Hello,
Which one did you ultimately go with? Would appreciate an update when you have time.
Thanks!
I love the 6CG7 9-pin. It's a great tube. It's cheap, too. (see http://www.diyaudio.com/forums/tubes-valves/9862-12au7-vs-12bh7-vs-6cg7-4.html)
If you don't have any "audio nervosa" and you know your target application, then build the Octal and use the 6SN7.
I believe the 9-pin with the 6CG7 is equivalent. The 9-pin version is cheaper, opens the opportunity of adjusting the gain by choosing a wider variety of input valves, and allows adjusting the output impedance by choosing the output valve.
If you don't have any "audio nervosa" and you know your target application, then build the Octal and use the 6SN7.
I believe the 9-pin with the 6CG7 is equivalent. The 9-pin version is cheaper, opens the opportunity of adjusting the gain by choosing a wider variety of input valves, and allows adjusting the output impedance by choosing the output valve.
Thanks for the input. I am hoping to pair it with an F5 clone for now. Maybe it would be a better option to go for the octals instead of the 9-pins if I would be using different amps with the pre, perhaps?
The FirstWatt series generally don't have industry-standard gains. Thank goodness! The F4 is the ultimate expression of non-compliance, having no (unity) gain.
With the Octal Akikido, your linestage will be either operating with a fixed gain of the 6SN7, or you will be searching for NOS tubes that offer different gain values (that's what Tube Depot or Partsconnexion is for).
With the Novel (9-pin) version, you'll have a huge selection of valves to choose from, if you want to tweak the preamp as you try different power amplifiers.
For example, I have changed the driver tube in my EL84 power amp several times. When I was using it with my iPod, it needed a 12AX7. Used as my primary power amp in my "main" system (where it is now), even a 12AT7 provided too much gain, and it's operating on a 12AU7. I'll probably swap it for a 12BH7 just for grins. However, each tube swap requires disassembly to change the cathode resistor and plate resistor. Ugh! I don't know how often you are willing to do that. If you don't envision taking apart your line stage to optimize the preamp/power amp interaction when you switch power amps, you may be happier sticking with a single configuration.
In my case, I am using a Kinergetics KPA-1 (solid stage) linestage, so I am modifying the power amp to fit the preamp. Like the tail wagging the dog?
Gain poisoning is a real issue with my system. I am using a Theta DAC (digial to analog converter), which has really high output. My Musical Fidelity DAC's output is also a bit high. The KPA-1 preamp adds some additional gain, so the signal voltage that reaches the power amplifier's input is high. Add the efficient Triangle Acoustics speakers, and the power amp hardly needs any voltage gain of its own. It just needs to convert the high-impedance input voltage to low-impedance output voltage.
In fact, a Pass F4 with no gain works reasonably well, because the Theta/KPA-1 combination delivers enough voltage!
So here is a question back to you: how much gain does your linestage really need? What is your source (i.e. CD player or external DAC), and what is the efficiency of the loudspeakers attached to the F5?
p.s. I plan on eventually replacing the KPA-1 with a buffered stepped attenuator or TVC (transformer volume control).
Thanks for taking the time and your extensive reply, it did give me a better understanding of that to look for. I'd still have to read up a bit to make sense of a few more things, perhaps.
As far as the tweaking goes, I should be OK with a resistor swap everytime I change the tube to match the amp. If it's just going to be a resistor and nothing else, would a pot with 3 resistors of the needed values work here if I decide on the types of tubes I need before-hand?
The sources would be a universal DVD player, a DAC and possibly a phono amp sometime down the line. The 2 speakers I have in mind have 85dB and 91dB sensitivities respectively.
Thanks again for your time and assistance, appreciate it much.
As far as the tweaking goes, I should be OK with a resistor swap everytime I change the tube to match the amp. If it's just going to be a resistor and nothing else, would a pot with 3 resistors of the needed values work here if I decide on the types of tubes I need before-hand?
The sources would be a universal DVD player, a DAC and possibly a phono amp sometime down the line. The 2 speakers I have in mind have 85dB and 91dB sensitivities respectively.
Thanks again for your time and assistance, appreciate it much.
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