hello!
well i have this 15 years old power amp at home..
it uses 2N6254 transistors in the output section...
now i've noticed a few things about this amp (it's a 100W/150W pow amp depending on the output impendance 4/2ohms)...
when i use it for amplifing vocals (with a microphone preamp) it is really loud and works fine, no problems..
but when i use it with guitar (guitar preamp of course) it just starts to fart (low frequencies) when trying to get the half of the volume, and bass guitar is no way to go for this pow amp since it cuts and farts on bass frequencies TERRIBLY!!
what's wrong with this, seems like the amp has a really poor frequency characteristic, is it omited by the power transistors characteristic or is it possible to flat it out somehow?
this is really frustrating since i tried to feed the amp with a "normal" music signal (line out of the cd player) and still it lacks bass... ALOT...
i've connected this amp to a 2x12" cabinet with 2 bass speakers (30Hz-3500Hz)...
heh... damn...
there should be tons of bass...
well i have this 15 years old power amp at home..
it uses 2N6254 transistors in the output section...
now i've noticed a few things about this amp (it's a 100W/150W pow amp depending on the output impendance 4/2ohms)...
when i use it for amplifing vocals (with a microphone preamp) it is really loud and works fine, no problems..
but when i use it with guitar (guitar preamp of course) it just starts to fart (low frequencies) when trying to get the half of the volume, and bass guitar is no way to go for this pow amp since it cuts and farts on bass frequencies TERRIBLY!!
what's wrong with this, seems like the amp has a really poor frequency characteristic, is it omited by the power transistors characteristic or is it possible to flat it out somehow?
this is really frustrating since i tried to feed the amp with a "normal" music signal (line out of the cd player) and still it lacks bass... ALOT...
i've connected this amp to a 2x12" cabinet with 2 bass speakers (30Hz-3500Hz)...
heh... damn...
there should be tons of bass...
Hi Branimir.
I've asked you the model because I have a whole bunch of RIZ schematics.ISKRA...thats a another story.But...maybe they have some common stuff.
Some of RIZ amplifiers are developed for public adress systems,like in hospitals,bus stations etc.They have a LP/HP filter.
These filters passes signals between 300Hz-2,5kHz,so they can sound "flat" as you said.These amps allready have a MIC preamplifier on the input,so connecting a source with 0,5V output(CD Player,Tuner)can cause strong distorsions.Maybe that is a reason for "farting"sound.
Everything is possible and if you are not sure what to do, take it to the local expert for a second opinion.I think the amp is ok.
By the way maybe some Slovenian guys on this forum can find some specs for your amp.
Regards.
I've asked you the model because I have a whole bunch of RIZ schematics.ISKRA...thats a another story.But...maybe they have some common stuff.
Some of RIZ amplifiers are developed for public adress systems,like in hospitals,bus stations etc.They have a LP/HP filter.
These filters passes signals between 300Hz-2,5kHz,so they can sound "flat" as you said.These amps allready have a MIC preamplifier on the input,so connecting a source with 0,5V output(CD Player,Tuner)can cause strong distorsions.Maybe that is a reason for "farting"sound.
Everything is possible and if you are not sure what to do, take it to the local expert for a second opinion.I think the amp is ok.By the way maybe some Slovenian guys on this forum can find some specs for your amp.
Regards.
hey...
this amp doesn't have a mic preamp, it has an output transformer for 70V and 100V line outs, and i have another one just 200W/300W (mono ofcourse) and it's dead for bout two years, haven't got time to check it out..
anyways, thanx...
i'm already building a 150W amp with two TDA7249, i'll just leave this one for vocal purposes..
cheers
this amp doesn't have a mic preamp, it has an output transformer for 70V and 100V line outs, and i have another one just 200W/300W (mono ofcourse) and it's dead for bout two years, haven't got time to check it out..
anyways, thanx...
i'm already building a 150W amp with two TDA7249, i'll just leave this one for vocal purposes..
cheers
HighTec said:
if interstage cap lost his value,then it's good to some highish F3.
when you try to amplify some lower frequencies,with lousy cap (especially with bad cap in place of decoupling (collectors,emiters)
you'll hear farting.
if you don't have CRO for troubleshootin' ,try with cheap PC spks as signal follower. just place some 1uF in series with input and start from input of amp.
you can use your finger as signal injector
I think you have already solved your problem. If it has the 70V output transformer, chances are, it was made for vocals. The output transformer may not have a deep frequency response. I was considering repairing an old Bogen amp the other day but had some bad feelings about the 70V output and put it back into the junk pile. Bogen was well known for its PA amps eg. amps for hospitals, stores, etc. where they don't need the whole frequency range.
Good luck,
Chris
Good luck,
Chris
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