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AR-3A Amplifer Dilema


James Bond

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I picked up a pair of AR-3A's at an estate sale for fairly cheap and have come intrigued by them and contemplating how I can use them. I will have a small listening room, 12 x 10 with 8 ft ceiling. These speakers sound like they're to go up against the wall, so they would probably be perfect speakers for this room. On inspection the surrounds on the woofers are rotted, the cabinet will need redoing and one of the emblems was missing. Everything seems to be original. The grilles were still glued to the cabinet, so for not probably a lot of money I can get them into shape. My problem is I don't have a suitable amp to drive them, I think. I'm right in the middle of rebuilding an Eico ST-40. The ST-40 is only a 20 watt amp. The ST-40 is not designed to push a second amp if I wanted to use the bi-amp option on the speakers, although I think it could be done anyway. Besides that I don't have a second amp. I want to use all tube gear, so what would be the minimum wattage for both bi-amping and using a single amp? Any other thoughts on this or any other thread you could refer me to would be appreciated.

JamesBond

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James,

Surely "Q" has something laying around that would work fine! :rolleyes:

I used an AR amp - 60WPC - for my 3As for a while (both back when they were in production, and recently) but it is not really enough to get the best out of 3As. I'd recommend AT LEAST 100WPC. Currently I'm using a 300WPC amp (Moscode 600) for my 3As and a 270WPC McIntosh for the LSTs. Yeah, I know, sounds like it's backwards but the listening results favor that setup.

Don't know anything about bi-amping them - AR never suggested doing it so I assume some mods would have to be made to do so.

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I'm right in the middle of rebuilding an Eico ST-40. The ST-40 is only a 20 watt amp. The ST-40 is not designed to push a second amp if I wanted to use the bi-amp option on the speakers, although I think it could be done anyway. Besides that I don't have a second amp. I want to use all tube gear, so what would be the minimum wattage for both bi-amping and using a single amp? Any other thoughts on this or any other thread you could refer me to would be appreciated.

JamesBond

Eico ST-40!! My very first amp was the 40's big brother, the Eico ST-70. I bought as a kit and my grandfather helped me put it together.

We did an imperfect job, but we had fun.

The best part of the Eico ST is it will keep you warm on those cold winter nights.

You could use it to bi-amp your 3a's, but I strongly, strongly recommend that you bring out a 4th terminal. The supply voltages on those old tube sets, will fry any ss amp. That is, the three terminal by-amp is way too risky in my opinion.

The 20 watt ST 40 would do just fine on the mids/tweeters, but as Mexicomike suggests, you really want a ss brute (100 wpc at 4 ohms) driving those power hungry woofers.

Hope this helps ...

Regards,

Jerry

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Welcome 007 :rolleyes:

In case you did not notice it, BE SURE to download and study the excellent AR 3a "Bible" put together by senior members of this forum:

http://www.classicspeakerpages.net/IP.Boar...?showtopic=4095

good luck

Kent

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I'm sympathetic because I too like tubes. I tried to drive my AR-5s (which are an easier 8 ohm load) with my Sonic Frontiers SFC-1 integrated EL-34 amp, and while it made nice music it just didn't have the tightness that an SS amp brings. I am currently using a Terry DeWick-upgraded McIntosh MA-5100 amp, which is about 55 watts/channel, and it certainly makes nice sounds, but then I don't listen at high levels. I have also used a Sony VFET integrated amp which sounds very clean but doesn't seem to quite grab the woofers. Perhaps the amp that gets them up the most is my AR amp (original model) that somehow just seems to make the music interesting. I speculate that it has to do with the interstage transformers and the early design of the transistor output section, but that's just a guess.

I do have a McCormack 125 wpc amp with associated preamp combo that I have to get out of the basement and try out, just to make the comparison.

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  • 3 weeks later...
Guest fwardell

Bond . . . James Bond, let me know what you end up doing. I aim to do the same, i.e., drive my AR3as with tubes. Right now I'm using a Fisher 500-C (35 watt/channel) receiver like you're doing with your Eico. It's OK at modest volume levels. My research so far indicates that the normal AR3a bi-amp set-up won't work well with tube stuff and that a 4th terminal is needed. Even then, how do you tie two tube amps together? Obviously the cleanest method would be a single beefy tube amp/receiver but not sure what's out there.

Two options I'm considering: (1) Going Dynaco: single PAS-3 tube pre-amp with a 70 watt/channel ST-70 tube amp driving EACH channel. Not quite the 100 wpc desired but closer. The SS version would be PAT-5 and one or two ST-120s. I've heard that the ST-120 was designed with the AR3a in mind and it's close to "tube sound". (2) Using my Fisher 500-C driving a subwoofer amp like the NHT MA1 (SS though) in which mid and high connections are straight-through, unboosted (for that "tube sound" where it's most important) and the sub signal is amplfied just in the lower freqencies. I'm thinking the SS amplification for just the woofers wouldn't detract from the tube sound. Now, wiring it is another matter.

All opinions appreciated.

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I picked up a pair of AR-3A's at an estate sale for fairly cheap and have come intrigued by them and contemplating how I can use them. I will have a small listening room, 12 x 10 with 8 ft ceiling. These speakers sound like they're to go up against the wall, so they would probably be perfect speakers for this room. On inspection the surrounds on the woofers are rotted, the cabinet will need redoing and one of the emblems was missing. Everything seems to be original. The grilles were still glued to the cabinet, so for not probably a lot of money I can get them into shape. My problem is I don't have a suitable amp to drive them, I think. I'm right in the middle of rebuilding an Eico ST-40. The ST-40 is only a 20 watt amp. The ST-40 is not designed to push a second amp if I wanted to use the bi-amp option on the speakers, although I think it could be done anyway. Besides that I don't have a second amp. I want to use all tube gear, so what would be the minimum wattage for both bi-amping and using a single amp? Any other thoughts on this or any other thread you could refer me to would be appreciated.

Power requirements are hugely dependent on your desired sound levels. AR's original power recommendation for the 3a was 25WPC for "normal" listening levels, which in classic AR thinking means you and your guests at a dinner party can hear each other well enough over the music to carry on a conversation without people having to raise their voices to be heard. Even at that modest (by today's home theater standards) level your ST-40 is going to be underpowered.

If the ST-40 doesn't have preamp-out jacks, a rebuild project might be a good time to examine the schematic for the proper place to put a tap and look for a spot on the rear panel to add them?

I'm currently using an early-80's Harman Kardon amp rated at 45WPC @ 8 ohms and an estimated 60 WPC @ 4 ohms (roughly the same as the old AR amplifier), and it's capable of cleanly driving my 3a's to higher levels than I'd care to subject my ears to, but I don't think I'd hook a SS amp with less to them to maintain a safety factor.

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Bond . . . James Bond, let me know what you end up doing. I aim to do the same, i.e., drive my AR3as with tubes. Right now I'm using a Fisher 500-C (35 watt/channel) receiver like you're doing with your Eico. It's OK at modest volume levels. My research so far indicates that the normal AR3a bi-amp set-up won't work well with tube stuff and that a 4th terminal is needed. Even then, how do you tie two tube amps together? Obviously the cleanest method would be a single beefy tube amp/receiver but not sure what's out there.

Two options I'm considering: (1) Going Dynaco: single PAS-3 tube pre-amp with a 70 watt/channel ST-70 tube amp driving EACH channel. Not quite the 100 wpc desired but closer. The SS version would be PAT-5 and one or two ST-120s. I've heard that the ST-120 was designed with the AR3a in mind and it's close to "tube sound". (2) Using my Fisher 500-C driving a subwoofer amp like the NHT MA1 (SS though) in which mid and high connections are straight-through, unboosted (for that "tube sound" where it's most important) and the sub signal is amplfied just in the lower freqencies. I'm thinking the SS amplification for just the woofers wouldn't detract from the tube sound. Now, wiring it is another matter.

All opinions appreciated.

I see Dynaco being mentioned here several times. Remember that the AR demonstration exhibit at Grand Central Station was using 60 W (per channel) Dynaco amplifiers (MkII and/or MkIII).

John

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I see Dynaco being mentioned here several times. Remember that the AR demonstration exhibit at Grand Central Station was using 60 W (per channel) Dynaco amplifiers (MkII and/or MkIII).

But also remember that the live vs. speakers demonstration systems were set up to simulate the sound levels of an unamplified chamber quartet, not Black Sabbath.

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Right now I'm using a Fisher 500-C (35 watt/channel) receiver like you're doing with your Eico. It's OK at modest volume levels. My research so far indicates that the normal AR3a bi-amp set-up won't work well with tube stuff and that a 4th terminal is needed. Even then, how do you tie two tube amps together?

fwardell, you don't actually "tie" the amps together. That 4th terminal allows the amps to "float" a little.

By the way, I said, that you can actually use the 3 terminal bi-amp with your Fisher. It's just a little tricker. The 4 ohm tap on the Fisher's output transformers is at ground potential!

Two options I'm considering: (1) Going Dynaco: single PAS-3 tube pre-amp with a 70 watt/channel ST-70 tube amp driving EACH channel. Not quite the 100 wpc desired but closer. The SS version would be PAT-5 and one or two ST-120s. I've heard that the ST-120 was designed with the AR3a in mind and it's close to "tube sound". (2) Using my Fisher 500-C driving a subwoofer amp like the NHT MA1 (SS though) in which mid and high connections are straight-through, unboosted (for that "tube sound" where it's most important) and the sub signal is amplfied just in the lower freqencies. I'm thinking the SS amplification for just the woofers wouldn't detract from the tube sound. Now, wiring it is another matter.

All opinions appreciated.

Two ST-70's would be more than enough power. You can get away with far smaller amps when bi-amping, if you have the ability to strip off the lower frequencies for the mid/tweeter amp. That is, you'd like tone controls and a volume control for each speaker half.

I would bet the ss amp closest to tube sound is the AR amp; due the its interstage transformers.

To be honest, I'd recommend an ss amp to power the woofers. Those woofers thrive on current and you'll never hear that warm tube sound (caused by even harmonics) like you would on the mids/tweeters.

Wiring an ss amp to power the woofers is simple. Wiring another ss amp to power the mids/tweeters is also simple. Wiring your Fisher to power the mids/tweeters is a little trickier and will require you to hook up the speakers in a non-standard method,

Hope this helps...

Regards,

Jerry

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It sounds like you want to use the ARs primarily for listening and not home theater. I actually use a PAS-3 as my phono stage/tape deck preamp. If you are looking for a Dynaco be forewarned that they are hard to find in decent shape. If you decide to go with the PAS email me and I can give you more details.

As for power amps, the 120 is actually Dynaco's first SS amp. It is not a tube amp. I own one, but use an NAD as my main amp because i want the home theater. I gave up on the Japanese stuff a long time ago because I just don't feel it's a good match for AR. You want something with a neutral sound--Cambridge, NAD, Rotel. If you are going with tubes and want Dynaco the earlier tube amps--the 70 and the MkII are a good bet and show up on fleabay. But you really roll the dice when you pick those up and the prices I have seen lately are inflated. Another online site to check out is Audiogon, although they tend to deal with high end exotics. Remember. most Dyancos were sold as kits and so the quality depends on how well they were first put together. MacIntosh is, of course the gold standard, but you pay for that quality.

In short, you will probably pay AT LEAST $200-600+ for an old tube pre-amp/amp and still have to put some money into them replacing caps, etc. Saturday Audio has NADs for that price.

I would suggest you might at least want to give Onplane's advice a shot. Find yourself a good audio dealer--NOT a big box--and audition a few there in terms of price/sound. Once you have narrowed things down most decent dealers will let you audition one at home with your own speakers if they are sure you are serious about buying.

Good luck and keep us posted on your progress. Once you rebuild those ARs as per Carl's suggestion you will wonder how you could have listened to anything else.

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