Low power amplifer recommedation for Altec 511B horn

**MerlinVSM** · January 22nd, 2013, 03:40 PM

Looking for amplifier (tube or solid state) recommendation to drive a pair of Altec 511B horns / driver GPA 902 8ohm.
These horns will be used with Acoustic Elegance 15 inch Dipole open baffle with an Altec 9440A power amplifier.

**fpitas** · January 22nd, 2013, 04:16 PM

I'm using a First Watt J2 to drive my 511s with Radian 475PB drivers. It's full Class-A 25W/ch:

SoundStageXtreme.com | UltraAudio.com | First Watt J2 Stereo Amplifier

FIRST WATT J2

If cost is a big issue, I've read that the First Watt F5 also does a good job.

If cost is a really big issue, a friend is using a 1W/ch headphone amp to drive his 511s:

Amazon.com: FiiO E9K High Output Desktop Headphone Amplifier and Dock for E17 (Not E7 Compatible): Electronics

At reasonable listening levels, it does a very good job. His drivers (BMS4550) are 16 ohms, so that may be an issue if yours are 8 ohms.

**bowtie427ss** · January 22nd, 2013, 05:07 PM

At reasonable listening levels, it does a very good job. His drivers (BMS4550) are 16 ohms, so that may be an issue if yours are 8 ohms.

Sensitivity will be the big issue. BMS 4550 has nearly 10db higher sensitivity than a 902.

Assuming ~500hz XO, 1 watt is probably gonna have a hard time cutting the dynamic mustard.

**alancohen** · January 22nd, 2013, 07:31 PM

I'm running Altec 416As on the bottom and 811s/802s on top. Right now I'm powering the whole things with a 15W OTL (glorious), but the long term plan is to build two 300B OTL monoblocks to run the 811s and leave the 15W to power the bottom through an active preamp. Here's a pic of both:

Tubes and Circuits by Bruce Rozenblit

The scuttlebutt from people way more experienced than me is that the 300B OTLs are the best 1.5W in audio, barre none. The kits are in process and I figure they'll be around $500/ch. Plus $300/ch for the tubes they're not cheap, but compared to what other high end audio costs...it's a bargain if you have some soldering skills and can follow directions.

The 15W SOB for $749 +tubes is like stealing.

**Alien_Shore** · January 23rd, 2013, 08:34 AM

If you are into DIY:

Bottlehead - they have a 2A3 SET kit for $750, or a dirt cheap starter kit.
Triode, USA has several Dynaco clone kits
Shannon Parks over at DIYTUBE - has a few kits as well - for the more experienced builder.

GM · January 23rd, 2013, 02:19 PM

Originally Posted by alancohen

The scuttlebutt from people way more experienced than me is that the 300B OTLs are the best 1.5W in audio, barre none.

Appears to be a high power pre-amp, so concept wise would tend to agree.

GM

**amandarae** · January 24th, 2013, 03:47 AM

Originally Posted by fpitas

His drivers (BMS4550) are 16 ohms, so that may be an issue if yours are 8 ohms.

No, 16 ohm LF and 8 ohm HF or vice versa is not going to be an issue, you just need to adjust the cross over calculations to reflect what impedance you have. I have several "Altec" friends with that kind of combo and I heard their system and cannot detect any problems. Every single one of them, using DHT SET amps.

Abe

**fpitas** · January 24th, 2013, 08:51 AM

I think he's bi-amping; if so, there's no crossover between the amp and driver. I was afraid the headphone amp wouldn't drive the 8 ohms properly, but bowtie427ss pointed out that 1W probably wasn't going to get the job done with a 902.

Originally Posted by amandarae

No, 16 ohm LF and 8 ohm HF or vice versa is not going to be an issue, you just need to adjust the cross over calculations to reflect what impedance you have. I have several "Altec" friends with that kind of combo and I heard their system and cannot detect any problems. Every single one of them, using DHT SET amps.

Abe

**bowtie427ss** · January 24th, 2013, 10:29 AM

I was afraid the headphone amp wouldn't drive the 8 ohms properly, but bowtie427ss pointed out that 1W probably wasn't going to get the job done with a 902.

Precisely.

The 4550 is so sensitive, that if you swap it into an existing Altec speaker system like a Valencia or model 19 additional padding is needed to properly balance the system. The stock network and pad cannot attenuate the 4550 enough.

So, while an active system using the 4550 HF on 1 solid state watt might well be sufficient, a 902 in the same system is probably going to be starved for power. A 1.5w SET with it's more forgiving even order harmonics might still be able to get the job done with the 902 however. Listening preferences of course would be a big factor as well.

I've tried the low power diet, if i only listened later at night i could probably live with it. However, lack of power always became the culprit in listening fatigue during extended sessions. When i find a color i like, i can live with the coloration of valves(tubes). But, fatigue caused by over-driven amplifiers is just not a compromise i can live with at the end of the day. Sign me up as a solid state class A space heater fanboy.

GM · January 24th, 2013, 12:27 PM

Originally Posted by bowtie427ss

But, fatigue caused by over-driven amplifiers is just not a compromise i can live with at the end of the day. Sign me up as a solid state class A space heater fanboy.

Ditto, though there's a certain synergy when a compression horn is driven with a ~matching output impedance, so want this as part of the system design.

GM