Recent content by Gingerbunny82

Hey folks, I'm building this steel platform to support a furnace, the furnace will weigh about 350kg and cover approximately the area shown below: The platform itself is mild steel sheet, 100cm x 100cm x 4mm thick. Each castor is rated for 300kg each. The problem I'm having is that even with...

- I'm thinking it primarily operates in Class-B to be honest, the driver transistors aren't mounted on the same heatsink as the output transistors, so the output transistors get hot whilst the drivers barely get above ambient. :P - I took a look at the output waveform on an oscilloscope, I can...

Thanks for all your replies folks, I'll take what you all said on board - and thanks for taking the time to help me out, cheers Gingerbunny82

- Thanks for the reply, I've removed the 220k resistors from the circuit. And added a bypass for the feedback. The Vbe of the output transistor increases as the collector current does, so the difference in Vbe between the driver and output transistors increases as the load does? I think I...

Thanks for your reply, I have taken some current measurements, I believe the bias current is set by the 3K3 resistors connected to the emitters of the drivers. Current measurements are in orange. The measurements have been taken with no input signal again. :)

I'll be honest, none I think. When I first started building this amp I only had basic knowledge of electronic design. I think I originally put them into set the mid-point or DC bias for the op-amp output signal. But I'm not sure they make a difference as the bias is controlled by the op-amp and...

Thanks for the reply, I thought that also, I thought they were supposed to be identical just opposite polarity. But I have a stereo version of the above circuit and both channels show the same difference in voltage. -0.85 for the NPN and +1.18v for the PNP. I can't see how the circuit could...

Thanks for the reply - I thought that because the driver transistors are also darlington transistors, that they would drop double the voltage a single transistor would. Therefore dropping say 1.2 - 1.3v enough to bias the output darlingtons? Like below??

- The TIP 126 data sheet says it has a small signal current gain Hfe of 1800 up to 20khz, the 3K3 resistor provides a base current of 5mA. If I make 3K3 a lower value say 1K5 the amplifier sounds horrible. Distorting even at low volumes. Why is this?

Hi folks thank you for all your replies, I have been reading through them carefully. Svein I will take a look at that link, thank you. And thank you thankz (lol) for the book suggestion - looks good. I have not changed the circuit yet, but I have taken some measurements @ ±18v of the circuit...

Thanks for your input Averagesupernova, What I meant is make all the NPN transistors the same model and all PNP transistors the same, so the above schematic would have (2x) TIP 121 NPN and (2x) TIP 126 PNP.

Firstly, many thanks for the replies folks, - I was under the impression that this voltage was provided by the driver transistors TIP 117 and TIP 112, is this incorrect? - I was hoping to get around 25w into 4Ω @ ±18v. Is this obtainable, my circuit draws 30mA with no input connected. - I...

Hi folks, I've designed this amplifier, it uses an Ne5532p op-amp for the voltage amplification and feedback in the non-inverting configuration. The output stage is handled by two Darlington transistors, TIP 121 and TIP 126, these are hopefully biased by TIP 117 and TIP 112. I was hoping that...