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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Line amp/AVC/TVC thoughts posted by pix on February 23, 2017 at 23:18:09:
Most sources (your phono preamp is a good example) have an output coupling cap.
Its very common for such units to have a particular output impedance, such as the 2KOhms of your phono section. But that is likely at 1KHz and its likely not the same at 20Hz where its probably a lot higher (maybe 10-20Kohms). This is often due to the size of the output coupling cap.
Driving 100K this is probably not an issue, but when the passive control is introduced, it can be. Imagine adding 25K to whatever output impedance you already have. This is why you might notice that the bass is best only when the control is at full volume. YMMV due to the resistance of the control and the actual 20Hz output impedance which varies widely from source to source.
So in addition to the rolloff that Tre' mentions, you have another rolloff to contend with. With its attendant phase shift (bass rolled off with phase shift, which reduces impact of what remains).
In short you can make passives work, but quite often an active line stage will work better- not as dry, sterile and often more involving. Tubes do the involving thing even better...
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Follow Ups
- low frequency rolloff issues - Ralph 10:41:13 02/24/17 (0)
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