Hi Vunce, can you point me to the details on the R21 psu modules you have mentioned in this thread, thanks.
Actually, there is 6 connection points aligned with Prasi’s CRC PCB. I’ve used 1 A diode cutoff wires for connection. On the picture, all connection points are not visible and this is 1.4 version PCB, where connection points were not well aligned with CRC PCB.
You say max 20 Watt in 4 Ohm.
That is a peak current of 3.16 Ampere.
Which means minimum 1.58 Ampere bias for Class A.
What bias do you use for 8 Ohm?
What bias do you recommend for 4 Ohm?
That is a peak current of 3.16 Ampere.
Which means minimum 1.58 Ampere bias for Class A.
What bias do you use for 8 Ohm?
What bias do you recommend for 4 Ohm?
Post #19
See first point in the list of objective development goals. 20 W is just extra bonus in AB class, still with distortion profile (measured, not simulated) worthy of class A operation.
See first point in the list of objective development goals. 20 W is just extra bonus in AB class, still with distortion profile (measured, not simulated) worthy of class A operation.
I have a similar amp in my simulation.
Opamp drive 0281/0302 in class AB.
THD 0.0007% at 1kHz
THD 0.015% at 20kHz.
Both are at the 1 Watt output in to 8 Ohm.
Opamp drive 0281/0302 in class AB.
THD 0.0007% at 1kHz
THD 0.015% at 20kHz.
Both are at the 1 Watt output in to 8 Ohm.
12V AC is not enough for 1 A average load. It would provide 15 V DC at most. Power supply considerations are at post #35.
My build is with regulated PS as this is my way of building an ultimate amplifier. 🙂
My build is with regulated PS as this is my way of building an ultimate amplifier. 🙂
Here is result of 32 tone signal test. From DAC with nominal 2Vrms output, 710 mV multitone was feed to amplifier input. That was maximum before REW signal generator would proclaim DAC output clipping. At amplifier output was chaotic signal with 16 V peak to peak. Through attenuator, output signal was forwarded to Cosmos ADC. Result speaks for itself. It looks like multitone measured direct at some DAC output, rather than from amplifier output.
@tombo56, in post #19 you mentioned you would add corresponding voltages for various bias currents as measured at R16 or R17. I can't see a post where you have listed that information, can you provide some details thanks. I have your pcb's half built, so would be looking for some biasing info in the next couple of weeks, thanks. would also be interested in your final bias selection for both 4ohm and 8ohm loads.
Regards,
Gary.
Regards,
Gary.
Didn’t expect anyone is near building phase.
Bias current can be measured through voltage at R16/R17 resistors.
Actual current depends on heatsink temperature. Lower voltage is for moderately warm heatsinks and higher is for heatsinks at 40 °C.
Bias current can be measured through voltage at R16/R17 resistors.
- 0.8 A 160 - 170 mV
- 1 A 250 - 270 mV
- 1.2 A 340 – 360 mV
Actual current depends on heatsink temperature. Lower voltage is for moderately warm heatsinks and higher is for heatsinks at 40 °C.
As this is an amplifier reaching above 1 MHz and using the whole outer PCB surfaces as grounded shields, it would be a good practice in principle to place resistors slightly above PCB surface, to minimize parasitic capacitances. It is good in principle but not required. During development, this amplifier worked and was harassed as a 1.8 – 2 MHz device. All was well.
It is enough to lift NFB resistors R3, R4, R5, R6. Rest, if you like.
My opinion is that good amplifier must have a great safety margin. For offering this to DIY fellows, frequency response was reduced to 1.3 MHz as this increases phase margin to some 80°.
Mine amplifier is exactly the same as published. I can’t have different pudding than offered to anyone else.
So, I used 0.5 mm thick Teflon strip to elevate resistors before soldering. I’m sure you can find something suitable as well.
It is enough to lift NFB resistors R3, R4, R5, R6. Rest, if you like.
My opinion is that good amplifier must have a great safety margin. For offering this to DIY fellows, frequency response was reduced to 1.3 MHz as this increases phase margin to some 80°.
Mine amplifier is exactly the same as published. I can’t have different pudding than offered to anyone else.
So, I used 0.5 mm thick Teflon strip to elevate resistors before soldering. I’m sure you can find something suitable as well.
Thanks for the bias info, now have that printed out. I am probably 40% through the build, taking it slowly. I thought I had some Exicon laterals stashed away, but now can't find them so will have to order from Profusion UK, so that will be 3 weeks delivery or so. Good tip on the resistors, I can do that., I normally sit 0.5W resistors 2mm above the pcb and 3W resistors 5mm above the pcb.
I thought Vunce might have started his build as well.
The boards I got from JLCPCB look great, you have done a great job with the layout. I see you have gone for the fashionable purple, I went for blue this time.
I thought Vunce might have started his build as well.
The boards I got from JLCPCB look great, you have done a great job with the layout. I see you have gone for the fashionable purple, I went for blue this time.
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Ah, no. I wouldn’t dare at 16 Vpp. It was 8 Ω resistor.
It is worth to mention that hash, rising with frequency from -150 to -135 dBV levels, was not produced by amplifier or used DAC. It is a Cosmos ADC artifact. Here is what designer measured for Cosmos ADC.
It is worth to mention that hash, rising with frequency from -150 to -135 dBV levels, was not produced by amplifier or used DAC. It is a Cosmos ADC artifact. Here is what designer measured for Cosmos ADC.