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Tube Amp Thoughts?

SimplySound

SimplySound

Kent Engineering & Fondry
I know this forum gets this question all the time... what tube amp should I buy?

Well I'll ask the question in context to help perhaps frame it more accurately. I am running a pair of Dunlavy SC-IV's (91db efficiency) with a Rogue ST-90 (~90-100w/Channel).

It sounds great and I've rolled it with KT-120's and currently with KT-88's (which it was designed around). I like the KT-88's, in that they have a smoother sound in my humble opinion, not as sharp as the KT-120's.

However, I feel like I'm running out of some headroom/punch (especially with the KT-88's). The bass isn't as well controlled as I'd like and just seems like they need more power to get them to light up a bit.

I've run these with SS amps and they definitely perform more dynamically, but since they are so accurate, you pick up the SS graininess. I guess I could consider something like a CJ MF-2500A, which from what I have read are probably the best tube rendition from SS. Perhaps that would really make them shine.

If I stay tubes, I'm thinking VTL ST-150 or perhaps the CF Premier-140 (don't really have room for 19"x19"), to get that extra punch.

Thought's on these amps and any alternatives would be much appreciated. Oh, and I'm a Jazz/Acoustic Rock guy... not really into Hard Rock/Metal.
 
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I am surprised. KT120 usually add some deep lows compare to a KT88. Maybe it's how your amp bias them.
Why don't you biamp your speakers with a SS amp for the lows?
 
Thanks Brice, yes the KT-120's did have more punch down low, but I thought the KT-88's sounded better in the mid-high range. I have tried these passively bi-amped (McCormack DNA SS), but I didn't have an external cross-over to isolate the amps and I ran into some impedance (gain?) mis-match. Not sure I want to go the Active cross-over route, but perhaps. Thoughts on that?

I do bi-wire, so I'm still thinking single amp, just more punch.
 
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Yes I know I had the same. I just use a passive stepped attenuator feeding the SS amp on the RCA/XLR side, that way I can "adjust" the amount of bass based on whatever tube amp I use for the mids and highs.
When you have it right, you get the best of both world.
 
I biamp my ADS M12’s with a Dynaco ST-70 for the tops and a Parasound HCA-1000A for the twin woofers with very good results. Previously, I was running them solely on the Dynaco, but it wasn’t enough with bassy music at high levels. I’m using a dbx DriveRack PA2. It works fine for me and doesn’t seem to affect anything negatively and is quite flexible. I use it in 3-way mode with a sub.
This type of setup seems to be ideal for less efficient speakers, and the SS amp definitely works the woofers better. If you go this route, I’d be curious to know what crossover you use and how it works out.
 
How loud do you listen? Adding another 50 watts of power is only good for about 1.5db. Its probably not enough to make a big difference. My guess is your speakers want something with with better damping to control the woofers more than they want more wattage. Unless you're running it very loud at least, then it might be legitimately running out of steam. If thats the case I suspect you'll need more than 50w anyway.
 
How about one of Luxman offerings?

MQ-300
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gadget73 said:
How loud do you listen? Adding another 50 watts of power is only good for about 1.5db. Its probably not enough to make a big difference. My guess is your speakers want something with with better damping to control the woofers more than they want more wattage. Unless you're running it very loud at least, then it might be legitimately running out of steam. If thats the case I suspect you'll need more than 50w anyway.
Click to expand...

I was thinking along similar lines. You can get to a maximum sound pressure level of 106dB (peak) and still have 3 dB of headroom before it starts to clip. Having run my system hard I can tell you that is really loud. I've measured the output of my system and 85 dB average, ~ 95 dB peak, is neighbor pounding on my door loud.

Shelly_D
 
Fairly loud, like Studio/Concert realism! ;)

I'm now thinking I may go back to bi-amping. My problem was that my McCormack DNA 0.5 kept going into protection mode. I guess it didn't like absorbing the extra signal components. It made me nervous about damaging the Dunlavy's, but is that really a concern?

Thanks for the suggestion on dbx NCDave. They have a two-way cross-over (223s) that might do the trick as well. Anyone else have experience with DBX?
 
Quick back of the envelope calculation, to get you to 110 dB average, you will need 100 watts per channel. To handle the musical peaks at that level, you need 10 times that power, or 1,000 watts (1 kilowatt). To add some degree of protection from clipping at those levels, you need to add at least another 3 db or power which takes you to 2000 watts.

Do you really want to take your home to those levels? Can your speakers handle it, even without distorting? Not trying to start any arguments here, just trying to put some real numbers to "Concert Level" volumes and a reality check on your speakers' capabilities.

Shelly_D
 
No argument needed... I don't push 110db, but I bet I'm up around 95 at times! :banana: Enough to clip my McCormack into protection mode!

Now I do have a McCormack DNA-1 I could put into the Bass circuit, but I'm trying to figure out if I really need an active x-over to separate the signals. The Dunlavy's sound like they are crossed around 30-50Hz, so I think I could dial in things relatively well.

Put it this way, augmenting the bass with SS amplification I already own, and would be more conducive to that application, is probably a less expensive approach than buying a new tube amp.
 
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This thread explains some things... "Instead of thinking of amplifiers as amplifying power, think of them as amplifying voltage, as indeed, the ideal amp is a voltage amp with infinite power."

So with an active crossover, you are making sure the amp is amplifying signal and not just generating heat!

OK, based on the comments in this thread about the issues using a "Pro-level Cross Over" because of the input signal strength, I think I'll give the Marchand XM66 a go over a DBX and save some cash compared to a larger tube amp! Thanks everyone for helping me through this!
 
SimplySound said:
I know this forum gets this question all the time... what tube amp should I buy?

Well I'll ask the question in context to help perhaps frame it more accurately. I am running a pair of Dunlavy SC-IV's (91db efficiency) with a Rogue ST-90 (~90-100w/Channel).

It sounds great and I've rolled it with KT-120's and currently with KT-88's (which it was designed around). I like the KT-88's, in that they have a smoother sound in my humble opinion, not as sharp as the KT-120's.

However, I feel like I'm running out of some headroom/punch (especially with the KT-88's). The bass isn't as well controlled as I'd like and just seems like they need more power to get them to light up a bit.

I've run these with SS amps and they definitely perform more dynamically, but since they are so accurate, you pick up the SS graininess. I guess I could consider something like a CJ MF-2500A, which from what I have read are probably the best tube rendition from SS. Perhaps that would really make them shine.

If I stay tubes, I'm thinking VTL ST-150 or perhaps the CF Premier-140 (don't really have room for 19"x19"), to get that extra punch.

Thought's on these amps and any alternatives would be much appreciated. Oh, and I'm a Jazz/Acoustic Rock guy... not really into Hard Rock/Metal.
Click to expand...

For Dunlavy, I would not try tubes at all. These speakers were designed to be studio monitors in late 1990s. At that time no one in pro audio used tube electronic other than in microphone preamps. Get good solid state amplifiers for them. I would try old (mid 2000s) Classe amplifiers.
 
Thanks P1 for the reply! Interestingly enough, I did have a Classe Fifteen driving them, but prefer the tubes. Different strokes I guess. I am thinking now that the active cross-over with the McCormack DNA1 on the low end might be what I'm looking for. We'll see and I'll report back!
 
OK; I considered a number of options to take another step up in my system. Each option presented additional costs, but with those costs, perhaps a better solution.

OPTION #1: $1000 - Invest in an active line x-over and run bi-amped. I looked at having a Marchand XM44 custom built to match my speakers. I talked to Phil Marchand and he thought a 340Hz low-pass and 85Hz high-pass setting would work for the Dunlavy's. They are based on a first-order passive x-over design so 6db slope seemed to make sense. However, I read in Stereophile they actually measured more like 12db, so I was torn about what was needed for the design of the XM-44. In the end, I decided that messing with the signal path, and having read that John Dunlavy had designed his speakers to be bi-wired but not bi-amped, lead me to consider option #2.

OPTION #2: $2000 - For additional money I could buy a VTL ST-150 listed on flea-Bay (it's still there), that looked great! It was the direction I was seriously thinking of moving in. Might cost a bit more, but it didn't mess with the signal input to different amps and got me a little more power to apply over my 90W Rogue ST-90. But of course, when you begin to look at amps....

OPTION #3: $3000 - Well, you know the drill; you look at your system, you identify a component that you think you need to upgrade to take that next step up in your sound and you begin to search for a better solution. You do some research, you think you know what you need to do, some helpful Karmites provide input and then you get to thinking. That's the dangerous stage!

I thought I was narrowing down on my purchase of the VTL, when I saw a nice pair of VAC Standard 160 Musicblocks for $3K. But was it worth the extra $1K to get basically the same power output as the VTL? Was VAC actually a better amp than VTL to be worth $1K. Oh the tangled web we weave!

In the end, I decided to purchase the VAC's. For some reason I believe the step up in power, plus the separation of mono-blocks, will be a more impactful improvement to the sound quality of my system. Will it be worth $1K? Well I wasn't able to do a comparison, so I'm on my own. I was impressed with the fact that Kevin Hayes had re-worked the Input/Driver stage of the Standard 160 Musicblocks with the Class A input design of the PHI 300, a really well respected amp in it's own right. I figured that getting into a pair of fairly current VAC mono-blocks at $3K was a fairly reasonable deal (VAC Amps are expensive). So we'll see how this goes... time to listen to some music!
 
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OMG! Well, I'm not going to state that Option #3 is better than Option #2, because I've never heard the VTL ST-150. However, I will state that no way would Option #1 compare to Option #3. Is it worth $2K more? Hard to say, but man, the VAC Musicblock 160's are SOLID! Like locked in solid! Control of the Bass like a SS amp, much better sound stage than the Rogue (you would figure with mono-blocks) and man, the depth in the mid-range is amazing.

Diana Krall's "Isn't it Romantic" is an exercise in mid-range vocal presentation and my specific reference. This setup raised that bar to a whole other level! God you gotta love it when you improve your sound. Now time to sell some gear to cover the cost of this upgrade! One happy camper here!
 
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