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In Reply to: RE: Is it possible to get Bass control with Tubes and A7 Speakers? posted by Monte Verdi on October 13, 2009 at 14:14:03
Can you define or identify "bass control" more precisely?
I can see four technical issues that may be involved:
1) Power. The Accuphase can deliver 50-100 watts, which if you needed it would severely limit your choice of tube amps.
2) Damping factor. The Accuphase offers a choice of 1, 5, or 50. Which one works in your setup? Or does it make any difference? This will give a lot of guidance in choice of tube amp.
3) Equalization. The A-7 is neither flat nor uniform in directivity in the bass, though the quality of the bass is widely admired. The Accuphase offers four different controls that adjust the bass response. Do you use or need any of them? If so, that will affect your choice of tube amp or preamp.
4) Power bandwidth. Tube amps have output transformers which limit how low a frequency can be delivered at full power. While most amps will adequately drive most speakers with most music, most of the time, it may be that for your music and your speakers you would need a tube amp with a greater inductance than the average. These are available, but you might need to be selective.
Not knowing which of those criteria (or others I haven't thought of) are important, it's hard to respond usefully.
1. Do not need Accuphase as part of biamp.
2. Accuphase is currently set to soft on rear damp switch.
3. Sound enhancement Bass and Treble RIAA EQ is engaged set flat.
Hope this helps.
Big help - thanks!
"Soft" is unity damping (according to the specs I found through google) at 8 ohms, i.e. an 8 ohm output impedance. An SET on the 16 ohm tap would provide about that much damping. This high output impedance will increase the bass output at certain frequencies (where the speaker impedance is high) by several dB and would be quite an audible difference. You can try the Accuphase at different damping settings to confirm that this is an important parameter in your setup (or discover if it is not).
Most push-pull amps will be pentodes with feedback, and will have a much higher damping factor. There are a few with an adjustable damping control or switch - the Heathkit UA-1 comes to mind. And there are a very few push-pull triode amps with no feedback that would behave similarly to SETs in this respect.
Otherwise you may find a series resistor of up to 8 ohms is needed to get that kind of bass behavior - note this will raise the speaker impedance even higher.
Hope that helps!
If I understand what you are saying, is that I should use amplifiers with a 16 Ohm tap and if possible a damping control. I must say I do like damping control on Accuphase and of course there are plenty of 16 Ohm tap amplifiers available. Anymore tube amplifier names would be appreciated with damping control, thanks.
Edits: 10/14/09
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