Hi.
Just like to share a cct. which I constructed and may be of interest to someone. I call it the LCA. Low Component Amp. Instead of a load resistor as the drain load I used an LM317T TO3 as a constant current source. I only used what I had in my parts bin and I managed to find an IRF120 which is an N channel enhancement mode mosfet in a TO3 package which matches my LM317T package. I connected it up as per the ZCA except I used the constant current source as the drain load. The constant current source is set at its limit but handles the current well at 1.6 amps. CCT No.1 I used with a mosfet IRF120 Which gave me a gain of approximately 11 (20dB) from a gain of about 4 (12dB)with a resistive load (resistive load distortion was in the order of 8%). This method gives you enough gain as a stand alone amp! The constant current source acts as a high impeadance load to the mosfet. I managed to find a box of MJ4035 darling ton transistors (TO3 case) and this worked even better with a gain of about 28. This is shown in CCT. No. 2. The bipolar transistor has a gain of about 28dB. Distortion on the fet was high at about 6% at 5 watts RMS. The transistor performed better at 3% at 5 watts RMS. I applied feedback to CCT. No.2 and wound it back to 20dB gain and this was substantialy better at about 1.5% distortion at 1Khz 5 watts RMS. The transistor has a little more output before clipping aswell. With CCT. No.3 I added a gain stage to aid in the distortion reduction. The total gain is set at approx. 22dB and the distortion now is much lower at 0.5% at 5 watts, 0.02% at 1 watt. IMO that is very acceptable. All ccts are a derivative of others. I just used what I had in my parts bin and the Darlington transistor was a good score! This amplifier is simplified due to the constant current source being a single component which not only improves the efficiency of the amplifier but also rejects ripple from the power supply. you can use these ccts without a choke and it still performs the same but one is still recommended. Please let me know of any corrections and or suggestions for improvement.
Regards
Billy D...
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Just like to share a cct. which I constructed and may be of interest to someone. I call it the LCA. Low Component Amp. Instead of a load resistor as the drain load I used an LM317T TO3 as a constant current source. I only used what I had in my parts bin and I managed to find an IRF120 which is an N channel enhancement mode mosfet in a TO3 package which matches my LM317T package. I connected it up as per the ZCA except I used the constant current source as the drain load. The constant current source is set at its limit but handles the current well at 1.6 amps. CCT No.1 I used with a mosfet IRF120 Which gave me a gain of approximately 11 (20dB) from a gain of about 4 (12dB)with a resistive load (resistive load distortion was in the order of 8%). This method gives you enough gain as a stand alone amp! The constant current source acts as a high impeadance load to the mosfet. I managed to find a box of MJ4035 darling ton transistors (TO3 case) and this worked even better with a gain of about 28. This is shown in CCT. No. 2. The bipolar transistor has a gain of about 28dB. Distortion on the fet was high at about 6% at 5 watts RMS. The transistor performed better at 3% at 5 watts RMS. I applied feedback to CCT. No.2 and wound it back to 20dB gain and this was substantialy better at about 1.5% distortion at 1Khz 5 watts RMS. The transistor has a little more output before clipping aswell. With CCT. No.3 I added a gain stage to aid in the distortion reduction. The total gain is set at approx. 22dB and the distortion now is much lower at 0.5% at 5 watts, 0.02% at 1 watt. IMO that is very acceptable. All ccts are a derivative of others. I just used what I had in my parts bin and the Darlington transistor was a good score! This amplifier is simplified due to the constant current source being a single component which not only improves the efficiency of the amplifier but also rejects ripple from the power supply. you can use these ccts without a choke and it still performs the same but one is still recommended. Please let me know of any corrections and or suggestions for improvement.
Regards
Billy D...
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Attachments
In my version it does
With the gate of the MosFet at a fix (somewhere halfway Vb) level an atempt to adjust the output voltage results only in a change of current.
Mona
No current source in my circuit.On the DC side the MosFet acts a source follower,keeping the output on a fix level, regardsless of the current.
From AC point it is a SRPP ,the gate is coupled to the collector through a 47n (could be somewhat bigger) capacitor.If the current changes in the BJT in the bottem the Fet changes too in the opposite direction,giving double current in the load.That is with bias 1.6A the peak current in the load gets near 2x1.6A.Not only 1.6A as with a CCS Fet.
Mona
From AC point it is a SRPP ,the gate is coupled to the collector through a 47n (could be somewhat bigger) capacitor.If the current changes in the BJT in the bottem the Fet changes too in the opposite direction,giving double current in the load.That is with bias 1.6A the peak current in the load gets near 2x1.6A.Not only 1.6A as with a CCS Fet.
Mona
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