Amplifier Testing

[sakis]

i wonder how many of these amps shown in this forum ....to begin with as schematics ever managed to make what destroyer x says real life and also let us for a minute define real life...... cause if real life means carefull listening ...(after scopes and simulation of course) of nice music with very good speakers .....its simply not enough ....at least for me ....

PA use or even better abuse should be the real thing working for 5-6 hours to a 100% or may be more .....overdriving ....bi amp... hotsuap of plugs ...distorted signals and goes on

Thats real life to me ..... and of course its not importand if amp is 45 or 600w abuse is abuse in any way you look at it .... and even if the use is PA i dont find any no reason why the sound should be also very nice there

i wonder what simulators have to say about that ..... also reminds me how many B&W speakers come in to my shop for repair after just a simple kids party ..... also amps ..... outputs shorted or even transformes burned to hell .....

still i belive that info existing in the forum is so critical and also the amazing will of people to do and share audio from scratch !!!!!!

happy easter to diyaudio !!!! all the best !!!!

[destroyer X]

Can you inform more things for us, please.

What amplifier was abused?

Can you please post schematic?

Was this abuse over resistive loads or speakers?

Can you, please, post some pictures?

Have you adjusted Bora amplifier to your needs?

What modifications have you done?

I will be happy to know.

good to see you here Mr. Petropoulos

Carlos

[unclejed613]

i work in a pro audio shop, and yes, these amps get abused. usually they are run for several hours at a time, at or near 100% power, with inadequate cooling and squirrelly loads (half of which also have blown drivers).
then about half way through the evening when everybody's ears have become numb from 120+db sound levels, they try to push the amp even harder........ quite often letting out the magic smoke .....


tom holman used to say that running a class AB amp at between 50 and 75% power was actually harder on the output devices, because they dissipated much more heat per output watt than they did at full power.

[sakis]

the original problem was when tryied to operate boras amp legend 4 with voltage 60-66vdc per rail ......

it all end up to almost 150 very expensive mosfets send to outer space while testing and trying to make it work ......

input was to sensitive to anything like a hot suap of plugs or just a litle bit of overdrive

bora of course recomended to add 0.18R 5W to the out of every mosfet as first change

and then a 33-56 pf miller styroflex capacitor between b and c on the MJE 340 vas amplifier to improove some ocilation was there

schematic is also available ......

still didnt work

destroyer x a very nice guy from brasil his original name is Carlos Eugênio Mergulhão - Destroyer x [B] and me worked out some mods and in real life this all seems to work no matter if used or abused ha ha ha ....

the new schematic is also available

[sakis]

this is the modified schematic by Carlos Eugênio Mergulhão - Destroyer x and me ....

any opinion will be very welcome ...thanks

[jaycee]

well the feedback was changed which is probably why its now stable.

Personally i wouldn't use bootstrap or the resistive current source, OR the diode but thats just me

[unclejed613]

personally i would use a dc servo instead of the offset cap. i don't like reactive components in the feedback loop...... offset caps launch the amp to the rails when they go bad. a dc servo uses caps, but with a much lower voltage rating and capacitance, and early warning signs of failure, such as high ESR are more easily troubleshot, since it tends to reduce the low freq gain of the amp first, rather than the first sign of trouble being the amp latching to the rail.

[sakis]

well thank you for posting in any way .....

all this is too much theory to me that i canot really understand ....you see i am a constructor ...a screwdriver guy i cannot come in so deep in theory ...i dont run simulators .....but i do construct .... often from scratch ....

so if you like to post a schematic with your opinion that will be very nice for me and carlos that bother with this story also .....

for anything that worths the amp as is now seems to be running like hell supplied with 66+66 vdc per rail .... and four of them worked in party ....abused like hell ... biamped......personaly take care of pushing them to the limit with out any problems ...even with models that had ..lets say not enough cooling the performance was nice and the temprature was very ok meaning that they got warm but not hot .....

since i dont run simulators ...to my ears sound was just perfect but on the other hand could i ever tell diference with some small changes on feedback ???? really dont know ....

any help is so welcome

[CBS240]

Originally posted by unclejed613
i work in a pro audio shop, and yes, these amps get abused. usually they are run for several hours at a time, at or near 100% power, with inadequate cooling and squirrelly loads (half of which also have blown drivers).
then about half way through the evening when everybody's ears have become numb from 120+db sound levels, they try to push the amp even harder........ quite often letting out the magic smoke .....


tom holman used to say that running a class AB amp at between 50 and 75% power was actually harder on the output devices, because they dissipated much more heat per output watt than they did at full power.

IMHO, the adjective 'pro' seems to be synonymous with 'loud'. Of course if you make it loud enough, then the sensitivity of peoples' ears will react to the sound pressure and they won't hear the distortion coming from the over-driven amp anyway.

[unclejed613]

there are real pro's out there that can run a system at far above 120db, but nobody will notice it, until they try to talk to somebody next to them. they run the system so clean that it doesn't sound "loud" at all. then there are the "pro's" that can't seem to get more than 100db out of a system, but it sounds "loud" (so severely overdriven that it sounds like exploding dog doo), and they're the ones that blow up amps and speakers on a regular basis