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Audio and Video Talk
Valves / Vacuum Tubes
Dynaco ST-70
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<blockquote data-quote="handsome" data-source="post: 803001" data-attributes="member: 772"><p>Unless there is a hum pickup issue (which should rather be solved at the source anyway) lowering the input resistance wont make any material difference to the amplifier performance. You can increase the gain of the amp by increasing the series feedback resistor (the 1k from 16R tap) AND bypassing the input pentodes' cathode resistor (620R) to maintain amplifier characteristics. But.... as ever, fiddling with feedback might bring on instability. </p><p></p><p>ST-70s are power amps and were designed to work with preamps. so converting to integrated will require more gain and thus as mentioned some fiddling within - which will change amplifier characteristics. digital sources output ~400mV average so a preamp of x3 gain will get you ~1.3V but x6 gain will take into account the odd album that was recorded slightly softer. why not build a simple valve preamp? its easy, informative and a lot of fun plus hard to get wrong due to simplicity.</p></blockquote><p></p>
[QUOTE="handsome, post: 803001, member: 772"] Unless there is a hum pickup issue (which should rather be solved at the source anyway) lowering the input resistance wont make any material difference to the amplifier performance. You can increase the gain of the amp by increasing the series feedback resistor (the 1k from 16R tap) AND bypassing the input pentodes' cathode resistor (620R) to maintain amplifier characteristics. But.... as ever, fiddling with feedback might bring on instability. ST-70s are power amps and were designed to work with preamps. so converting to integrated will require more gain and thus as mentioned some fiddling within - which will change amplifier characteristics. digital sources output ~400mV average so a preamp of x3 gain will get you ~1.3V but x6 gain will take into account the odd album that was recorded slightly softer. why not build a simple valve preamp? its easy, informative and a lot of fun plus hard to get wrong due to simplicity. [/QUOTE]
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Audio and Video Talk
Valves / Vacuum Tubes
Dynaco ST-70
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