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Audible Illusions Modulus

Can you drop me that note too please?
I'll say it out loud- the microphonics are a result of unintended VHF oscillation from using a high gm tube. The cure is a grid stopper resistor, typically 1k, placed right at the grid pin.

The 6DJ8 familay are great tubes but you have to be very careful with them since they want to work at RF whether you want them to or not.
 
I had a phono preamp, for moving coils, from Roger Modjeski. It was all 6DJ8s and worked without any problems. I'm guessing he was competent in the circuit details for it to work at those high gains while being quiet.

I have to say, anyone not using a grid stopper on those tubes for audio is certainly incompetent. I expected the fix to be more esoteric than that.
 
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have to say, anyone not using a grid stopper on those tubes for audio is certainly incompetent.
There's a lot of that in the tube world. I've also seen grid stoppers that were placed too far from the pin, through an inch or two of PCB trace. It's an invitation for disaster.

Roger was a fine designer. With his and Tim dP's passing, there are very few of them left.
 
If you ever pull it out and are feeling ambitious, drop me a note and I'll walk you through how to cure that.
Thanks for the offer. It was my preamp for a couple decades. I retired it a few years back when it stopped outputting sound. I reached out to AA and asked about sending it to them to go through/ recondition, and retube, and the guy told me it wasn't worth it. He offered to sell me a used M3, but he had no interest in working on mine.

The dampening rings, etc. I tried on the tubes over the years had very little effect. Overall microphonics were just a minor annoyance. But for the last 10 years of its life -0-- in my current house -- it would occasionally pick up CB or walkie-talkie signals and blast them out at a pretty good volume considering I left the volume knobs turned very low if I was not listening at the time.
 
I have an AI Modulus IID that I picked up on eBay in the early 90s for I think it was $750. I've been through many DACs, speakers and power amps over the years, but the IID has stayed. Totally love it. It adds a gorgeous warmth and three dimensionality to the sound, with no audible distortion or muddiness. Of course, I barely listen to my speaker system anymore--mostly only to headphones--but I don't plan to ever part with it.
 
The dampening rings, etc. I tried on the tubes over the years had very little effect. Overall microphonics were just a minor annoyance. But for the last 10 years of its life -0-- in my current house -- it would occasionally pick up CB or walkie-talkie signals and blast them out at a pretty good volume
Again, classic symptoms of not treating a high gm frame grid triode casually in the design and layout.
 
Should I be concerned about this being hard on tubes, leading to issues? How often do I need to change the tubes? The company is reputed to have very poor customer support. I'll be using it with four 100 watt amps so I'm worried about reliability.

 
Should I be concerned about this being hard on tubes, leading to issues? How often do I need to change the tubes? The company is reputed to have very poor customer support. I'll be using it with four 100 watt amps so I'm worried about reliability.

It needs to be modified by a competent tech. Or tossed and a competent preamp substituted. Throwing new tubes at it is a futile (and expensive) endeavor.
 
The manual says 4” minimum vertical clearance. Will this be okay?
IMG_1105.jpeg
 
I got it working, but it seems only the tape input works. It add tons of gain and my DAC is high output so I have to turn the volumes down to 2 notches or it's super loud. With nothing playing, I hear hissing and popping, rushing and some buzzing. Also it sounds a little distorted. I'm probably going to change the tubes today to see if that's helps any.
 
I got it working, but it seems only the tape input works. It add tons of gain and my DAC is high output so I have to turn the volumes down to 2 notches or it's super loud. With nothing playing, I hear hissing and popping, rushing and some buzzing. Also it sounds a little distorted. I'm probably going to change the tubes today to see if that's helps any.
It’s oscillating. New tubes will either not fix or not fix for long.
 
It’s oscillating. New tubes will either not fix or not fix for long.
Should I have it looked at? The “rushing” sound is not bad with music playing, with levels set right.

The distortion I'm hearing might just be normal tube distortion.
 
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Should I have it looked at? The “rushing” sound is not bad with music playing, with levels set right.
You need the grid stopper resistors SIY has written about. Those are a pretty simple addition for any decent tech with a smattering of tube knowledge. I would be leery of placing it so close to a TV as that may emit some higher frequency junk that would cause the oscillation. If you get the grid stoppers in place not likely a problem.

In my friend's experience with them, some tubes were fine for a couple years at a time and some were not good right away. NOS Sylvania tubes from the 1960s or JAN 6922 tubes worked well in his. I'm not up to date on what is available these days.
 
the TV doesn't appear to affect the sound, at least turning it on or off makes no difference.

The issue is hiss and slight hum when close to the speakers without music playing. Not really an issue with music playing, but will new tubes possibly fix this? Or are you saying it needs modification anyway?

I can get some today but not sure if the Russian ones are available, I may go with mil spec American tubes.
 
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The tube rush doesn't change much with volume change. That means it's not the tubes, right?
 
I could swear I had one of these loaned to me in the 1990s. I remember it as being a competent but very "tubey" sounding phono preamp, a bit noisy. Nothing all that special. I recall the phono section of a Scott 299B I owned sounding better.
 
The tube rush doesn't change much with volume change. That means it's not the tubes, right?
No, it doesn't mean that because the volume control is before the tubes. If you're hearing rushing, buzzing, distortion, and popping, you've got oscillation. 6DJ8-family implemented properly are very quiet tubes unless the stage gain is set ridiculously high (which could be).

Honestly, you probably don't need a preamp if your source is a DAC that has variable gain. If you insist on having a preamp, get a competent tech to install grid stopper resistors right at the tube pins (pins 2 and 6 for that type of tube).
 
The sound is mostly rushing, with a very slight buzz in the left side. It doesn't change much with volume changes. I'm thinking of taking it to my tech and will mention what you said.
No, it doesn't mean that because the volume control is before the tubes. If you're hearing rushing, buzzing, distortion, and popping, you've got oscillation. 6DJ8-family implemented properly are very quiet tubes unless the stage gain is set ridiculously high (which could be).

Honestly, you probably don't need a preamp if your source is a DAC that has variable gain. If you insist on having a preamp, get a competent tech to install grid stopper resistors right at the tube pins (pins 2 and 6 for that type of tube).
 
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If it is hissing and popping, then I would return it.
(Mine was quiet.)
It's not popping, it's more of rushing sound. My friends says "it's nothing" since it's only audible with your ear placed against the speaker.
Am I over-reacting? I can get new tubes but I'm going to wait and see how it goes for a few days, then maybe have it looked at by my tech if I am still not happy, and let them decide if it needs tubes or not. Also I will mention the mod SIY has talked about.

Also the sound could be from system matching. My amps are 100 watts x 4 so lots of power to amplify the inherent noise of the pre.
 
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