Thought process can be fun, even when a bit foolish.
I’ve been using an Adcom GFP-565 preamp for three years in my main system, which I built around the notion of “what was cool and obscure in the late 80’s, 90’s and 00’s that I can afford.” But it has developed some problems and needs some time in the fixit pile. So, I'm aiming at post-70’s hi-fi boom, pre-HT dominance, when “stereo” was still a word.
So, requirements:
1. Active gain—it needs enough output voltage to fully drive an incoming Buckeye NC-502MP amp, which has an input sensitivity of around 2.8 volts as I recall for single-ended inputs. I have old sources rated for hundreds of millivolts of output, and some that put out two full volts (all continuous and RMS). The Adcom amp meets its spec at 4 volts continuous RMS (with peak RMS at 10 volts), so that became a requirement.
2. EQ/processor loop. My PEQ is an external unit, and I use it with analog sources so computer EQ doesn’t fulfill the requirement. I don’t want to use a tape loop for this—it’s a pain having to use dubbing controls just for listening.
3. Inaudible quiescent hiss. I have to go on reputation for this—it’s never spec’d or even measured in most lab tests.
4. THD better than -90, which isn’t demanding now but used to be.
5. Respected phono input with low and adjustable loading. The Adcom’s phono input was spec’d at 100 pf, but my cartridge is reportedly happier with less than 200 pf of total capacitance, and I doubt my arm wiring and cables were low enough to achieve that with the Adcom. 50 pf in the preamp input would be better.
6. At least one tape loop. I have been running my ADC and DAC through a tape loop, but I never monitor so any record bus output I can Y off of will work for that. I have a dbx 400x for integrating various tape decks into that tape loop, and it provides full deck-to-deck dubbing (even though that isn’t a use case for me).
7. Balanced outputs if possible. What I ended up buying didn’t have them, but it was an optional add-on, so I might be able to implement it. I can deal without it.
8. Source inputs for computer, two CD players, tuner, turntable, plus whatever else I’m playing with. That’s at least 5 line-level inputs plus phono.
9. My theme favors brands not found in mainstream department or electronics stores, so I prefer USA brands, if possible unless the product is cool enough to overcome the theme. I have plenty of more mainstream stuff in other systems. The rest of the system includes Revel F12 speakers, Thorens turntable, Yamaha commercial PEQ, Cambridge Audio 640C CD player, Cambridge Audio CXC+Topping E30 (cool enough to break the theme), Carver tuner, Nakamichi BX-300 cassette deck, Teac open-reel deck, dbx 400x routing switcher, and (currently) B&K Reference 125.2 amps.
10. Decent headphone amp.
11. Quality construction—good components, discrete where possible for maintainability, such as 1% precision resistors, film caps, and so on.
The GFP-565 fits the theme well, but the source switches are unreliable and I was ready for something different. Also, it’s op-amp-based, Walt Jung’s design notwithstanding. An Apt Holman would be perfect, buts it’s a dozen years older. There are surprisingly few full-featured preamps from that later period, especially with upmarket pretensions. Onkyo and Kenwood offerings didn’t fit the theme (I own both in other systems).
And the winner is: A B&K Sonata MC-101, now on its way to me.
I’ll report when the jury comes back.
Rick “eschewing minimalism” Denney
I’ve been using an Adcom GFP-565 preamp for three years in my main system, which I built around the notion of “what was cool and obscure in the late 80’s, 90’s and 00’s that I can afford.” But it has developed some problems and needs some time in the fixit pile. So, I'm aiming at post-70’s hi-fi boom, pre-HT dominance, when “stereo” was still a word.
So, requirements:
1. Active gain—it needs enough output voltage to fully drive an incoming Buckeye NC-502MP amp, which has an input sensitivity of around 2.8 volts as I recall for single-ended inputs. I have old sources rated for hundreds of millivolts of output, and some that put out two full volts (all continuous and RMS). The Adcom amp meets its spec at 4 volts continuous RMS (with peak RMS at 10 volts), so that became a requirement.
2. EQ/processor loop. My PEQ is an external unit, and I use it with analog sources so computer EQ doesn’t fulfill the requirement. I don’t want to use a tape loop for this—it’s a pain having to use dubbing controls just for listening.
3. Inaudible quiescent hiss. I have to go on reputation for this—it’s never spec’d or even measured in most lab tests.
4. THD better than -90, which isn’t demanding now but used to be.
5. Respected phono input with low and adjustable loading. The Adcom’s phono input was spec’d at 100 pf, but my cartridge is reportedly happier with less than 200 pf of total capacitance, and I doubt my arm wiring and cables were low enough to achieve that with the Adcom. 50 pf in the preamp input would be better.
6. At least one tape loop. I have been running my ADC and DAC through a tape loop, but I never monitor so any record bus output I can Y off of will work for that. I have a dbx 400x for integrating various tape decks into that tape loop, and it provides full deck-to-deck dubbing (even though that isn’t a use case for me).
7. Balanced outputs if possible. What I ended up buying didn’t have them, but it was an optional add-on, so I might be able to implement it. I can deal without it.
8. Source inputs for computer, two CD players, tuner, turntable, plus whatever else I’m playing with. That’s at least 5 line-level inputs plus phono.
9. My theme favors brands not found in mainstream department or electronics stores, so I prefer USA brands, if possible unless the product is cool enough to overcome the theme. I have plenty of more mainstream stuff in other systems. The rest of the system includes Revel F12 speakers, Thorens turntable, Yamaha commercial PEQ, Cambridge Audio 640C CD player, Cambridge Audio CXC+Topping E30 (cool enough to break the theme), Carver tuner, Nakamichi BX-300 cassette deck, Teac open-reel deck, dbx 400x routing switcher, and (currently) B&K Reference 125.2 amps.
10. Decent headphone amp.
11. Quality construction—good components, discrete where possible for maintainability, such as 1% precision resistors, film caps, and so on.
The GFP-565 fits the theme well, but the source switches are unreliable and I was ready for something different. Also, it’s op-amp-based, Walt Jung’s design notwithstanding. An Apt Holman would be perfect, buts it’s a dozen years older. There are surprisingly few full-featured preamps from that later period, especially with upmarket pretensions. Onkyo and Kenwood offerings didn’t fit the theme (I own both in other systems).
And the winner is: A B&K Sonata MC-101, now on its way to me.
I’ll report when the jury comes back.
Rick “eschewing minimalism” Denney