Silicon chip studio 350: HELP NEEDED (please!) - Page 2

81gl · 25th September 2006, 08:25 AM

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.

quasi · 25th September 2006, 10:10 AM

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

clem_o · 25th September 2006, 01:04 PM

This may work:

Put your finger on the 6R8 5W resistor near the output terminals of the amp. Without any signal going in, that resistor is supposed to remain stone-cold. Any warmth means your amplifier is oscillating. Verify against the other channel's resistor to be sure...

Cheers!

Nigel Goodwin · 25th September 2006, 01:38 PM

Any UK members might be interested that EPE has just reprinted the SiliconChip article, part one this month (circuit etc.), part 2 next month (PCB layout).

But, like others here, I would suggest checking the bias current - you've never mentioned what you have them set at?.

81gl · 26th September 2006, 05:14 AM

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.

81gl · 2nd October 2006, 11:41 AM

Bump...

Things are going great with the amplifier, my my they sound nice!

Just wondering what people are using for volume control ? as siad, are there any decent pre-amp kits out there that will work well?

Cheers all,

Nick.

25th September 2006, 10:10 AM	#12
quasi diyAudio Member Join Date: Sep 2004 Location: Adelaide, Australia	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 __________________ http://sites.google.com/site/quasisdiyaudiosite/

25th September 2006, 01:38 PM	#14
Nigel Goodwin diyAudio Member Join Date: Jul 2005 Location: North Derbyshire	Any UK members might be interested that EPE has just reprinted the SiliconChip article, part one this month (circuit etc.), part 2 next month (PCB layout). But, like others here, I would suggest checking the bias current - you've never mentioned what you have them set at?. __________________ Nigel Goodwin

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25th September 2006, 08:25 AM	#11
81gl diyAudio Member Join Date: Sep 2006	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.

25th September 2006, 01:04 PM	#13
clem_o diyAudio Member Join Date: Jun 2005 Location: Manila	This may work: Put your finger on the 6R8 5W resistor near the output terminals of the amp. Without any signal going in, that resistor is supposed to remain stone-cold. Any warmth means your amplifier is oscillating. Verify against the other channel's resistor to be sure... Cheers!

26th September 2006, 05:14 AM	#15
81gl diyAudio Member Join Date: Sep 2006	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.

2nd October 2006, 11:41 AM	#16
81gl diyAudio Member Join Date: Sep 2006	Bump... Things are going great with the amplifier, my my they sound nice! Just wondering what people are using for volume control ? as siad, are there any decent pre-amp kits out there that will work well? Cheers all, Nick.

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