Peculiar problem with IRS Gamma

[marknoir]

Hello all
I recently acquired Infinity Gammas in need of some restoration. From the start they played fine. EMIMs and EMITs need the usual magnet rust cleaning. But they have a very peculiar problem: while checking servo operation, I noticed that slave woofers move in different directions. So if I gently push the control woofer IN on, let’s say, left speaker, slave woofer moves out. On the right speaker it moves IN, in unison with the control woofer. System never goes into that horrendous bass loop feedback when controller shuts it down. I checked and re-checked wiring and slave woofers also seem to be wired correctly. Unsoldered and checked polarity of slave woofers, all correct. It’s a mystery to me... Oh, I have to say that somebody’s been inside, all circuit breakers are by-passed and zeners removed. I installed a fuse on speaker line temporarily. Any ideas what is going on in here? Seems like on of the accelerometers is kaput? Any help appreciated.

 

[okeeteekid]

Something has to be wrong for the woofer to do that, I would double check the wiring and even the crossover or even the fill in the cabinet, I don't know how the cabinet is for the woofers on your speakers but I would think the slave woofer would move out as the servo woofer is pushed in because they are in a sealed system, did you check this while the system was turned on? if so what does the slave woofer do when you push the servo woofer in with the system turned off?

Also how does the sound of the bass compare between the two speakers?

 

[marknoir]

Something has to be wrong for the woofer to do that, I would double check the wiring and even the crossover or even the fill in the cabinet, I don't know how the cabinet is for the woofers on your speakers but I would think the slave woofer would move out as the servo woofer is pushed in because they are in a sealed system, did you check this while the system was turned on? if so what does the slave woofer do when you push the servo woofer in with the system turned off?

Also how does the sound of the bass compare between the two speakers?

Yes, this happens with servo on. I understand now that one of the accelerometer circuits is kaput. Will have to trace it. If accelerometer itself is dead then Im in for some expenditure...thx for reply.

 

[7.62]

Congrats ! I sure hope your able to find the problem.

 

[marknoir]

So yes, one of the accelerometers is dead. Are they available at all? Anything can be substituted? If not, I might as well just part these out or use them as Delta only.

 

[okeeteekid]

Yes, this happens with servo on. I understand now that one of the accelerometer circuits is kaput. Will have to trace it. If accelerometer itself is dead then Im in for some expenditure...thx for reply.

Can you switch the speaker with the problem to the other channel of the SCU and amp to see if the problem is in the speaker.

 

[swechsler]

These are rare enough, please don't part it out. Use it as a Delta until you can find the correct woofer. They come up on eBay occasionally; certainly not cheap, but worth it for a speaker of this calibre.

The same woofer was used in the IRS V, Beta, and possibly the Epsilon.

 

[marknoir]

Ok, so I have calmed down a bit. Disassembled bot speakers. Found a disconnected ground wire on the control woofer in question Ready to reassemble. But, there is a slight difference between the two control woofers: one has a 2.4K resistor between plus and minus of the accelerometer sensor, and measures 881 ohms. The other woofer ( working) has no resistor and measures 1.34K. Should I install a 2.4K resistor on it too? Thanks in advance.

 

[marknoir]

These are rare enough, please don't part it out. Use it as a Delta until you can find the correct woofer. They come up on eBay occasionally; certainly not cheap, but worth it for a speaker of this calibre.

The same woofer was used in the IRS V, Beta, and possibly the Epsilon.

Will not part out! )

 

[rvito]

Some had the resistor some didn't. Some had a little circuit board on the woofer. When you lightly push in on the control woofer (top one) you should feel it push back. When you push in very slightly you should see the bottom one move in unison. When you check the wiring the woofers should be wired in series. If it doesn't push back the issue could be in the cables or plugs. Also the servo controllers are prone to bad solder connections where the rca plugs attach to the circuit board. Swap the speaker out that works with the one in question and see what it does then. I own Gammas and Betas and have a lot of experience with these.

 

[marknoir]

Some had the resistor some didn't. Some had a little circuit board on the woofer. When you lightly push in on the control woofer (top one) you should feel it push back. When you push in very slightly you should see the bottom one move in unison. When you check the wiring the woofers should be wired in series. If it doesn't push back the issue could be in the cables or plugs. Also the servo controllers are prone to bad solder connections where the rca plugs attach to the circuit board. Swap the speaker out that works with the one in question and see what it does then. I own Gammas and Betas and have a lot of experience with these.

Thank you. So I shouldn't try to add a resistor? So far I found a broken ground wire to the sensor on a problematic woofer. Will try to swap tonight.

 

[marknoir]

Some had the resistor some didn't. Some had a little circuit board on the woofer. When you lightly push in on the control woofer (top one) you should feel it push back. When you push in very slightly you should see the bottom one move in unison. When you check the wiring the woofers should be wired in series. If it doesn't push back the issue could be in the cables or plugs. Also the servo controllers are prone to bad solder connections where the rca plugs attach to the circuit board. Swap the speaker out that works with the one in question and see what it does then. I own Gammas and Betas and have a lot of experience with these.

Hi. Thx. Here's what I found: I took the woofers out and pulled out all stuffing. Of course on a non-working woofer ground wire from sensor was hanging loose. And woofers were connected with crimp-on automotive style plugs, which fell apart in my hands. Whomever worked on my Gammas before did a pretty lousy job. Now both woofers are working. They pass the “tap” test easily. But the “push” test, where all woofets move in unison, works only on one. It has no resistor across sensor terminals and measures 1.34K. The one that doesn’t move has a 2.4K resistor across and measures 840 ohms. So do my Beta woofers. You can measure this at DIN connector. Apparently, from my understanding, lowered sensor resistance (impedance?) is preventing SCU from reacting to very low, near-DC movements of the control woofer. I will remove the resistor today and check my theory. Beta woofers are next, and if that’s the case, sensors are fine, and it’s just that they don’t react to “push” test. I don’t know if I should remove the resistors or let them be...

My old Beta controller seems to be working ok but I can hear some buzzing. I will re-cap it soon. Controller that I got with Gammas is out of wack, bass is severely exaggerrated, I will re-cap it too, and then will try to find some info or somebody who knows how to adjust all the pots inside. Facility in Germany charges $800 to rebuild and update them, I know, may be mine just needs adjustment.

So today things look a bit brighter.
Thank you for your help and patience!

 

[rvito]

I had my servo control unit serviced by Bill Thalman at music technology. He did a great job and also is friends with Bascom King who designed the Scu. My Scu for my Gammas had a slight buzz and I resoldered the Rca connections on the board and it went away

 

[marknoir]

I had my servo control unit serviced by Bill Thalman at music technology. He did a great job and also is friends with Bascom King who designed the Scu. My Scu for my Gammas had a slight buzz and I resoldered the Rca connections on the board and it went away

Thanks for the info. I will look up Bill Thalman at Music Technology. And re-solder RCAs.

 

[marknoir]

After more searching the problem was traced to bad servo cables ))) All woofers are working now, this is a nice holiday present.

 

[okeeteekid]

Glad you got them working.

 

[rvito]

Awesome news

 

[jtucker]

It has been quite a few years now since I sold my Gammas. I did re-cap the controller at one point. Mine was always drifting so that one side had more bass than the other, less so after the re-cap, but still needed to be adjusted occasionally. IIRC, there are two pots for each channel, one for gain and one for dc offset. If you have access to an oscilloscope and a test tone CD, it is not too difficult to adjust them. I did a recap and adjustment for the late, great Bobby Shred (that tells you how long ago it was, he passed several years ago) also. If you decide to work on it yourself, I can probably answer questions for you. I am pretty sure I still have my notes on this.

 

[marknoir]

It has been quite a few years now since I sold my Gammas. I did re-cap the controller at one point. Mine was always drifting so that one side had more bass than the other, less so after the re-cap, but still needed to be adjusted occasionally. IIRC, there are two pots for each channel, one for gain and one for dc offset. If you have access to an oscilloscope and a test tone CD, it is not too difficult to adjust them. I did a recap and adjustment for the late, great Bobby Shred (that tells you how long ago it was, he passed several years ago) also. If you decide to work on it yourself, I can probably answer questions for you. I am pretty sure I still have my notes on this.

Thank you for reply! I did re-cap my SCU because electrolytics were kaput. Everything sounds very good now, but it would be great if I could adjust it. Yes, I have generator and scope. All I need is to figure which pot is for what...
PS I remember Bobby’s page well :-((((. Sadly we are all guests in this world.