Audible Illusions Modulus L1 - Wheezy Channel

[NashAudio]

Hi guys. My first post here, please be gentle.

I am trying to diagnose and fix a problem with my tube preamp (Audible illusions Modulus L1). The left channel sounds wheezy and intermittent when the unit starts. Then the problem goes away after 20-30 minutes of music playing. Audio forums suggest that "it's almost always the tubes". However; I have replaced the tubes a few times and the same problem repeated itself. I have the unit opened trying to isolate and replicate the issue when the unit is working well. I was able to replicate the effect by wiggling one of the capacitors (shown on the photograph). I am not sure it is the source, but it is a possibility. This is where my comfort level ends. I don't know how to test a capacitor and determine if it is faulty. It could be as silly as a bad solder contact, which I could have fixed I think, but it's attached very well. Before taking it to the shop, where I'll be charged a few hundred bucks for something that could be a really simple issue, I thought I'd check here. Any suggestions would be appreciated. Also, if you do agree it could be a capacitor, these are almost 30 years old. Which brand I should look for and where would be the best place to have them ordered? Thank you.

 

[DesertRatt]

Easier to just replace it than to test it.

 

[NashAudio]

I think ( I THINK) this could the problem. This capacitor from the left channel circuit looks bad. It did measure 170 μF (vs. 150 nominal capacitance). But it could be just dried out after 30 years of service. The other one from the right looks fine but I soldered it out as I want to replace both just in case. Next question: Where would you suggest sourcing good quality capacitors online?

 

[Lavane]

The one defenetly looks like it's gone bad. Mouser or Digikey is your best bet to find replacements.
Being that they're that close to those heat sinks, go for 105° caps, not 85°.
Both Mouser and Digikey are reputable, and carry various brands like Nichicon, Panisonic, etc. You can go up in voltage rating a little too. It will probably be easier to find decent replacement caps in the 16v to 25v range. The problem could have been that the 12v cap was being run at its upper voltage limit. Measuring the voltage would tell.

 

[NashAudio]

Thanks, Lavane. Would you be so kind to throw a couple of links at me with replacements matching this one? Also, what doe +672D+ marking mean?

 

[NashAudio]

Sorry to be a bother, guys, but I could still use a bit of help. I've filtered the search at both Mouser and Digi-key down to 150uF can-type aluminum capacitors rated for 105°C. There is NOTHING anywhere available at 12 VDC, so I am checking 16V, 20V and 35VDC, which is not a concern, I understand. There are a few options available from Nichicon, Panasonic and Kemet, but they are all REALLY small - some are twice smaller in size than the original ones (10mm diameter x 20mm height). How could they dissipate heat being so small??? Should I be concerned? Also, is there any attention to be paid for ESR and Ripple Current values in this circuit case? Apologies if my questions are totally noob's (they are). These are the ones that I've filtered out. Please have a look and assist. Thanks.

1. https://www.mouser.ca/ProductDetail/United-Chemi-Con/APSG160ELL151MF05S?qs=RpYEFuZ7GTi/F8VrJmKTXQ==
2. https://www.digikey.ca/en/products/detail/nichicon/PLX1D151MDL1/4991380
3. https://www.digikey.ca/en/products/detail/panasonic-electronic-components/16SEQP150M/4833007
4. https://www.mouser.ca/ProductDetail/Nichicon/RNU1V151MDN1?qs=JR74jXm5AK%2BkmAZmaWcQBQ==
5. https://www.mouser.ca/ProductDetail/710-870055675010
6. https://www.mouser.ca/ProductDetail/667-16SEPC150MD+S

I think I found the exact match. 672D is a series used by Sprague, which am now 100% sure was the original manufacturer. It is available on tedss.com, which doesn't have prices listed for some reason. And only in large bulk quantities from digikey...
https://www.tedss.com/2020114922

 

[Lavane]

What is the spacing of the leads in mm's.

 

[Lavane]

I found this 105° electrolytic. Newer caps can be physically smaller than older ones.
https://www.mouser.com/ProductDetai...GAEpiMZZMvwFf0viD3Y3asoeH%2BozipbqavAnj1kev0=

 

[arts]

The Sprague 672D with the epoxy end-seal is very common in test equipment and in many other high-reliability applications. It is also one of the most failure prone electrolytics I encounter. In fact, this cap, along with the notorious "bumblebee" cap, has made it onto my shoot-on-sight list. The last time one of these took a dump it fried part of the power supply in one of my Keithley meters

Frankly, anything would be an improvement...

 

[Lavane]

Ya, I suggested that Nichicon 105° cap just because it's kind of close to the heat sink.

 

[NashAudio]

The Sprague 672D with the epoxy end-seal is very common in test equipment and in many other high-reliability applications. It is also one of the most failure prone electrolytics I encounter. In fact, this cap, along with the notorious "bumblebee" cap, has made it onto my shoot-on-sight list. The last time one of these took a dump it fried part of the power supply in one of my Keithley meters

Frankly, anything would be an improvement...

I am in no position to argue one way or another... But FWIW, these original Sprague capacitors performed excellent for 30 years. I have two large audio-systems with Modulus L1 preamps in both. They have both been amazing.

I found this 105° electrolytic. Newer caps can be physically smaller than older ones.
https://www.mouser.com/ProductDetail/Nichicon/UPM1C151MED1TD?qs=sGAEpiMZZMvwFf0viD3Y3asoeH%2BozipbqavAnj1kev0=

Thanks, but the lead spacing on this one is only 2.5mm. Mine is 5mm. I have ordered these ones:
https://www.mouser.com/ProductDetail/710-860080675012

Wurth capacitors are made in Germany and generally have very good reviews for reliability. They are rated 50 VDC (against the original 12VDC) but this shouldn't be a problem (right?). Also, they are 5mm taller than the original, but there is enough room, so not a concern. I don't know the ESR and Ripple current values of the original capacitors, which worries me a little bit, but from everything I was able to read this shouldn't cause any negative effect on the sound quality and circuitry performance (fingers crossed). The Wurth ones have 68 mOhms and 870 mA values, respectively. I chose the lowest ESR value from the available in-stock capacitors fitting the main criteria (150uF, under 50VDC, 105 °C rating, 5mm lead spacing, 10mm diameter). Any comments?

 

[Lavane]

I saw that brand, but haven't ever used them or heard of them. I do use other German brand caps both film and electrolytic.

 

[NashAudio]

I am going to keep this thread alive just so that people could find things in future which might be useful and save them time researching.

As an update, I was able to get in touch with Jerry, the Service Manager at Audible Illusions. He told me to discard Wurth capacitors (which turned out to be made in China and not in Germany), I found Vishay-Sprague 150uF/12VDC/672D-series capacitors matching exactly the original ones, but Jerry wasn't concerned much about them. He suggested any 2 Nichicon 150uF electrolytic capacitors with 5mm lead spacing and under 50V would do just fine in that location (C37 and C38). He then suggested to replace 4 x 220uF vertical electrolytic capacitors located at the line stage just under the Audible Illusions logo on the photograph at the top of this thread as they are known to leak with age. He specified these ones: https://www.digikey.ca/en/products/...?s=N4IgTCBcDaIKoDEDiBGAamMKCyAFbKAKgCIgC6AvkA. They are made in Japan and are called "Fine Gold" series (excellent ones, according to Jerry). Cost is about $1/piece plus shipping, which was nothing. So, I got everything delivered in two days and installed this morning, And bummer... same fuzzy left channel. I am so frustrated right now...

Found a diagram for the Audible Illusions Modulus L1 electronic diagram:
https://usermanual.wiki/Document/AudibleIllusionsModulus1Preamp.1634238248

Any further hints as to where I should look at for culprit?

 

[drentech]

Hi guys. My first post here, please be gentle.

I am trying to diagnose and fix a problem with my tube preamp (Audible illusions Modulus L1). The left channel sounds wheezy and intermittent when the unit starts. Then the problem goes away after 20-30 minutes of music playing. Audio forums suggest that "it's almost always the tubes". However; I have replaced the tubes a few times and the same problem repeated itself. I have the unit opened trying to isolate and replicate the issue when the unit is working well. I was able to replicate the effect by wiggling one of the capacitors (shown on the photograph). I am not sure it is the source, but it is a possibility. This is where my comfort level ends. I don't know how to test a capacitor and determine if it is faulty. It could be as silly as a bad solder contact, which I could have fixed I think, but it's attached very well. Before taking it to the shop, where I'll be charged a few hundred bucks for something that could be a really simple issue, I thought I'd check here. Any suggestions would be appreciated. Also, if you do agree it could be a capacitor, these are almost 30 years old. Which brand I should look for and where would be the best place to have them ordered? Thank you.

Hi guys. My first post here, please be gentle.

I am trying to diagnose and fix a problem with my tube preamp (Audible illusions Modulus L1). The left channel sounds wheezy and intermittent when the unit starts. Then the problem goes away after 20-30 minutes of music playing. Audio forums suggest that "it's almost always the tubes". However; I have replaced the tubes a few times and the same problem repeated itself. I have the unit opened trying to isolate and replicate the issue when the unit is working well. I was able to replicate the effect by wiggling one of the capacitors (shown on the photograph). I am not sure it is the source, but it is a possibility. This is where my comfort level ends. I don't know how to test a capacitor and determine if it is faulty. It could be as silly as a bad solder contact, which I could have fixed I think, but it's attached very well. Before taking it to the shop, where I'll be charged a few hundred bucks for something that could be a really simple issue, I thought I'd check here. Any suggestions would be appreciated. Also, if you do agree it could be a capacitor, these are almost 30 years old. Which brand I should look for and where would be the best place to have them ordered? Thank you.

I am going to keep this thread alive just so that people could find things in future which might be useful and save them time researching.

As an update, I was able to get in touch with Jerry, the Service Manager at Audible Illusions. He told me to discard Wurth capacitors (which turned out to be made in China and not in Germany), I found Vishay-Sprague 150uF/12VDC/672D-series capacitors matching exactly the original ones, but Jerry wasn't concerned much about them. He suggested any 2 Nichicon 150uF electrolytic capacitors with 5mm lead spacing and under 50V would do just fine in that location (C37 and C38). He then suggested to replace 4 x 220uF vertical electrolytic capacitors located at the line stage just under the Audible Illusions logo on the photograph at the top of this thread as they are known to leak with age. He specified these ones: https://www.digikey.ca/en/products/...?s=N4IgTCBcDaIKoDEDiBGAamMKCyAFbKAKgCIgC6AvkA. They are made in Japan and are called "Fine Gold" series (excellent ones, according to Jerry). Cost is about $1/piece plus shipping, which was nothing. So, I got everything delivered in two days and installed this morning, And bummer... same fuzzy left channel. I am so frustrated right now...

Found a diagram for the Audible Illusions Modulus L1 electronic diagram:
https://usermanual.wiki/Document/AudibleIllusionsModulus1Preamp.1634238248

Any further hints as to where I should look at for culprit?

 

[drentech]

Hi, Perhaps I can help? Feel free to message me here or at: wheezer1@comcast.net
Cheers,
W

 

[drentech]

Hi guys. My first post here, please be gentle.

I am trying to diagnose and fix a problem with my tube preamp (Audible illusions Modulus L1). The left channel sounds wheezy and intermittent when the unit starts. Then the problem goes away after 20-30 minutes of music playing. Audio forums suggest that "it's almost always the tubes". However; I have replaced the tubes a few times and the same problem repeated itself. I have the unit opened trying to isolate and replicate the issue when the unit is working well. I was able to replicate the effect by wiggling one of the capacitors (shown on the photograph). I am not sure it is the source, but it is a possibility. This is where my comfort level ends. I don't know how to test a capacitor and determine if it is faulty. It could be as silly as a bad solder contact, which I could have fixed I think, but it's attached very well. Before taking it to the shop, where I'll be charged a few hundred bucks for something that could be a really simple issue, I thought I'd check here. Any suggestions would be appreciated. Also, if you do agree it could be a capacitor, these are almost 30 years old. Which brand I should look for and where would be the best place to have them ordered? Thank you.

The noise is most times from the tube, socket and/or tube pins. I suggest cleaning them and tightening them.
Cheers,
-W

 

[GordonW]

I fear that the capacitor- while probably needing replacement relatively soon- is not the cause of this problem.

That low of a voltage, is likely in the heater circuit. Those usually won't interrupt the audio.

I suspect that by wiggling the cap, the circuit board is being flexed- which is causing the real culprit to flex, and cause noise and or drop-outs.

Given that it happens on startup (transition from cold to warm), I suspect a bad resistor. Probably cracked or crumbling inside. When the unit is cold- the resistor- which has ostensibly slightly shrunk from being cold- has a crack that opens up, causing the problem. When it warms up, the resistor would expand- with the two sides of the crack also expanding closer into each other- making a relatively reliable connection...

This is a case, where some "freeze spray" may ferret out the problem. If a cracked resistor is suddenly cooled- it will shrink, sometimes revealing the presence of cracks by becoming noisy or having a signal drop out...

Regards,
Gordon.

 

[grindfix]

I'd add to Gordon's post to not spray at random. Power supply resistors can get hot and that is normal. Scary thought to spray a resistor that is actually hot. That extreme temperature difference can possibly crack a perfectly well operating part. Resistor that would cause any kind of noise in one channel only will be somewhere around that channel's tube

 

[grindfix]

Found a diagram for the Audible Illusions Modulus L1 electronic diagram:

That is not a diagram for your preamp. This is a Modulus 1 schematic that has a phono stage. Yours is the Modulus L1, line stage only

 

[GordonW]

I'd add to Gordon's post to not spray at random. Power supply resistors can get hot and that is normal. Scary thought to spray a resistor that is actually hot. That extreme temperature difference can possibly crack a perfectly well operating part. Resistor that would cause any kind of noise in one channel only will be somewhere around that channel's tube

Yes, it's going to likely be something like a plate or cathode resistor, on a tube. Should be very close to the tube.

It's not likely power supply anyway- as that should cause noise in BOTH channels. As this is only one channel, that realistically exonerates the power supply.

Regards,
Gordon.