Hum problems
Hi john, thanks for the tips, well grounding the input does not produce any hum. I have had to modify the circuit as shown in the attachement. Its stable at this point. i had added a resistor between Q1 and the +ve rail and this also helped in adding more hum since it was forcing current to flow through the VAs but the simulation graphs showed better linerity. I will try add a current mirror to the circuit, remove C1 and see if the PSRR improves. But this version has a very inaudible hum when placing the ear next to the speaker with a +-15V psu filtered with 2x4700uF. I'll keep posted about the effect of the current mirror.
thanks
Patrice
Hi john, thanks for the tips, well grounding the input does not produce any hum. I have had to modify the circuit as shown in the attachement. Its stable at this point. i had added a resistor between Q1 and the +ve rail and this also helped in adding more hum since it was forcing current to flow through the VAs but the simulation graphs showed better linerity. I will try add a current mirror to the circuit, remove C1 and see if the PSRR improves. But this version has a very inaudible hum when placing the ear next to the speaker with a +-15V psu filtered with 2x4700uF. I'll keep posted about the effect of the current mirror.
thanks
Patrice
Attachments
Hi zeus-threat
It's pretty straightforward. Start with the current you need. Call this I. With a 5.6V zener diode on the base of the CCS, the voltage across the emitter resistor of the CCS transistor is about 5V. So this makes the resistor 5/I ohms.
The 5.6V zener diode needs between 2 and 5 mA to bias it normally, and it is tempting to run at lower currents than higher. In any case this should be at least 10 times the base current of the CCS transistor.
Normally a BC237B, BC307B or similar device has a gain of 200 and the base current is likely to be ~10 uA for a CCS of 2 mA. So 2mA in the zener is pretty high, and won't be affected by Ib.
If the decoupling zener is 10V, then a 2.2k resistor will give (10-5.6)/2.2 or 2 mA to bias the 5.6V zener.
The final calculation is to set the resistor to feed the current to the 10V zener, the 5.6V zener and the CCS all together. If the CCS had a 2.2k resistor in the emitter, then the CCS is going to be 5/2.2=2.27 mA. The CCS and 5.6V zener take a total of 4.27 mA in this case.
The 10V zener should run at a minimum of 2 mA to ensure it operates in the zener region (actually avalanche). You need to allow for the minimum power supply voltage. Suppose you have a 50W amp running from +/- 35V capacitors, but on load these drop to 30V.
The resistance should be (30-10)/(4.27+2)=3.2 k and you could choose 3.3k nearest.
I generally run the 10V zener at a little higher current (4-5 mA) to allow for bigger voltage drops and use a resistor of (30-10)/(4.27+4) = 2.2k nearest. This also allows the CCS to get up to working current faster during power turn-on when the voltage starts to rise from zero.
One more point - the power dissipation in this resistor to the power line needs to be checked. This time, the worst case is with the highest power rail voltage. Let's say we use a 2.2k resistor, and on light loading the power supply reaches 38V. The power is (38-10)*(38-10)/2.2k = .36W so you should use a 1W resistor (in theory a 0.5W resistor would do but this is a little close to the limit).
hope this explains it!
cheers
John
It's pretty straightforward. Start with the current you need. Call this I. With a 5.6V zener diode on the base of the CCS, the voltage across the emitter resistor of the CCS transistor is about 5V. So this makes the resistor 5/I ohms.
The 5.6V zener diode needs between 2 and 5 mA to bias it normally, and it is tempting to run at lower currents than higher. In any case this should be at least 10 times the base current of the CCS transistor.
Normally a BC237B, BC307B or similar device has a gain of 200 and the base current is likely to be ~10 uA for a CCS of 2 mA. So 2mA in the zener is pretty high, and won't be affected by Ib.
If the decoupling zener is 10V, then a 2.2k resistor will give (10-5.6)/2.2 or 2 mA to bias the 5.6V zener.
The final calculation is to set the resistor to feed the current to the 10V zener, the 5.6V zener and the CCS all together. If the CCS had a 2.2k resistor in the emitter, then the CCS is going to be 5/2.2=2.27 mA. The CCS and 5.6V zener take a total of 4.27 mA in this case.
The 10V zener should run at a minimum of 2 mA to ensure it operates in the zener region (actually avalanche). You need to allow for the minimum power supply voltage. Suppose you have a 50W amp running from +/- 35V capacitors, but on load these drop to 30V.
The resistance should be (30-10)/(4.27+2)=3.2 k and you could choose 3.3k nearest.
I generally run the 10V zener at a little higher current (4-5 mA) to allow for bigger voltage drops and use a resistor of (30-10)/(4.27+4) = 2.2k nearest. This also allows the CCS to get up to working current faster during power turn-on when the voltage starts to rise from zero.
One more point - the power dissipation in this resistor to the power line needs to be checked. This time, the worst case is with the highest power rail voltage. Let's say we use a 2.2k resistor, and on light loading the power supply reaches 38V. The power is (38-10)*(38-10)/2.2k = .36W so you should use a 1W resistor (in theory a 0.5W resistor would do but this is a little close to the limit).
hope this explains it!
cheers
John
CCS
Hi John thanks for the reply. I will try to work out the values and tell you how things have been going. In the mean time i replaced TIP2955/3055 with 2SA1673/2sc4388 and BD139/140 with 2SA635/2SC2285. The performance and the kick in the lows is much better i even tried it in a triamp LR4 X-over and the performance is really good. My only concern at this point is that the outputs are staying cool all the time even with an iddle current of 70mA. I need to recheck my connections.
Thanks again
Patrice
Hi John thanks for the reply. I will try to work out the values and tell you how things have been going. In the mean time i replaced TIP2955/3055 with 2SA1673/2sc4388 and BD139/140 with 2SA635/2SC2285. The performance and the kick in the lows is much better i even tried it in a triamp LR4 X-over and the performance is really good. My only concern at this point is that the outputs are staying cool all the time even with an iddle current of 70mA. I need to recheck my connections.
Thanks again
Patrice
Where is the PCB for TIP35+36
Dear Bro
Where is the PCB For you AMP[ TIP35c and TIP36c]
i found a PCB that using a pair 35&36 check urself
http://www.elecfree.com/electronic/...power-amp-super-bridge-120w-by-ic-tda2030.jpg
Dear Bro
Where is the PCB For you AMP[ TIP35c and TIP36c]
i found a PCB that using a pair 35&36 check urself
http://www.elecfree.com/electronic/...power-amp-super-bridge-120w-by-ic-tda2030.jpg
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.