ATC and tube amps

[reignofchaos]

Well I always believed that ATCs - especially those with super linear drivers like SCM19/SCM20/SCM50 etc need big fat solid state amplifiers to sound their best. This is the notion world wide and most folks in major forums also say the same. Suffice to say they sounded wonderful with my pair of O&B mono blocks which have been my prized possession for the last year and half. Before I go anywhere, let me mention these amps sound like proper high end amps for very little money. They have all the dynamics, smoothness, presence that you want from solid state - perfect definition of an iron fist in a velvet glove. I've compared these with very many megabuck solid state amps and it has always come on top. At the price they sell, they are a literal steal.

Over the last month or so Dr Bass (aka Abhi) got a pair of tube mono blocks (EL34 quad on each side) from a Hong Kong company called Audio Space that have been building high end tube amplifiers over the last 20-30 years. While it sounded wonderful with his Tannoy Turnberrys, he wanted something more so he put them up for sale as they sounded a bit too sweet for his taste. I thought of just trying them out casually. So curiosity got the best of me even though I was not looking for any amplifiers.

Initially I connected the amps to my Blumenhofer thinking these will be a potential upgrade for my Conrad Johnson power amp but somehow the combination didn't work at all. I guess Blumenhofer needs a warmer silkier amplifier compared to the neutrality that the Audio Space provides. The CJ was a much much better match. i was disappointed and thought of returning it before Abhi telling me to try it once with the ATC as apparently Audio Space used ATC loudspeakers to test their amps' drive.

I connected up the amps with negative feedback set to zero in triode mode (30W/ch) and while the sound was nice, though it sounded a bit loose not able to control the midwoofers. I increased the negative feedback to one step (this amp allows negative feedback control from the face plate) and lo and behold - the speakers started singing - singing in a manner I had never experienced before. I loved the sound so much, I ended up spending half the night just listening to them. This was easily the best I'd heard out of the ATCs and all my inhibitions about tubes with ATC were just thrown out of the window. The sound had drive, grip low down, incredibly articulate bass, sweetness in the right amount and an incredible holographic sound stage. This was still with the stock chinese tubes it came with which is typically unheard of.

Last night I replaced the front three driver tubes (2x 12AU7 and 1x 12AX7) with 2x Brimars and 1x GE 5751. The four EL34 power tubes remained the same. Immediately I felt a much more refined sound. The backgrounds became darker, any hint of harshness was history and the details and midrange - especially female vocals just jumped at you. I've never heard ATCs sound this mellifluous ever. It was almost the perfect sound. This tiny 30W amp was absolutely destroying my 300W mono blocks in everything - even in things where you expect a SS muscle amp to have obvious advantages such as dynamics were a no contest.

End of the day all my notions about ATCs being hard to drive and needing big SS muscle amps have been shattered. I'm now a tube convert for life!

 

[muralimmreddy]

Last night I replaced the front three driver tubes (2x 12AU7 and 1x 12AX7) with 2x Brimars and 1x GE 5751. The four EL34 power tubes remained the same. Immediately I felt a much more refined sound. The backgrounds became darker, any hint of harshness was history and the details and midrange - especially female vocals just jumped at you. I've never heard ATCs sound this mellifluous ever. It was almost the perfect sound. This tiny 30W amp was absolutely destroying my 300W mono blocks in everything - even in things where you expect a SS muscle amp to have obvious advantages such as dynamics were a no contest.

Nice write up. Just curious, have you heard el34 tube amps earlier? Sounds more of el34 magic to me.

 

[reignofchaos]

Nice write up. Just curious, have you heard el34 tube amps earlier? Sounds more of el34 magic to me.

Have heard the AN EL34 based cobra amp before on home demo. This is just very different.

 

[Dr.Bass]

Well I always believed that ATCs - especially those with super linear drivers like SCM19/SCM20/SCM50 etc need big fat solid state amplifiers to sound their best. This is the notion world wide and most folks in major forums also say the same. Suffice to say they sounded wonderful with my pair of O&B mono blocks which have been my prized possession for the last year and half. Before I go anywhere, let me mention these amps sound like proper high end amps for very little money. They have all the dynamics, smoothness, presence that you want from solid state - perfect definition of an iron fist in a velvet glove. I've compared these with very many megabuck solid state amps and it has always come on top. At the price they sell, they are a literal steal.

Over the last month or so Dr Bass (aka Abhi) got a pair of tube mono blocks (EL34 quad on each side) from a Hong Kong company called Audio Space that have been building high end tube amplifiers over the last 20-30 years. While it sounded wonderful with his Tannoy Turnberrys, he wanted something more so he put them up for sale as they sounded a bit too sweet for his taste. I thought of just trying them out casually. So curiosity got the best of me even though I was not looking for any amplifiers.

Initially I connected the amps to my Blumenhofer thinking these will be a potential upgrade for my Conrad Johnson power amp but somehow the combination didn't work at all. I guess Blumenhofer needs a warmer silkier amplifier compared to the neutrality that the Audio Space provides. The CJ was a much much better match. i was disappointed and thought of returning it before Abhi telling me to try it once with the ATC as apparently Audio Space used ATC loudspeakers to test their amps' drive.

I connected up the amps with negative feedback set to zero in triode mode (30W/ch) and while the sound was nice, though it sounded a bit loose not able to control the midwoofers. I increased the negative feedback to one step (this amp allows negative feedback control from the face plate) and lo and behold - the speakers started singing - singing in a manner I had never experienced before. I loved the sound so much, I ended up spending half the night just listening to them. This was easily the best I'd heard out of the ATCs and all my inhibitions about tubes with ATC were just thrown out of the window. The sound had drive, grip low down, incredibly articulate bass, sweetness in the right amount and an incredible holographic sound stage. This was still with the stock chinese tubes it came with which is typically unheard of.

Last night I replaced the front three driver tubes (2x 12AU7 and 1x 12AX7) with 2x Brimars and 1x GE 5751. The four EL34 power tubes remained the same. Immediately I felt a much more refined sound. The backgrounds became darker, any hint of harshness was history and the details and midrange - especially female vocals just jumped at you. I've never heard ATCs sound this mellifluous ever. It was almost the perfect sound. This tiny 30W amp was absolutely destroying my 300W mono blocks in everything - even in things where you expect a SS muscle amp to have obvious advantages such as dynamics were a no contest.

End of the day all my notions about ATCs being hard to drive and needing big SS muscle amps have been shattered. I'm now a tube convert for life!

Audio Space uses ATC speakers in their factory to test their amps. They are very popular in Japanese audiophile community. I like everything about this amp. Such a neat and powerful sound. My Tannoys however do better with drier sounding tubes like KT88 and DHTs. Else I would have been all set for good 5 years. I only wonder how special it will sound with a set of NOS Mullard EL34s

 

[arj]

those tubes x8 will cost more than the amp itself . would be good to start with a good 6CA7 which have better specs.

 

[yogibear]

Quite a while back played my puny 3.5 wpc SE 6L6 tube amp on a friends ATC BS, rated under 85dB. Though the amp could not drive them very loud, he was surprised at the low end control and quality, including the other traits.

So with tubes it’s a suspense until you pair the speakers. Yes, as ARJ pointed out, be clever with choice of tubes. Either they should be affordable or very long life. And don’t fall into the rolling pit. In my books, all tubes sound the same and I choose nos tubes and it’s the operating parameters of the amp that really makes a difference.

 

[Analogous]

I'm now a tube convert for life!

Welcome to the endangered tribe!

 

[reignofchaos]

those tubes x8 will cost more than the amp itself . would be good to start with a good 6CA7 which have better specs.

Out of the various reissues of 6CA7, what do you recommend I try?

Quite a while back played my puny 3.5 wpc SE 6L6 tube amp on a friends ATC BS, rated under 85dB. Though the amp could not drive them very loud, he was surprised at the low end control and quality, including the other traits.

So with tubes it’s a suspense until you pair the speakers. Yes, as ARJ pointed out, be clever with choice of tubes. Either they should be affordable or very long life. And don’t fall into the rolling pit. In my books, all tubes sound the same and I choose nos tubes and it’s the operating parameters of the amp that really makes a difference.

That is the great thing about this amp - you can change the bias and feedback both and tailor the sound a bit towards what you like.

 

[yogibear]

That is the great thing about this amp - you can change the bias and feedback both and tailor the sound a bit towards what you like.

Nothing wrong with feedback in any tube amp. In fact it’s an added feature. It helps you tailor the speakers to your amp. Bias helps you when you change the tubes.

 

[yogibear]

Out of the various reissues of 6CA7, what do you recommend I try?

Sovtek or EH 6CA7EH (Tube Depot). But not those which say EL34 / 6CA7.

 

[arj]

Out of the various reissues of 6CA7, what do you recommend I try?

6CA7 EH is apparently excellent is what I was told..not too expensive either, yOU can expect a tighter bass and more HF extension with this compared to any EL34.

The K77 are also replacement but was told unless the amps are designed for it it will not sound as goo but experts like Yogibear can perhaps guide around that with respect to the bias currents.

 

[Yelamanchili manohar]

Out of the various reissues of 6CA7, what do you recommend I try?


That is the great thing about this amp - you can change the bias and feedback both and tailor the sound a bit towards what you like.

Happy to read your findings

I would encourage to under bias the amp by atleast 20%. In my case, the recommended bias for EL34's is 380 mv. And I keep them at 320 mv or round abouts. I find that it makes the sound more richer / lusher, even with negative feedback set at zero.

And pay no attention to folks who point out the distortion. The best speaker's bass drivers distort upto 3%, not to mention the mundane ones. So even a 1% distortion at the amps is less than the speakers .

For most real world speakers, not to mention very high efficiency ones, EL34 is probably the closest we can get to the elusive 300B seduction. Happy to know you discovered the magic. Enjoy

Edit : I have'nt tried many tubes. Probably only Electro harmonix and JJ. And I find the JJ to be richer and fatter in the mid range, though EH sounded a bit more extended in the treble I think. Of course the input tube matters too. I moved from EH to Gold lion, it improved the clarity a bit I think. The shift was a few years back, so not really sure about my findings now.

 

[arj]

=

Happy to read your findings

I would encourage to under bias the amp by atleast 20%. In my case, the recommended bias for EL34's is 380 mv. And I keep them at 320 mv or round abouts. I find that it makes the sound more richer / lusher, even with negative feedback set at zero.

Underbiasing increases the Output as my understanding is it changes the grid current. Not sure if that is recommended at least as per what my designer told me as it also reduces life of tubes as well as reduce dynamics and its better to run a tube within its range.

I am guessing that if a speaker sounds better with underbiasing then the speaker might need more power ?

 

[Yelamanchili manohar]

=

Underbiasing increases the Output as my understanding is it changes the grid current. Not sure if that is recommended at least as per what my designer told me as it also reduces life of tubes as well as reduce dynamics and its better to run a tube within its range.

I am guessing that if a speaker sounds better with underbiasing then the speaker might need more power ?

Hi Arj

Your suggestion could be possibly right. I was given to understand that the vacuum tube is at its most linear performance at the correct bias current. And under biasing it, takes the tube away from its linearity, and into slight distortion.

I have been struggling with excessive heat in my listening room as I cant fit an AC. Searching for a solution to reduce the heat led me to suggestions of under biasing from a few tube amp users. It apparently runs the power tubes cooler and prolongs tube life. I dont know if the tubes are running any cooler, as Iam still sweating after 15 mins. But somehow Iam liking the distortion Iam getting now . I could probably over bias and get the same distortion, but it might run the tubes hotter and shorten their life.

 

[arj]

Hi Arj

Your suggestion could be possibly right. I was given to understand that the vacuum tube is at its most linear performance at the correct bias current. And under biasing it, takes the tube away from its linearity, and into slight distortion.

I have been struggling with excessive heat in my listening room as I cant fit an AC. Searching for a solution to reduce the heat led me to suggestions of under biasing from a few tube amp users. It apparently runs the power tubes cooler and prolongs tube life. I dont know if the tubes are running any cooler, as Iam still sweating after 15 mins. But somehow Iam liking the distortion Iam getting now . I could probably over bias and get the same distortion, but it might run the tubes hotter and shorten their life.

my laymen understanding is if you are underbiasing, the DC current goes down and hence the power output goes up. To reduce the output you need to increase the biasing current.

But I don want to tread into less known territories @yogibear , perhaps you are the right person to clarify

 

[Yelamanchili manohar]

my laymen understanding is if you are underbiasing, the DC current goes down and hence the power output goes up. To reduce the output you need to increase the biasing current.

But I don want to tread into less known territories @yogibear , perhaps you are the right person to clarify

Oh okay...thanks for that. Then probably the added power too might be helping along with the distortion. There are more powerful SS amps in the room, and there definitely is an ease to the music when using them. However, I really like the presentation of the EL34 tubes, and they dont seem to be struggling audibly, as the speakers are atleast 90db and above efficient. The other tube alternatives are 845 DHT's which run even more hotter, so are presently only for show

 

[Analogous]

On the heat issue: I gave up on the Lampizator (Tube DAC) after several months of enduring the heat. The SQ was lovely but the physical discomfort was too much after half an hour of listening. AC was not an option in that room for some reasons. Reluctantly moved on.

 

[Yelamanchili manohar]

On the heat issue: I gave up on the Lampizator (Tube DAC) after several months of enduring the heat. The SQ was lovely but the physical discomfort was too much after half an hour of listening. AC was not an option in that room for some reasons. Reluctantly moved on.

Same pinch sir

 

[reignofchaos]

On the heat issue: I gave up on the Lampizator (Tube DAC) after several months of enduring the heat. The SQ was lovely but the physical discomfort was too much after half an hour of listening. AC was not an option in that room for some reasons. Reluctantly moved on.

Same with my AMR dac - it gets really hot! But thankfully I have air conditioning so it doesn't bother me much.

These Audio Space amps get pretty hot as well. I am having to use lower temperatures in my AC unit or else it gets uncomfortable. Earlier 26-27 used to be okay but with these amps, I'm having to use 24.

 

[Analogous]

They things we endure, the lengths we go in pursuit of spectacular sound is amazing and probably ridiculous to those immune to such temptations.