dear fellows
I received for service an audio research D300 amp, with the claim that the amplifier blew the speakers .
the amplifier is OK, I asked the customer if he turned on the preamp after the power amp, and the answer was yes, this amp is a new acquisition, never had problems with other amps.
this amplifier does not have a dc coupling cap at the input, so any dc disturbance goes directly to the output . My idea was to put a delay/protection circuit, but it does not fit, and the + output connector is soldered to the PCB, so some heavily mods had to be done, which I don't like.
I am about to put cap at the input, I dunno if this is the correct approach to protect the output for DC.
any suggestion is welcome
thanx
I received for service an audio research D300 amp, with the claim that the amplifier blew the speakers .
the amplifier is OK, I asked the customer if he turned on the preamp after the power amp, and the answer was yes, this amp is a new acquisition, never had problems with other amps.
this amplifier does not have a dc coupling cap at the input, so any dc disturbance goes directly to the output . My idea was to put a delay/protection circuit, but it does not fit, and the + output connector is soldered to the PCB, so some heavily mods had to be done, which I don't like.
I am about to put cap at the input, I dunno if this is the correct approach to protect the output for DC.
any suggestion is welcome
thanx
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The best way to "solve" this problem doesn't require anything more than turning on the equipment in the proper order. Simply turn the on preamp before the power amp, problem solved, no modifications necessary.
Mike
Mike
imho if there are doubts you can use a capacitor 4.7u NP for decoupling dc.
especially for use with PC audio output.
especially for use with PC audio output.
I should have added to my prior post that if you suspect DC at the amp outputs, you should check it to be sure, anything under 100mV is OK - the lower the better. If there is a DC offset greater than that, I recommend finding the actual reason for it and tackle it from that angle rather than just tossing a cap at it and hoping for the best.
Mike
Mike
thanx so far for the answers.
the amplifier shows a dc offset only if there is a dc at the input.
danger is, if the customer switches on the power amp before the preamp.
turning both on at the same time, is also a hazard..
reagrds
the amplifier shows a dc offset only if there is a dc at the input.
danger is, if the customer switches on the power amp before the preamp.
turning both on at the same time, is also a hazard..
reagrds
Many amplifiers have dual input ac and dc as oscilloscope.
also dc protection circuit is not a bad idea.especially in case of output stage failure.
also dc protection circuit is not a bad idea.especially in case of output stage failure.
thank you vibroking...
no, this amp does not have two inputs. the board was a good idea, but the speaker binding post is soldered to the pcb..
will try your suggestion of a 4.7 uf cap
regards
no, this amp does not have two inputs. the board was a good idea, but the speaker binding post is soldered to the pcb..
will try your suggestion of a 4.7 uf cap
regards
A few suggestions:
1) Do unsolder the speaker binding post from the pcb. In fact there should be better options available for more modern speaker binding posts, without spending that much.
2) Add a good quality switch at the input adding a film type capacitor, never a BP electrolytic. Or if you want this problem never to happen again, leave the cap always on-line.
3) A DC sensing protection and/or delay switch is not a bad idea. If they delay just the power, the chance of having DC at the output should be diminished. That is as long as that takes 5 to 10 seconds to turn on, because if it's less there might be a preamp thump.
4) Tell the owner to leave the preamp always on. That might not be energy wise, but at least would prevent preamp thumps.
thank you for your advice, Carl
what is wrong using a Muse Bipolar cap ? a 4.7 film capacitor is too big.
suggestion of changing the binding posts is interesting, that way I can wire the protection board, but am hesitant to propose this to my client as the amplifier might be downgraded (in price, not performance) due modifications.
I always see that modified amps, have lower reselling prices, or am I wrong ?
best regards
Alex
what is wrong using a Muse Bipolar cap ? a 4.7 film capacitor is too big.
suggestion of changing the binding posts is interesting, that way I can wire the protection board, but am hesitant to propose this to my client as the amplifier might be downgraded (in price, not performance) due modifications.
I always see that modified amps, have lower reselling prices, or am I wrong ?
best regards
Alex
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