Acoustic Research AR-5 rebuild service

[RoyC]

6 hours ago, Aadams said:

IS it practical to a adapt a 3a mid to 8ohm use in an AR 5?

Sure, a 2.5 ohm resistor in series with an AR-3a mid will bring it very close to an AR-5 mid.

Roy

[ctjetta]

12 hours ago, Jimmie Holland said:

I just happened to stumble across the ebay listing a couple days ago and the seller had it listed for $89.99 and it was the second driver he sold. I wish I could have purchased both midrange drivers as they are difficult to find in good condition.

Jimmie

Lucky for you he had only the one; if had two I would have long ago purchased them. I'm happy you were able to use it.

[JKent]

9 hours ago, RoyC said:

a 2.5 ohm resistor in series with an AR-3a mid will bring it very close to an AR-5 mid.

So if my reading of the AR-3a restoration manual is correct, that would also apply to mids from the 10-Pi, 11 and LST.

Also, a mid from an LST-2 should be a direct replacement for the 5. So there are "some" choices.

Kent

[RoyC]

2 hours ago, JKent said:

So if my reading of the AR-3a restoration manual is correct, that would also apply to mids from the 10-Pi, 11 and LST.

Also, a mid from an LST-2 should be a direct replacement for the 5. So there are "some" choices.

Kent

Yes...and all of the LST-2 drivers are the same as the AR-5 drivers.

Roy

[Pete B]

On 8/9/2018 at 1:13 AM, RoyC said:

Sure, a 2.5 ohm resistor in series with an AR-3a mid will bring it very close to an AR-5 mid.

Roy

Do you know the DCR of the AR-5 midrange?  I saw 4.8 in an ebay ad but who knows if they zeroed

the meter.  I measured AR-11 mids at 3.8 DCR so based on this we could probably get away with

just 1 to 1.5 ohms in series.  2.5 will give up a lot of sensitivity have you tried it and compared?

[RoyC]

50 minutes ago, Pete B said:

Do you know the DCR of the AR-5 midrange?  I saw 4.8 in an ebay ad but who knows if they zeroed

the meter.  I measured AR-11 mids at 3.8 DCR so based on this we could probably get away with

just 1 to 1.5 ohms in series.  2.5 will give up a lot of sensitivity have you tried it and compared?

Pete,

Earlier front-wired 3a mids measure below 3 ohms. Later back-wired mids through the AR-9 typically measure 3.2 to 3.5 ohms. (Your AR-11 mid seems to be a bit on the high side.). Two later back-wired AR-5 mids I recently measured were both 5.2 ohms. All the AR-5 mids I've measured in the past have been around 5 ohms, with earlier front-wired specimens, like the 3a mids, being on the lower end of the range. I estimated the series resistance on the high side primarily because the white dot/"normal" setting of the AR-5 mid pot is nearly 50% off maximum (around 6.5 ohms in series), so there is plenty of output to be had with the AR-5 mid.

The prudent way to go would be to measure dcr and add enough series resistance to the intended low impedance mid to achieve 5 ohms. This would put it well within the desired spec. It should also be noted that the original "15 ohm" pots can vary by as much as .5  to 1 ohm one way or the other, and should be measured as well.

Roy

[Pete B]

This is the first I've heard that the front wired are so different from rear, didn't know that.

Seems the resistance depends on what you have to work with.

[Pete B]

On 8/10/2018 at 5:17 PM, RoyC said:

Pete,

Earlier front-wired 3a mids measure below 3 ohms. Later back-wired mids through the AR-9 typically measure 3.2 to 3.5 ohms. (Your AR-11 mid seems to be a bit on the high side.). Two later back-wired AR-5 mids I recently measured were both 5.2 ohms. All the AR-5 mids I've measured in the past have been around 5 ohms, with earlier front-wired specimens, like the 3a mids, being on the lower end of the range. I estimated the series resistance on the high side primarily because the white dot/"normal" setting of the AR-5 mid pot is nearly 50% off maximum (around 6.5 ohms in series), so there is plenty of output to be had with the AR-5 mid.

The prudent way to go would be to measure dcr and add enough series resistance to the intended low impedance mid to achieve 5 ohms. This would put it well within the desired spec. It should also be noted that the original "15 ohm" pots can vary by as much as .5  to 1 ohm one way or the other, and should be measured as well.

Roy

My mistake, I just looked at the AR-11 mid that I was talking about and I wrote 3.18 ohms on the 

back not 3.8.  That suggests that 1.6 ohms would might still be enough.

[Terkel]

I have a pair of original AR 5 units!