2w SET amp : OB w/ 15" boomer or TL BOFU ?

mahleriana

Member
2007-11-13 12:49 pm
Hello,
I have two different 2w SET amps (one EL84, the other 45) and a few pairs of fostex 103e or 167e in TQWT, BR or open backs.
For a few years I was happy with it, but recently my ears did some kind of "reset" and lack of bass(OB, BR) or peaks/dips (in TQWT) became really annoying to me. A hint of a real(istic) bass foundation is wanted here...
I don't like BSC as it removes a lot of the SET magic...and efficiency, while Zobel is often interesting in reducing rising frequency response.
I am thinking of two options :
- 103e in OB with eminence Alpha 15a "à la MJK and...XO" : but will a 2w SET be able to produce any kind of bass from these huge bass boomers ? :confused:
- or a BOFU (sealed or Nelson Pass TL),
Both options are globally the same price for me due to shipping to France or acces to second hand market. I may even try both.
Thanks in advance for your advice,
Best regards
eric
 

woody

Member
Paid Member
2002-01-15 12:57 am
Tyrone Ga. U.S.A.
Somewhere in the MJK OB thread Martin says he played them on a friend's tube amp and wasn't verry pleased. I don't rember any details. I built this but used a
different driver in place of the 103's and a 6db/oct xover so you can't realy go by
my results. But having said that they sound a lot better on my F5 clone than my
cheap Antique Sound Labs tube amp.
 

ra7

Member
Paid Member
2009-02-07 6:47 am
Davis, CA
I think you'll be a little short on power with a 2W SET job, even for the full range driver on an OB. The full range driver may need to be padded down to match the level of the woofer at the low end ~30-40 Hz.

At least 10 Watts.

I don't know why people use tube amps with a high Q driver. A tube amp goes really well with a low Q driver, ala 8" fostex and AN. With a high Q driver, like the Eminence alpha 15, you are much better off with an SS amp having a large damping factor.

If you are going to cross actively and bi-amp, you might get away with the 2W on the full range driver, but I doubt it. I have a miniwatt with 2.5W per channel and it runs out of steam pretty quickly. On the other hand, it does really well when I use it with a voight pipe.
 
I think you'll be a little short on power with a 2W SET job, even for the full range driver on an OB. The full range driver may need to be padded down to match the level of the woofer at the low end ~30-40 Hz.

At least 10 Watts...

Agree, Here is a suggestion that doesn't need much power but would stay within a maximum requirement of ~10 W:

b:)
 

Attachments

  • Alu-6.25inch-T-TQWT.JPG
    Alu-6.25inch-T-TQWT.JPG
    626.6 KB · Views: 342
I don't think 2 watts will work well at all with the Alpha 15... regardless of the 95db per watt spec i feel you need 100 watts - i use SS with them. The higher power seems to wake the drivers up. Not enough power and they slog along all muddy and lifeless.

The Fostex or the BOFU present a real matter of taste. They sound totally different but good. IMO, if you like a brighter more forward and detailed sound go for the fostex. If you want mellow and relaxed go for BOFU. I also feel if you like to listen critically go for the fostex... you will find they play all the detail. If you don't go for the BOFU... B20, whatever you call it.
 
I built an MJK style OB using Fostex FF85K and Alpha 15 with passive XO. I drive it with a Yahama CR-1000 receiver (classic 1970s SS) with great success. I also have a 2.5 wpc MiniWatt amp which I really like on single full range drivers, but not on the OB; 2.5 wpc just isn't enough to get it done.

Cheers, Jim
 

mahleriana

Member
2007-11-13 12:49 pm
I guess I'll go with a BOFU (B20) pair, trying BIB, sealed and TL or even BR (using chipboard to stay low in price for the moment)... shipping to France is 70 $ ! :eek:
I tried recently a second hand vintage SS amplifier but i wasn't really convinced with it...so i'll stay for the moment with my SETS until I'll perhaps try one day one of Mr Nelson Pass's designs.
I just can't go too large a baffle : that is with i had thought of the 1.26 qts alpha 15a allowing to stay reasonable (20" large)
Thanks everyone for answers concerning the boomers/SET no future relationship.
Bjorno, I jus't can't read the image you attached...too small !
 
FR's with 'Boomers'

- 103e in OB with eminence Alpha 15a "à la MJK and...XO" : but will a 2w SET be able to produce any kind of bass from these huge bass boomers ?
Best regards
eric


Eric,

You will do just fine if you run the RF's off the 45 SET, and the 'boomers' from a plate amp. Just adjust the plate amps built-in crossover and gain control to blend with the FR's. You will be amazed by how improved the sound will be with this setup. You can probably get by pretty well with this (or you wouldn't be using a 45 SET!), but will be better off limiting the bass going to the FR's (and save power) by adding a line level high pass filter. Just choose coupling caps (in the preamp or pwr amp) to roll off wherever you want to 'cross over'. This can get expensive with quality caps, so just pick values giving a rolloff around 150Hz, and adjust the plate amp crossover to blend with the FR's.

Regards,

Bob
 

mahleriana

Member
2007-11-13 12:49 pm
With this solution it really looks like an FR + standard active subwoofer.
This could be a cheap solution buying a sub second hand. But I often find by friends that a subwoofer is more often boom-boom than really blending with anything.
By the way, How do you create a mono line out ?
 
A plate amp as it has been suggested ,it may be confusing...Since subs need to be cut real low (<90 Hz) ,and most of plate amps don't allow to select frequency over the range 40-200 Hz ,it may be unsuitable for your needs.
A separate electronic crossover unit would fit . To mix two channels passively ,just two resistors (15-47 K Ohm) and two electrolytics back to back (1-10 uF),plus a reference resistor (47-100K) to ground