Studio 350 bias problem

Howardc · 26th July 2005, 06:32 AM

I have a friend who has built 2 of the studio 350 amps featured in Jan/Feb 2004 Silicon Chip magazine. They both have the same bias problem, where the output is at rail volts. All components have been double-checked, esp. transistor pinouts. The only way I could get the output voltage close to zero was to reduce the value of resistors in Q4 & Q5 collectors. This causes high currents, & tends to overheat these transistors.

Has anyone had a similar problem with this amp?

Howard

AllanA · 15th August 2005, 06:58 AM

I have had the same problem. I also note that another user (Silicon Chip issue 194, Nov 04) encountered this problem. Silicon Chip advised him:
"Our guess is that you have swapped a pair of transistors or you have an open-circuit solder connection somewhere. Replace the fried resistors and power up the board again, with the resistors across the fuseholders, and check each transistor for a base-emitter voltage of about 0.7V. An incorrect reading indicates a fault in the transistor or its associated components".
In my case, I have exhaustively checked component positioning. I have also checked all resistors and most other components by multimeter. I have checked all solder joints. In the end I replaced diodes D1, D2, D3 and transistors Q1- Q9. Didn't make any difference. In my case, the problem is focussed on 3 voltages which are hopelessly out of spec:
- across 6.8k 1W resistor near base of Q6 (123V, should be 60V)
- +70V to collector of Q6 (132V, should be 69V)
- -70V to collector of Q5 (4V, should be 69V)

rpapps · 15th August 2005, 09:11 AM

Hi all
Here are some notes and errata from the Silicon Chip web site.

Studio 350 Power Amplifier Module, January 2004: The 470ìF 100V electrolytic capacitor connected to the -70V rail (adjacent to fuse F2) is shown reversed on the circuit diagram (Fig.7). (02/04)

Studio 350 Power Amplifier Module, February 2004: The ±70V power supply wiring colours shown on the overlay diagram (Fig.1) disagrees with the wiring colours shown on the power supply wiring diagram (Fig.6). In all cases, the +70V wiring should be red and the -70V wiring blue. The ±70V markings on the PC board and diagrams are correct. The wiring diagram for the Silicon Chip Online website is correct. (04/04)

Hope this is of some help
Cheers
Rob

vargasmongo3435 · 23rd June 2011, 01:22 PM

Hi guy!

Hey I got a new PCB layout for studio 350 power amp and I just wondering if the polarity of the cap close to F2 is correct before I order a couple of boards?

vargasmongo3435 · 23rd June 2011, 01:24 PM

Sorry I did specify, the 470uF cap it goes that way or the positive pointing up?

vargasmongo3435 · 23rd June 2011, 01:28 PM

damn stupid me ! " I didn't specify" sorry English is my second language

Tube_Dude · 24th June 2011, 07:23 AM

Quote:

Originally Posted by vargasmongo3435

Sorry I did specify, the 470uF cap it goes that way or the positive pointing up?

Hola

The capacitor orientation is correct. The (+) must be in the lower side...

vargasmongo3435 · 24th June 2011, 12:04 PM

muchas gracias señor

vorezky04 · 20th November 2011, 12:11 AM

what this power??

nazirdigi · 20th November 2011, 03:16 AM

check the resistors they are one percent tolerence.

26th July 2005, 06:32 AM	#1
Howardc diyAudio Member Join Date: Jul 2005 Location: Sydney	Studio 350 bias problem I have a friend who has built 2 of the studio 350 amps featured in Jan/Feb 2004 Silicon Chip magazine. They both have the same bias problem, where the output is at rail volts. All components have been double-checked, esp. transistor pinouts. The only way I could get the output voltage close to zero was to reduce the value of resistors in Q4 & Q5 collectors. This causes high currents, & tends to overheat these transistors. Has anyone had a similar problem with this amp? Howard

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15th August 2005, 06:58 AM	#2
AllanA diyAudio Member Join Date: Aug 2005	I have had the same problem. I also note that another user (Silicon Chip issue 194, Nov 04) encountered this problem. Silicon Chip advised him: "Our guess is that you have swapped a pair of transistors or you have an open-circuit solder connection somewhere. Replace the fried resistors and power up the board again, with the resistors across the fuseholders, and check each transistor for a base-emitter voltage of about 0.7V. An incorrect reading indicates a fault in the transistor or its associated components". In my case, I have exhaustively checked component positioning. I have also checked all resistors and most other components by multimeter. I have checked all solder joints. In the end I replaced diodes D1, D2, D3 and transistors Q1- Q9. Didn't make any difference. In my case, the problem is focussed on 3 voltages which are hopelessly out of spec: - across 6.8k 1W resistor near base of Q6 (123V, should be 60V) - +70V to collector of Q6 (132V, should be 69V) - -70V to collector of Q5 (4V, should be 69V)

15th August 2005, 09:11 AM	#3
rpapps diyAudio Member Join Date: Jul 2004 Location: nowhere of interest	Hi all Here are some notes and errata from the Silicon Chip web site. Studio 350 Power Amplifier Module, January 2004: The 470ìF 100V electrolytic capacitor connected to the -70V rail (adjacent to fuse F2) is shown reversed on the circuit diagram (Fig.7). (02/04) Studio 350 Power Amplifier Module, February 2004: The ±70V power supply wiring colours shown on the overlay diagram (Fig.1) disagrees with the wiring colours shown on the power supply wiring diagram (Fig.6). In all cases, the +70V wiring should be red and the -70V wiring blue. The ±70V markings on the PC board and diagrams are correct. The wiring diagram for the Silicon Chip Online website is correct. (04/04) Hope this is of some help Cheers Rob

23rd June 2011, 01:22 PM	#4
vargasmongo3435 diyAudio Member Join Date: May 2011 Location: Quebradillas, Puerto Rico	Hi guy! Hey I got a new PCB layout for studio 350 power amp and I just wondering if the polarity of the cap close to F2 is correct before I order a couple of boards?

23rd June 2011, 01:24 PM	#5
vargasmongo3435 diyAudio Member Join Date: May 2011 Location: Quebradillas, Puerto Rico	Sorry I did specify, the 470uF cap it goes that way or the positive pointing up?

23rd June 2011, 01:28 PM	#6
vargasmongo3435 diyAudio Member Join Date: May 2011 Location: Quebradillas, Puerto Rico	damn stupid me ! " I didn't specify" sorry English is my second language

24th June 2011, 12:04 PM	#8
vargasmongo3435 diyAudio Member Join Date: May 2011 Location: Quebradillas, Puerto Rico	muchas gracias señor

20th November 2011, 12:11 AM	#9
vorezky04 diyAudio Member Join Date: Dec 2010 Location: Medan, North Sumatera	what this power??

20th November 2011, 03:16 AM	#10
nazirdigi diyAudio Member Join Date: Oct 2009	check the resistors they are one percent tolerence.