hartke 3500 amp .. problem blowing speakers

[anunusualleopard]

hi there .. i'm new to here but found you on google .. and here is my dilhema..

we have a hartke 3500 bass amp - well it was a friends and he used for years without problem. We used it with a behringer BA 115 cabinet (supposedly 600w but in reality about 180w RMS) and it worked fine for nearly a year, then some noise appeared and we returned it to the dealer and got a new one. This happened two further times .. same speaker, 6 months or the second one and 4 days for the third ... a replacement is on its way again ( cannot upgrade until this one blows !!) ... we have come to the conclusion that the amp is too powerful ...

then i purchased a secondhand peavey 215bw cabinet in a market .. .. black widows i thought ... this will last for years .. it was old, but in good condition and built in the US !!

this sounded like an army coming over the hill ... for about an hour it was great .. then the sound became distorted. i took the amp and speaker to a tech guy ... the speakers are blown !!! .. and the amp is fine ... he has tested it for hours and can find nothing wrong with it ...

i am worried about ever using it again .. more costs and speakers ... any ideas .. is this a rogue amp or am i just cursed with dodgy speakers ..

anyone with any clues would be welcome

p.s. we do not play loud ... psychedelic dub fusion ...

[PRNDL]

I'd check to make certain there's no DC on the speaker output, which will burn out the speaker coil.

This could happen if the amp is improperly grounded (someone clipped off the ground on the AC cord), or, more likely, if one of the power supply rails (B+/-) isn't working, which could be bad electrolytics or a shorted power transistor.

A dummy load is best for this test. If DC is present, it will get pretty hot, and the speaker wire may melt.

[tim]

clipping the ground off a 3 prong plug won't cause an amp to DC...also, if you're trying to determine if there is DC on the output, you don't want to hook it up to a dummy load...if there is DC, it'll most likely blow a fuse (or worse) if it's hooked to a load. just turn the amp on with no input signal and check the output terminals with a voltmeter...it should read 0 volts DC. It might read several millivolts but if it's reading anymore than a few millivolts DC than there are issues with the amp. Then if it is reading zero volts, you could hook a load to the speaker terminals (large 8 ohm resistor, like 50 watts or more), and put power to the load and monitor the output with the volt meter to see if the amp starts DCing after it warms up.
I gather from what you wrote that it happened over time...it's possible that you have a bad solder joint in the power amp circuit somewhere that, as the amp heats up, unbalances the power amp, causing the output to put DC on the speaker. Until the root problem is fixed, you'll keep blowing speakers.

[oc disorder]

A couple of things here firstly the Hartke 3500 has a DC detection circuit and a protection relay, to prevent a major breakdown (dc on output) from blowing the speakers.
When you first power it up after a couple of seconds you should hear a click as it connects the speaker jack to the power amp.
It can deliver 350 watts rms into a 4 ohm load and 240w into 8 ohms.
There were several variations over the years of the circuit and layout.
The early ones were notorious for being riddled with dry or cracked solder joints especially on the front pre amp board.
I would get the tech to remove the board (you have to straighten out the led leads to slide the connector off or try to undo the glue) and resolder all the tall components particularly the regulators and capacitors.
These faulty connections "play up" with vibration and heat.
Belt it with a rubber hammer and you will hear ....

"we do not play loud ... psychedelic dub fusion ... "
Um you don't use a distortion box on bass by any chance?

Also it would be feasible that its just burning out the speaker due to its wattage.

[Steve Conner]

To me, "Dub" suggests enormous speaker-blowing basslines. You might not play subjectively loud, but if you boost the bass all the way up on the amp, you get huge amounts of low frequency energy. Subjective loudness is mostly down to the midrange: cymbals, distortion boxes and so on.

If you use a 5 string bass, that's even worse.

The Hartke VX series cabs seem like pretty good value for money, I've jammed with a guy who used a 3500 and a stack of the VX410 and VX115. And a 5 string bass

I owned the VX215 for a while, and it could shake the place even with a fairly low powered amp. Goodness knows what it would be like with a 3500. I sold it because I got fed up carrying it up 8 flights of stairs to my apartment.

They are slightly cheesy Made In China quality, but probably no worse than the 3500 itself. If you blow the woofers again, you could always stick a couple of Eminences in there. You could do that with your Peavey cab or your Behringer too, I guess. Just watch that the box stays properly tuned, especially with a 5 string.

[mac1amps]

'definately agree with the tone/EQ boost factor (why are so many bassists obsessed with always cranking the bass control, which [almost always] results in a "farty" sounding low-end). Another factor I've run into with a few of my clients is over-boosting the bass tone control on an active bass, which often results in premature speaker failure, ESPECIALLY when the strings are attacked hard (i.e. "slappy-hand" playing)....and, BTW.....when a SS amp is putting out DC, it's accompanied by a loud hum, which would make the amp unplayable.

[tim]

'when a SS amp is putting out DC, it's accompanied by a loud hum, which would make the amp unplayable.

I agree with this if the DC is at the rails but I've seen amps where there is sometimes only 10-15 volts on the output and in this case there is little to any hum but because the speaker is pushed out a certain amount (or pulled in as the case may be) depending on the amount of DC, the sound is distorted and basically sounds horrible. It's not enough to burn out a speaker (at 10 vdc into 8 ohms, it's about 12ish watts) but it certainly is enough to make the speaker sound like crapola...