Hey guys,
New to the forum but things on here look pretty damn cool.
Okay with out blabbing to much here is the problem:
Recently built my self a pair of studio 350's, how ever these were not in kit form, all has been done from scratch.
The problem im having is that the sound coming out is bassically all treble, no lows no mids.
The other thing i have noted is that the main transistors are getting hot relatively quickly, and the amplifers arent even going overly loud.
Im guessing that there might be a problem with the inductor in the circuit knocking off all the lower end of the music, as this would explain the lack of low end, and also the heating of the transistors.
If anyone has had similar resulst please pass it on.... starting to be pushed by this project being so big....
Thanks all in advance!
Nick.
New to the forum but things on here look pretty damn cool.
Okay with out blabbing to much here is the problem:
Recently built my self a pair of studio 350's, how ever these were not in kit form, all has been done from scratch.
The problem im having is that the sound coming out is bassically all treble, no lows no mids.
The other thing i have noted is that the main transistors are getting hot relatively quickly, and the amplifers arent even going overly loud.
Im guessing that there might be a problem with the inductor in the circuit knocking off all the lower end of the music, as this would explain the lack of low end, and also the heating of the transistors.
If anyone has had similar resulst please pass it on.... starting to be pushed by this project being so big....
Thanks all in advance!
Nick.
If your output inductor is like everybody else's (i.e. wound with 14awg - 20awg wire), then I strongly doubt it is the output inductor ruining your low freq response.
For the (over)heating transistors, I'd check:
1) Output stage bias setting
2) Mounting of Vbias transistor
3) Compensation caps (high freq instability?)
4) Connection to base of output devices (high freq instability?)
5) Inadequate heatsinks
6) Decoupling (or lack of)
For the lack of bass, I'd check:
1) Value of input dc blocking cap (if any)
2) Value of feedback dc cap (if any)
3) Main PSU caps (too small?)
Anytime you need to troubleshoot a discrete power amp, a good starting point is to cover the basics, then take the schematic diagram, measure the voltages at key points and see if they make sense. Good luck.
For the (over)heating transistors, I'd check:
1) Output stage bias setting
2) Mounting of Vbias transistor
3) Compensation caps (high freq instability?)
4) Connection to base of output devices (high freq instability?)
5) Inadequate heatsinks
6) Decoupling (or lack of)
For the lack of bass, I'd check:
1) Value of input dc blocking cap (if any)
2) Value of feedback dc cap (if any)
3) Main PSU caps (too small?)
Anytime you need to troubleshoot a discrete power amp, a good starting point is to cover the basics, then take the schematic diagram, measure the voltages at key points and see if they make sense. Good luck.
I have the schematic here.
First make sure that you are indeed getting clear treble and not something else that is a bit trebly but more distorted.
Are you getting the same result on both channels?
If it is clear treble then first check the input capacitor, it should be 1uF. Then check the feedback capacitor, this should be 47uF (maybe replace it with a different brand).
The only other thing I can think of at this stage is the output network. Make sure you haven't transposed the coil and the filter capacitor.
Can you post a photo of your boards, I can then compare these with the layout I have here.
Does your output go through a DC protection circuit? Somethimes these run a capacitor across relay contacts and if there is a fault some treble gets through to the speakers.
Cheers
Quasi
First make sure that you are indeed getting clear treble and not something else that is a bit trebly but more distorted.
Are you getting the same result on both channels?
If it is clear treble then first check the input capacitor, it should be 1uF. Then check the feedback capacitor, this should be 47uF (maybe replace it with a different brand).
The only other thing I can think of at this stage is the output network. Make sure you haven't transposed the coil and the filter capacitor.
Can you post a photo of your boards, I can then compare these with the layout I have here.
Does your output go through a DC protection circuit? Somethimes these run a capacitor across relay contacts and if there is a fault some treble gets through to the speakers.
Cheers
Quasi
Thanks for the help guys...
Ive spent the day looking all confused as i havnt been able to fault the circuit at all... (not being full of my self either...), and all voltages are reading text book...
Ended-up changing the source from my computer (as i usually use on all my amps and they are fine) to my cd player (dare i say... mini hifi), and long behold things sound bloody nice...
So thats my stupid fault there i spose....
How ever... i am finding that one of the modules runs abit hotter than the other. Im guessing this could also be due to the voltage being set different via VR2 giving a different current through that main output transistors? then causing more heat?
Heat sink isnt a problem... using the fan assist job from jaycar with twin 80mm fans.... (over kill i know.... lol)
Hmm... well sus the heat thing out tomorow.
THanks so much for the help guys! was getting the feeling i was alone...
Cheers again!
Nick.
PS: here is the link; http://www.siliconchip.com.au/cms/A_100503/article.html
&
http://www.siliconchip.com.au/cms/A_100618/article.html
Ive spent the day looking all confused as i havnt been able to fault the circuit at all... (not being full of my self either...), and all voltages are reading text book...
Ended-up changing the source from my computer (as i usually use on all my amps and they are fine) to my cd player (dare i say... mini hifi), and long behold things sound bloody nice...
So thats my stupid fault there i spose....
How ever... i am finding that one of the modules runs abit hotter than the other. Im guessing this could also be due to the voltage being set different via VR2 giving a different current through that main output transistors? then causing more heat?
Heat sink isnt a problem... using the fan assist job from jaycar with twin 80mm fans.... (over kill i know.... lol)
Hmm... well sus the heat thing out tomorow.
THanks so much for the help guys! was getting the feeling i was alone...
Cheers again!
Nick.
PS: here is the link; http://www.siliconchip.com.au/cms/A_100503/article.html
&
http://www.siliconchip.com.au/cms/A_100618/article.html
Hey guys,
Have spent this morning re-setting the voltages on the amp, re adjusting VR1 & VR2.
How ever, there is still one module running alot hotter than the other. Like alot!
when i say running hot, meaning that both banks of output transistors are running pretty hot, especially compared to the other module.
Both modules have the same situation, driving the same speakers, same input etc.
the sound coming from the speakers is the same, and both are sounding great =P!
Anyone got some suggestions? (still looking my self)
Cheers in advance!
Nick.
Have spent this morning re-setting the voltages on the amp, re adjusting VR1 & VR2.
How ever, there is still one module running alot hotter than the other. Like alot!
when i say running hot, meaning that both banks of output transistors are running pretty hot, especially compared to the other module.
Both modules have the same situation, driving the same speakers, same input etc.
the sound coming from the speakers is the same, and both are sounding great =P!
Anyone got some suggestions? (still looking my self)
Cheers in advance!
Nick.
Okay, well.... still getting the sam results after some more probing around.... all voltages look great, but after a while the output transistors keep heating (both banks) on one of the boards...
Unfortunatly i havnt got access to a CRO =[ would be handy...
...and im not really getting when you say oscillation??? in reference to what in the circuit?
Cheers again.
Nick.
Unfortunatly i havnt got access to a CRO =[ would be handy...
...and im not really getting when you say oscillation??? in reference to what in the circuit?
Cheers again.
Nick.
It is possible that one module is oscillating at a very high frequency (possibly Mhz?) and this would not be audible.
But I would do first is measure the voltage across all the emitter resistors (0.47 ohm) on one module and add them all up. Then do the same to the other module and compare. Do this without the input or the output connected.
While you do this, try and see if there is a big variance between the resistors also, this will give an idea of current sharing.
Cheers
Q
But I would do first is measure the voltage across all the emitter resistors (0.47 ohm) on one module and add them all up. Then do the same to the other module and compare. Do this without the input or the output connected.
While you do this, try and see if there is a big variance between the resistors also, this will give an idea of current sharing.
Cheers
Q
Hello again all,
Okay? really kinda baffled at the moment?
Spent all morning running through some of the above, and also double checking voltages as specified by S/C.
Once again everything looking great by the multi metre screen. plug it in, yep still sounds the same, let it run for a while err? hang on? it aint getting hot now?
Both channels are sounding rather nice and both are staying in the same heat range (lol, no the other one hasnt heated up to match!)
Im still thinking of what ive done? but to be honest all i have done is bolt Q8 & Q9 to the heat sink (was waiting on Nylon bolts to bolt these driver transistors down), and adjusted voltages via VR1 & VR2 ? so if anyone can see somthing there which would do it that i cant see?????
Am keeping an eye on things closely regardless though.
Now somthing that just jogged my mind... What do people recommend to use as a preamp ? Is there any kits around that would get on well with this amplifier ???
Thanks again for all the help guys!
Nick.
Okay? really kinda baffled at the moment?
Spent all morning running through some of the above, and also double checking voltages as specified by S/C.
Once again everything looking great by the multi metre screen. plug it in, yep still sounds the same, let it run for a while err? hang on? it aint getting hot now?
Both channels are sounding rather nice and both are staying in the same heat range (lol, no the other one hasnt heated up to match!)
Im still thinking of what ive done? but to be honest all i have done is bolt Q8 & Q9 to the heat sink (was waiting on Nylon bolts to bolt these driver transistors down), and adjusted voltages via VR1 & VR2 ? so if anyone can see somthing there which would do it that i cant see?????
Am keeping an eye on things closely regardless though.
Now somthing that just jogged my mind... What do people recommend to use as a preamp ? Is there any kits around that would get on well with this amplifier ???
Thanks again for all the help guys!
Nick.
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