Whoa! This is a whole new ballgame since we must design for max efficiency, which among other things dictates a dead on Fb = actual Fs! What's its output impedance and I don't mean terminal rating unless it's a true matching impedance amp as we have to factor it in, raising Qts = bigger box.
Oy! Well this is something I did not consider and didn't understand, but it makes total sense as much as I can grok what you've just said GM. The amp was built by Alan Eaton in California, he makes them one at a time, so I've just written and asked him. You are referring to the impedance of the output trannies right? They're 60s Tamura iron, he builds these 45s around them, I hope he knows.
I'm not sure if this is what you're asking for GM, but Alan says "the input impedance from the volume control is 100,000 ohms".
Thanks alot for teh plot!
It is true that the HF response on the data sheet looks weird but by listening I find it very sweet using a stock Eminence crossover and a variable L-pad. Maybe I’m getting deaf with age. Celestion have also designed a few suitable crossovers for it for various applications but none for hifi use. I find passive crossovers so expensive now that I rather save for some DSP solutions. Anyway good luck with your project and please post pics of the build. Given the research you put in here I’m sure it’s going to be good. I’m more trail and error type of guy, I can’t be bothered with the theory and measurement I rather do by ear and instinct. I cannot recommend that approach but I can recommend the Celestion over Eminence Beta CX Asd1001 combo. I still think the Kappalite is very interesting. To bad it’s about to be discontinued.
Nope, ask for damping factor and if he's still clueless, then search 'amp output impedance' and probably have to measure it.
OK GM I've written him again and tried to 'splain, my guess is I'm about to learn how to measure amp output impedance. I'm making my way through the paper you linked, super interesting but I have to read it very slowly and three times each paragraph (okay maybe four). Thank you.
Question - am I looking for the impedance the speakers are "seeing" when they look at the amp? As in 2-4 ohms kind of thing?
EDIT: I hope he has an answer, trying to learn this is breaking my brain.
Question - am I looking for the impedance the speakers are "seeing" when they look at the amp? As in 2-4 ohms kind of thing?
EDIT: I hope he has an answer, trying to learn this is breaking my brain.
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Alan wrote back, and here is what he said:
"Since our amps do not utilize inverse feedback we have no means of controlling damping factor. Also we have a desire to maintain absolute simplicity in our circuit. Simplicity is one of the key factors in the sound quality of our amplifiers."
So.....that may not be very helpful, and the chance of me measuring this seems a bit beyond my capabilities. I was reading up on it last night and gave up after it seemed like people didn't even agree on the proper way to do it, and people seemed to be measuring different things.
I'll give the research another go when I'm home from work today, but all I have is a DMM, although I do have a little class D amp I can use as this seemed like one of the ways to go about measuring the DF.
At the end of the day, would it be possible to just try to make an alignment that's more 'one size fits all' efficient like we were designing for market? These speakers will probably see use with my 25-35wpc tubie (depending on output tubes) as well.
This amp is really worth the trouble, Alan's little 45s are cult classics and true old fashioned built-in-the-garage style, although I modded mine and dressed it up a bit. But now I'm wishing it was at least a 2A3 or something with a little more juice.
Keep in mind this little thing drove a pair of Klipsch RP600Ms decently, and if I remember correctly John Atkinson measured their sens. at 89.
Or should I just go all back loaded horn here, would that raise output a bit?
Apologies, I didn't expect this to be such a PITA, but maybe there's some learning in it for people besides me. I'm definitely all ears 🙂
"Since our amps do not utilize inverse feedback we have no means of controlling damping factor. Also we have a desire to maintain absolute simplicity in our circuit. Simplicity is one of the key factors in the sound quality of our amplifiers."
So.....that may not be very helpful, and the chance of me measuring this seems a bit beyond my capabilities. I was reading up on it last night and gave up after it seemed like people didn't even agree on the proper way to do it, and people seemed to be measuring different things.
I'll give the research another go when I'm home from work today, but all I have is a DMM, although I do have a little class D amp I can use as this seemed like one of the ways to go about measuring the DF.
At the end of the day, would it be possible to just try to make an alignment that's more 'one size fits all' efficient like we were designing for market? These speakers will probably see use with my 25-35wpc tubie (depending on output tubes) as well.
This amp is really worth the trouble, Alan's little 45s are cult classics and true old fashioned built-in-the-garage style, although I modded mine and dressed it up a bit. But now I'm wishing it was at least a 2A3 or something with a little more juice.
Keep in mind this little thing drove a pair of Klipsch RP600Ms decently, and if I remember correctly John Atkinson measured their sens. at 89.
Or should I just go all back loaded horn here, would that raise output a bit?
Apologies, I didn't expect this to be such a PITA, but maybe there's some learning in it for people besides me. I'm definitely all ears 🙂
Read the pearl audio critical woofer damping article post 41. This article comes from 1954 when tube amps were the standard. High damping factor in amps in 1954 was moderately expensive, and a bit rare.
They are talking about the tendency of a high fi woofer to pump voltage back to the amplifier due to the spring effect o the suspension & mass. The worst case of this effect is a large coil woofer with a big magnet, a big coil, and heavy cone mass, in a vented bass reflex enclosure underdamped at the resonant frequency of the driver. The worst case of a SS amplifier for holding the output voltage constant against the oscillation of the woofer is a Class A with no feedback. So you may find your Alan Little 45 lets the woofer buzz at speaker resonant frequency if any of that frequency is present in the source track. OTOH an equivalent wattage high feedback amp like a LM1875 or something,with the same woofer & bass reflex enclosure, would sound better at low bass frequencies.
Enclosures that damp off the resonant frequency of the woofer, like sealed boxes with a lot of stuffing, may sound better with the Alan Little 45. But they won't have any bass at the resonant frequency.
I listen at 1/8 watt (1 Vaverage) frequently to my 15" 98 db 1w1m speaker. But my class AB amplifier has a damping factor of 100, with significant feedback. No buzzing, even on pipe organ or low note piano tracks.
They are talking about the tendency of a high fi woofer to pump voltage back to the amplifier due to the spring effect o the suspension & mass. The worst case of this effect is a large coil woofer with a big magnet, a big coil, and heavy cone mass, in a vented bass reflex enclosure underdamped at the resonant frequency of the driver. The worst case of a SS amplifier for holding the output voltage constant against the oscillation of the woofer is a Class A with no feedback. So you may find your Alan Little 45 lets the woofer buzz at speaker resonant frequency if any of that frequency is present in the source track. OTOH an equivalent wattage high feedback amp like a LM1875 or something,with the same woofer & bass reflex enclosure, would sound better at low bass frequencies.
Enclosures that damp off the resonant frequency of the woofer, like sealed boxes with a lot of stuffing, may sound better with the Alan Little 45. But they won't have any bass at the resonant frequency.
I listen at 1/8 watt (1 Vaverage) frequently to my 15" 98 db 1w1m speaker. But my class AB amplifier has a damping factor of 100, with significant feedback. No buzzing, even on pipe organ or low note piano tracks.
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https://danielhertz.com/collections...urce-floor-standing-speaker-pair-black-walnut
Mark Levinson chose the Eminence for this system without the dustcap.
Mark Levinson chose the Eminence for this system without the dustcap.
IMO one reason people like these type of amps (SET, zero feedback etc) is precisely because they have low damping factor and the way they interact with the speaker is preferable to the listener. Therefore, we need to think carefully about designing a speaker with optimal damping because it might not be subjectivly preferable.
I'd like to suggest an experiment for the OP - take you class D amp and do some listening comparisons next to your SET amp. After getting handle on the differences, add some series resistance between the class D amp and the speaker. Start at 4 ohms, then 8 ohms and see how it affects the sound. This simple 'trick' will probably bring the class D a warmer more bouncy sound closer in character to the SET amp. It won't be identical of course, but note the change in character.
I'd like to suggest an experiment for the OP - take you class D amp and do some listening comparisons next to your SET amp. After getting handle on the differences, add some series resistance between the class D amp and the speaker. Start at 4 ohms, then 8 ohms and see how it affects the sound. This simple 'trick' will probably bring the class D a warmer more bouncy sound closer in character to the SET amp. It won't be identical of course, but note the change in character.
Looks more like a B&C to me. The Eminence has a tripple role surround while the B&C has the same double role surround. Also the gasket is totally different, same as B&C!
Well, I'm reading the Pearl Audio paper, and thank you indianajo for your concise summary, it helped me get the gist.
Just so I'm clear, higher impedance would result in higher damping of the woofer, right?
It seems like the DF of this amp is variable if I'm reading correctly, but probably over a slim range. Isn't there a "usual" impedance range for small set amps? I've read anywhere from 2-6ohms, really low.
I'll go back to reading that paper, and thanks to everyone for your posts.
Just so I'm clear, higher impedance would result in higher damping of the woofer, right?
This is interesting and it makes me think of all the people with these simple little SET amps, running them on all kinds of speakers and loving what they hear. If achieving critical damping is definitely the way to go though, Can someone please help me weed through the jungle of information and differing approaches and present a way to measure the damping factor of this amp? I don't have a scope or anything besides my DATS and my DMM.
It seems like the DF of this amp is variable if I'm reading correctly, but probably over a slim range. Isn't there a "usual" impedance range for small set amps? I've read anywhere from 2-6ohms, really low.
I'll go back to reading that paper, and thanks to everyone for your posts.
Another question. Let's say this thing does have impedance of 6ohms or something crazy low like that. How would I adjust the alignment to move closer to 'critical damping"? I'm guessing I'd want to use a smaller box,higher tuning. Or would I want to tune to the Fs, like GM was saying earlier? Is that just port tuning or some way of sizing the box for Helmholtz frequency?
What is clear from the pearl article, higher amp damping factor leads to damping of a woofer tendency to generate oscillatory voltages. I don't know if that is also higher amp output impedance. I measure damping factor by reading the sales brochure of the amp. The pearl article talks about increased feedback increasing DF. Your allen little 45 amp has no feedback.
Maybe people that favor class A amps have tiny little low weight woofers. You are proposing a speaker with a quite large woofer. You are talking about a bass reflex cabinet with very low bass extension, which unloads the woofer at low frequency. The faital 12hx240 has cone mass of 53.6 g. At least that is lighter than the Peavey 1505-8kadt I listen to at 1/8 watt with 68.5 g. But my vented cabinet is tuned to 55 hz, not 45.
As far as measuring anything AC with a cheap DVM, the ones I own produce random numbers on the 200 vac scale (the lowest) on music of any frequency other than 50 or 60 hz. The power line frequencies they are designed to measure. I can get somewhat accurate measurements of music with a Simpson 266xlpm analog meter which has a 5000 ohms/volte 2.5 vac scale, also 20 vac and 50 vac.
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I'm with you there indianajo, except for one thing - pretty much the standard for little SET amps is 15" woofers, more often with a giant CD in a big horn. High 90s+ sens., like the countless Altecs and Tannoys I drool over.
This whole thing about damping factor has really put me on my heels, I didn't know about it. I am starting to understand the principle, but I do feel a bit lost in the forest and don't want to fail at this project, which I'm pretty confident can work if I'm patient enough.
The article speaks about amp resistance, and that higher resistance leads to lower damping because of the lower current available to counter resonance oscillations.
I apologize if I seem dense, some of the concepts and terms are not familiar to me, and it's taking time to really internalize them in a functional way.
This whole thing about damping factor has really put me on my heels, I didn't know about it. I am starting to understand the principle, but I do feel a bit lost in the forest and don't want to fail at this project, which I'm pretty confident can work if I'm patient enough.
The article speaks about amp resistance, and that higher resistance leads to lower damping because of the lower current available to counter resonance oscillations.
I apologize if I seem dense, some of the concepts and terms are not familiar to me, and it's taking time to really internalize them in a functional way.
Apparently too much to ask you to do; I got this among a bunch of other useful info right away: Measuring output impedance and searching on-line audio generators there's numerous ones to choose from if DATS can't.......
Another old damping doc to refer to in the same thread
Need to read the posts after it also............
Need to read the posts after it also............
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Measuring output impedance
Yes, way back when I'd do a max flat alignment and suggest that they insert a 25 ohm pot in series to dial in a response to 'taste' in room and measure/replace with an appropriate power resistor or grid as required to get the desired power handling.
Just to clear something for Brian, higher resistance from the amp output (output impedance) gives 'worse' damping. 6 ohms output impedance would be considered extreeamly high. 1 ohm or lower is common even among tube amps. Less than 0.1 ohms easily achieved by solid state.
Usually outputs have a low impedance so current can flow unimpeded. Line inputs have a high impedance so they don't draw current.
Try the experiment I suggest and see if you like high output impedance.
Usually outputs have a low impedance so current can flow unimpeded. Line inputs have a high impedance so they don't draw current.
Try the experiment I suggest and see if you like high output impedance.