For posterity, here are details on a fix I recently did to my Hafler Iris Preamp. Perhaps it will help others to keep their Iris up and running.
Problem:
The balance drifted slowly towards the left speaker. Nudging the balance or volume knob (local or remote) would cause the image to jump back to center, but in a few seconds it would drift back to the left.
Fix:
With a scope I found that the Left channel amplitude was growing over time (the Right channel was stable). After much pottering, I replaced two tantalum caps in the left channel circuitry. I replaced the 4.7uF at the TL082 Error Integrator, and the 2.2 uF at the LM308 E>I converter. Problem fixed.
Probably only one of those caps was bad, but it was easiest to just do both at one time. They both measured fine with my cap meter, in circuit and out, but under load one was obviously bad.
This is the second tant replacement I've done on this unit in recent years; next time I have to open it up I'll probably go ahead and replace all the tants and electrolytics just as a precaution.
I love this preamp - even after 30 years this thing still sounds great!
Problem:
The balance drifted slowly towards the left speaker. Nudging the balance or volume knob (local or remote) would cause the image to jump back to center, but in a few seconds it would drift back to the left.
Fix:
With a scope I found that the Left channel amplitude was growing over time (the Right channel was stable). After much pottering, I replaced two tantalum caps in the left channel circuitry. I replaced the 4.7uF at the TL082 Error Integrator, and the 2.2 uF at the LM308 E>I converter. Problem fixed.
Probably only one of those caps was bad, but it was easiest to just do both at one time. They both measured fine with my cap meter, in circuit and out, but under load one was obviously bad.
This is the second tant replacement I've done on this unit in recent years; next time I have to open it up I'll probably go ahead and replace all the tants and electrolytics just as a precaution.
I love this preamp - even after 30 years this thing still sounds great!
This might possibly be cured by adjustment of the trim pots.
For each channel there is a Lo and a Hi trim pot, referred to on the schematic as "Null CCW vol" and "+20db CW vol" respectively. They control overall gain, as well as gain tracking between the channels and also nulling of the output when the volume knob is set very low. (If out of adjustment, the volume in one or both channels can even INCREASE slightly as the knob is rotated CCW at very low settings).
Unfortunately I do not know a good procedure for adjustment, perhaps another forum member has this information.
-J
JB,
My IRIS preamp has an odd problem with balance. When I turn the balance knob to one side, I still get sound out of the other. Quiet sound but still sound. Its the same on either side. The only way I can kill a channel completely is to pull the amp input for that side. Do you think this is a balance control issue, or is it something wrong in a different place on the circuit?
At the age of this unit I'm thinking I might go in and start looking for juicy capacitors, so I'm not worried about getting my hands dirty on this one.
My IRIS preamp has an odd problem with balance. When I turn the balance knob to one side, I still get sound out of the other. Quiet sound but still sound. Its the same on either side. The only way I can kill a channel completely is to pull the amp input for that side. Do you think this is a balance control issue, or is it something wrong in a different place on the circuit?
At the age of this unit I'm thinking I might go in and start looking for juicy capacitors, so I'm not worried about getting my hands dirty on this one.
Hi everyone,
ON my side it doesn't move slowly to one channel, it happens suddenly The left side become probably 20% of the right side. I tought it was the volume know that was problematic but I had it check and it seems to be a more complex problem. It does go back when I am pushing the volume knob. Any idea on how to fix it ?
Thank you!
ON my side it doesn't move slowly to one channel, it happens suddenly The left side become probably 20% of the right side. I tought it was the volume know that was problematic but I had it check and it seems to be a more complex problem. It does go back when I am pushing the volume knob. Any idea on how to fix it ?
Thank you!
Your front panel volume and balance are probably dirty or perhaps starting to fail. They're onto-electronic instead of the typical potentiometer, and they were custom made for Hafler, so I have no advice on how to clean them. I don't think you'll be able to find direct replacements either. One of the guys here was selling a new version of the opto controls but I don't remember who it was.
Have you thought about adding a remote control? Thats one way of "fixing" your front panel controls. You just need the remote and the remote decoder that plugs into the preamp. The auction site has a remote in new condition for a reasonable price, and another guy has the remote cards for a very reasonable price. Before you buy the board, open your preamp up and make sure you need one - not many people bought these preamps without remotes, so yours might already have one. Its a daughterboard that "floats" above the main board. They're very easy to install.
Have you thought about adding a remote control? Thats one way of "fixing" your front panel controls. You just need the remote and the remote decoder that plugs into the preamp. The auction site has a remote in new condition for a reasonable price, and another guy has the remote cards for a very reasonable price. Before you buy the board, open your preamp up and make sure you need one - not many people bought these preamps without remotes, so yours might already have one. Its a daughterboard that "floats" above the main board. They're very easy to install.
The potentiometers for volume and balance are conventional. They merely control an optically isolated circuit.
My volume potentiometer was worn out and I have successfully replaced it. As I recall the volume pot was 5K, but you need a long shaft version.
Also check the wire connections from the volume and balance pots that go down to the PCB. I had a cold solder joint on one.
If you are having drift replace the 4 tantalums on the board with 35v versions.
I think not having a remote for volume control definitely contributes to faster potentiometer wear.
I'm working on a modern remote setup for the IRIS that is less expensive...
https://www.diyaudio.com/community/threads/making-a-hafler-iris-remote-control.381530/
My volume potentiometer was worn out and I have successfully replaced it. As I recall the volume pot was 5K, but you need a long shaft version.
Also check the wire connections from the volume and balance pots that go down to the PCB. I had a cold solder joint on one.
If you are having drift replace the 4 tantalums on the board with 35v versions.
I think not having a remote for volume control definitely contributes to faster potentiometer wear.
I'm working on a modern remote setup for the IRIS that is less expensive...
https://www.diyaudio.com/community/threads/making-a-hafler-iris-remote-control.381530/
Thats good to know. There was a discussion about this years ago and I was told that this circuit was proprietary and impossible to replace. George stepped in and said it was a cruder version of his LSA circuit.I assumed everyone was speaking of the potentiometer.
I'm curious - how is it that the pots on the amp and the remote switch control between the two using touch?
I'm curious - how is it that the pots on the amp and the remote switch control between the two using touch?
The remote has a capacitive touch sensor on the potentiometers. A "remote Vol/Bal" select signal along with 0-255 digital value is sent over IR link.
On the amp there is a dv/dt circuit on the volume and balance pots. If you turn the vol/bal on the amp then the remote vol/bal is immediately deselected.
Conversely, if you touch the remote vol/bal pots then they are again selected.
My alternate implementation for the remote will use conventional up/down left/right buttons on a conventional ir remote to control volume/balance.
FWIW, I posted the Hafler IRIS schematic in the above forum link.
On the amp there is a dv/dt circuit on the volume and balance pots. If you turn the vol/bal on the amp then the remote vol/bal is immediately deselected.
Conversely, if you touch the remote vol/bal pots then they are again selected.
My alternate implementation for the remote will use conventional up/down left/right buttons on a conventional ir remote to control volume/balance.
FWIW, I posted the Hafler IRIS schematic in the above forum link.
Fantastic info. See my comment in your remote replacement thread.
Side note: One of the preamps I'm working on here is giving me some trouble. I did the tantalum recap using UFG 2.2uF and 4.7uF caps, which is how I usually bring them back in line. This one, however, is doing a very odd thing: it powers up and settles into the usual input (Tuner, I think) but when I punch any other preset it goes into Video1 and stays there. I have to power it off and back on to get it to go into Tuner. I've fully recapped this one and it doesn't have a remote board mounted (I haven't serviced it yet), so would you say this is a logic chip issue? I have a full package of NOS chips if I need to replace anything.
Side note: One of the preamps I'm working on here is giving me some trouble. I did the tantalum recap using UFG 2.2uF and 4.7uF caps, which is how I usually bring them back in line. This one, however, is doing a very odd thing: it powers up and settles into the usual input (Tuner, I think) but when I punch any other preset it goes into Video1 and stays there. I have to power it off and back on to get it to go into Tuner. I've fully recapped this one and it doesn't have a remote board mounted (I haven't serviced it yet), so would you say this is a logic chip issue? I have a full package of NOS chips if I need to replace anything.
Does anyone have a recommended part number for the IRIS preamp volume/balance potentiometers? I am looking at 502-0312 NTE Electronics 50K OHM 1/5W LINEAR that appears to work. I picked up a nearly mint IRIS preamp that had the usual volume issues. Replacing the tantalums didn't correct the issue but replacing the rest of the electroylytics and resoldering the CLM8500/2 photoresistive cells did take care of the issue. Unfortunately the knobs were on so tight the volume pot was damaged.
Both set screws were removed first. I think they were over tightened and displaced some of the aluminum shaft into the knob. I did grip the shaft but there wasn't much to hold onto and ended up cracking the resistive board inside the volume pot. After the knobs were removed they still wouldn't push back onto the shaft. I was able to grip the shafts and use some lubricant to work the knobs back onto the shafts without further resistance.
That unfortunate. According to the schematic those are 50k linear pots. Easy enough to find but most of them show a 1/4 inch shaft, and I think the original part is an inch long, perhaps more. Strickland didn't use anything from the Hafler parts store to design these, either, because previous Hafler preamps used log pots for everything but balance, and the resistance was substantially different. I have a few sources to check with so I'll give it a look.
This is going to be difficult to find. If the part is anything like the other Hafler products it should be a 25mm actuator length, 6mm in diameter. Can you remove your potentiometer and confirm this? I have several IRIS here myself but they're assembled and I really would prefer to keep them that way.