A question for EE's & amp experts..........

[zipper]

Just got a B&K ST-202+ & I have an issue with it. It's supposed to be 2X200 wpc but I have some serious doubts about it. While the innards look intact & worthy(huge caps & torroidal) it is a wimp. I've heard from some on this forum that B&K overstates the power of their amps but this is ridiculous.
I'm using my Yammy 3300 as mostly a pre now(have some older cheaper amps that I have bridged) & I added this with the idea of moving the other amps to the rear surrounds. While the sound produced by the B&K is nice & warm & airy, it doesn't seem to have even as much power as my receivers' amp does..........there's no way it is 200 wpc.
My question is this............the unit didn't come with a power cord so I fitted it with one from a computer(same plug size). But can there be a problem with the amp internally although it's still producing a nice sound through both speakers? Are there situations that an amp can be faulty to produce this kind of scenario?.........need help as if this is what is normal overstatement from B&K, I won't buy any more of their products.

Thanks........

 

[Electone]

Most computer power cords are only 18 awg. You might want to try a beefier power cord at 12 or 14 awg.

 

[zipper]

Thanks.............I considered that but it seemed too simple of a solution, if you know what I mean........

I'll try it.

 

[rschleicher]

I don't mean to re-state the obvious, but what symptoms are you observing to conclude that the B&K amp isn't putting out full power? Is it clipping, or shutting down? If it is just a case of "volume knob setting of X produces less loudness through the B&K amps than it did through the receiver's own power amps", then maybe there really isn't a problem. In addition to having a power rating, power amps provide different levels of signal gain - often on the order of 25 dB or thereabouts. One amp might be set at only 20 dB of gain, while another company's amp might be providing 30 dB of gain. Depending on how the gain of the B&K amp compares to the power amp stage of your receiver, it may take a different volume knob setting to get the same loudness. Separate power amps usually have a gain adjustment of some kind (if not actual knobs, then perhaps trim-pots), but it is normally a set it once and forget it adjustment (and then the pre-amp's volume knob is used for in-use volume adjustments).

I don't know B&K model numbers, and so am assuming that it is a separate power amp? If it is actually an integrated amp, then the pre-outs of your receiver need to get connected to the power-amp inputs of the B&K, rather than the line-level inputs of the pre-amp stage of the B&K.

Like I said above, pardon me if all of this has nothing to do with your issue.

 

[zipper]

It's more the latter case in that this amp just does not produce volume or punch like I believe 200wpc should............yes , it's a seperate with no control knobs.....just plug & play. The Yamaha 3300 is rated at 130wpc. We can figure that it's probably at least a little overstated. I have some other separate amps that are 2x125wpc but are bridged for mono @ 250wpc. They have VU meters & a clip indicator which comes on at 80% amp power. I cannot drive them, in bridged mode, to anywhere near clipping. Just too loud for the room I'm in. The Yammy,before I attached amps, was similar although I had driven that to clipping briefly once. But once again too loud.

I understand what you're asking & your subsequent explanation. I also suspected that perhaps this amp has a more non-linear power gain curve than my 3300 or the other amps, but I don't find any particular volume level where this thing "kicks in" or out-performs the the 3300s power supply. Or that it ever puts out it's rated power. Hence my suspicion that perhaps it may be faulty, although most instances of faulty equipment usually involve noise or complete failure.

I don't really want more power for volumes sake..........I want it for the performance it provides at lower volumes. Is this what the attraction of tube amps is? The 3300 at low volumes, even with the bass boost on, doesn't provide a great balanced sound..........I have to turn the volume up a ways to get much bass out of the axioms.

Thanks for the reply..........I appreciate it.

 

[dohanc]

Run it a pretty loud volume for a while then feel around it for heat. If it's not warm at all, then your probally right - it has a lot more power available to it.

Check the sensitivity ratings for the inputs (in the specs) and maybe compare that to the voltage ratings for the outputs of your receiver. Or post them here so we can compare. It's usually some voltage and some resistance load. ie. 1.2v 1.2kohm (I'm just making up numbers).

 

[zipper]

dohanc....................It has big heat sinks on the back of the unit & they get pretty warm at even low volume. Unfortunately, I bought this unit off ebay & the manual wasn't included. It has has balanced inputs on the back(along with the rca plugs which is what i'm using) & a button which, when pushed in, kills the output............I'm assuming the button is for switching from the rca's to the bal. in's............was hoping it was for running the amp in mono but there is absolutely no indication on the back that this is possible.

Can't dig up any info @ B&K's website either...................perhaps I'm just out of $340...

 

[Votrax]

If the amp has gain controls for the left and right channel be sure they're turned all the way up. If it has a push button switch for balanced mode ensure the switch isn't in balanced mode otherwise your output will be low. I believe the switch should be out to turn balance mode off.

 

[mtrycrafts]

I don't really want more power for volumes sake..........I want it for the performance it provides at lower volumes. Is this what the attraction of tube amps is? The 3300 at low volumes, even with the bass boost on, doesn't provide a great balanced sound..........I have to turn the volume up a ways to get much bass out of the axioms.

Thanks for the reply..........I appreciate it.

What performance are you looking for at low volume that you don't think you are getting? I am not sure what you are looking for at say a 1 watt output? That would be 2.83V. You may want to check it with a meter?

Hard to say what the attraction to tube amp is.

Bass out of the Axioms? Maybe it has a response problem there? You just cannot hear the output at such low levels. Maybe the source has bass issues?
I seriously doubt it is your amp.

Maybe you should do some analysis: compare spl levels with other amps and see when the others put out the bass you think you are missing with the amp in question. You probably need meters to rule the amp in or out of the problem question.
Maybe your expectation is unrealistic?

 

[zipper]

Getting back to the reason for my thread, I'm not getting out of the B&K amp what I had expected or hoped for................I've got two old Optimus amps that I have in mono right now (FL & FR speakers). Upon hooking them up there was immediately an improvement in the overall response from the Axioms. Better bass at normal volume,better separation,etc. I had hoped that a quality unit such as a B&K would be an improvement, however slight that may be. Well, after playing around with my setup(different speakers,front to back, back to front,2 ch stereo,5 ch stereo,etc) this thing might possibly be on par with the power output of my 3300............the overall sound through the B&K is better than the Yammy but the power is no better.

Perhaps my expectations WERE unrealistic. I figured adding a quality piece of gear(albeit older) to my setup would be an improvement. I figured if the cheapee amps improved the sound that much then a B&K amp of similar power would be a bit better. Hey, I don't have a ton of experience behind me in dealing in separates. I realize that some gear isn't necessarily better than others in the same price range, but maybe just different. Perhaps dohanc is on the right track in saying that the input resistance for this amp is just higher than the others I'm dealing with. I don't know so I thought I would bounce this off of all of you in here that have more experience than I.

This is my 1st excursion into gear since before the digital era. I started over about 2 years ago with a Yamaha RX-V620, 4 Klipsch KB1.1's & a cheap Klipsch center & have evolved to this point. I can't( or won't) afford to go out & drop $10K on gear so I'm building (& learning) as I go, hoping not to make any expensive mistakes.

I appreciate all the responses & will take all of the advice into consideration, probably starting by getting a proper power cord for this thing.

Thanks again fellas & if anyone has anything else to relate please do so........

 

[Rob Babcock]

I appreciate all the responses & will take all of the advice into consideration, probably starting by getting a proper power cord for this thing.

Holy crap! I'm gonna head for cover before Mtrycrafts or WMaX sees this! Just kidding. If you're totally dissatisfied with the amp, don't expect miracles from a better power cord. If the one you have isn't up to the electrical specs, maybe...but I wouldn't bet the farm.

I'm not familiar with that amp. It could be rated for 200 W into 4 ohms, not 8 ohms. That's one trick that sellers/vendors will use to fluff up the power ratings. In truth it may be no stouter than what you already had.

Watts are getting cheaper, but the fact is you still have to shell out some cash for a bigger amp. You can often get a used Carver or Adcom in the 200 W+ catagory in decent shape for $300-$400 on Ebay, and that might get it done for you. Brand new, expect to pay $700 or so USD, a bit less for a pro amp. Pro amps (Crown, Samson, etc) will crank out some serious power for not much $, but they aren't ideal for home use in that they often have noisey fans and use TRS or XLR inputs and Speakon terminals instead of 5-Way binding posts. You just have to look around.

 

[zipper]

Thanks for the response Rob.............yeah, can't seem to get around the fact that good,clean power cost money. I've been searching ebay for months & sure enough, everyone else wants what I want . I'll keep this thing & chalk it up to experience. Not going to blame the unit, it's just a caveat of buying a piece of gear you nothing about. Have a chance to pick up a new B&K Ref 200.5 amp at a local for $1700. They have a great 30 day return policy so perhaps I'll do that & see how it sounds......................but what if I like it?

 

[jaxvon]

Oh Wow! An old ST-202 Plus! My dad has one of those, and has had it for years. He uses it with an old Superphon Revelation Basic preamp to drive some Magnepan MGICs. The amp sounds great, it's just too bad that the Maggies are trashed now. Ok, enough about that.

A few years ago, I went to put on some music. When I turned it on, smoke started coming out near the switch! After talking to local dealers, my dad ended up calling B&K. They said that as long as he was willing to pay shipping, they would fix it for free. So, he packed it up, sent it off, and got it back a week later in working order.

I'd suggest that you try to call up B&K. I'm not sure if the warranty is transferable, though. But come to think of it, my dad picked it up used in the days before eBay, so...maybe it is. Anyway, it can't do any harm to call them up. Good luck!

 

[zipper]

Thanks jaxvon............... This thing is probably a decade out of warranty, but perhaps if I can find someplace to bench test it & there is a problem, I'll give them a call & see what they can do...........

 

[mtrycrafts]

Getting back to the reason for my thread, I'm not getting out of the B&K amp what I had expected or hoped for................I've got two old Optimus amps that I have in mono right now (FL & FR speakers). Upon hooking them up there was immediately an improvement in the overall response from the Axioms. Better bass at normal volume,better separation,etc. I had hoped that a quality unit such as a B&K would be an improvement, however slight that may be. Well, after playing around with my setup(different speakers,front to back, back to front,2 ch stereo,5 ch stereo,etc) this thing might possibly be on par with the power output of my 3300............the overall sound through the B&K is better than the Yammy but the power is no better.

Perhaps my expectations WERE unrealistic. I figured adding a quality piece of gear(albeit older) to my setup would be an improvement. I figured if the cheapee amps improved the sound that much then a B&K amp of similar power would be a bit better. Hey, I don't have a ton of experience behind me in dealing in separates. I realize that some gear isn't necessarily better than others in the same price range, but maybe just different. Perhaps dohanc is on the right track in saying that the input resistance for this amp is just higher than the others I'm dealing with. I don't know so I thought I would bounce this off of all of you in here that have more experience than I.

This is my 1st excursion into gear since before the digital era. I started over about 2 years ago with a Yamaha RX-V620, 4 Klipsch KB1.1's & a cheap Klipsch center & have evolved to this point. I can't( or won't) afford to go out & drop $10K on gear so I'm building (& learning) as I go, hoping not to make any expensive mistakes.

I appreciate all the responses & will take all of the advice into consideration, probably starting by getting a proper power cord for this thing.

Thanks again fellas & if anyone has anything else to relate please do so........

One of these days you should invest the time in setting up a carefully level matched setup, in this case amps, and compare them under blind conditions and see how well you can guess which amp is which, say out of 15 trials. Many have tried, very few succeed.
Or, if you are in a part of the US where there is a good audio club that does this, you should contact them and see when they have a demonstration.
AH has a poster who recently joined such a club.

 

[zipper]

Thanks for the idea...............sounds like fun. I'd love a chance to hear a bunch of different amps. Magnolia is the closest local that boasts separates but they only carry a limited # of amps(B&K, Krell Showcase). There is a Definitive Audio outlet in Seattle that carries Rotel & Marantz along with a couple specialty items..............was able to poke my head in during an audition of some B&W Nautilaus speakers & a massive Linn amp.

I've heard all the names but can't find where they're sold..............& I'm not particularly interested in my ability, or lack thereof, to blindly pick an amp out of a lineup. Just in search of a sound that eludes me............

 

[zipper]

It appears as though a couple of you were correct..................it appears to be an input impedence issue. I reconnected my mains to the B&K & shut eveything else off again & just played some more with it..............it's fine. In fact it sounds pretty good. There is about a 20 point difference in receiver volume setting between the B&K & the other amps to achieve similar listening volumes..................never imagined I'd have the 3300 set at -30 for a rather normal listening range...............that is loud with the receivers' amp alone & flat out cranked with the other amps.


My bad..................my ignorance. Thanks for all the input fellas. I appreciate it.

 

[dohanc]

Good to hear your convinced there is nothing wrong with the amp. Gains are relative since 0dB of an amp requires a certain input voltage. Not having a standard input voltage causes this type of confusion. I know for the pro audio community they have widely used +4dBu and -10dbm input voltages. -10dbm is around what home audio components use however I haven't seen any strict followings of this. I have a +4dBu cd player that absolutely blows out a hundred times louder than any other component. Quite annoying.

Were you even able to change the pre-amp levels out of your receiver to help match between amps?

 

[zipper]

I don't think I have enough play in the receiver settings to get a match but the other amps have level controls. I'd ultimately just like to get another 2-ch B&K & dump the cheapees..........