AR MGC-1

[Guest]

I am looking for anyone who owns a pair of these rare AR speakers. I am doing a complete restoration of a pair and would like to share information etc.

Thanks

[kkantor]

I stop by here from time to time, and would be happy to answer any questions I can. But be forewarned... I am opinionated on the topic....

[Guest]

Dear Mr. Kantor

Thank you so much for your response. I have been unable to find any information regarding your design other than reviews in several older audio magazines. The pair of MGC-1’s I found are in good working condition so I have been able to set them up and run them in a bit. Both myself and my colleagues in the film music industry (my profession) were very impressed by the soundstage and detail this design provides. What an amazing alternative to the multi-channel madness in the audio/video wars currently underway. I am aware of the limitations that some older designs provide but, I am determined to restore these speakers and if possible upgrade any of the components if possible. I have been able to find new (original) replacement drivers for all but the dual-driver plate. I was informed that the midrange dome was not repairable because the parts are no longer available. I have been searching eBay and other sources for other AR speakers that used this driver in hopes of finding a replacement (just in case…). Do you have any thoughts or information on this? I am also looking at the crossover and would like to replace any of the older parts that might be deteriorating because of their age to avoid potential problems. The controller amp is in excellent condition but I wish there were some way to get the schematic in case repair is necessary at some point. All in all, I am looking for your advice and thoughts on this wonderful and unique speaker design and any assistance will be greatly appreciated. Thank you so much for all your wonderful designs over the years that have brought so much enjoyment to myself and countless others.

Sincerely

Patrick Kennedy

Digital Music Technologies

[kkantor]

Thanks!!

1- Somewhere, I have a circuit diagram for the control unit. But "somewhere" is a tricky concept, as in a rental storage unit piled high with boxes. I will look for all the documentation I can find. If we get lucky, it could be days. Unlucky? Months.

2- I don't remember anything about the crossover topology, nor do I remember having a print. But I can trace the circuit from my pair without too much trouble. Once I dig them out....

3- The dual-dome was a service nightmare. That's the main reason it was discontinued. If yours is working, count your blessings. There should be no reason to mess with it unless it was damaged due to power abuse. In this case, a really skilled driver person, with access to specialized parts, glues, tools, etc, could repair it. But this is far beyond the capability of most speaker repair places. Perhaps a bribe-able tech at a speaker company. If needed, I will ask around. Also, it is always worth contacting Alex Barsotti at AB Tech Services. You never know what he has around. 1-800-225-9847.

4- If I were to ever redo my pair, I might replace the external processor with a small collection of pro rack gear that would accomplish the same functions. This would allow much better bandwidth and S/N from the side speakers than the technology of their day allowed. You would basically need a L/R matrixer (such as a Behringer EX-1), a digital delay, a filter and an amp.

5- The deep bass was always a weak link on the MGC-1, in my opinion. The Q is too high, as is Fs. Think subwoofer. Or skill saw.

Your turn....

[Guest]

Hello Ken

Sorry for the delay in response but, I was on the east coast on Feb. 11th and decided to stay with my friends during these difficult times.

Thanks so much for the information, I really appreciate it.

I have managed to track down two pairs of the mid/tweeter plates so I feel better now about having some spares.

Work is progressing on the speakers. We have removed all the drivers and have been testing them. The crossover is quite amazing and rather complex. I know from past experience that some of these components can go south after about 10 years and that a simple replacement of a few parts along with upgrading of the internal wiring can make an audible difference. Here is the plan so far and any comments or suggestions will be appreciated.

1. Remove and test all drivers

2. Remove Crossover and check for defective, aging or failing parts. Replace as needed.

3. Replace and upgrade all internal wiring.

4. Replace umbilical cable between speakers and control unit. Also, check connectors for possible upgrade.

5. Replace speaker connectors.

6. Investigate improving bass performance.

Now for the tricky part.

6. Go over control unit. Clean and replace any parts as needed. Look for ways to improve performance (if any).

7. Repair cabinet and grill covers. (the previous owner drilled huge holes in the base of each speaker to accommodate very large spikes).

And so, thats the basic plan. I am not in any huge rush to finish this project so if you can come up with any suggestions or materials after you locate your pair etc. I will look forward to anything you can provide. Unfortunatly, the owners manual on the web is hard to read and does not seem complete. I have only been able to locate reviews from Audio, Stereo Review and High Fidelity. I also believe a British publication reviewed these speakers but no luck there yet.

Finally, I have two basic questions.

1. Amplifier power? They seem rather hungry. Did you try them with tubes? Do you remember what Amp you were driving them with?

2. Room size. Was an ideal (or near ideal) room size ever determined. Given the unique properties of this design any suggestions?

Thanks and best regards

Patrick Kennedy

[Guest]

Sorry for the stupid error above. I, of course, meant Sept. 11 not Feb.

Sorry

[kkantor]

hi hi....

1- Yes, of course, always a good idea.

2- Yes, but try to replace crossover parts with similar units. Trying to "improve" the quality of crossover parts can mess up the target response, assuming the designer was experienced enough to include real-world component behavior into the mix.

3- Replace, sure, but careful about "upgrade", per my comments above.

4- I wouldn't suggest replacing this cable if you don't have to. It was hard to build a cable that passed high level output and low level input signals in such a manner that oscillation would not occur. Unless you are really willing and able to tackle that level of cable design sophistication, I would leave well-enough alone.

5- Why?

6- Yes! For political reasons I don't want to remind myself of, the MGC bass was under-damped and not very deep. A properly damped 10" sealed woofer would be my choice. But, you know, knock yourself out.

6a- The electronics in the control unit, are adequate, but not great. But they only effect the side-firing drivers, so they don't have a huge influence on the sound. One thing I would like to do is extend the bandwidth of the side speakers up from the present 5 KHz to about 10+ KHz. No way you are going to be able to do that with the CCD delay lines that are currently used. Too much noise, too low a sample rate, etc. You would need to design a simple DDL to replace them, or use an external box, as I have mentioned elsewhere in this thread.

7- OK.

1- Power Question:

Any good speaker is going to benefit from the availability of an excess of clean power, and I would use 200+ W/ch myself. I'm not very fussy about amps... I don't think SS ones sound very different most of the time. At AR, we had all kinds, mostly "pro", like Crowns and that kind of stuff. We found the newly resurgent tweakiness about power amps rather comical.

Tubes? Hey, if you don't mind the power limitations, and like the sound of the distortions, go for it! I wouldn't use anything but tubes on my guitars, but never found them to be more than equalizers when it comes to hifi.

2- The MGC-1's seemed to me to work best in mid-sized home listening rooms, though I have gotten good sound in venues as big as, say 40ft x 50ft, given reasonable room damping and lots of amp power. I think the bass air-movement limitations of the originals were the main problem.

Enough for tonight.... ready for your next questions!!

[Guest]

Hello,

I have a pair of MGC-II, I've just wondered what is the difference between MGC-I AND MGC-II?

Any help would be much appreciated.

CWILSON

[Guest]

Hello

If you check the "Classic Speakers" section of this website under AR/MGC-1 you will find a picture and manual that should answer your question regarding differences between these speakers.

Best regards

Patrick Kennedy

[Guest]

Hello Ken

Thanks for all the great information in your last note. I am still waiting for the MGC-1 cabinets to be returned to me but don't expect them until early Jan/02. We finished working on the control/amp unit and ended up just cleaning pots etc. Without a schematic it would not be practical to attempt any changes. It seems to be working fine and is "quiet" so that will be OK for now. I particularly appreciated your comments regarding the connecting cable between the speakers and amp. I could tell it would be a tough replacement and didn't want to go there at all. The problem we were having was solved by re-seating the connector so it wasn't a short in the cable after all.

I only have one question this time and that's regarding the crossover. So much has been written in this forum and others about aging crossover parts and how they can change values and, in some cases, destroy drivers. Upgrading parts can sometimes totally change or ruin the sound of a speaker. Do you have any suggestions as regarding the Crossover of the MGC-1? There is a schematic of the MGC-2 crossover on this site but it is completely different so as to be of no help at all. Do you have any suggestions regarding possible vulnerabilities in the crossover that could be caused by age? I know that this may seem extreme but I have worked on old speakers before only to have a crossover component go bad after a few weeks of completion. It's very frustrating. You also put a "Why?" after my remark that I was going to replace the speaker connectors on the back of the speaker. I am doing this because I use spade lugs most of the time on my bigger amps. The older speaker connectors often crack when you tighten them so it's more practical to change them for something more heavy duty to avoid this problem.

Thanks again and I hope you have a great holiday season.

Patrick Kennedy

[kkantor]

Electrolytic cap technology was starting to get good around the time the MGC-1's were built. I have never had to replace any in my pair, but I realize that that might be, to some extent, luck. At any rate, quality speakers made in the 80's should have an indefinite lifetime, provided they were not exposed to really excessive power or ambient heat. Speakers made in the 50's, 60's and 70's a totally different story, and almost always need new caps.

I suppose you need to use your intuition, your ears and maybe a good capacitance meter. If you do decide to replace, try to find reasonable matches to the originals, and avoid expensive "improvement" parts. We knew what we were doing when we voiced a crossover, and the parts characteristics are factored into the response. It you replace an electrolytic with a film, for example, you might wind up with a treble boost, or an underdamped resonance.

I don't think I have an MGC-1 schematic, but I will dig around. You could ask Alex Barsotti at AB Tech. 1-800-225-9847.

Have fun!