Single Ended vs Push Pull tube amplifiers

[Hiten]

Sometimes i wonder why there is no high power SET [Tube or Transistor] amplifier. :indifferent14:

May be for our purist audiophile brothers there is very little to gain even if audiophiles from other camp push there ideas hard and pull everything in their practice and theory to quiet the noise purists make with out giving proper feedback from their audition.

different strokes for different folks

'warm' regards

 

[kanwar]

Hiten,

High power certainly has benefits with low efficiency speakers and not every audiophile has inclination towards high efficiency or horn type speakers. Its just i am surprised about the fact that why single ended class-A amps are hell expensive, just having a niche segment doesn't means that the prices should sky rocket.

Kanwar

 

[stevieboy]

Absolutely, SET amp power is a given - low output but high quality watts. You need to get the right speakers - atleast 94db sensitivity. Any decent speaker from Klipsch would be great(have got great results with a Klipsch RB61). 2A3 amps are typically 3.5 watt per channel and they sound quite robust with a sensitive speaker such as the Klipsch even in the bass.

I would love to audition the Lyrita 2A3 in Bangalore if I could. Never heard a 300B, would love to audition that too if I could. I will be building the Tp1 front horns next month to go with my Almarro A205A SEP.

Beast,

You're welcome to drop in for a listen Pm me. I use the 45 globe tubes in Virens 2A3 SET but can put in the 2A3s for you. I'd love to drop in too to hear your set up and connect with you. You seem to have the same tastes as me and I've always wanted to hear an almarro.

Regards


Torque ain't cheap but it sure knocks yer socks off

 

[stevieboy]

Sometimes i wonder why there is no high power SET [Tube or Transistor] amplifier. :indifferent14:

Hi Kanwar,

The tubes in SET amps output a few watts by nature and design. There are very few high powered SET amps. In general SET amps partner well with high efficiency speakers with strengths complementing each other. Also SET amps sound more dynamic and somehow louder than push pull. I was surprised to hear my 1.5 watt SET sound louder and more dynamic than my earlier 15 or was it 12 watt el84 push pull amp. Those who go the SET route generally are going for that quality first watt rather than quantity and power. I think the transformers in SET amps drive the price up plus since the designs are simple each part has to be of good quality else it's going to show up.

Regards


Torque ain't cheap but it sure knocks yer socks off

 

[heliumflight]

I also have experienced that SET2A3 watts sound more louder than Push Pull 10-15 watt tube amp

 

[Hiten]

Hiten,

High power certainly has benefits with low efficiency speakers and not every audiophile has inclination towards high efficiency or horn type speakers. Its just i am surprised about the fact that why single ended class-A amps are hell expensive, just having a niche segment doesn't means that the prices should sky rocket.

Kanwar

I like powerfull amps and I incline towards them. I also like 'tube' sound. I think for good bandwidth tube amps have high quality output transformers which may contribute to the price. (Some use silver wires) I read somewhere high efficiency speakers have very thin pulp cones which with repeated use contributes to the distortion in the long run. I dont know if any new things have come up with speakers designs.
Also as you said being niche market volumes are low so may be they HAD to sell at higher margins reluctantly.
If I had the money I would have all types of amps, speakers, source formats.
Regards

 

[Beast_of_burden]

Beast,

You're welcome to drop in for a listen Pm me. I use the 45 globe tubes in Virens 2A3 SET but can put in the 2A3s for you. I'd love to drop in too to hear your set up and connect with you. You seem to have the same tastes as me and I've always wanted to hear an almarro.

Regards


Torque ain't cheap but it sure knocks yer socks off

An audition would be terrific. I have read the glowing review of the Yamamoto 45 amp on stereophile. To actually listen to the 45 would indeed be a thrill. I was interested in Viren's 2A3 SET but have been putting it off until I got a chance to audition the amp. I Just might take the plunge after listening.

My current speakers which are a Fostex 206 in BLH are a poor match for the Almarro. Having prototyped the TP1 front horns with Lowther DX3s, I intend to build proper examples in April. I will invite you for an audition when these gigantic front horns are ready.

 

[alpha1]

Hiten,

High power certainly has benefits with low efficiency speakers and not every audiophile has inclination towards high efficiency or horn type speakers. Its just i am surprised about the fact that why single ended class-A amps are hell expensive, just having a niche segment doesn't means that the prices should sky rocket.

Kanwar

Price has nothing to do with cost.
High/exclusive demand = high price becomes sustainable
High price = exclusivity, desirable

Its kind of like Catch-22

 

[shafic]

Very nice explanation sir, i respect your wisdom.

 

[shafic]

you are right, sir!!

 

[captrajesh]

Sometimes i wonder why there is no high power SET [Tube or Transistor] amplifier. :indifferent14:

There are a few. Some are expensive and some are not so expensive.

I just got one, Dared VP845. A 35 WPC integrated amp with the following tubes:

1. 2 x 12AX7B tubes in the line stage.

2. 2 x 6SN7GT tubes in the driver stage.

3. 2 x 845 tubes in the power stage.

A few of our forum members have listened to it. I've gotten terribly busy with some office stuff and not able to pen down my impressions.

We've also compared it with a Class D Power amp paired with a Dared preamp MC7P which is currently in my possession and also a SSP preamp.

Very interesting results we have got.

 

[Hari Iyer]

300B SET amp also sounds quite loud for thier size. I think 9 watts is quite enough for a room size of around 200 sq.ft with moderate furniture. With an external pre-amp this amp can do wonders.

My speakers are around 90dB SPL and can easily be played by the 300B.
In my experience speakers that are designed for solid-state amplifiers sound quite different when played with Tube amps. The reason being a solid state amp output drops with the increase in impedance of the speaker, but in a tube amp as the speaker impedance increases the output also increases with the rising impedance. This could be one of the reason why a tube amplifier sounds louder than the SS counterpart. In my experience the output of a 10 watt SET will be equal to a 50 Watt SS amp.

With my past one month experience using the 300B tubes, i strongly now believe the speakers that were designed for SS amp may not be good enough for a tube amp unless the impedances of the speakers are flat (like the Thiel's) or one that has been well controlled in the mid and high frequency region. If the impedance of the speaker falls at the mid-high frequency region then the power response of this speaker will be severly affected and you could loose details in the high-end.

Most of the commercial vented enclousres having a rising impedance at the mid to high frequency region can actually make the sound stage very harsh and fatigue prone when played with tube amps. Hence its very important to check the speakers impedance curve when pairing it with a tube amp and not only at the FR curve and make the judgement.

 

[jai1611]

The reason being a solid state amp output drops with the increase in impedance of the speaker, but in a tube amp as the speaker impedance increases the output also increases with the rising impedance.

Another big difference is the damping factor of tube amps, which is in single digits for tube amps but usually much higher for solid state amps (except some class A designs). This is also the reason why tube amp bass can sound lose or woolly with some speakers that need a high damping factor. It can also manifest itself as a lack of speed / slightly sluggish sound with some speakers.

 

[jls001]

For the power hungry, here are some SET tube amps:

1) Wavac HE 833 v1.3 using the 833 tube. 150 Watts. It uses a KT88 which is usually used as a power tube as a driver tube!

2) AM 833 from China. Also uses 833 tube. 130 Watts. This model also uses a KT88 as a driver.

3) Allnic A10000. THis uses the Kron KR242 tube. This model will be launched next month at the Munich show.

4) And at 50 Watts, here's the "baby" of this lineup from the Czech Rep's KR Audio using their T1610 tube: Kronzilla SX.

 

[Hari Iyer]

Another big difference is the damping factor of tube amps, which is in single digits for tube amps but usually much higher for solid state amps (except some class A designs). This is also the reason why tube amp bass can sound lose or woolly with some speakers that need a high damping factor. It can also manifest itself as a lack of speed / slightly sluggish sound with some speakers.

Yes, the damping factor in tube amp is low because of the output transformer. The output transformer is required to stepdown the voltage which is around 400V to may be 1000V in some cases to around 25V to 45V depending upon the design. This is required for operating the speakers and hence the output impedance of a tube amp is high. Also there need not be any negative feedback required with tube amps (SET ones) due to the output transformer. Also the problem of the back EMF from the woofer cone motion creeping into the amp at low frequencies and distorting the signal will not arise in the tube amp because of the transformer. Hence with tube amp you really do not need high damping factor because of the output transformer as the transformer stops all back EMF from the woofer cone.

Speaker impedance is of paramount importance when paring it with a tube amp else it can ruin the design of the tube completely. Full-range speakers can benefit here sometimes due to absence of any cross-overs and can be one of the reasons why they pair well with tubes. 2 way / 3 way design needs to consider this aspect when they pair it with the tubes.

 

[gobble]

Also there need not be any negative feedback required with tube amps (SET ones) due to the output transformer.

Full-range speakers can benefit here sometimes due to absence of any cross-overs and can be one of the reasons why they pair well with tubes. 2 way / 3 way design needs to consider this aspect when they pair it with the tubes.

Hari-Ji

Not true.
My DIY SEP amp (single-ended Pentode) is based on a Williamson circuit and this type of circuit supposedly requires generous amounts of NFB to function correctly, otherwise it can oscillate. Indeed I once removed the circuit elements to make it a non-NFB one (going by an online mod article) and it refused to play any sound (strange, an oscillation should result in squealing not silence, and I don't know what else went wrong). I didn't have any ability or capacity to troubleshoot electronics so I quickly soldered them back into the pcb.

There is a Nelson Pass article on the web about how FR drivers sound great with high current amps more than voltage driven ones. Check it out. Based on that idea, I started using my foster speakers connected to the 4ohm terminal rather than 8ohm one and it sound marginally better.

I believe the reason FR pair well with low power tubes is that the absence of a crossover means it requires less energy to drive the speakers. The caps and inductor in the crossover require a lot of power. And as the power requirement increases the distortion output by the amp also increase. Hence the combination of late night+clean powerlines+low volume and power+low distortion+FR speakers makes it a much touted musical experience. It is not a completely accepted theory that tube distortion is good or that 2nd harmonic distortion makes tubes sound better. There are articles online that contest this claim.


My next amp is going to be a push-pull DIY one just for a taste of the hobby. But thats for next year...

G0bble

 

[jai1611]

With a lot of FR speakers, they work much better with tubes than solid state due to the high damping factor of solid state amps causing them to sound dry/lean. Solid state designs that manage to do well with such speakers are ones with a low damping factor (quite a few Firstwatt designs fall into this category).

The lack of synergy of full range speakers with even very good solid state amplification is something I've experienced first hand. Currently I have a ACA amplifier (5w, class A, damping factor of 3) handy which I suspect will do very well with full rangers. Havent tried it yet as my Rethms are still packed up but hope to do so soon.

 

[quad]

The output transformer is required to stepdown the voltage which is around 400V to may be 1000V in some cases to around 25V to 45V depending upon the design. This is required for operating the speakers and hence the output impedance of a tube amp is high.

Pl provide the source of this info.

 

[Hari Iyer]

Pl provide the source of this info.

@QUAD
Here you go. Check out all the tabs in the links if you need to be a tube basics expert.

Output Transformers

 

[Hari Iyer]

Hari-Ji

Not true.
My DIY SEP amp (single-ended Pentode) is based on a Williamson circuit and this type of circuit supposedly requires generous amounts of NFB to function correctly, otherwise it can oscillate. Indeed I once removed the circuit elements to make it a non-NFB one (going by an online mod article) and it refused to play any sound (strange, an oscillation should result in squealing not silence, and I don't know what else went wrong). I didn't have any ability or capacity to troubleshoot electronics so I quickly soldered them back into the pcb.

There is a Nelson Pass article on the web about how FR drivers sound great with high current amps more than voltage driven ones. Check it out. Based on that idea, I started using my foster speakers connected to the 4ohm terminal rather than 8ohm one and it sound marginally better.

I believe the reason FR pair well with low power tubes is that the absence of a crossover means it requires less energy to drive the speakers. The caps and inductor in the crossover require a lot of power. And as the power requirement increases the distortion output by the amp also increase. Hence the combination of late night+clean powerlines+low volume and power+low distortion+FR speakers makes it a much touted musical experience. It is not a completely accepted theory that tube distortion is good or that 2nd harmonic distortion makes tubes sound better. There are articles online that contest this claim.


My next amp is going to be a push-pull DIY one just for a taste of the hobby. But thats for next year...

G0bble

Non-NFB works only for an SET amp. For push-pull type you need NFB else it will oscillate. I think the bias changes when you remove the feedback loop. Check out this article for more info on the Williamson topology and desgin techniques.

About speakers, again going by this article, the inductors and capacitors do lower the SPL by the amount of dB loss across them, but again in a tube amp, the voltage increases when the impedance increases to keep a constant current across the tubes. Hence overall speaker system impedance should be reasonably flat for a good frequency response. Any major dips in the impedance curve will have a similar effect in the frequency domain too. Due to the output transformer the damping for the tube amp (SET) is quite low and hence even more the speakers need to have reasonably flat impedance.

Output Stage