• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

AR3a midrange distorting after restoration

David Brehm

David Brehm

New Member
Hi speaker experts,

I am trying to restore some 1969 AR3a's. I have followed the guidance from the speaker restoration pages, re-capped the speakers, and gotten the spider's on the woofer's repaired by Larry at vintage-ar.

I replaced the pots with some new ones from hifiaudio on ebay:
AR-3 AR-3a AR-2 AR-2ax AR-4 AR-4x AR-5 AR-6 wirewound potentiometer pot

But I'm still stuck. My issue is that I am occasionally getting distortion from the midrange drivers.

I took the midrange pot out, wired it again, and got it working. Then put it back and it started distorting again. I have wiggled every connection and cannot reproduce the distortion at will.

Did I make a mistake on the wiring? Is it the proximity of the two pots next to each other that is causing this? Is it something else?

How can I troubleshoot this? I have a second set of speakers with an A/B switch so I can go back and forth. I have test equipment, the REW EQ software on my mac and a mic to measure distortion.

I have attached a picture of the wiring. Any help would be gladly appreciated....

David Brehmar3a wiring.png
 
Register to hide this ad
Both midranges are distorting? Have another amp you can try?

You mention "midranges", but only one pot, so I'm not clear if it's both.

If it's only one, bypass the wiper in the pot with a jumper cable, and see
if that clears the sound up.
 
Last edited:
RxDx said:
Both midranges are distorting? Have another amp you can try?

You mention "midranges", but only one pot, so I'm not clear if it's both.

If it's only one, bypass the wiper in the pot with a jumper cable, and see
if that clears the sound up.
Click to expand...

***************
I replaced all four pots. They were shot...

There are 3
RxDx said:
Both midranges are distorting? Have another amp you can try?

You mention "midranges", but only one pot, so I'm not clear if it's both.

If it's only one, bypass the wiper in the pot with a jumper cable, and see
if that clears the sound up.
Click to expand...


**************
I replaced all the pots with new ones...
I'll try a different amp. I'll test the other midrange but both seemed to be distorting.

If I jumper the Pots, where do I connect the jumper. From the diagram, I would connect the green wire to #1 connector on the pot? or #2? or both?

upload_2020-6-26_18-35-27.png
 
Green to #1 looks like it would maintain the resistor coil of the pot while
bypassing the wiper.
 
RxDx said:
Green to #1 looks like it would maintain the resistor coil of the pot while
bypassing the wiper.
Click to expand...


So this would be like turning the midranges all the way up with the knob. Yes? Interesting.

Maybe I should get the midranges restored like GD70. I wanted to use these speakers to listen to Dave Brubeck....
 
Last edited:
Yes, the jumper would be all the way up.

I'd want to know they were actually malfunctioning before going to the trouble.
At least try another amp/preamp chain or two. Eliminate what you can that
might be causing distortion. If you've changed everything else and still have
it, then, yeah, they need some attention. That both are distorting seems less
likely to be a driver problem, but still doesn't eliminate them.
 
Roy C has found that the fibreglass under the mesh, can get into the dome voice coil. Removing and repositioning it can clear up the distortion.
 
Bypassed the pot. Still distorting.

when I removed the pot I turned the speaker on its side. maybe it shifted the fiberglass. I’ll take a look.
 
StimpyWan said:
Roy C has found that the fibreglass under the mesh, can get into the dome voice coil. Removing and repositioning it can clear up the distortion.
Click to expand...
That’s interesting as I thought there was a flexible sealer around the base of the dome that covers the VC. The fiberglass disk shift under the screen should not cause any distortion. You can use needle nose pliers to Nudge it to recenter it under the screen. Have you tried listening to them at low volume directly connected to you amp?

Roy just rebuilt the mids and tweeters or my 3s. I asked Roy to leave the screens off The mids so I could see what differences in sound I could hear with the screens and fiberglass damping disk off vs. on. Regardless, the fiberglass disk has nothing to do with distortion.
 
Last edited:
GD70 said:
That’s interesting as I thought there was a flexible sealer around the base of the come that covers the VC. The fiberglass disk shift under the screen should not cause any distortion. You can use needle nose pliers to Nudge it to recenter it under the screen. Have you tried listening to them at low volume directly connected to you amp?

Roy just rebuilt the mids and tweeters or my 3s. I asked Roy to leave the screens off The mids so I could see what differences in sound I could hear with the screens and fiberglass damping disk off vs. on. Regardless, the fiberglass disk has nothing to do with distortion.
Click to expand...

*** Can you show me the pictures of the mids when you took them out for repair? I looked for this last night but could not find it. -- David ***
 
StimpyWan said:
Roy C has found that the fibreglass under the mesh, can get into the dome voice coil. Removing and repositioning it can clear up the distortion.
Click to expand...

So you are saying the white part under the mesh is moving? Would I just move it around until it stops distorting?

So I stood the speaker back up, left it overnight, and it is not distorting any more. Thank you for your help. I'd like to get the to root cause of this to understand what is really going on...
 
GD70 said:
That’s interesting as I thought there was a flexible sealer around the base of the come that covers the VC. The fiberglass disk shift under the screen should not cause any distortion. You can use needle nose pliers to Nudge it to recenter it under the screen. Have you tried listening to them at low volume directly connected to you amp?

Roy just rebuilt the mids and tweeters or my 3s. I asked Roy to leave the screens off The mids so I could see what differences in sound I could hear with the screens and fiberglass damping disk off vs. on. Regardless, the fiberglass disk has nothing to do with distortion.
Click to expand...

**** if they start distorting, I'll try connecting them at low volumes directly to the amp bypassing the crossovers.... ***
 
David Brehm said:
So you are saying the white part under the mesh is moving? Would I just move it around until it stops distorting?

So I stood the speaker back up, left it overnight, and it is not distorting any more. Thank you for your help. I'd like to get the to root cause of this to understand what is really going on...
Click to expand...

I'm looking for the thread, at Classic Speaker Pages, where Roy C discusses midrange issues. As soon as I find it, I'll post a link.
 
Ok...well now it is sounding amazing! I'm wondering if moving it around freed it up?

Is there any advice on putting the woofer back in. It seems to be a really tight fit. Maybe I used too much 3M strip calk? Do you just use two strips of caulk along all the wood and then put the woofer on top of it? I did not have this much trouble on the other one...

Thank you for all the help. These are amazing sounding speakers.

David
 
David Brehm said:
Ok...well now it is sounding amazing! I'm wondering if moving it around freed it up?

Is there any advice on putting the woofer back in. It seems to be a really tight fit. Maybe I used too much 3M strip calk? Do you just use two strips of caulk along all the wood and then put the woofer on top of it? I did not have this much trouble on the other one...

Thank you for all the help. These are amazing sounding speakers.

David
Click to expand...
I use air duct sealing putty, which is very similar to what was originally used. Costs like 2 bucks for a block of it at Home Depot. I put it on the cab rolled up like a long worm, then work it down a bit covering the entire surface and both sides around the screw holes. Screwing down the woofer flattens the putty as the screws are tightened. Once done, gently push the woofer cone in and let it go. It should return slowly.

Glenn
 
I decided to jump in to clear up some apparent confusion regarding the repair of AR-3 and 3a midrange drivers. AR-3 mids frequently have output issues, and can often be refurbished. The AR-3a mid (ie David's mid) does not typically exhibit problems, and there is no way to restore it if it does. The voice coil of the 3a mid is covered by the cloth roll of the dome, and nothing can get into it.The mid drivers I refurbished for Glenn are AR-3 mids, which have a troublesome, coated, exposed voice coil gap...so apples and oranges.

I'm not sure what may have cleared up David's midrange distortion issue, but I'm sure it had nothing to do with anything under the mid's screen. It sounds to me like a possible unsatisfactory wire connection. If the problem is occurring with both mids, it is almost always the connection between the enameled wire of the small inductor and the wire of the midrange's #1 pot terminal. A common oversight is to fail to sufficiently clean the enamel coating off the wire before making the connection. This is easily the most common 3a midrange issue for novice 3a restorers.

Speaking of mids...After looking at David's photo, I'm wondering why there is a resistor connected to the mid's 50uf capacitor. If it is the small-value series resistor mentioned as a tweak for use with film capacitors in the 3a restoration guide, it shouldn't be there. That capacitor is not a film capacitor. (Frankly, given the nature of the variable level controls, I lobbied against the mention of these resistors with any type capacitor when we were putting the guide together.)

Roy
 
No way the speakers were tweaked, when re-attaching to the cabinet? Do they sound better, if you back off the screws, just a bit? :idea:
 
You must log in or register to reply here.
Back
Top Bottom