fostex, and most particularly a Sigmas in a BLH before confusing things by adding woofer(s) & additional amps - get the "wide-range" part of the system dialed in first. If you're game to try a DIY/Kit, something like Decware (EL84 "family" ), Bottlehead Stereomour ( 2A3 / 45 DHT)or Tubelab Simple SE - much wider range of output types optional.

Decware:
Amp kits

Bottlehead:
Stereomour Stereo Single Ended 2A3/45 Integrated Amplifier Kit

Tubelab:
Simple SE
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Last edited by chrisb; 2nd January 2011 at 05:47 AM.
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Old 2nd January 2011, 03:36 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

With 150W on tap its very easy to simply try series resistors of various
values to hear the effects of having valve like high output impedance.

rgds, sreten.
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Old 2nd January 2011, 05:17 PM   #5
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Thanks for the tips about damping, and the advice about tube amps. When I built the Fostex speakers, I'd planned to build a 2A3 amp, too, but I never found the time to do it. I was sort of hoping the T-amp (based on the famed, or maybe fabled, Tripath 2024 chip) would deliver the tube-like sound at a rock-bottom price (I've got a family now, so it's harder to justify shelling out $750 for a tube amp kit, appealing as it may be otherwise). The T-amp wouldn't necessarily address the damping issue, though.
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Old 2nd January 2011, 08:12 PM   #6
sreten is offline sreten  United Kingdom
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Hi,

You can also modify the feedback loop of any amplifier to give output resistance.

rgds, sreten.
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Old 3rd January 2011, 05:35 AM   #7
chrisb is offline chrisb  Canada
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jay;

if it's not too late, take a look at the Virtue amps

Virtue Audio. We make audio lovers audiophiles. Better sound by design.

my son bought one a few months ago to drive a pair of Mark Audio CHR70s bookshelf cabinets in a small bedroom system, and it's by far the best of half a dozen or so class T amps I've heard
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Old 3rd January 2011, 09:15 AM   #8
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Quote:
Originally Posted by sreten View Post
Hi,

You can also modify the feedback loop of any amplifier to give output resistance.

rgds, sreten.
Even a T-amp?

Regards /Bo
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