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Audio and Video Talk
Valves / Vacuum Tubes
EL84 push-pull kit with 12AT7 split load phase inverter
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<blockquote data-quote="Mars" data-source="post: 854410" data-attributes="member: 817"><p>Here is an aside around the above design:</p><p></p><p>Baxandall's 5 Watt Design</p><p></p><p>In March 1957, Baxandall returned to the field of audio amplifier design with a simplified, relatively low power (5W) design, because he felt that there was a niche for an inexpensive design intended for use with relatively efficient loudspeaker systems (Baxandall, P.J., Wireless World, pp. 108-113, March 1957). In this design, of which I have shown the circuit in FIG. 9, Baxandall retained both the use of output pentodes and a fairly high level of NFB to keep the residual hum level low, and the total harmonic distortion (THD) below the 0.1% target level at 400Hz and 5 watts output, though he now used the split load phase-splitter system (V2) proposed by Williamson.</p><p></p><p>FIG. 9 Baxandall's simple amp</p><p></p><p><img src="http://www.gammaelectronics.xyz/images/tube-trans-amp_6-9.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>The use of high levels of NFB with an output transformer of relatively simple construction brought with it the probability of HF instability - which, if it occurred while handling a speech or music signal, would lead to a greater degree of impairment in the audible quality than any possible improvement due to reduced steady-state THD. To provide the very necessary correction to the poor HF loop stability, Baxandall added a further output Zobel network (R22,C10) across the whole secondary of the transformer, in addition to the networks (C8, R20, C10, R21) retained across the output transformer half primaries. Further circuit refinements for the purposes of HF NFB loop compensation were the lag-lead networks (C2, R8 + C3, R9) interposed in the signal line between V1 and V2.</p><p></p><p>article here <a href="http://www.gammaelectronics.xyz/vtaa_6.html" target="_blank">http://www.gammaelectronics.xyz/vtaa_6.html</a></p></blockquote><p></p>
[QUOTE="Mars, post: 854410, member: 817"] Here is an aside around the above design: Baxandall's 5 Watt Design In March 1957, Baxandall returned to the field of audio amplifier design with a simplified, relatively low power (5W) design, because he felt that there was a niche for an inexpensive design intended for use with relatively efficient loudspeaker systems (Baxandall, P.J., Wireless World, pp. 108-113, March 1957). In this design, of which I have shown the circuit in FIG. 9, Baxandall retained both the use of output pentodes and a fairly high level of NFB to keep the residual hum level low, and the total harmonic distortion (THD) below the 0.1% target level at 400Hz and 5 watts output, though he now used the split load phase-splitter system (V2) proposed by Williamson. FIG. 9 Baxandall's simple amp [IMG]http://www.gammaelectronics.xyz/images/tube-trans-amp_6-9.jpg[/IMG] The use of high levels of NFB with an output transformer of relatively simple construction brought with it the probability of HF instability - which, if it occurred while handling a speech or music signal, would lead to a greater degree of impairment in the audible quality than any possible improvement due to reduced steady-state THD. To provide the very necessary correction to the poor HF loop stability, Baxandall added a further output Zobel network (R22,C10) across the whole secondary of the transformer, in addition to the networks (C8, R20, C10, R21) retained across the output transformer half primaries. Further circuit refinements for the purposes of HF NFB loop compensation were the lag-lead networks (C2, R8 + C3, R9) interposed in the signal line between V1 and V2. article here [url=http://www.gammaelectronics.xyz/vtaa_6.html]http://www.gammaelectronics.xyz/vtaa_6.html[/url] [/QUOTE]
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Audio and Video Talk
Valves / Vacuum Tubes
EL84 push-pull kit with 12AT7 split load phase inverter
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