I'm just wondering where the best place to put a resistor divider is in my system. My setup is that volume control is in software on my Mac Pro, which is my only source for everything. I have an amp which is 6SN7 into 2a3. The volume on that is perfect for my room - I don't need any more gain. However, I have a 2P29L line stage which improves the sound if I put in front. Problem here is far too much gain. 2P29L has a mu of 9. I really only want a 2x gain.
So looks like I could put a resistor divider in front of the 2P29L or in front of the 6SN7 or both, in fact. So where would be the most effective? The 2P29L is a better sound than the 6SN7. I may replace the 6SN7 with two 6AH4 or 1626 or something low gain like that. But for now it would be useful to put a resistor divider somewhere.
So where?
So looks like I could put a resistor divider in front of the 2P29L or in front of the 6SN7 or both, in fact. So where would be the most effective? The 2P29L is a better sound than the 6SN7. I may replace the 6SN7 with two 6AH4 or 1626 or something low gain like that. But for now it would be useful to put a resistor divider somewhere.
So where?
Both.
This gives you more options to select proper amount of harmonics you desire.
I used to play with tube preamps and at the end used two volume pots. One before preamp and one after preamp.
My logic for that is well described in srpp thread.
Edit: i meant to say, do to use dividing resistors, those are fixed and offer little flexibility. Use to volume pots, one before line stage, one before the amp.
I know you have digital volume control, just just more options to experiment with.
This gives you more options to select proper amount of harmonics you desire.
I used to play with tube preamps and at the end used two volume pots. One before preamp and one after preamp.
My logic for that is well described in srpp thread.
Edit: i meant to say, do to use dividing resistors, those are fixed and offer little flexibility. Use to volume pots, one before line stage, one before the amp.
I know you have digital volume control, just just more options to experiment with.
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Why don't you just add a 100K attenuator to the preamp? Most preamps have a volume control anyway. Set it for the optimum gain and continue to use the software volume control.
That's the obvious thing to do, but I wonder about putting a resistor divider in front of the 6SN7. I should try both and see which sounds better.
Remove the cathode bypass capacitor on 6sn7.
That's a possibility. I'll look at that.
But I think I've made a step forward. I have a simple volume pot with phonos in and out. First I connected it at the input of the 2P29 stage. Didn't sound very good - the DHT sound was rather flattened. Remember the 2P29L is better sounding than the 6SN7 stage. So then I put the volume control after the 2P29L and before the 6SN7 stage and the sound was audibly better - much more of the 2P29L sound came through. This is pretty much what I expected would happen. So next step would be to take out the volume control and replace it with a resistor divider. This is a learning experience for a 3 stage amp.
So I was using a driver stage with far too much mu, i.e. 20. My goal would be a mu of 4 or upwards. Even 3 would work in my own system, but generally following a 2P29L you'd want a mu of 5 or 6. So I'm assuming that putting a resistor divider in front of the 6SN7 reduces that to a low mu valve.
How does this sound, guys?
Update - made a resistor divider with 27K between input and wiper and 68K from wiper to ground. This is in the ballpark. Holco resistors. This before the 6SN7 driver stage. Best guess for now - sounds OK.
You could try a 6P5 in place of the 6SN7. It's the octal equivalent of a 76, with an amplification factor of 14. You'd need to adjust the cathode and plate resistors upward, to about 470R and 47K respectively. It's a nice-sounding tube.
Yes indeed, that's on my list to try. I had some previously. Nice valve. First I'm going to try 1626 and 6AH4 which I also used many years ago and liked. Out of laziness I'll start with indirectly heated valves. Better would be 46, 47 or 10Y all of which I have, or even a second 2P29L stage or a 4P1L. But 3 stages of DHTs, however nice, ends up taking up a lot of real estate. OK for a once-in-a-lifetime system but I like experimenting. Some other valves to try are 843, 6AF5, 6AE5, ML4 but they're not common ones.
