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I'm a newcomer to tube amps, and I'm auditioning an AirTight ATM-2 amp. I'm using it with Living Voice OBXR-2 speakers, a nice vinyl front end, a CD and also use it for DVD sound in 2 channel mode.I have been trying it with a Music First passive pre-amp, which is a magnetic transformer design and quite well thought of, and have also tried it with an Audio Research LS16 mk II, and also with a direct input to the amplifier.
When coupled directly, the sound is quite neutral. With the passive pre-amp, it is more detailed and transparent, but loses a little weight, and with the Audio Research it is fuller with more drive, but a little less detailed. Why is this? Opinions are divided on passive versus active line stages, but using either type appears to add something to the sound - and perhaps take something away too!
I have read posts that state that direct coupling is the best for sound - I'm not sure though. I also have 3-4 inputs, so this is a challenge. If I elect to use a line stage, should I consider blanking off or by-passing the switch and attenuators or leave them as is? Alternatively, I could use a splitter for the CD/DVD and have the vinyl going straight into the front, although fiddling with two attenuators is not that practical!
Or should I consider other amplifiers like the Rogue 150 Monoblocks? Is the ATM-2 still a good amp (as a used purchase)as technology may have advanced in the intervening years.
Musical taste is Rock/progressive, some jazz (this sounds very good)
Also I don't quite understand the balance biasing versus the normal valve biasing.
Any comments appreciated - thanks in advance!
Follow Ups:
IMHO ATM2 is more transparent without preamp but more musical with
THE preamp which is the best for it :ATC2 of Air-Tight .I'm using
ATM2(and ATC2) since ten years and I don't know other amp which
give more good music .Best results with Air-Tight KT88 but too
expensive .EH are very good .I know Mr.Miura who advise me to put
the needle of the Bias between the bottom of the area and the first
point on the left : better for the musicality and the longlife of
the KT88 .The best sound with Siemens 12AX7 and 12AU7 .
Regards
Yves
If the ATM2 has as much gain as the ATM3 which I have owned and used for more than a dozen years (and I suspect it does) you're likely not to meet with much success mating it with a high gain line stage as the ARC, especially if you use very high efficiency loudspeakers. You probably end up frustrated with the narrow window of dynamic contrasts and changes with such a pairing. I couldn't make an ARC SP10 work with the ATM3s and have since just connected my phono stage direct to them. But I work with only one source, while you say you do not.If you live in an environment with wildly fluctuating mains voltage, you may have to watch the bias on the amp a little more carefully. I use mine with a voltage regulator wired with an accurate AC meter and set the bias a little over the minimum for what I believe sounds best on my system.
The ATM-2 is still one of the best of its type (push-pull pentode) using excellent parts (ex: Tamradio output transformer).
The problem is that it sounds TOO transparent, if you call that a problem. :)
I used a passive preamp for years, but have switched to an active tube preamp for more tube sound.
Reduce the output bias to the middle of the meter will also make the midrange sweeter, but you will drop the bass control a little bit.
Looking back, I paid too much for this amp (~10K), and will never pay this much for any hi-fi item.
Many thanks for your reply. Should each valve be set to the middle of the meter or just numbers 2 and 4 that have the word "bias" on the adjuster? (Sorry I'm a bit dim on this!)Thanks
Hi Clennard,You turn the Bias (#2 and #4) to approximately set the overall bias to the middle area, and then you turn the Balance (#1 and #3) to give each tube the exact & equal bias level.
You use the front meter to monitor this procedure. It should take no more than a minute when you are familiar with it.
Be careful and insulate your screwdriver with some kind of tape because you COULD touch the amp interior in this process.
Please experiment with the bias level to your liking, but no lower than 3 dots from the bias “bubble”, where distortion appears.
I use Magnepan speaker, so the bass is still pretty fast at the lower bias setting.
Some people think this amp does not sound like a typical tube amp, and I agree. It has strong bass and does not roll off the treble.
For your reference, I use Telefunken 12AX7 and 12AU7, GE 12BH7, Electro-Harmonix KT88 and 6550.
You could also use Electro-Harmonix 12AX7/12AU7/12BH7 for a lot more bass and treble at a cost of a little more graininess.
I believe this amp was rated Stereophile class A 10-12 years ago.I hope this helps.
Regards,
-who (my real name :) after the English translation)
Who,
I have an AirTight ATM-2 also and love it. I'm using TungSol 6550, RCA 12AX7, and RCA 12AU7. I've also got a set of the Siemens (ECC82 and ECC83) that I'm gonna test in the next few months. Have you done any modifications to the speaker wire posts and the power cable? The originals look pretty cheap. I'm wondering if replacing those with something a little more high quality will improve sound. And if so, is it a pretty involved process?
Hi Winston,I keep my all stock. I have no doubt that the speaker wire posts and the power cable modifications could change the sound, but the ROI (return on investment) could be low:
- It is impossible to do A/B test to know for sure if they make any difference
- It could decrease the resale value
- I am too lazyI prefer reversible tweaks like the tube rolling that you plan to do. I do like different sound from time to time and have tried 211 and 845 monoblocks.
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