Vibration Abatement For The Pass Labs X600.5 Power Amp and XP-30 And XP-25 Preamps

DarqueKnight

Introduction

I finally decided to take action against the rattle and ringing of the case top of my Pass Laboratories X600.5 power amplifiers. Tapping my finger on the 1/8th inch thick top panel produced a very un-highendish sounding rattle and ring. In addition to this, when I was playing bass heavy music, the case top would "sing" (softly rattle) in synch with the bass line. However, I could only hear this when my ears were within three feet of the amplifier.

Bear in mind that the results achieved from vibration abatement depend on several factors such as: the component's construction quality and methods, susceptibility to mechanically induced electrical noise, the acoustic environment (particularly the amount of bass energy), and the resolution of the component.

The first solution I tried was brass damping weights from edenSound Audio (yes, the first "e" is small). I first saw them used on a pair of Pass XA160.5 power amps:


Figure 1. Someone else's Pass Labs XA160.5 monoblock amps with edenSound brass dampers.

I ordered an assortment of edenSound brass dampers with cork pads.


Figure 2. edenSound brass dampers.


Figure 3. edenSound brass damper cork pads.

A variety of damper configurations was used, placing one to three 2 pound dampers on the X600.5's top panel.


Figure 4. One brass weight did not sound good.


Figure 5. The sound was progressively worse with added weight.

The dampers produced a very noticeable veiling, which increased as more dampers were added. I also tried various damper combinations on the Adcom GFA-5500 power amps and Sony TA-P9000ES preamp in my home theater system. I heard no difference at all.

My first thought was to send the dampers back for a refund, but I decided to keep them and use them in an abstract sculpture project.

The dampers never did completely eliminate the X600.5's case top ringing, it was just significantly damped. I think the vibrations in the case top were being transferred to the input module circuit board, which is very near the case top at the rear as shown in figure 6. The brass dampers, which were not rigidly attached to the case top, may have just substituted one vibration for another of lower frequency. I also suspect that the brass, which is conductive, may have had some audible interaction with the amplifier's magnetic field.


Figure 6. Input circuit module at rear of X600.5 amplifier.

If I wasn't a bass head with 64" tall speakers known for copious bass output, I would probably not have had an issue with the amp's case top vibrating.

The next thing I wanted to try was Dynamat Xtreme, but I had to get permission first. Nelson Pass does not take too kindly to people modifying his amplifiers. I sent an email to Pass Labs asking if there would be any warranty-voiding issues if I applied Dynamat to the X600.5's case top. I was told that they have used Dynamat in projects before and that there would be no warranty issues. I was advised to stop the Dynamat strips just short of the input module. Pass Labs said they did a strength test, and the case top supports over 200 pounds, but they did not do a "clunk" test for the case top's acoustic and vibrational properties.

Dynamat Xtreme was applied to the case top as shown in figure 7. The outer strips are 15" x 1". The inner three strips are 3.5" x 11" and 3/8" x 11". Dynamat killed the ringing. There was also a small improvement in image weight and overall detail. I reported these results to Pass Labs and they said they would investigate to see if vibration abatement was something worth implementing in production.


Figure 7. X600.5 case top with Dynamat Xtreme strips.

The case tops of my amplifiers fit very snugly. I made a tool out of a 6" length of clothes hanger wire to assist in gently pulling the case top up. One end has a 1" curved hook and the other end has a flat end with a 1/2" 90 degree angle bend. The flat end was inserted into one of the case tops vent slots near the front of the amp. A bundle of tape was wrapped around the tool 1/2" from the end to prevent it accidentally falling into the amp and shorting something. The large capacitors still hold a charge even when the amp is unplugged.

After installing Dynamat in the X600.5s, I placed the brass dampers on top again out of curiosity. Veiling was again heard, but not to the same degree as before.

After achieving Such Good Sound treating the X600.5s with Dyanmat Xtreme, I decided to treat the cases of my Pass XP-30 line level preamp and Pass XP-25 phono preamp. Figures 8-12 show Dynamat Xtreme application to the interior and bottom exterior of the XP-25's power supply. The degree of improvement with the XP-30 was less than that of the X600.5 and smaller still with the XP-25, but it was not subtle. Prior to installing Dynamat, the case panels of the XP-30 and XP-25 produced a hollow metallic ring when tapped with a finger. After Dynamat treatment, the cases sounded like thick hardcover books when tapped.

I had some concern about how easily the Dynamat could be removed if I didn't like the results. I tested a small strip on both the heavily powder coated aluminum X600.5 top and the brushed aluminum top panel of the XP-25. In both cases, the Dynamat peeled off with some effort, leaving little to no adhesive residue. What little residue was left was easily wiped off with mineral spirits. The total amount of Dynamat Xtreme used was 9.4 square feet at a cost of $43 (three-fourths of one Door Kit). I love cheap tweaks.


Figure 8. Dynamat application to XP-25 power supply front.


Figure 9. Dynamat application to XP-25 power supply rear.


Figure 10. Dynamat application to XP-25 power supply side.


Figure 11. Dynamat application to XP-25 power supply top.


Figure 12. Dynamat application to XP-25 power supply bottom.


References

Pass-Labs-X600.5-Monoblock-Power-Amplifiers

Pass-Labs-XP-30-Line-Level-Preamplifier

Pass-Labs-XP-25-Phono-Stage-Is-It-That-Much-Better-Than-The-Xono

BlueFox

Interesting observation about the top of the amps vibrating. I never rapped on the top, so it never occurred to me. There is something in my kitchen that vibrates when the music is loud with low bass, but I haven't heard the amps vibrate. Yet. Thanks for implanting that thought in my mind. :biggrin:

Another good and thorough review, maybe I will try this also.

nooshinjohn

Dynamat is some pretty impressive stuff. I used it extensively inside the transformer covers on my amps with amazing results. A tap of the finger on them results in a dull "thud" and nothing more. As always DK, great write-up.

headrott

Thanks Ray for the great write up! Interesting that you found that placing brass weights on the amp detracted from the audio. As you stated, maybe the brass was affecting the magnetic field of the transformer and therefore affecting the audio.

That said, I wanted to add my input of vibration abatement (I also used dynamat xtreme in my amp, pre-amp, sources and DAC). I recently (about 2.5 months ago) purchased a set of Marigo Audio "Mystery Feet VXi" for my Theta Jade transport as well as some "Mystery Feet RHX" my BAT VK-200 amp. These feet are designed to reduce vibration produced externally (bass vibrational energy) and internally (i.e. transport motors, etc.). I must say that these are by far the best component isolation devices I have used. I have tried Vibra Pods/Cones, Carbon cones but these by far are better than any other vibration reduction (isolation) I have used. They are expensive, but if bought used, they are very much worth the money. I have read that they are composed of 36 seperate pieces and require a lot of labor to produce. I noticed a great improvement in detail and clarity when I placed the Mystery Feet under my transports, amp, pre-amp, and DAC. It was as if a "grunge" or veil had been lifted from the audio signal increasing detail, clarity and transparency. I highly recommend them to anyone wanting to reduce vibration and increase clarity, detail and transparency from their audio. A link to the Marigo site is below:

http://marigoaudio.com/isolation-feet/mystery-feet/

F1nut

You just can't go wrong with Dynamat Extreme. I use it in all my gear including lining the inside of the plastic double gang boxes used with the PS Audio Soloist outlets. I even covered the motor housing for my garage door opener, which resulted in a noticeable noise reduction.

zane77

I knew about it but had never used it until putting it on my driver baskets on my 2.3's. But after that I have found several uses for it for vibration control. Thanks for the great write up DK

steveinaz

I wonder how rubber "o" rings between the chasis top and chasis, where every screw is, would work? Of course you'd still have "air born" vibration to deal with.

GlennDog

F1nut wrote: »

You just can't go wrong with Dynamat Extreme. I use it in all my gear including lining the inside of the plastic double gang boxes used with the PS Audio Soloist outlets. I even covered the motor housing for my garage door opener, which resulted in a noticeable noise reduction.

AMAZING product! Good to know . . . ty

Jhayman

Great product been using it for yrs in my car audio installs..
Used a ton of it on my Grand Prix car install, it can make a mess though under extreme heat conditions, like sweltering heat inside a car on a hot humid day.

BlueFox

DK, did you try playing the amps with the top off? That should eliminate vibrations, ringing, etc. On the other hand, there are dust, safety, and other issues with the top off, but if it sounds better then they can be handled.

DarqueKnight

headrott wrote: »

Thanks Ray for the great write up! Interesting that you found that placing brass weights on the amp detracted from the audio. As you stated, maybe the brass was affecting the magnetic field of the transformer and therefore affecting the audio.

A high power amp generates a larger field, that is probably why the lower powered XA160.5 and my Adcom amps didn't experience any problems.

BlueFox wrote: »

DK, did you try playing the amps with the top off?

No. If I had known, or even thought, there would be some sonic benefit from treating the case top, I would have compared the untreated top to no top and the treated top. However, even if no top sounded better, I wouldn't do it.