Dear all,
I tried to build a balanced zen line stage several weeks ago, and now
it's almost finished. However, there seems to be some low frequency oscillation
because each time I connected the bzls to my power amp for test( a simple diy
LM3886) after the power transient has settled down, the bass cone kept thumping
forward and backward furiously about seven or eight times per second (both channel
). I thought it was some kind of layout problem, but I tried Mr.Pass's original
layout but omitted the negative input and output related parts and the oscillation
didn't go away. Now I have no idea what else I can do.
Here are some more detail about my modification to my circuit:
1. IRF630 instead of IRF610 for Q1 and Q2
2. Omitted R9, R11, P3, C1 (negative output)
3. Shorted R14 (negative input)
4. Used two 3kohm/2W in parallel instead of the Source resistors
5. Used two 1.5kohm/1W in parallel intead of the Drain resistors
6. used 400ohm instead of R15 and P5 (between Sources of the
transistors)
7. The rail voltages are about +/-58V. All pin voltages of the
transistors are just the same as Mr. Pass described in his article.
8. The biasing current is somewhat smaller that usual, which is
about 65mA each chanel.
9. I don't have an oscilloscope, but I can see the output of this
circuit drifting with my multimeter (input grounded)
Can anybody kindly give me some advice about what is wrong about my circuit
? Thank you!!
EJ.
I tried to build a balanced zen line stage several weeks ago, and now
it's almost finished. However, there seems to be some low frequency oscillation
because each time I connected the bzls to my power amp for test( a simple diy
LM3886) after the power transient has settled down, the bass cone kept thumping
forward and backward furiously about seven or eight times per second (both channel
). I thought it was some kind of layout problem, but I tried Mr.Pass's original
layout but omitted the negative input and output related parts and the oscillation
didn't go away. Now I have no idea what else I can do.
Here are some more detail about my modification to my circuit:
1. IRF630 instead of IRF610 for Q1 and Q2
2. Omitted R9, R11, P3, C1 (negative output)
3. Shorted R14 (negative input)
4. Used two 3kohm/2W in parallel instead of the Source resistors
5. Used two 1.5kohm/1W in parallel intead of the Drain resistors
6. used 400ohm instead of R15 and P5 (between Sources of the
transistors)
7. The rail voltages are about +/-58V. All pin voltages of the
transistors are just the same as Mr. Pass described in his article.
8. The biasing current is somewhat smaller that usual, which is
about 65mA each chanel.
9. I don't have an oscilloscope, but I can see the output of this
circuit drifting with my multimeter (input grounded)
Can anybody kindly give me some advice about what is wrong about my circuit
? Thank you!!
EJ.