N801 type crossover build for 878B Santiagos

[Elitopus1]

Well, you guys are following Bowtie / Tom, and I think that is good. From everything I see about him, I have to say, he is most knowledgeable, mature, and has my full respect.

Tom comes out of the Pro Sound industry, from what I gather. I don't doubt the Ashley amps sound good.

I have a different background, than many of you. I have been chasing good sonics, ever since my Dad brought home that second 604B when I was eight years old. That was 64 years ago !

Lets talk ALTEC for a moment.

They were designed to be efficient. IF ( a big word ) you pay attention to amp-to-speaker wiring, and crossover wiring, and crossover-to-driver wiring, to IMPROVE the transfer efficiency of the entire chain, you have a speaker that seldom needs more than about 3/4 s of a Watt in a home / living room environment, to play VERY loud. I have a 2A3 SET amp, well made, and I never have a " want " for more power than what it produces.

A Manufacturer and long time audio-friend, Dennis Fraker, of Serious Stereo, used eight VOTTs in each movie theatre he owned, but at home - a JBL Paragon was his reference speaker. Dennis spent $10,000 on Ensemble wire, to make it "go", NOT the stock JBL wiring at all. When he rewired, he was able to go from his 30 Watt Jadis Push-Pull tube amp, to his newly designed ( 1989 ) 2A3 SET amp, operating at a single Watt or less, 90% of the time.

An Ashley amp, made some time ago, is designed for pro sound and HIGH power applications. The ALTEC, when well-wired internally, ( just like Dennis' rewired Paragon ), needs ONLY a low powered amp, one that is FABULOUS, optimized for the first Watt of playback.

If you run ALTECS with less than optimized wiring, then likely you may need a high-powered amp, to make up for the poor Transfer Efficiency, of the ENTIRE chain. But if you TRY to optimize the transfer efficiency, of the ENTIRE chain, I would think, on such a optimized speaker, an amp optimized for the FIRST Watt, will murder a 200 Watt Mosfet amp, in all parameters.

Let me give you an axample,

I have in my 2A3 SET DC amp, a set of bypass caps, experimentally used, that can do 64 A. continuous, but can do about 1500 Amperes instantaneous. It is in a L1/C1/L2/C2 B+ filter, leading to my Finals, bypassing C1 and C2.. It does the leading edge of a transient, starting with the bass, quicker and better than ANYTHING I have heard anywhere. I am guessing, six years ago, this technology did not exist.

But, my Altec friends, it gets better, I also use this cap experimentally, as a bypass cap in my home-brew 800 HZ 12 dB VOTT crossover, for both the the tweeter and the woofer capacitor bundles.


Likely, I am the only person, world-wide, having such caps, in the amps and also in the speaker crossovers

So, if we were to A-B amps , with my experimental set up, on my system, with my wiring, I think there will be "no contest ". On someone else's system, with less-than-optimized wiring, poor transfer efficiency, and a stock crossover of the " normal" variety, the special caps in my amp, may never be heard as they were designed to be heard, in my optimized system.

This is just some of MY audio system thinking, as of January 2017.

I am currently rebuilding my dual-mono 2A3 amp, into two pure monoblocjks, this month and next. The sole purpose for this rebuild is a true mono amp will allow me to execute a better layout, easier than a dual mono amp, and lay out is critical on such a piece.

I intend to get my system up and running, with a new passive attenuator, so I can use my Blu Ray player ( Pioneer BDP-09FD ) and my Phono system ( Sutherland battery powered PH3D ) for the rest of this year, and " happily ever after". I plan to "go out" with what I came in with, " ALTEC ". Its been a long journey in audio for me.

Now you may have a better unbderstanding, from where I am coming from. Hopefully, my posts may make more sense to some now. Its FUN to be back into the ALTEC camp. If anyone has any legitimate questions, ( other than the experimental cap, too soon ) contact me. Regards and best wishes, have FUN.

Jeff Medwin .... LowOhms.

How loud is "very loud" to you using a decibel meter?

Also I have heard about "tube" watts but really, comparing 1 tube watt to 200 SS watts? Can you make you woofers hit the baffle boards with your 1 watt? Because I can make mine hit with the 200 watts. There is plenty of power transfer there.
If I was losing 200 watts in the wiring I would need heatsinks on my wires

[LowOhms]

Greg,

If your speaker is 98 dB or higher, a single 2A3 will be superb, IF the amp is executed well, and IF the speaker is wired well.

My favorite amp in this world, for a well-set-up 604 or A7-800, would be the Serious Stereo 2A3 amp, any of them made since 1989, and the latest is the best. It just got written up by Stereophile reviewer, Herb Reichert, as being in one of the two best sounding rooms, among literally hundreds of audio displays, at the recent October 2016 RMAF show. A ex - movie theater guy named Dennis Fraker, designed and builds these today. He offers a GPA based 604 MLTL speaker solution also- VERY well done. Dennis is my friend, for 30 years now.

The topology of said amp is a two tube stages, direct coupled with three runs of 18 AWG silver wire, connecting the two stages, with a mu of 100 driver / input tube. The mu of 100 is essential. It has a tube rectifier, 5U4GB will do fine, and a L1/C1/L2/C2 B+ filter to the Finals tube, which is the latest JJ 2A3-40. The chokes are all under 10 Ohms DCR, and L1 does NOT meet old-fashioned "critical inductance" ever . The C1 and C2 caps are 50 uF or less, multiple high quality FILM caps.

The reason why the caps in the filter supply, at C1 and C2 are iIMPORTANT can be expressed in one sage audio sentence.....

" In the end, we all listen to a modulated power supply ".

I like to add

" How good is it, in quality and performance ? ".


If you seek more info on such an amp design, write to me and I can email you a paper I did on it.

Jeff Medwin

[xinu]

Greg,
...If your speaker is 98 dB or higher, a single 2A3 will be superb...
Jeff Medwin

Well, fortunately, my ALTEC 878Bs are rated at 91db pressure sensitivity. I say fortunately because the type of 2A3 SETs you are referencing are beyond the expense I could justify to change out all of the unworthy components and connections that amp would reveal.

[GM]

True, but compression horns want to 'feel' a matching impedance, so 2a3, 300b or similar SET tube amp for the HF, class A or A/B SS if at least the 1st 10 W is class A is about the best one can hope for without resorting to a monster low output impedance tube amp in its own Frigidaire for the woofer.

GM

[xinu]

Installed the first completed crossover today and after solving an unspeakerable dumb ass problem... it works! Now on to the next one.

Greg

[Elitopus1]

How does the new one sound compared to the original xover?

[LowOhms]

True, but compression horns want to 'feel' a matching impedance, so 2a3, 300b or similar SET tube amp for the HF, class A or A/B SS if at least the 1st 10 W is class A is about the best one can hope for without resorting to a monster low output impedance tube amp in its own Frigidaire for the woofer.

GM

Thanks GM.

Gee, I'can't hit the baffle board with my 515B woofer cone - using my JJ 2A3-40 amp. I never knew THAT was the performance criteria we need to aspire to in audio.

Dumb me, I will need to lay low now.

I was always under the impression it was music reproduction of voice and acoustic instruments we were all after. Silly silly me.

In fact, I have been sorta proud over the last six months, that under heavy bass transients, I can not even notice the 515B cone moving at all, to my eyes, and to my amazement. A friend, Dennis Fraker, told me" that was ideal damping of the cone", whatever that means, I don't know for sure. I'm no EE.

Oh well, we all live and learn. Thanks for posting.

Jeff Medwin

[xinu]

How does the new one sound compared to the original xover?

Haven't had much listening time at this point but immediately I've noticed 2 differences between old and new:

1) Upper midrange smoothness with new XO

2) I need to dial the L-Pad to 10 (out of circuit) to balance the HF with the old side L-Pad on the previous setting. The question I'm asking myself - Could the new x-over have introduced more loss or would this be due to the more delicate HF character introduced by the XO?

I'll have to get busy building the left side.

BTW I also recapped the 30904.

Greg

[BillWojo]

Greg, that looks good, nice build. Keep us posted, I keep getting side tracked with my own build, to much crap going on in my life at the moment.

BillWojo

[GM]

Thanks GM.

In fact, I have been sorta proud over the last six months, that under heavy bass transients, I can not even notice the 515B cone moving at all, to my eyes, and to my amazement. A friend, Dennis Fraker, told me" that was ideal damping of the cone", whatever that means, I don't know for sure. I'm no EE.

You're welcome!

Right, the performance goal is to have sufficient acoustic efficiency, driver control to minimize amplitude modulation distortion [AMD], so generally speaking a driver's linear movement is frequency limited, i.e. the wider its intended use bandwidth [BW] the less it should move, so while a subwoofer that's only reproducing up to 80 Hz can use all of its Xmax [assuming ~10% distortion is acceptable, which is very reasonable considering our near non-existent hearing acuity down low], a 15" used up to 500 Hz ideally should barely move when reproducing the signal's lowest frequencies and if used up to 1200 Hz, just 'buzz'; though as the M19 and many other designs have proved, our hearing acuity really isn't that good except in a very narrow BW peaking at 2 kHz on average, so while an A/B comparison will prove the lower AMD speaker the more accurate reproducer, the higher one is quite acceptable to most folks if its treble range that defines our critical [~250-2500 Hz 'phone'] BW's transients leading edges are critically damped.

Those of us that were 'raised' on the ~critically damped, acoustically efficient systems that very low power 'demands' tend to regard M19, etc., as more casual/party/DJ systems than for critical reproduction and considering what is by several orders of magnitude the most common consumer system designs in the world, only the 'phone' BW need be well done.

In short, regardless of type, lofty goals usually have to take a 'back seat' to financial realities and not all folks have the same performance goals, but most importantly, we all hear the same, yet not so much, so we should always keep this in mind when posting, i.e. unless there's some good technical knowledge available to the public at large to back it up, then it's just hearsay, personal opinion and should be presented as such, then leave it up to the 'gentle reader' to do as little/much research required to determine if it should be a design consideration/goal in their intended app.

GM