Thump?

[lpd]

Whenever I power up and power down my Threshold S-150 I get a thump through the bass drivers on my 4333's. Is this ok? If not how do I remedy the situation? Can't hear any sound from the compression drivers, just the bass drivers which move out with the thump and move in on power down ?

Thanks from a excessive worrier......

Peter

[Mr. Widget]

It probably isn't terrible, but it may also be less than ideal. A subtle thump that causes the woofer to move is not uncommon. Don't worry about the HF drivers as they are protected by their crossover (if one is present).

I suppose it depends on how loud the thump is. It may be caused by a problem in the amp. Ian Mackenzie here on the forum seems to be a bit of a Nelson Pass fan and may know more about this amp. Many amps have caps to block any DC from appearing at the outputs, but a Pass design may not.

Are you sure it is coming from the amp alone? In my HT system, if I shut down the active crossovers before the power amps have fully discharged it makes quite a spectacular popping noise. (Like a gun shot.)

[lpd]

I'm quite sure its the amp as it didn't do this with the Dyna 70 that I was using beforehand. Its not a loud thump, just a low thump when the amp "clicks off and on". The driver moves out abit, but nothing else. Just curious if anyone else has this situation. Thanks for the insight.

[Ian Mackenzie]

I have refered LPD to the master himself...Mr Pass.

LDP, can you post a pic so I can have a squiz, and give us a mini review of the amp.

Ian

[lpd]

Well Ian,
I'm not what one would consider an audiophile by any stretch of the imagination. First impressions....sizzling highs, I mean very sizzly but not to a point were I experience listeners fatigue. Take for example Pink Floyd "Time". The chimes on this recording just ring!!! Now the next noticable and appreciated difference between this amp and others I've owned, is the control of the bass. The bass is tight, yet has a warmth to it..(sounds like I'm a wine critic) :) I don't find this amp to be sterile like the Acoustat Twin 200 I owned, but just as warm as my Dynaco 70, with a much richer bass by far. I vowed to never use ss amps until I heard this one. Now I may be converted!!! 75 watts per channel and at 1/3 volume I'm very satisfied with the range it provides. Even on crappy 50's recordings (cd format) it seems half as sterile as the Acoustat I owned. One other difference I've noticed is the clarity of the soundstage it creates. Each instrument has its own place. I was listening to the song "Cherokee" by Marcus Roberts which is an instrumental piano piece recorded in St. Josephs Cathedral New Orleans (Source: Novus 3130-2-N), and I swear I can feel the timber of the keys and the wires. Unbelievable. I listen to lots of small jazz combos and now I can hear each musician in his/her place with no blurr. I also tested with a bluegrass recording by Alison Krause and was amazed with detail of separation. I even have a more finite image, although I have room problems which comprimise my imaging.

Now of course I'm comparing this amp to a Dynaco 70, Acoustat Trans Nova Twin 200 (which was much to dry and sterile for my tastes), and a few other oddball amps friends have brought over when we get together to play music. I stumbled upon this amp at a very low cost, and am blown away by its performance in every way.

http://members.shaw.ca/mbeka/Threshold1.jpg
http://members.shaw.ca/mbeka/Threshold3.jpg :D :D :D

[Ian Mackenzie]

Great Peter,

Sounds very much like a Pass Theshold.

The more recent Aleph series is similar in character and perhaps even more engaging and romantic.

If you ever plan to biamp there should be a diy Passlabs crossover out soon. Sent me a PM and I can help you put together an Aleph 60 for the horn and top end.

Ian:smthsail:

[gyusher]

I use a "Enhanced" Forte' M3. . .A Nelson Pass design. . .See pic and you will see what I mean by "Enhanced" Dual toroid instead of one, bigger caps. . . .This guy thumps very lightly when those big caps discharge, about 5 minutes. . .No turn on thump but a slight pop at discharge. I understand this amp has DC protection. . . .I agree with the Thresholds sound description, as I would describe this guys sound the same way. . .Not to say it can compete with the Threshold but a fine Pass design none the less. Makes my L-112s come alive. . .

[lpd]

Nice amp!!! I'm sending my amp to Jon Sodeberg for a filter cap replacement next spring. He services these amps and apparently is one of the only people to do so!!! I'll keep you posted as I service the unit. I think my power switch might be going too!! Looks to be any easy repair though!!

[gyusher]

You will notice my Power Switch is right in front of the toroids. . .It was pushed out during travel. . .I found the maker of the original switch. . .Arcolectrics. . . I can send you the link but they are easy to find with GOOGLE. . .I got mine in 2 days out of St. louis. . . I would like to find a power switch with right angle blades as it is very tight where its at now. . .BTW I have a friend who did the work on my amp, most of the upgrade was recomended by Nelson Pass. . .I have a list of everything that was done if you are interested. . .My biggest concern was not power although its 282 watts at clipping into 8ohms, but for reliability. No increase in voltage but more power supply among other things. . .The sound is very "Krell" like in the upper midrange and extremly detailed high end. Bass is fine. . . .Hell I have enough power to light a small town but a very well behaved amp. . .No turn on thumps only a little pop when the caps finally discharge. . .

[Ian Mackenzie]

So the lights dim in Ohio I see, great.

That Forte looks really cool.

See 's a look inside the Passlabs X 600 mono block. It has a soft start to avoid a large inrush surge on the mains.

Ian:)

[gyusher]

I dont know about the lights dimming in Ohio but they do in my 9x9 room. . .Inrush is about like my Adcom GFA565. . .I use it as a welder when not in use for HT. . .LOL. . .
The 565s have a little stronger bottom but the Forte' sounds much nicer on top than the 565s about as much power. . .I will say that when the 565s are running full tilt you better not make popcorn because if you do you will do it in the dark. . . .Also I cannot turn them both on at once. . .Made that mistake already. . .
I use the 565s for HT and the Forte' for stereo music and "AM Radio". . . .Yes AM radio. . . .Matter of fact I am listening to AM radio right now. . .Talk radio. . . .

[Alex Lancaster]

Here´s a little item that could help with the turn-on current:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2573108625&category=42899

Alex.

[Ian Mackenzie]

On the subject of amps I'm upgrading my current rig to a new Passlabs design called Aleph X.

The idea is to make full use of balanced inputs to create absolute symmetry with floating +ve & -ve outputs, all in full class A mode with minimal feedback.

A bit like bridging a normal amp but integral to the design and very clever use of feedback to make both side symmetrical.

So far I have only trial a 30 watt version running on split 14 volt dc supplies with about 9 amps of DC bias.

The results are most exciting and has the finesse of the best tubes but the sledge hammer attack and dynamic contrast of super amp on tap.

I will post more details as the project progresses

[lpd]

Hey Ian,
Thanks for the lead to Mr. Pass. He indicates that the "thump" emitting from my amplifier is perfectly normal. So no worries, all is well. This spring an upgrade to the power supply caps and then maybe a tube amp for bi-amplification.

[Bernard Wolf]

hey - hows about just leaving the amp powered up all the time? Many people do this. No thump.

B

[lpd]

Well if I leave the amp on full time it will wear the caps much quicker. 24hrs * 365 days a year =8760hrs per year!!! Yowzaaaa!!!

[Bernard Wolf]

Well, i'm no expert in this but I do believe that many people do recomend doing just that. I have friends of mine that have had their amps on for years, and I do mean years as in 10 !! Perhaps the on and off cycle is as damagaing....??? I don't know. Just a suggestion.

B:confused:

[gyusher]

My Forte' gets hot enough now to cook meat after a couple hours. . .Mine runs Class A for the first 20 watts. . . .I think I will put a fan on it or by it aimed at it. . . .Its not too hot but very warm. . .I dont think I want it running 24/7. . .,
BTW since warming this guy up the thump went away. . . .No more shut down thump. . . . . .

[Don McRitchie]

The Thresholds are quasi Class A designs meaning they draw a substantial current even at idle. If you can handle the power bills and air conditioning necessary to offset the BTU's thrown off by these amps, leaving them on shouldn't hurt them. (Speaking as a longtime Threshold 400A owner)

[gyusher]

Do anyone of you know what the correct Bias current should be for my Forte' Model 3?? Right now I am at 40mv. . . .I had it at around 90ma but it was just too hot, not unruly hot but hotter than I like it to be. When I set it the bias was 0. . .And it ran as cold as a cuccumber. . .Too cool, but sounded fine. . .Since warming it up it sounds better. . .a little warmer bottom. Since comming down from 90 to 40 she still sounds great but not near as hot. Very warm now but not near hot. . . .