Amp Basics: Tube Preamp w/Solid State Power Amp.

Elf73,

Apart from compatible sensitivity and output impedance of the linestage vs. input impedance of the amp, there are other "mystery" compatibility issues that can only be figured out by trying the components together. I have heard quite a number of combinations that looked respectable on paper that sounded really bad, even when the individual components were expensive and respectable.

In particular, some tube linestages seem unpredictable in how they match with amps, particularly solidstate amps. If you can, give the combination a trial.

I liked the Clayton amp I heard (don't know the model). That should be a promising choice with almost any linestage you select. The output impedance of the Prologue, as you have shown above, is fairly high, but it should still be compatible with the 47k ohm input impedance of the Clayton. I don't know how to convert the voltage gain specification of the Clayton to a sensitivity figure, but, 12 db of gain from a linestage is usually way more than enough unless you are also juggling other considerations, such as a low output phono cartridge and a low gain phonostage.

Good luck with your search.

Thinking of this combo....(of course, I'm a newbie and am entirely open to suggestion and criticism)... just been reading various reviews on the internet. I'll have to pick up that primer on Hi-Fi.

Clayton S40 Power Amp:

* Rated power output: 50-watts continuous RMS into 8 ohms, pure Class-A, 100-watts continuous RMS into 4 ohms, pure Class-A
*Voltage gain: 26dB
*Input impedance: 47K
*Negative feedback: Virtually zero

PrimaLuna Prologue 3:

Specifications
Freq. Response: 4Hz-85kHz +/- 3dB
Gain: 11.5dB
THD: Less than 1% at full power
S/N Ratio: 109dB unweighted
Input Sensitivity: 200mV
Input Impedance: 100k Ohms
Output Impedance: 3.5k Ohms
Power Consumption: 48 watts
Tube Compliment: 2 - 12AX7, 2 - 12AU7, 2 - 5AR4
Dimensions: 11" x 7.5 " x 15.5" (WxHxD)
Weight: 23.5 lbs
Inputs: 4 pair RCA
Outputs: 2 pairs of pre-amp outputs + tape monitor out

I agree with Jmcgrogan2. One thing to add is if your preamp does not have a cathode follower, then you'll want to keep your cabling between the pre and power pretty short. Depending on the cable, longer runs could roll off the high frequencies.

If the pre does have a cathode follower in the ouput stage, then longer cable runs should be OK.

best
John

Thanks, lots of help. The information I was looking for.

Do a search for tube preamps, there's been quite a bit of discussion on them.

I run a TAD150sig tube pre into a McCormack DNA1 power amp. This has been a very good combo in many folks systems...including mine. I run power-hungry 4 ohm speakers & the gain-volume control issue hasn't been an issue in my system.

McCormack power amps have a great reputation & can easily be had for 1-2K, depending on the power you need & it's upgrade status. Steve McCormack will do upgrades on the amp if you want..this gives you some upgrade headroom down the road without switching to another amp.

If you're looking ofr an overall primer on audio system basics...Robert Harley has a Guide to High End Audio book that is useful.

If you don't want to worry about matching impedence, you should look for a little device callled a Burson buffer. It would make the output impedence of your preamp look more compatible with say a low input impedence ss amp. Pretty cool.You can google Burson buffer and get the info.

The only other thing I'd add to John's advice is to be aware of that if you mate a high gain power amp ( a separate issue from power rating ) to a high gain preamp, you can have too little range of effective volume control before things get too loud. It's not a fatal flaw, inline attenuators can ameliorate that with no sonic penalty. The Prima Luna's 12db is pretty middle of the road in the gain department, shouldn't be any cause for concern with the majority of amps you'd pair it with.

The wattage of the power amp is more of a matching issue between amp and speakers. The key matching preamp to amp is the output impedence of the preamp and the input impedence of the amp. The general rule of thumb is that the input impedence of the power amp should be 'AT LEAST' 10X's the output impedence of the preamp. I say 'AT LEAST' because the higher the ratio the better, in fact some manufacturers will recommend a 20-30X ratio to be the minimum. In other words, your PrimaLuna Prologue 3 tube preamp has an output impedence of 2800 ohms, which is very high for a preamp. You should look for an amp with an input impedence of AT LEAST 28Kohms. 100K would be better yet.

As for reco's it depends on what type of sound you are looking for. If looking for rich, warm sound, there currently is an older Jeff Rowland Model 1 amp, which has adjustable input impedence of 600 ohms, 20Kohms and 100Kohms. Obviously you would be best to use the 100Kohm setting. It also has selectable gain of 20, 26, 29.5, 32 dB which should help match your preamp even more.
If you're looking for more power and/or a a faster, more transparent amp, there is a Belles 350A Reference for sale with an input impedence of 50Kohm.

Obviously these are only two, there are more amps out there. With your preamp's high output impedence you will just have to be careful that the amp's input impedence is high enough to match. FWIW, impedence mis-match is not lethal, it will just roll off the high's and low's.

Cheers,
John