Cool-running Krell - Oxymoron?

[onemug]

I wonder if there is a recommended maximum ratio?

Never heard that too high of a ratio is bad.

I see you prefer tubed pre-amps, and am wondering what their “characteristic” output impedance is? What if it is much higher than the solid-state designs have, like in the kOhms area? What is the input impedance of your EXCELLENT (!!!) XA30.5 power amp? About the same as Bedini’s, i.e. 50 kOhm, I would guess?

The CJ ART is around 500. Tube preamps often use a 'cathode follower' circuit which lowers the OI. In the case of my LS7 which does have a CF, it's 100 ohms. The CJ ART does not use one. It's effect on the sound is debatable. I'd rather not have the signal go thru one but it comes down to how well designed the preamp is...with or without a CF.

The 30.5' is rated at 20k rca and 30k balanced.

regarding tubed pre-amps: what is the average lifespan of the tubes employed (what are the factors in play here: work hours, amount of On/Off cycles…), and what is the required maintenance (bias current adjustment, e.g.)?

Lifespan varies. Some designers run the tubes harder so naturally they won't last as long. I can get years on mine.
No bias adjusting. Not much other maintenance.

 

[Soun!]

I presume you auditioned PASS Labs pre-amps, and yet at the end decided to get tubed gear... I used to believe the best synergy could be achieved using components from the same manufacturer... What were the deciding factors for you, @onemug , please?
Have you considered any of the Balanced Audio Technology (BAT) preamplifiers? You are not the first expert recommending tubed pre and SS power amp for the best synergy...
In your opinion, can I do better than Bedini 45/45 or Threshold SA/3 power amps for the budget of up to 1.5K?

 

[onemug]

I presume you auditioned PASS Labs pre-amps

Yes I have. If I ever make a move to a SS preamp, Pass would be at the top of the list. For the last 10 yrs, my CJ's have never failed me and have been no trouble whatsoever, so no need or desire to change.

Have you considered any of the Balanced Audio Technology (BAT) preamplifiers?

No, but I've heard good things about them.

You are not the first expert recommending tubed pre and SS power amp for the best synergy..

I don't necessarily recommend everyone use a tube pre with a ss amp. A stereo system is a series of component choices. Each choice should make your system sound better. I've heard some 'lush' sounding tube preamps and some 'lush' sounding ss amps. That may be too lush for my tastes but everyone should pursue what sounds good to them.

can I do better than Bedini 45/45 or Threshold SA/3 power amps for the budget of up to 1.5K

Maybe. What is the sound you are hoping for? How loud do you like to listen to?

I have a feeling you might be happy with Pass's X.5 amps. Less heat, less money and probably easier to find. They run more in the class A region than most AB amps.

 

[Soun!]

I have a feeling you might be happy with Pass's X.5 amps.

I wish I could afford 30.5... 30 W/ch in class-A would have been plenty for me: I never listen above 65-70 dB at my sitting spot. How hot is XA30.5 running vs. Bedini 45/45, please?
Found Threshold T200 but am not sure if this is a good deal (both in terms of the SOUND and price)... The seller notes: the unit has less than 500 hours of usage! Providing 100 W/ch in class-A, it is probably way too hot-running for me anyway...
I wonder why it is for sale... The technology is too old, and, therefor, unserviceable?

 

[Silentnet]

Excellent deal on the T200.

Doubt they'll go down on it, though, and after shipping and import duties to Canada (you'd definitely want it insured for actual value) it's probably well above the $1500 you were looking to spend.

 

[onemug]

How hot is XA30.5 running vs. Bedini 45/45, please?

My Bedini runs cooler than the 30.5. The 30.5 measures around 128 F. Never measured the Bedini but I could leave my hand on it for hours.

Curious...what are your reasons for wanting class A and why the need for it to be cool running?

 

[Soun!]

Yes, you are correct, @Silentnet , they will not go down on the price and T200 is over my budget, unfortunately... Will continue my hunting...

My Bedini runs cooler than the 30.5. The 30.5 measures around 128 F. Never measured the Bedini but I could leave my hand on it for hours.

Interesting: 45W/ch Bedini runs cooler than 30W/ch XA30.5. Should it not be the other way around?

Curious...what are your reasons for wanting class A and why the need for it to be cool running?

Class-A to me has always sounded warmer and more full, nothing to me has replicated that. It doesn't always sound super-detailed, but I always prefer it. In my understanding, the reason class-A amplifiers may have such appeal to me is that they produce mainly even order harmonics in their distortion spectrum while class-AB amps produce odd order harmonics. And tube amplifiers produce, for the most part, even order harmonics. It has been observed that we tend to tolerate even order harmonics easier than odd order harmonics. I believe this is the main reason class-A solid state amplifiers may exhibit a "tube sound”, which I prefer.
My study I am building a modest Hi-Fi setup for is only 12' x 11' with an opening into my sitting room, hence the requirement for a "cool-running" power amp.

So far no luck finding either 45/45 or SA/3, unfortunately... What do you, dear experts, think of Pioneer M-22? They have been in service for about 40 years, and, probably, at the end of their lifespan...

Please chime in!

 

[onemug]

In my understanding, the reason class-A amplifiers may have such appeal to me is that they produce mainly even order harmonics in their distortion spectrum while class-AB amps produce odd order harmonics. And tube amplifiers produce, for the most part, even order harmonics

Not exactly true. But the bottom line is you like their sound. So do I.

 

[Soun!]

Have just had an opportunity to audition Bryston 4B SST2 class-AB power amplifier (via Tannoy Monitor Gold 15″), and I can tell you I was very impressed, to say the least. I guess not all class-AB amps created equal…

Curious...what are your reasons for wanting class A and why the need for it to be cool running?

I must admit I was wrong looking for class-A exclusively... Could you please give me a few names in class-AB to check? If my budget of up to 1.5K is insufficient, I can probably stretch it to about 2K, if necessary...
Please chime in!

 

[Silentnet]

I'm quite partial to the Nakamichi PA-7A, should be within budget but plan to have it restored if it hasn't been already.

There should be a few Threshold amps available in your price range. Can't go wrong there. The Bryston you auditioned is also well thought of and should be within reach.

Some used Pass Labs amps should also be in budget. Also consider Krell's "sister" brand, Aragon. Might even find a pair of the Paladium mono-blocks.

 

[Soun!]

Thank you very kindly, @Silentnet !

I'm quite partial to the Nakamichi PA-7A, should be within budget but plan to have it restored if it hasn't been already.

What are the differences between PA-7A and the one you have, PA-7AII? What needs to be restored: electrolitic capacitors, output transistors, ...? How would you describe the sound of your Nak?

 

[Silentnet]

Thank you very kindly, @Silentnet !

What are the differences between PA-7A and the one you have, PA-7AII? What needs to be restored: electrolitic capacitors, output transistors, ...? How would you describe the sound of your Nak?

There are minimal differences between the 7A and 7AII; some prefer one, some the other, I honestly don't think it matters much.

As for its sound, uncolored but authoritative, with excellent bass control. Outputs should be fine, the capacitors will likely need replacement though.

 

[Soun!]

Thank you very kindly, @Silentnet !
Can you confirm your PA-7AII is equipped with 700W toroidal transformer, please?