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Gershman A-G crossovers - pic

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Posted on February 22, 2021 at 14:52:18
BS64
Audiophile

Posts: 2423
Joined: July 17, 2000



I am finally getting ready to refurb my Gershman Avant-Garde's, original model. A couple of issues lead me to gutting them and tidying things up. First and foremost, a 25-30 pound burlap bag of tiny lead shot that had ripped open.

Then I found the crossovers mounted directly behind the woofers. Crossovers are wired-up with Audio Research HF-164 monster cable, the insulation of which is tacky/gummy, I believe due to the outgassing of the hot glue they used to hold everything together. Connections are slip-on type at the driver ends, and solder tabs cut to make a spade at the binding post end.

I bought some 20 AWG solid core, silver plated copper hook-up wire, and invested in a small solder pot and 1/2 pound of 7% silver solder. Goal is to solder the leads at the drivers, and make spades at the binding post end by dipping in the solder pot. Contemplating mounting the xovers outside the cabinets. Need to examine that possibility more closely.

Anyway, attached a pic for those who are interested. The blue wires that are tied together went to the toggle switch mounted to the binding post plate. It simply bypassed a resistor in the "on" position. So I bypassed the switch. I like my HF's. Not sure what role the white wire bypass plays. Hard to tell with all the glue covering the connections. But I will eliminate the slip-on connector and hardwire that jumper.

 

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RE: Gershman A-G crossovers - pic, posted on February 22, 2021 at 20:37:53
hahax@verizon.net
Audiophile

Posts: 3759
Location: New Jersey
Joined: March 22, 2006
Moving crossovers outside the speaker reduces microphonics in the crossover which can be significant. It will be interesting especially moving the crossover from being near to the woofer. The magnetic field of a near by magnet can affect the values of inductors.

 

RE: Gershman A-G crossovers - pic, posted on February 24, 2021 at 08:38:36
Palustris
Audiophile

Posts: 2176
Location: Cape Cod
Joined: September 12, 2008
"Moving crossovers outside the speaker reduces microphonics in the crossover which can be significant. It will be interesting especially moving the crossover from being near to the woofer. The magnetic field of a near by magnet can affect the values of inductors."

Good call!

If this were mine, I would attempt to find the schematic. I see iron core inductors and other low grade parts. When I was using Altecs, I reproduced the crossover using high quality parts and mounted them in boxes behind the speakers.

 

RE: Gershman A-G crossovers - pic, posted on February 24, 2021 at 20:41:18
hahax@verizon.net
Audiophile

Posts: 3759
Location: New Jersey
Joined: March 22, 2006
Not naming names but a friend of mine designed a crossover for a well known speaker manufacturer and he complained it didn't work. When he sent a picture of what he built from the plans the crossover was mounted on the woofer magnet.

 

RE: Gershman A-G crossovers - pic, posted on February 25, 2021 at 10:20:55
madisonears
Audiophile

Posts: 1550
Location: midwest
Joined: September 6, 2006
If you're going to solder leads directly to driver terminals instead of using clips, be certain to temporarily attach some sort of heatsinking device between the solder point and the voice coils. No matter how good your soldering skills, you might fry the insulation on the voice coils and end up with dead speakers. It's very easy to do, especially tweeters.

Clips, if they're clean and tight, are not such a terrible option.

Moving xovers outside the enclosure is always a good move.

You might also consider different gauge wire for different drivers, as the strength of current conducted is quite variable. I would not use coated wire, but that's a personal choice.

Peace,
Tom E
berate is 8 and benign is 9

 

RE: Gershman A-G crossovers - pic, posted on February 26, 2021 at 08:26:12
BS64
Audiophile

Posts: 2423
Joined: July 17, 2000
I thought about contacting Gershman about the schematic but decided to keep things simple. They sound very good as they are. But the negative aspects I listed in my original post were always on my mind while sitting in the sweet spot.

Speaking of the sweet spot, when I bought these speakers we were in a different house. My system was in the family room, allowing me to listen casually as well as critically year round. My system now resides in a semi-dedicated room upstairs and down the hall over the 2-car garage. I like the isolation of the room, but I don't like the isolation.

Most of my listening is done during the winter months. I literally go a month without firing the system up during the warmer, more pleasant months. I'd rather be doing yard work or hanging out by the pool. My point being, if I was listening more frequently I would put a little more effort into this refurb.

My long-term goal is to move on to something different. And preferably new. I got into this hobby in early 2000 and that was the only time I purchased a new pair of speakers. All my gear since then has been used except for the Cary 303/300 cdp and my most recent purchase of a Zero Zone tube preamp. I'd like to treat myself to a new amp and speakers and enjoy them for the next 20 years without the worry of re-capping, etc. But that won't happen for at least a couple of more years.

 

Insulation? Tweeter pic..., posted on February 26, 2021 at 08:45:35
BS64
Audiophile

Posts: 2423
Joined: July 17, 2000



Here's a pic of the tweeter. I was going to do 3 runs of the 20 AWG to each of the + and - from the xover to the tweeter. Twist the ends, loop through the opening in the solder tab and then solder in place. I see the VC wire on the back of the solder tab but I'm not sure what insulation you are referring to?

 

RE: Insulation? Tweeter pic..., posted on February 26, 2021 at 20:23:45
madisonears
Audiophile

Posts: 1550
Location: midwest
Joined: September 6, 2006
Every voice coil consists of a coil of insulated wire. The insulation is VERY thin and VERY important. If the coil overheats from too much current passing OR from any high heat source such as a soldering iron applied to the input terminals, the insulation will melt and adjacent winds of the coil will short circuit to one another. Dead speaker.

You do NOT need three runs of 20 gauge wire to a tweeter. A single piece of 20ga on each terminal is adequate. There is NO advantage whatsoever to adding excess wire to a tweeter, and it is very likely you can damage the tweeter terminals with too much weight hanging off of them or damaging the voice coil as detailed above.

Peace,
Tom E
berate is 8 and benign is 9

 

got it, posted on February 27, 2021 at 12:06:23
BS64
Audiophile

Posts: 2423
Joined: July 17, 2000
I was not envisioning the coil of wire wrapped around the base of the cone that resides within the magnet.

As far as wire gauge from xover to driver, I assumed one run of 20 AWG to the tweeter would be sufficient. But I want to cover all the bases while I'm in there. Maybe double up? That would be 17 equivalent. It would take 6 runs of 20 AWG to equal the 12 AWG it's replacing.

Then there's the mid and woofer. Would you recommend single runs to those as well? Or would you beef those up by a couple of runs? The Infinity RS-4/B's I bought as back-ups have what appears to be 20 AWG to each driver.

 

RE: got it, posted on February 27, 2021 at 14:05:12
madisonears
Audiophile

Posts: 1550
Location: midwest
Joined: September 6, 2006
Single 20ga to tweeter is plenty, and there is no advantage to adding more, and, actually, some risk. Double up for the mid, then maybe just leave the humongous stuff on the woofers that is already there. I know it's difficult to let something be when you have a hot iron and wire cutters in your hand, but really all the woofers need is current, and lots of it. Fancy wire will not do much for them. You could try running a strand of the new 20ga in parallel to the existing, see if that improves anything.
berate is 8 and benign is 9

 

RE: got it, posted on March 1, 2021 at 20:51:49
Duster
Audiophile

Posts: 16927
Location: Pacific Northwest
Joined: August 25, 2002
A single 20 AWG for the tweeter, twist two 20 AWG wires together for the the midrange (17 AWG aggregate/effective gauge), and twist four 20 AWG wires in a bundle for the the woofer (14 AWG aggregate/effective gauge).

You may achieve better integrity between the drivers by using the same wire for all the drivers, but each frequency band with double the cross section as you go lower.

 

Thanks, guys..., posted on March 2, 2021 at 23:10:50
BS64
Audiophile

Posts: 2423
Joined: July 17, 2000
Your advice will be applied accordingly. I like the idea of doubling up from one freq range down to the next. Either way, the sticky stranded copper is coming out. Just need to find the time. Hoping to get started this week.

 

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