R Tobey & J Dinsdale published an article "Transistor Audio Power Amplifier" in Wireless World in Nov 1961. This was modified by them in Jan 65. A Retrospect was published by them in WW in Nov 69. The first one is available in Self's site:
The Wireless World Archive
This circuit was adopted to Silicon Planar Transistors by John Lawrence Linsley Hood (JLH) and published in WW in Feb 70. At that time, I made notes and drew the circuit in my note book. I am reproducing below the circuit as well as my notes. I do not remember whether it is a regular article, circuit idea or in Letters to the Editor.
---Modified Dinsdale amplifier for use with Silicon Planar Transistors. Output 10W, 15 ohms or 15W 8 ohms. Suitable for use with either +ve or -ve ht line depending on Transistor type. Amended component values are underlined. Capacitor C5, Diode D1, and Resistors R5, R9, R10 & R12 in the original design are omitted.
The distortion is typically 0.07% at 1 KHz and 10W and the square wave response is free from overshoot or ringing even with capacitive loads upto beyond 20 KHz.
The circuit can be used with -ve HT rail with Tr types shown in table, provided the electrolytic capacitors are reversed. The numbering of the components is that used in the original article in Jan65.
The loud speaker plop on switching on is avoided by DC coupling the NFB to the first transistor via R16. This causes the potential at the loud speaker output to rise fairly slowly as C charges. This arrangement reduces hum pickup on badly smoothed HT supplies....
Geoff may kindly add this diagram and notes to his site if it is found suitable.
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www.samritatrust.org
The Wireless World Archive
This circuit was adopted to Silicon Planar Transistors by John Lawrence Linsley Hood (JLH) and published in WW in Feb 70. At that time, I made notes and drew the circuit in my note book. I am reproducing below the circuit as well as my notes. I do not remember whether it is a regular article, circuit idea or in Letters to the Editor.
---Modified Dinsdale amplifier for use with Silicon Planar Transistors. Output 10W, 15 ohms or 15W 8 ohms. Suitable for use with either +ve or -ve ht line depending on Transistor type. Amended component values are underlined. Capacitor C5, Diode D1, and Resistors R5, R9, R10 & R12 in the original design are omitted.
The distortion is typically 0.07% at 1 KHz and 10W and the square wave response is free from overshoot or ringing even with capacitive loads upto beyond 20 KHz.
The circuit can be used with -ve HT rail with Tr types shown in table, provided the electrolytic capacitors are reversed. The numbering of the components is that used in the original article in Jan65.
The loud speaker plop on switching on is avoided by DC coupling the NFB to the first transistor via R16. This causes the potential at the loud speaker output to rise fairly slowly as C charges. This arrangement reduces hum pickup on badly smoothed HT supplies....
Geoff may kindly add this diagram and notes to his site if it is found suitable.
----------------------------
www.samritatrust.org
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Nice circuit, Gannaji, though it uses CFP output stage in Class AB, which I have found is not the best for crossover distortion.
How are you coming along with your FetZilla, which also uses current feedback at the emitter of the input device?
Hugh
How are you coming along with your FetZilla, which also uses current feedback at the emitter of the input device?
Hugh
Nice circuit but is it going any where thermal stability not great due to no compensation other than high value emitter resistors on the output devices
I honestly do not like the fact that their is no bias adjust in order to obtain best results
Aksa I have myself had great results with CFP output stages with care-full selection of devices and current setngs 0.02 at 1 khz and 8 oms @ 1 watt on a 30 watt unit that was even back in the early 1980,s
Regards Trev
I honestly do not like the fact that their is no bias adjust in order to obtain best results
Aksa I have myself had great results with CFP output stages with care-full selection of devices and current setngs 0.02 at 1 khz and 8 oms @ 1 watt on a 30 watt unit that was even back in the early 1980,s
Regards Trev
Thank you Hugh for your observation.
I shall be getting the Laterals and Heatsinks when my son visits me in April. I am sourcing the other parts meanwhile and waiting!
Regards,
gannaji.
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