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Old 1st August 2008, 07:00 AM   #1
hdlcx2 is offline hdlcx2  United States
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Default Please Explain difference Mono vs Push Pull vs Single End etc

Hello everyone

Could someone please explain to me the difference both technically and also sonically and also your own opinion and preferences between Push Pull and Mono Blocks and Single Ends and whatever other configuration or design there is using tube amplification?

For example, what is a push pull and what is a monoblock and which do you prefer and why? What is the sound difference and what is the output difference?

It would be greatly appreciated.

Cheers

Wills
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Old 1st August 2008, 07:19 AM   #2
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Default A Glossary of Common Amplifier Terms

There are lots of good sites around to expain these things.

Here is one of them.

http://www.aikenamps.com/AmpTerms.html

Cheers,
Ian
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Old 1st August 2008, 10:00 AM   #3
hdlcx2 is offline hdlcx2  United States
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Thats a big help Ian.

Thanks mate.

Cheers

Will
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Old 1st August 2008, 11:00 AM   #4
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Wills,

If you do a search on this forum you should be able to find plenty of useful material about this, mainly concerning differences between push-pull (PP) and single-ended (SE).

The following very brief notes may help.

SE means a single tube, or multiple tubes in parallel, driving the speaker through an output transformer which has a single primary winding with no center tap. SE has to operate in Class A, i.e. the tube(s) conduct for the entire cycle. This is the least efficient way to use output tubes, in terms of the available power.

SE causes the full distortion spectrum produced by the ouput tube(s) to be heard through the speaker. The distortion is thus 'balanced' and the tubes typically used in SE amps tend not to produce much distortion, anyway, so distortion is not usually considered to be a big issue.

SE requires a very efficient speaker because it's difficult to build a high power SE amplifier.

With SE the full current of the OP tube(s) passes through the primary of the OP transformer, resulting in a strong unidirectional magnetic field which can saturate the OP transformer's steel core unless there is an air-gap in the core. This means that the core must be made very large to be effective and results in OP transformers for SE being bulky, heavy and expensive in relation to the output power.

PP means one or more pairs of output tubes driving the speaker by working in anti-phase into a center-tapped output transformer. It can be made more efficient than Class A by using Class AB, which allows more power to be obtained than would be available from two tubes in Class A. In Class AB, each side of the PP arrangement conducts for less than a full cycle, which would not be possible in an SE design because it would be hopelessly distorted. PP gets asway with it because the signal is reconstructed in the OP transformer to give a full cycle.

PP can also be operated in pure Class A but the additional efficiency is lost. Class AB is inclined to produced in more distortion, so it's a trade-off.

An important feature of PP is that even-order harmonic distortion produced by the OP tubes is canceled (assuming it's well-balance), leaving only the odd-order harmonics. The distortion is thus not 'balanced'. Since even-order harmonics are pleasant to the ear but odd-order harmonics are unpleasant, this can result in a PP amp sounding harsh. It's one of the accusations leveled aginst PP by the SE advocates.

Another feature of PP is that there is no net magnetic field in the OP transformer's core, because the OP tubes take their current in opposite directions through the center-tapped OP transformer primary. This allows the OP transformer to be bult with no gap in its core and so it is a very much smaller transforme than that required by an SE amp of equivalent power.

Some people prefer the sound of SE and others prefer PP. There are arguments on both sides and it's largely a matter of taste. Of course, a true hi-fi amp has no business sounding like anything - its job is to reproduce music, not color it. I won't go there.

Monobloc construction simply means building the two stereo channels indepentently, i.e. each is a stand-alone monophonic (a.k.a monaural) amp on its own chassis. Two of them are used together for stereo.

The main reasons for going the monobloc way are to avoid having a single stereo amp that is too heavy; or to enable each amp to be closer to the speaker it's driving; or because it is believed that separating the channels like that gives better sound through elimination of cross-talk.

There are many design variations within the basic PP/SE options, including pentode/beam tetrode, ultralinear and triode connections of multi-grid tubes, directly-heated triodes and other designs, one of the main ones being output transformerless (OTL). As its name suggests, this desiagn doeas away with the OP transfomer, which has limited bandwidth and is large and expensive. It does this by using a large number of tubes that have very low output impedance. OTL is a specialized design that generates a lot of heat and is tricky to get stable.
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Old 1st August 2008, 07:08 PM   #5
hdlcx2 is offline hdlcx2  United States
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Thank you Ray

WoW, You seem very knowledgable.

And yes that is a big help. A brief but very good description of which I will copy if you dont mind and add to my audio notes.

I'm can now keep looking around from here for further info to expand on this. I have just purchased a small 10w push pull and was wanting to know the difference.

Thanks again

Wills
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Old 1st August 2008, 09:31 PM   #6
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Wills,

You're welcome. In addition to the very good Aiken Amps link from Ian, I've also found the following link quite useful. Max Robinson was a college teacher and explains things quite well.
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Old 2nd August 2008, 09:05 AM   #7
hdlcx2 is offline hdlcx2  United States
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Hi

Thanks again Ray.

I have just signed onto the group you suggested and look forward to the future of that forum as well. It appears dedicated to tubes.

Cheers

Will
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Old 2nd August 2008, 09:40 AM   #8
dubdub is offline dubdub  United Kingdom
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Thanks for that good summery - i wasnt too sure myself...more research now
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Old 2nd August 2008, 11:07 AM   #9
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Quote:
Originally posted by ray_moth
...

SE causes the full distortion spectrum produced by the ouput tube(s) to be heard through the speaker. The distortion is thus 'balanced' and the tubes typically used in SE amps tend not to produce much distortion, anyway, so distortion is not usually considered to be a big issue. ...
PP
An important feature of PP is that even-order harmonic distortion produced by the OP tubes is canceled (assuming it's well-balance), leaving only the odd-order harmonics. The distortion is thus not 'balanced'. Since even-order harmonics are pleasant to the ear but odd-order harmonics are unpleasant, this can result in a PP amp sounding harsh. It's one of the accusations leveled aginst PP by the SE advocates.
http://www.diyaudio.com/forums/showt...52#post1571852

http://www.diyaudio.com/forums/showt...49#post1572349
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Old 2nd August 2008, 11:18 AM   #10
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Wills,

I don't know what Max Robonson's forum is like, to be honest. I meant that you might find his articles interesting. You can find them by looking further down the first page of his website.
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