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Tubed Power Amplifiers. Are the disadvantages too great ?


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I run a PP AB Triode strapped EL34 amp into ML-1's, 87db and 8ohms nominal and don't drop below 5.8ohms I think it is. Wouldn't change a thing, love the sound and it can go plenty loud in this unit and never reach 12 o'clock on the dial...............usually 9oclock is plenty......... No complaints.

 

I could be considered a light user when averaged out so essentially on my first set of EL34s and haven't needed to change the small signal tubes either after 11 years since the build, PS filter caps are 2x 2 Mundorf HV 200uf +200uf /500v in series with balancing resistors for for 1000v handling, so they still have plenty of life to go.

 

Edit: music taste ranges from smooth jazz to rock.

Edited by muon*
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On 31 January 2020 at 6:08 AM, rockeater said:

Most of us do.

There indeed are (disadvantages) and I would ever consider tube amp for only certain kind of music. Like small combo of piano or guitar  and bass. Maybe vocal or soft piano trio.

 

And disadvantages are numerous.

Firstly - to my surprise - I have been told at a recent GTG, that when paired with very high efficiency speakers, tube amps hum. 

I did hear this on numerous occasions and always thought of this as either fault or due to interference induced into some non-shielded audiophile cables.

But apparently not so. 

My 100W/ch solid state EC amplification is dead silent when fully open and so is 40 years old Quad 45/405. Admittedly into much less efficient speakers.

 

Then, there is a fact of their high output impedance and hence unsuitability to be used in power amps. Even when transformers are used on the output, their control of bass driver is poor. 

 

Next disadvantage is their high cost.

Most of the time only simple single ended designs are built and in recent times I have seen only one balanced Sonic Frontiers pre-amp for sale here on SNA. I am sure that there are some very good balanced power amps too, but hardly any at a price lower than a car.

 

Durability is not great either. Not many survive in fully working order for decades without extensive renovations. That Quad 45/405 I mentioned above is 40 years old and started to hum after being left abandoned in a tin shed for 3 years. Replacement of two 47µF capacitors in the pre-amp (worth $1.50 in total) made it as good as new.

 

So despite their undeniable appeal there is a reason for valves' limited uptake.

My actual experience with various valve amps when used in my system is in the majority of cases at odds with just about all of the various disadvantages you either talk about or have been told about.

 

I have various SS and tube power amps, pre-amps, phono stages and Integrateds, all amplification gear has strengths and weaknesses, just like all components do. Synergy between components is the secret to a great sound system, not whether it's tube or SS based.

 

cheers,

Terry

Edited by TerryO
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The right tube amps can do Rock no problems and do it well.

 

Reliability is not so different to SS.

 

High cost, not really.

 

No problems with most speakers if matched correctly.

 

Noise? what noise?

 

Durability? not a problem.

 

Just like not all SS amps are the same, not all tube amps are the same.

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My 2c worth.  I guess we all are seeking some kind of perfect sound, what ever that may be.

You can argue mine is better than your's!!

You can try to reinvent the wheel with a fancy catch phrase or marketing BS! or an alternative is back to basics, and it is not for everyone but can be scaled down. (if you want to stay married)

youtube.com/watch?v=DWurHRY-3gU  (if the link does not work Joe Roberts Silbatone Acoustics)

 

Steve.

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On 30/01/2020 at 6:50 PM, Addicted to music said:

Depends on the speaker you want to use them on.

I agree 1000%. – amplifier / speaker synergy is paramount.

 

Regarding the issue of hum / noise with SET amps driving high efficiency speakers...

I use Absolare paralleled 845 SET amps to drive 102dB field coil Voxativ 9.87 speakers and there is no noise whatsoever – are silent.

 

 

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On 31/01/2020 at 8:04 AM, aussievintage said:

there's no reason valves should hum more than SS.  It just comes down to design. 

I thought there were valid reasons valve amps hum more than SS, but on a quick scan of my usual technical sources I can't find any references...it certainly could be just design:

  • single ended designs (eg SET valve amps, but also SS) won't have as much Power Supply Rejection Ratio (PSRR) as push/pull designs, so noise on the power rails will be more audible 
  • class A designs (which include all single ended, and some push/pull) have very high current demands on their power supplies, so if the power supply is not appropriately designed, more ripple may exist, increasing hum
  • interaction between the power supply transformer and the output transformers on valve amps could increase hum in valve amps. SS amps won't suffer from this.
  • it is common for SS amps to have higher levels of negative feedback than valves, and the greater negative feedback would reduce hum

I know of one highly respected valve amp manufacturer that quotes their hum figures (full respect to that manufacturer) - that would lead me to think there is some truth that valve amps are more prone to hum than SS...but again it may be through design (eg lower negative feedback)

 

Class A is a lot more common in valve amps than SS, and I've never come across a valve amp that wasn't hot.

I live in Brisbane, and it's just way too hot to run class A amps of any sort (valve or SS).

I did run some 10W class A transistor amps for while on my tweeters. The heat they generated was one reason I moved them on.

I've gone back to all SS class AB, and the heatsinks stay at ambient.

 

A key reason why good valve amps cost a lot is the quality of the output transformers - they can make or break the sound of a valve amp...and good output transformers are expensive.

 

cheers

Mike

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Lots of AB valve amps, maybe are advertised as Class A when it is only in part of the front end that is Class A operation,  and they are actually Class AB (common in advertising with Chinese amps in the lower price brackets),. SE amps are often Class A but PP ones It's more common they are AB.

Edited by muon*
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On 31/01/2020 at 6:08 AM, rockeater said:

Most of the time only simple single ended designs are built and in recent times I have seen only one balanced Sonic Frontiers pre-amp for sale here on SNA. I am sure that there are some very good balanced power amps too, 

terminology can confuse people - I'm sure you mean "push/pull" rather than "balanced" ...lots of valve power amps are push/pull, but there are also lots of single ended valve amps (eg SET).

 

It's interesting that back in the 50/60s before transistors took over all high end valve amps were push/pull (Quad, Leak, McIntosh). Single ended designs were for mantle radios and other low fi requirements.

It's far more recent that SET style valve amps have gained in popularity for "HiFi" - they were never deemed good enough when only valve amps were available.

 

cheers

Mike

Edited by almikel
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1 minute ago, almikel said:

by definition any single ended amp is always class A

Cheers. always nice to get a better clarity on things, and never too late for me :thumb:

 

I wonder if I was confused by dodgy advertising :/

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12 minutes ago, muon* said:

Cheers. always nice to get a better clarity on things, and never too late for me :thumb:

 

I wonder if I was confused by dodgy advertising :/

think about it this way - with single ended you only have a single output device (ignoring paralleled output devices for a sec) to manage the entire voltage swing - so always class A

 

cheers

Mike

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On 31/01/2020 at 7:28 AM, doogie44 said:

This seems to be a personal rather than a technical discussion--which is fine. There is only one compelling reason for my attraction to valve amps: they sound more like music to me. 

 

Unless you enter  the stratosphere of SS implementation. And not that all valve amps sound good. Or for every kind of music.

 

But even the amps of yesteryear like the Quad/Leak/Rogers/Dynaco sound very good to me, and as for the Shindo/Leben/Audio Note/Earle Weston/Supratek of today, then I just can't help smiling widely when I hear them!

 

Good thing I'm not an electrical engineer or I'd be worried about distortion and such...

I agree with these comments, I Run a supratek into 300b's and love it. 89db efficient box speakers and they just sing. It doesn't blow the house down and isn't the final word in resolution sure, but it just creates lovely music.

 

Most tube amps will create hum (mine do) but you only hear it within 1-2m of the speakers, when no music is playing.

 

Not looking forward to replacing tubes though as a quad of decent 300B's start at $1k. But it could be many years before I need them.. (Anyone have any they want to move let me know :).)

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1 hour ago, almikel said:

I live in Brisbane, and it's just way too hot to run class A amps of any sort (valve or SS).

as in many things, it depends.  I run class A SET amps in Brisbane all the time with no problems.  Just like hum problems, you just design to control the "problem".

 

1 hour ago, almikel said:

A key reason why good valve amps cost a lot is the quality of the output transformers - they can make or break the sound of a valve amp...and good output transformers are expensive.

 

While expensive in component costs terms, those costs often get swamped by the audiophile markup factor, so in the end, other things determine what the end cost to the consumer will be.

 

1 hour ago, almikel said:

single ended designs (eg SET valve amps, but also SS) won't have as much Power Supply Rejection Ratio (PSRR) as push/pull designs, so noise on the power rails will be more audible 

 

So you just design the power supply to have less noise.  Target sufficient filtering so that the noise is inaudible.

 

 

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1 hour ago, muon* said:

Lots of AB valve amps, maybe are advertised as Class A when it is only in part of the front end that is Class A operation,  and they are actually Class AB (common in advertising with Chinese amps in the lower price brackets),. SE amps are often Class A but PP ones It's more common they are AB.

 

It's not so much the front - end that is class A.  ALL class AB outputs operate in class A for low level signals, so by raising the bias on the output devices, and making them stay in class A for longer, the marketing then claims it is a class A amp, when it's really just a high-biased class AB.  

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1 minute ago, aussievintage said:

 

It's not so much the front - end that is class A.  ALL class AB outputs operate in class A for low level signals, so by raising the bias on the output devices, and making them stay in class A for longer, the marketing then claims it is a class A amp, when it's really just a high-biased class AB.  

I was specifically thinking of ones that are not biased hard on the output tubes, and have the earlier stage operating in class A.

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1 hour ago, almikel said:

Single ended designs were for mantle radios and other low fi requirements.

It's far more recent that SET style valve amps have gained in popularity for "HiFi" - they were never deemed good enough when only valve amps were available.

 

This correct, but it's because in those low-fi designs, they used a tiny cheap output transformer and operated at what was considered to be too little power for hifi. 

 

Some people eventually realised the sound from a simple class A single ended amp, was actually very pleasing to them, and by usinghigh efficiency speakers, they could enjoy the topology. Designs were developed that were more hifi - using bigger and better constructed (and more expensive) transformers to achieve full bandwidth

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Like I mentioned, more so with cheaper Chinese amps being refereed to as class A when they are not and the earlier stage is the only thing operating in class A and this is where they get the claim from.

 

They seem to do this advertising these Yaqin amps often, and as far back as the original version of the MC-10L

 

https://www.ebay.com.au/itm/YAQIN-SR-8800-6CA7-BL-Vacuum-Tube-Hi-end-Integrated-Amplifier-MC-10T-EXPORT-VER/263084921244?hash=item3d4115519c:g:liMAAOSwd4tUHA4L

Edited by muon*
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1 minute ago, muon* said:

and have the earlier stage operating in class A.

 

Usually we don't bother describing anything but the output stage as having a class.   That all comes about because of the choices of technology adopted to achieve high output power.      Nearly all low power voltage amplification stages were/are class A and single ended, until opamps were invented.  So yes you CAN say valve preamps are class A if you want.

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1 minute ago, aussievintage said:

 

Usually we don't bother describing anything but the output stage as having a class.   That all comes about because of the choices of technology adopted to achieve high output power.      Nearly all low power voltage amplification stages were/are class A and single ended, until opamps were invented.  So yes you CAN say valve preamps are class A if you want.

Yes and this is how they justify stating class A amp in ebay adverts..

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1 hour ago, muon* said:

I was wondering what he meant with Balanced.

The ones used in pro audio and in top of the range domestic designs.

You can recognise them from the outside by having XLR connectors (though of course not everything with XLRs is truly balanced).

They have two separate symmetrical amplifiers which are used for the hot and cold parts of the signal. Preferably differential in design.

Not many of these are made with valves ?

Edited by rockeater
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1 hour ago, rockeater said:

The ones used in pro audio and in top of the range domestic designs.

You can recognise them from the outside by having XLR connectors (though of course not everything with XLRs is truly balanced).

They have two separate symmetrical amplifiers which are used for the hot and cold parts of the signal. Preferably differential in design.

Not many of these are made with valves ?

I accept that all pro audio kit is designed with balanced inputs and outputs (assuming a pre-amp of any description - power amps don't have balanced outputs, they just have an output) - for good reasons - in the pro world they may run very long interconnects, with gear powered off different power circuits with different earth references - by running "balanced" they avoid earth loops and hum.

Many top of the range domestic designs aren't fully balanced - as they don't need to be - although I completely accept that in a domestic system, it's a complete PITA if you have an earth loop and need to track it down and eradicate it...

1 hour ago, rockeater said:

They have two separate symmetrical amplifiers which are used for the hot and cold parts of the signal

Possibly for the input stage of the power amp - but never for the output stage of the power amp

 

A fully balanced input stage will have additional components on the input of the amp - but this is only a slightly more complex summing junction that a non balanced amplifier input would have...in SS this could be op-amps - so yes separate symmetrical amplifiers - and almost guaranteed to be op-amps in pro gear...but a balanced/unbalanced input doesn't define good vs bad...

 

1 hour ago, rockeater said:

Preferably differential in design.

I don't know enough about valve power amp design, but I do know every unbalanced SS amp design will use a differential input pair of transistors/mosfets/devices...and by definition all amplifiers work on "differences" between the +/- inputs...so I'm not sure what you mean by "differential in design" - they all work that way.

 

Mike

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