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I inherited these nice speakers from my father, and am planning to install new caps.
Considering driving them with an upgraded SCA-35 in my wife's system. Would that amp have enough power and match the speakers well? Or is it better to wait for something else with more power?
Thanks, David
Follow Ups:
It really depends on what size room the speakers are in, what kind of music is being listened to, and how loudly you or your wife listen. In a modest size room, if you're not listening too loudly, it should be OK. After all, Dyna designed the SCA-35 for modest systems, and they designed their speakers to be compatible with their amps in terms of power demands. But again, they designed the SCA-35 for modest cost systems. For example a bedroom system would probably be fine - unless you live in a mansion. However if you're talking a large room at head-banging levels, not a good idea.
The music also matters - a lot of pop music, especially recently, is compressed so the level doesn't vary much. On the other hand, simply recorded classical muscic can have a lot of dynamic range. As someone else has pointed out, it's not the average levels so much as the peaks that can take a lot of power.
I tried driving Dynaco A-25's with an SCA-35 and I did not like the results. It was fine for Simon and Garfunkel but useless for classical and rock. Note that I don't listen to music very loud and A-25's are very easy to drive.
Dave
Pass on it. Even if you don't listen real loud there is no substitute for headroom of which your scenario would have almost none. 3db headroom would require twice the power. If you are going tube things almost always go better when you don't run them at or near full boat.SS might not sound good near full boat either but it wouldnt shorten device life like it may shorten tube life in a tube amp.
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
Edits: 11/02/16
According to the chart at the link at the bottom of my post, the minimum power recommended for the Dynaco A-40XL was 15 watts. The SCA-35 just barely gets you there at the rated 17.5 WPC, but stock, it probably didn't meet that spec.You said your SCA-35 was upgraded, but didn't say how. If you haven't done the EFB mod , you might consider it for both better sound, reduced output tube wear, and getting a bit more power out of it. Given that it only costs a few dollars in parts, the mod is well worth it. Below is the "Before and After" (EFB mod) power and distortion spec chart.
EFB also reduces the 6BQ5 current draw from 35mA to 27mA per tube, increasing their life. In my case it allowed me to use the great sounding Gold Lion EL-84 tubes, which Jim McShane didn't want to sell me for my SCA-35 until I told him I had done the EFB mod. He had no problems selling them to me after he heard that.
Since you already have the amp and speakers, I'd try it, and see if you hear any clipping. As long as you keep the volume at reasonable levels, you're probably good to go.[Edit] I say "You're probably good to go" based on my experience while owning the power hungry Dahlquist DQ-10 speakers years ago. Their minimum recommended amp power was 60 watts per channel (if I remember correctly) and I used to run them with a 100 WPC solid state amp. I remember being very nervous the first time I tried driving them with a Dynaco ST-70, given that it was only about 25 WPC. But as long as I kept the volume reasonable, the ST-70 drove the Dahlquists just fine, and sounded far better doing it than the Jim Bongiorno designed SAE SS amp I had been using for many years.
That said, my disclaimer is that you're still technically risking your speaker's tweeters, even with softer tube clipping. I wouldn't hesitate to try it though, just don't push it to rock concert levels. Good luck.
Edits: 11/01/16
Thanks, I have been considering getting the SCA-35 for those speakers. it does have Dave's boards.
I thought you already had the SCA-35.
I'd still think it might have enough power for you, depending on your listening habits, especially with the EFB.
I might want a bit more headroom, but that said, I much prefer listening to music with my SCA-35 with the EFB mod than I do with my ST-70s, either stock or with the VTA input board. I've tried the VTA amp with original Mullard EL-34, Gold Lion KT-77, etc. but still find the modded SCA-35 more musical, even with the 7199 input.
Sensitivity has to be specified in order to make a good recommendation. However, the A-40XL is a sealed design, which implies not so good sensitivity. I suspect that more power than the 15 or so WPC PP 6BQ5s yield is appropriate. Something with EL34s or 7591s is probably in order.
Eli D.
Below: Underside of the SC ASR-433. Lots of Auricaps.
Below: KLH 23 (left), KLH 17 (right)
Below: Faceplate SC ASR-433 with black aluminum knobs.
Maybe enough power.....Maybe not.
I have a pair of KLH-17 speakers that I resurrected with the help of Bold Eagle (Jerry) and they sound absolutely glorious with a 12 wpc Stromberg Carlson ASR-433 driving them. Understand, that the power supply has been significantly upgraded so headroom is most certainly better but, it still only puts out a little over 12 wpc (14.4 wpc in 8 ohms is what the tech measured).
Re-sealing the cloth surrounds with GE 100% silicone bathtub sealant REALLY tightened up the bass. Subjectively, the bass went from a really loose sounding 80 hz. To a mucho tighter sounding low 40ish hz.
I have no idea what the efficiency specs are on the sealed box design KLH-17 are, but they play as loud as I care to listen with a push/pull EL84 integrated.
I guess there's only one way to know - Hook 'em up.
Meat; It's the right thing to do. Romans 14:2
The KLH 17's in their Model 20 alter ego were mated to a "claimed" 15 W/ch in the Model 20 compact system. The model 20 woofer was a 4 ohm version to get a bit more out of the little SS amp; but my recollection was that a Model 20 could play pretty loud.
I used my KLH 17's with a variety of amps; both tube and SS and always felt that 30-35 w/ch was about right. The Dynaco XL speakers used a more sensitive SEAS woofer than the original A25, gaining 2-3 dB for approximately 87 dB sensitivity and pretty close to an Advent or KLH 17.
The real key to unclipped levels is the amp's dynamic headroom. A Stereo 70, for example, on dynamic musical peaks, clips at about 45 w/ch, as does the MC225, and so did the Pioneer SX990 I had at the time.
Jerry
A Stereo 70 (or a pair of Mark IV's) would hit the sweet spot with any of those speakers except the Advent, which was not a tube friendly load, IMO. Of course more power wouldn't hurt, but less power would not work for me.
Dave
A watt or two into even an inefficient speaker is quite loud on average. That's not the problem. The problem is very fast peaks which in classical music can be 20 to 30 dB once in a while. That's 100 to 1000 times the average power. Then your peaks are clipped destroying fidelity there. And if the amp isn't super stable it may oscillate for a short time again hurting fidelity. And worst of all the amp may oscillate at full power at high frequencies which may blow a tweeter. And this is especially true for older tweeters. Modern ones are much more robust.
So too much power(in a good amp) is better than too little. The one plus with a small tube amp is that if driven into oscillation, the clipping is usually less chaotic than a solid state amp making it less dangerous for tweeters.
So what are you doing with the KLH 23s? That was always one of my favorites in the KLH line.
Below: Fisher 500c with 220k (instead of the original 330k) grid resistors, and Russian K-40 coupling caps.
Below: Big slab of wood sitting atop of a antique sewing machine frame.
Fisher 500c and a cheap carousel spinner.
The KLH 23s are sitting atop 3 gallon Redwing crocks at the hunting cabin where the Paradigms (pictured) were.
It's not really a cabin per say as its a year round place. We try to keep it tip top just in case Julian Assange needs a place to hid out if it gets too dicey in England......At least until Trump gives him asylum.
The Paradigm Studio Reference 40v3's are now in my listening room while the crossovers in my horns get updated/modified.
Meat; It's the right thing to do. Romans 14:2
I'd hang out there myself.That would be perfect for old Julian.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
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