IRS Gamma Servo Control

The servo control on my IRS Gamma system is acting up again. It appears to be functioning, but the output from the left channel is very low. I have found that the cable connection had a broken pin in the speaker cabinet. I don't think that is related but I could be wrong.

Anyway I have had problems with the output level of the servo drifting before. I know there are pots internal to the unit that can adjust the level, but that is probably just compensating for the real problem rather than fixing it. I have already replaced all the electrolytic capacitors inside the unit. In the past, the left side has always been higher rather than lower than teh right side, now the opposite is true.

Anybody have any ideas whahere I should look next? Is tehre any repair facility that I could send the unit to? I have the schematic, but not the assembly drawing for the internal pcb, so it is difficult to figure out which component is which wthout following the signal traces. Does anyone out there have any additional documentation such as an assembly drawing, service manual or calibration procedure?

Thanks,

J. Tucker

Hi there jtucker.The internal PCB diagram can be found at www.infinity-classics.de
I am experiencing similar problems but I think that it is the control driver.Have you tried swapping the signal path completly to see if the problem follows or stays the same.

I have also read on another forum subject that someone took there servo controller to Krell in CT.There is a technician that supposably fixes the servo controller.In addition to my answer,do you anybody who has any accelerometers for sale or even the control drivers for the delta/gamma because I am experiencing problems myself.If you come across any sort of proceedure on how to adjust the servo controller,please post it here for future AK members and referance.

As I am also having IRS Gamma Servo/Woofer/Accelerometer system problems. I don't know which component(s) are at fault. The left channel works correctly, but the right channel is freaking out. My Hafler DH220's right channel ended up with 300+mv DC on the output (same problem channel as the servo/woofer system). I hooked up another amp (QSC 1500 pro amp), and the left channel worked fine, but the right channel was wacky.
Next is to check the left channel (amp & servo) hooked up to the right speaker woofer/accelerometer and see what happens.
Any suggestions are welcome.
thanks,
(desperate) Dave

Update:

I disconnected the whole servo system.
I took the servo woofers out and checked the connections to the transducers. I will not report the embarrassing condition of this importand connection. Let's say I fixed it. Put the driver back in its place.

Then I started at one end are carefully wired the servo system back up properly.

It works, or should I say functions. It sounds terrible. Nothing under 60Hz. Running in Delta/extended mode off the VTL's sounded much better. Right now I listening to the VTL Compact !00's on the tops and the QSC 1500 on the woofers, biamped in Delta/extended mode. Me like. Gotta get servo fixed up rite!!

I wonder if the way my speakers were done @ re-foam is causing the servo to not correct properly. I need to find out which holes should be pulgged/open and what type of dust cap is proper. Also, shouldn't all 4 woofers be done the same way? They are connected in series in the Delta/Gamma system.

Just to follow up...

I recallibrated the gain and offset of both channels. I used a 50 Hz reference tone at faily low volume and matched the gain and offset form the input to the output. Recheck a couple weeks later and they are still right on. Sounds correct again. I guess I will just have to check these every 6 months or so.

jtucker:
There are a handful of us Gamma/Delta owners on AK that are in various stages of refurbish/renewal of our systems. We all have challenges at different parts of the servo system and I believe it's time to all get together to help each other out. Please PM me and I'll give you some of my ideas.
Thanks,
Dave

Well I have your answer. When I brought my Krell amps to get re-furbished I was talking to the tech (there are only 3 ) in the service are and he told me that he has fixed the servo controllers before. He does this as a side business. I suggest you call the Krell service dept in Ct. and ask for the guy who can fix the controllers. His name escapes me

I can't offer help, but on a related note is there a simple way to tell if the servo unit is working?
Can one simply remove the feedback cables/connector and expect to experience very different results, meaning the unit is working?
Infinity describes a "tap" test on a vertical axis of the control woofer and you are supposed to hear the "tap" in the other woofers. I can not produce this effect with any obvious results. I have not removed the cables or any potential "stupid" test, because I don't know the effects. I do know there is a destructive low frequency feedback that can ruin the speaker if it is hooked up wrong.

Reason I'm asking is I am driving both HF panel and LF towers with 330/w ch, and I have to cut the LF towers back by approximately 9 db due to overwhelming bass. I know these speakers are known to produce large bass, but if I can be sure everything is working I could sleep better.

Any advice?
Keith

I can't help much with the "tap test" at this point, as my servo is out of the loop. My best suggestion would be to tap as described with the servo unit swithch on and, then off, and listen/feel for differences. That would be very safe.
As for the -9db setting, there is a gain compensation switch on the back panel of the servo unit that you may find useful. It is used to compensate between different gain structures of the different amps that could be used in the system.

I could use your input, too...
http://audiokarma.org/forums/showthread.php?t=278543

Dave

Servo Control Unit - Issues and Questions

I'm a newbie to AK, but thought I would revive this thread as I'm having difficulties with my Servo Control Unit and was hoping to get some advice as how to proceed with correcting the problem. I located a pair of Gammas and SCU, without servo cables about 4 months ago, and have already refoamed the woofers, replaced one of the resettable internal speaker fuses and replaced one EMIT diaphragm, so the speakers themselves have been tested, sound great in Delta mode, and are ready to go. However, when I hook up the servo control unit all I get is a buzzing noise. The green servo light comes on as it should, and I can hear the source material if I turn it up, but the buzzing is unbearable. I know there are no issues with my power amps and preamp. I've already replaced the bridge rectificer and one of the voltage regulators, so the +-15 volt power supplies are working properly and a local repairman hooked it up to his scope and said there is no AC ripple. The buzzing sound seems like there is a ground loop somewhere, but when I install my other electronic crossover in its place, all is dead quiet. I can passively biamp the system without the SCU and have no issues whatsoever. I have tried hooking up the SCU with and without the servo cables I manufactured according to the information I found on the web (4 Pin DIN connections with shielded cables), and there is no difference. The "tap" test does not work; I can't hear sound from the other channel when performing this test. Also, is there a difference between right and left channels? I don't see any inidication of which speaker is left and which is right anywhere on the terminal cup. The manual notes that one of the accelerometer cables has a red mark on one end and this corresponds to the right channel. Is there any difference in the way this cable is manufactured versus the left channel cable? Has anyone experienced a similar problem with humming/buzzing? I don't think this is the full power oscillation the owers manual refers to, and I've triple checked my wiring to and from the SCU and speakers. Is this something that the open loop gain setting would produce if set too high? Any ideas or suggestions would be greatly appreciated.

engelder2 said:

. I have tried hooking up the SCU with and without the servo cables I manufactured according to the information I found on the web (4 Pin DIN connections with shielded cables), and there is no difference. The "tap" test does not work; I can't hear sound from the other channel when performing this test. Also, is there a difference between right and left channels? I don't see any inidication of which speaker is left and which is right anywhere on the terminal cup. The manual notes that one of the accelerometer cables has a red mark on one end and this corresponds to the right channel. Is there any difference in the way this cable is manufactured versus the left channel cable? Has anyone experienced a similar problem with humming/buzzing? I don't think this is the full power oscillation the owers manual refers to, and I've triple checked my wiring to and from the SCU and speakers. Is this something that the open loop gain setting would produce if set too high? Any ideas or suggestions would be greatly appreciated.

Click to expand...

When you checked you wiring on the servo cables, remember it is a mirror image. ALSO pull the servo connection from the back of the speaker and check that wiring and make sure (visibly) that the pins align with the wires of your jacks...all the way back to the SCU. I had this problem with my IRS betas. The cables were remade by someone and with wiring was to an open pin.

Also what is your gain setting on the back of the servo? 0, -6, or -12? I had to set mine ot -12 to work with my amps. But that did not cause a "buzzing" it caused something more like a small earthquake. I no longer own the speakers so this is all off memory. But maybe someone can chime in to tell you which woofer has the accelarometer on it, so you can pull that unit and see if it is intact. It is unlikely that both the left and right units are failing simultaneously.

Nikkoholic - I will double check the wiring of the servo cables back to the speaker and also to the input of the SCU. As far as the gain setting, I have it set to 0 right now, and it seems to be fine. I believe it is some kind of grounding issue at the input of the SCU at the RCA jacks, but I'm not sure. It could also be a loose ground somewhere else on the board. Thanks for your response and for your suggestions.

I had a bad ground in my servo unit, it was intermittent .. one of the RCA jacks had a boken ground, I found it by moving the rca jacks up and down a side to side very carefully on the back of the servo unit. They have the rca jacks mounted on plastic inside and can break.
It May not be your problem but it's good to check it.

My .02

John M

I had the same problem with my Gamma or Beta, can't remember for sure. Anyway, the issue was a very loud buzz. I checked the SCU & the woofers without success. The problem turned out to be a DIN receptacle in one of the speakers. My cat found the problem! One day while I was trying to rectify the problem, Goombah, the cat, decided to rest against the back of one speaker & the buzz went away. When I told him not to get near the speaker, he got up to move & the loud buzz came back, immediately. So, I checked the DIN plug & found that I could stop the noise if I tilted the connector upwards. I made some wood blocks with notches on top to elevate the connector to enable proper contact or something & the problem was solved. I never did try to fix the fault. I showed the new owner what to do when I sold the speakers. I now remember that they were Gammas. The Betas came later. HTH.

Hello John,

Yes, I believe this is a grounding issue and not something with the power supply. I will try to gently wiggle the RCA jacks around on the back of the unit while powered up and see what happens. Unfortunately for me, this is not intermittent, and the buzzing is always there when the unit is turned on.

buddyiramae,
I also noticed that the DIN receptacles are not that firmly attached to the back of the unit and can be wiggled around slightly. I will also try moving these around gently and see if the buzzing gets worse or does nothing at all.

Thanks for both of your suggestions. For now my Sumo Delilah electronic crossover is working well with no buzzing whatsoever, but I really want to get the SCU working to see/hear the benefits of the servo control to the woofers.

I don't think your problem is the servo cables-yet. Try to get it to work without the cables first. It won't work as intended, but the crossover part will work. When the signal issue is worked out, then plug in the servo cables and check from there. ALWAYS power down the system when messing with the servo. Obvious, but it must be said. Of course, also, I could be wrong....
Good luck, and keep us posted.
D

Dave has a good point also & you could check the rca jack outside grounds to each other or to a ground inside with a meter.

Good luck ..

John M

Hello John,

You were exactly correct! Thanks to you (and Dave & everyone else) for the suggestions. I checked the ground continuity between all 8 RCA jacks on the rear panel and only the outputs and bypass jacks were connected. The inputs are not being grounded. So I took a piece of wire and connected the ground of the inputs to any of the other jacks and the terrible buzzing completely subsided. Now I have to find the broken wire, or trace but that should be easy enough, since the problem is now isolated. Maybe the plastic piece is broken? I will fix and then try the servo cables and see what happens next. This RCA grounding issue seems to be a design flaw with the unit since it has happened to others.

I'll keep everyone posted on my progress with the feedback section.

FYI: My input jacks also failed; twice. Sometimes I get disappointed in the way that Infinity had poor implementation of fantastic ideas....