Author Topic: Phase Splitters Good or Bad ?  (Read 2760 times)

Offline rollo

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Phase Splitters Good or Bad ?
« on: August 12, 2017, 08:47:20 AM »
  I call it the Humpty Dumpty effect. Can the signal actually be put back together properly ? Are SET designs without such an advantage ?
 

charles
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Offline tmazz

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Re: Phase Splitters Good or Bad ?
« Reply #1 on: August 12, 2017, 10:34:01 AM »
Like everything else in audio, amplifier design is a series of trade offs. No one circuit topology does everything right, they all have advantages and drawbacks. Set Designs are simple and have very few components in the signal path. but the also produce high amounts of second harmonic distortion and tend to require large  (and expensive) output transformers because of the DC current that flow continuously through the primary windings. They are also extremely limited in the power output they can produce from given tube. (for example SET circuits designed around using a single KT-88 in triode mode will produce about 5 watts whereas a KT-88 used in a class AB push-pull circuit can easily produce 50.)

SET amps are also notoriously inefficient, although the cost of providing AC power toan amp is rarely a concer to a high end audiophile, especially at the low output wattages that most high end SET amps produce.

Push pull circuits do produce more power but at the cost of more circuit complexity such as the require for a phase splitter.
While this is a downside, it also allows the amp to be with a much wider selection of speakers including designs that have efficiency ratings that would  them from being used with SET amps. The use of lower efficiency speakers/higher wattage amps also lowers the impact of noise in the system. Several milliwatts of noise into a 100+ db efficient speaker can produce some easily noticeable sound, whereas that same amount of noise put through a speaker system with an 89db or lower rating might barely move the cones.

So is it really not a matter if phase splitters are good or bad. If you use a push pull design, you need the phase splitter. This is just another way of asking is a SET topology "better" than a push-pull topology.   And in my mind that is a question that has no definitive answer. They both have pluses and minuses and they both can be the right or wrong choice, depending on the rest of the equipment being used with them.

Once again we are back to the same place, Synergy Synergy Synergy and personal preference. But then again, isn't that what this whole hobby is about?
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Offline dBe

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Re: Phase Splitters Good or Bad ?
« Reply #2 on: August 12, 2017, 02:07:00 PM »
Like everything else in audio, amplifier design is a series of trade offs. No one circuit topology does everything right...

Once again we are back to the same place, Synergy Synergy Synergy and personal preference. But then again, isn't that what this whole hobby is about?
I've heard amps of every type that have just knocked me out, and those same amps in applications that sucked.  Like you said - synergy.  We need to chose wisely  :thumb:

Offline steve

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Re: Phase Splitters Good or Bad ?
« Reply #3 on: August 12, 2017, 07:00:11 PM »
Years ago, I designed a phase splitter that was so good that I could not tell any difference when it was in or out of the system. Great, natural sonics, little artificial flavorings. Difficult to design, some. Made it to my monoblocks.

A phase splitter does not pull the signal apart and then put it together again, but I think I understand what is meant. Almost all phase splitters will have different output impedances (Z) per left and right output, although some designs only slightly. 180 degree out of phase is also important over a wide range of frequencies, and that can be achieved as well. This is best achieved by using high Gm and low plate resistance tubes. Of course SS is more complex by definition.

Simply put, the input signal is applied in such a way that the two output signals are 180 degrees out of phase over a very wide frequency range. Voltage is the main consideration, but some current is also needed to charge and discharge the output capacitance, interconnect capacitance, and amplifier input capacitance. The capacitances will depend upon the IC capacitance and device/gain of the amp input device.

Cheers

Steve
« Last Edit: August 12, 2017, 07:07:37 PM by steve »
Steve Sammet (Owner, Electron Eng, SAS Audio Labs, Ret)
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Offline rollo

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Re: Phase Splitters Good or Bad ?
« Reply #4 on: August 13, 2017, 10:12:29 AM »
Years ago, I designed a phase splitter that was so good that I could not tell any difference when it was in or out of the system. Great, natural sonics, little artificial flavorings. Difficult to design, some. Made it to my monoblocks.

A phase splitter does not pull the signal apart and then put it together again, but I think I understand what is meant. Almost all phase splitters will have different output impedances (Z) per left and right output, although some designs only slightly. 180 degree out of phase is also important over a wide range of frequencies, and that can be achieved as well. This is best achieved by using high Gm and low plate resistance tubes. Of course SS is more complex by definition.

Simply put, the input signal is applied in such a way that the two output signals are 180 degrees out of phase over a very wide frequency range. Voltage is the main consideration, but some current is also needed to charge and discharge the output capacitance, interconnect capacitance, and amplifier input capacitance. The capacitances will depend upon the IC capacitance and device/gain of the amp input device.

Cheers

Steve


  Thanks for explanation Steve. Synergy of components is a well known fact. But actually what is behind synergy ? Is it electrical characteristics of each component that meld together ? Is is something else related to sonic character of components ?
  I find it a tired argument or phrase used to explain why certain components go well with each other. T
here must be an engineering reason I would like ALL to know. Maybe I should start a new topic.


charles
contact me  at rollo14@verizon.net or visit us on Facebook
Lamm Industries - Aqua Acoustic, Formula & La Scala DAC- INNUOS  - Rethm - Kuzma - QLN - Audio Hungary Qualiton - Fritz speakers -Gigawatt -Vinnie Rossi,TWL, Swiss Cables, Merason DAC.

Offline steve

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Re: Phase Splitters Good or Bad ?
« Reply #5 on: August 13, 2017, 05:49:18 PM »
Years ago, I designed a phase splitter that was so good that I could not tell any difference when it was in or out of the system. Great, natural sonics, little artificial flavorings. Difficult to design, some. Made it to my monoblocks.

A phase splitter does not pull the signal apart and then put it together again, but I think I understand what is meant. Almost all phase splitters will have different output impedances (Z) per left and right output, although some designs only slightly. 180 degree out of phase is also important over a wide range of frequencies, and that can be achieved as well. This is best achieved by using high Gm and low plate resistance tubes. Of course SS is more complex by definition.

Simply put, the input signal is applied in such a way that the two output signals are 180 degrees out of phase over a very wide frequency range. Voltage is the main consideration, but some current is also needed to charge and discharge the output capacitance, interconnect capacitance, and amplifier input capacitance. The capacitances will depend upon the IC capacitance and device/gain of the amp input device.

Cheers

Steve


  Thanks for explanation Steve. Synergy of components is a well known fact. But actually what is behind synergy ? Is it electrical characteristics of each component that meld together ? Is is something else related to sonic character of components ?
  I find it a tired argument or phrase used to explain why certain components go well with each other. T
here must be an engineering reason I would like ALL to know. Maybe I should start a new topic.

charles

All synergy is, is an attempt to combine separate elements to obtain maximum sonic quality. Synergy is variable as it depends upon how the combination sonic quality compares to perfect entities that are combined. (Let's leave out the room and speakers for now.)
The main culprits are lack of correct designing, and lack of understanding how sensitive the "ear" is.

Virtually every part is critical to the sonic properties of a component. That includes parts in the power supply (and number of stages), parts quality in the rest of the circuit, harmonic distortion properties, frequency response etc.

The "ear" is incredibly sensitive to tonal abnormalities etc based upon Olson, Rane, Fletcher, Jensen, RCA Radiotron Designers Handbook etc, and I have confirmed before and after reading these sources over the years. 

If we are dealing with a preamplifier to amplifier combination, we look for enough signal voltage to drive the amplifier. This is usually not any problem. What could be a problem though, is output signal current capability of the preamplifier. Is that signal current enough to drive the output capacitance, IC capacitance, and amplifier input capacitance?

With not enough signal current, as the frequency rises, the HD distortion rises. I have seen sine waves become triangular waves as the frequency rises. But one does not need a buffer stage. A 12au7/6sn7/6dj8 type tubes generally provide plenty without any buffer. If a buffer is needed, there is one more stage to degrade the music.

As a very simple example of synergy; if a preamplifier is full sounding, we tend to find an amplifier that is thin sounding to compensate. Unfortunately, there is usually more than one flaw in a component, unless we are dealing with superb pieces of equipment. 
And some flaws one cannot cancel out. For instance, how does one cancel smearing caused by a component? If a component is so full it loses detail, how can that inner detail be recreated? Some of the biggest problems I see in components are;

1. Insufficient power supply filtering stages
2. Insufficient size and quality of coupling capacitors in tube components

My philosophy is to perform listening tests over months for each part, if possible, and each component for accuracy in absolute terms. With proper design, there will be less signal degradation, thus higher synergy can be achieved. Then I would design the speaker.

A couple of reasons why speaker sound so different are:

1. Different frequency responses and price range.
2. Different venue testing the speaker
3. Different quality components in the speaker.
4. Different quality active components in the test system. If a designer is using components that lack sufficient high frequency response, then the speaker will probably be bright sounding.
Etc.

Based upon these reasons, I would provide variable adjustments so the customer can create the best synergy possible. I have three adjustments on my speakers alone.

Cheers
Steve



Steve Sammet (Owner, Electron Eng, SAS Audio Labs, Ret)
SAS "V" 39pf/m 6N copper ICs,
SAS Test Phono Stage
Acutex 320 STR Mov Iron Cart
SAS 11A Perfect Tube Preamp
SAS 25 W Ref Triode/UL Monoblocks
2 way Floor Standing Test Speakers