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Single ended differential inputs (rca)


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 So apparently my marantz mono blocks have a differential input stage using rca type connection.

At the bottom of the attachment there is a diagram of the differential input stage, I've also included the amps schematics.

The music link sc-22 preamp that is this models (music link) preamp has two rca outputs, one in phase and one out of phase. Although as the power amp only has a single input I don't see how this is relevant but it might be? ( I don't own this preamp)

Also the diagram shows the output coming from a BTL (bridged source) again probably irrelevant.

From my limited research I will run a twisted pair rca IC in the hopes the opp amps in the differential stage work to create a differential signal from a single (I believe this is possible?), To achieve some common mode noise reduction.

Anyway if anyone could help my understanding it would be much appreciated and hopefully somewhat interesting to you as well.

 

Joel

Marantz_MA-24_AllegroSound.pdf hfe_marantz_ma-24_schematic.pdf

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The input is single ended, and referenced to signal ground.  The input circuit is a differential pair (of transistors) one of them has it's input at a DC potential set by the DC offset adjustment, the other, receiving the input signal from the RCA socket.  A normal RCA interconnect is all that is needed.

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Excellent, thank you very much for that. Twisted pair going in the dumpster 😉

10 minutes ago, aussievintage said:

The input is single ended, and referenced to signal ground.  The input circuit is a differential pair (of transistors) one of them has it's input at a DC potential set by the DC offset adjustment, the other, receiving the input signal from the RCA socket.  A normal RCA interconnect is all that is needed.

 

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as above

virtually every power amp will run a differential input stage - it's the standard input stage design for power amps

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22 minutes ago, almikel said:

as above

virtually every power amp will run a differential input stage - it's the standard input stage design for power amps

I see, well it's good to know, thanks for the information 👍 I watched something on YouTube and fell down a rabbit hole 😂

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On 11/10/2020 at 7:01 PM, JoelG said:

I see, well it's good to know, thanks for the information 👍 I watched something on YouTube and fell down a rabbit hole 😂

amplifier output stages are very different - single ended vs push/pull - was that the rabbit hole you fell into?

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On 11/10/2020 at 6:24 PM, Decky said:

Yep what he said - nothing special about the circuit. 

 

On 11/10/2020 at 7:34 PM, almikel said:

as above

virtually every power amp will run a differential input stage - it's the standard input stage design for power amps

 

Mmmm - so WTF do power amp mfrs go into print about a "a differential input stage " if it's standard procedure?  Sheeeesh! :(

 

Andy

 

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1 hour ago, andyr said:

 

 

Mmmm - so WTF do power amp mfrs go into print about a "a differential input stage " if it's standard procedure?  Sheeeesh! :(

 

Andy

 

It is an improvement over simple single ended inputs, but has been around so long,  any marketer who thinks it is worth mentioning is, well, old-fashioned :) 

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16 hours ago, almikel said:

amplifier output stages are very different - single ended vs push/pull - was that the rabbit hole you fell into?

Hi, no, the particular hole was about single ended input(rca) connection that acted like a balanced input but requires a twisted pair IC to work. (Common mode noise reduction) he said that about 25% of amplifiers (usually high end)use this method but it has been overlooked for a long time in the industry.

I did find a lot of corroborating evidence and many car amps seem to use twisted pairs to work with this type of input, but as usual also many contrary statements. 

 

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11 hours ago, JoelG said:

Hi, no, the particular hole was about single ended input(rca) connection that acted like a balanced input but requires a twisted pair IC to work.

just be cautious of terminology - on my first read I saw twisted pair "integrated circuit" then realised IC = interconnect

On his white board it shows DI as "differential input", but any pro guy sees DI as "Direct Input" eg an acoustic guitar using a DI input into the mixing desk...

 

11 hours ago, JoelG said:

the particular hole was about single ended input(rca) connection that acted like a balanced input but requires a twisted pair IC to work. (Common mode noise reduction) he said that about 25% of amplifiers (usually high end)use this method but it has been overlooked for a long time in the industry.

Every power amp I've ever looked at the schematic of simply amplifies the difference between the +/- inputs, and will inherently have a reasonable Common Mode Rejection Ratio (CMRR) if the noise is across both the +/- inputs.

 

The video you attached is confusing fully balanced audio (2 conductors + shield) used in the pro world with single ended audio with only 2 conductors (+/-).

Fully balanced kit will never use RCA connectors for balanced inputs/outputs - sure the kit may have one/some RCA inputs/outputs, but they are single ended inputs/outputs with the balanced inputs/outputs being XLR or TRS etc

 

All that said - the single ended design in the video will still just amplify the difference between +/- of the input lead, as will the "differential" design, but yes there may be a 3dB difference in output.

When building car audio systems, which are typically electrically noisy environments, but mostly because I need to create a "virtual earth" midway between 0 and 12V, I would normally design all pre-amps/power amps with an additional op-amp on the input side as a buffer/differential input stage - keeping in mind with car audio, the ground terminal of the battery is actually -6V from the power amps perspective - you need to create a "virtual" earth at 6V to get a +/- 6V swing between the rails - commercial car audio gear manages all of this...including inverters to increase voltage for decent power...it's only when designing car audio crossovers/amps from scratch you need to consider a "virtual earth".

 

Home audio is different - there's plenty of voltage swing available, and typically the earth pin of an RCA cable connects to earth somewhere - but the amp is still just amplifying the voltage difference between the two wires, and will inherently reject noise that's common across both input wires.

 

I wouldn't recommend random interconnection between fully balanced gear and unbalanced gear - try to stick with one or the other.

A CD player unbalanced input to a balanced system is likely fine.

An unbalanced unit in between 2 balanced units could easily cause issues with earth loops etc...

A good guide is here: https://www.ranecommercial.com/kb_article.php?article=2107

 

cheers

Mike

 

 

 

 

 

 

 

 

 

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12 hours ago, almikel said:

just be cautious of terminology - on my first read I saw twisted pair "integrated circuit" then realised IC = interconnect

On his white board it shows DI as "differential input", but any pro guy sees DI as "Direct Input" eg an acoustic guitar using a DI input into the mixing desk...

 

Every power amp I've ever looked at the schematic of simply amplifies the difference between the +/- inputs, and will inherently have a reasonable Common Mode Rejection Ratio (CMRR) if the noise is across both the +/- inputs.

 

The video you attached is confusing fully balanced audio (2 conductors + shield) used in the pro world with single ended audio with only 2 conductors (+/-).

Fully balanced kit will never use RCA connectors for balanced inputs/outputs - sure the kit may have one/some RCA inputs/outputs, but they are single ended inputs/outputs with the balanced inputs/outputs being XLR or TRS etc

 

All that said - the single ended design in the video will still just amplify the difference between +/- of the input lead, as will the "differential" design, but yes there may be a 3dB difference in output.

When building car audio systems, which are typically electrically noisy environments, but mostly because I need to create a "virtual earth" midway between 0 and 12V, I would normally design all pre-amps/power amps with an additional op-amp on the input side as a buffer/differential input stage - keeping in mind with car audio, the ground terminal of the battery is actually -6V from the power amps perspective - you need to create a "virtual" earth at 6V to get a +/- 6V swing between the rails - commercial car audio gear manages all of this...including inverters to increase voltage for decent power...it's only when designing car audio crossovers/amps from scratch you need to consider a "virtual earth".

 

Home audio is different - there's plenty of voltage swing available, and typically the earth pin of an RCA cable connects to earth somewhere - but the amp is still just amplifying the voltage difference between the two wires, and will inherently reject noise that's common across both input wires.

 

I wouldn't recommend random interconnection between fully balanced gear and unbalanced gear - try to stick with one or the other.

A CD player unbalanced input to a balanced system is likely fine.

An unbalanced unit in between 2 balanced units could easily cause issues with earth loops etc...

A good guide is here: https://www.ranecommercial.com/kb_article.php?article=2107

 

cheers

Mike

 

 

 

 

 

 

 

 

 

Thanks Mike, much appreciate you answer.  

Yes, sticking with single to single. 

It's all very interesting stuff, just started scratching the surface. 

Cheers,

 

Joel

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16 hours ago, almikel said:

 

The video you attached is confusing fully balanced audio (2 conductors + shield) used in the pro world with single ended audio with only 2 conductors (+/-).

 

 

You've left out the way I build my interconnects, Mike!  xD  This is:

 

2 conductors (gnd & signal) under a shield.

 

the shield is either:

  • earthed to the gnd connection of the source RCA plug.  (Being connected at only one end, the shield doesn't form part of the signal path but is connected to earth.)
  • or - better - the shield is picked apart to form a 'tail' which gets its earthing from the earth terminal on the component at either the source or the destination end.

 

So they are single-ended, unbalanced RCA interconnects ... but use 2 wires + shield.  :)  (Sometimes known as 'psuedo-balanced'.)  The advantage of this construction method is twofold:

  1. I can use solid-core wire for both signal and gnd connections, and
  2. the gnd connection does not pick up noise from RFI, like the shield of a coax connection does.

 

Andy

 

Edited by andyr
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On 16/10/2020 at 1:50 PM, andyr said:

 

You've left out the way I build my interconnects, Mike!  xD  This is:

 

2 conductors (gnd & signal) under a shield.

 

the shield is either:

  • earthed to the gnd connection of the source RCA plug.  (Being connected at only one end, the shield doesn't form part of the signal path but is connected to earth.)
  • or - better - the shield is picked apart to form a 'tail' which gets its earthing from the earth terminal on the component at either the source or the destination end.

 

So they are single-ended, unbalanced RCA interconnects ... but use 2 wires + shield.  :)  (Sometimes known as 'psuedo-balanced'.)  The advantage of this construction method is twofold:

  1. I can use solid-core wire for both signal and gnd connections, and
  2. the gnd connection does not pick up noise from RFI, like the shield of a coax connection does.

 

Andy

 

 

cheers Andy,

 

I'm fine with your approach, but it means all your interconnect cables are custom builds...not many people (me included) custom build their own interconnect cables...

...and it would completely negate the ability for people to swap in outrageously overpriced interconnects...

 

...you have a business opportunity there...:

  • AndysInterconnects
  • AndesInterconnects
  • MountainInterconnects
  • PrecipiceConnections

The marketing campaign is right there, "mountainous sound from the solid core connectors, and 'chasm like' reduction in noise from the shielding"

 

:)

Mike

 

 

 

 

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12 minutes ago, almikel said:

 

cheers Andy,

 

I'm fine with your approach, but it means all your interconnect cables are custom builds

 

 

Correct, Mike.

 

And my digital cables - also spkr cables.

 

12 minutes ago, almikel said:

 

...and it would completely negate the ability for people to swap in outrageously overpriced interconnects...

 

 

I don't see why?  People can try mine ... and then buy an interconnect at 10 times the price, at any time.  :)

 

12 minutes ago, almikel said:

 

...you have a business opportunity there...:

  • AndysInterconnects
  • AndesInterconnects
  • MountainInterconnects
  • PrecipiceConnections

The marketing campaign is right there, "mountainous sound from the solid core connectors, and 'chasm like' reduction in noise from the shielding"

 

:)

Mike

 

 

 

The people who have bought my interconnects like them.  :)  I'm not sure that a 'marketing campaign' would deliver an improvement, in terms of sales?

 

Andy

 

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On 16/10/2020 at 12:30 PM, JoelG said:

Yes, sticking with single to single. 

Hi Joel,

Apologies for being pedantic, but terminology is important - I assume you mean you intend to interconnect "unbalanced" gear to "unbalanced" gear - which is fine and usual - most consumer gear is unbalanced.

 

The term "single ended" is usually associated with power amps (although pre-amps can also be single ended).

A single ended power amp must be class A, with the output device/s managing the entire +/- voltage swing to the load (the speaker).

 

Plenty of people regard single ended power amps the ultimate in sound - Single Ended Triode (SET) amps are an example of this topology.

 

Most modern solid state (transistor/mosfet etc) power amps are push/pull, not single ended - where 2 symmetrical devices amplify the signal.

A push/pull output stage can be biased in 3 ways:

  1. Class A - both output devices turned on all of the time managing +ve and -ve swings
  2. Class A/B - both output devices conducting at low output levels (not necessarily equally), but at high output levels one side manages +ve swings, and the other side manages -ve swings
  3. Class B - +ve swings managed by 1 device, and -ve swings managed by the other device

Most modern solid state amps are push/pull class A/B - ie option 2 above.

 

I did run some very nice sounding single ended class A "Valvet" transistor amps in my system for a while, but to hit my SPL/volume levels at my listening position I ran them into clipping too often, and class A amps don't mix well with Brisbane summers - geez those amps ran hot - I don't need the extra heat class A amps shed.

 

cheers

Mike

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8 hours ago, almikel said:

 

A single ended power amp must be class A, with the output device/s managing the entire +/- voltage swing to the load (the speaker).

 

 

However, a Class A amp does not have to be single-ended; I'm building a pair of Class A amps which have +/- DC rails!  :)

 

Andy

 

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21 hours ago, almikel said:

Hi Joel,

Apologies for being pedantic, but terminology is important - I assume you mean you intend to interconnect "unbalanced" gear to "unbalanced" gear - which is fine and usual - most consumer gear is unbalanced.

 

The term "single ended" is usually associated with power amps (although pre-amps can also be single ended).

A single ended power amp must be class A, with the output device/s managing the entire +/- voltage swing to the load (the speaker).

 

Plenty of people regard single ended power amps the ultimate in sound - Single Ended Triode (SET) amps are an example of this topology.

 

Most modern solid state (transistor/mosfet etc) power amps are push/pull, not single ended - where 2 symmetrical devices amplify the signal.

A push/pull output stage can be biased in 3 ways:

  1. Class A - both output devices turned on all of the time managing +ve and -ve swings
  2. Class A/B - both output devices conducting at low output levels (not necessarily equally), but at high output levels one side manages +ve swings, and the other side manages -ve swings
  3. Class B - +ve swings managed by 1 device, and -ve swings managed by the other device

Most modern solid state amps are push/pull class A/B - ie option 2 above.

 

I did run some very nice sounding single ended class A "Valvet" transistor amps in my system for a while, but to hit my SPL/volume levels at my listening position I ran them into clipping too often, and class A amps don't mix well with Brisbane summers - geez those amps ran hot - I don't need the extra heat class A amps shed.

 

cheers

Mike

Hi Mike, good to get your message.

I was referring to single ended inputs (unbalanced)  rca.

My amps are class A (30watts) push pull/ MOSFET output stage.  They do run pretty hot.(good for cold winters)

I'll do some research on single ended class A output stages, sounds interesting.

The question originated from the attached video  which  stated some amps are able can convert a normal single ended signal(unbalanced) (rca)  into a differential signal (balanced)using a twisted pair IC  to achieve some sort of common mode noise reduction not dissimilar to true balanced gear.. anyway that what he thinks.. (unless I got it totally wrong) 

So yes atm  just using single ended unbalanced to SE unbalanced.

 

Here's a good article that explains.

https://jlaudio.zendesk.com/hc/en-us/articles/209357588-Differential-Balanced-Inputs?mobile_site=true

Thanks 

 

Joel

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On 21/10/2020 at 10:57 AM, JoelG said:

which  stated some amps are able can convert a normal single ended signal(unbalanced) (rca)  into a differential signal (balanced)using a twisted pair IC  to achieve some sort of common mode noise reduction not dissimilar to true balanced gear..

there's no "conversion" going on - every single amp I've ever looked at the schematic of will run a "differential input pair" of transistors/mosfets whatever - and this design will have inherent common mode rejection - noise that's common across the inputs won't be amplified, only differences between the inputs will be amplified.

 

On 21/10/2020 at 10:57 AM, JoelG said:

This primarily relates to car audio, and as I mentioned in an earlier post, car audio works in noisy environments and grounding has the additional challenge that the -ve terminal of the car battery is essentially the -ve rail of the power amp and a "virtual earth" is required.

 

 

There's no question that for car audio you need to consider how to manage DC offsets and noise - the only car system I designed/built, I ran an extra buffer/differential input stage prior to all the power amps and between the head unit and the DIY active crossover (a 3 way 18dB/octave butterworth - I'd never heard of Linkwitz Riley LR4 back then...circa mid 1990s)

 

For some reason I was obsessed with building a car stereo that could run on power amps without inverters, so I bought a bunch of these little stereo power amps that output 18W rms per channel (internally bridged).

1 amp for the tweeters on the dash, 1 for the front door speakers, and 2 for the 4x8" woofers that went in a custom panel behind the back seat.

It wouldn't have won any SPL contests, but 4 x stereo 18W rms of amplification with an active crossover sounded pretty fine.

 

The buffer/differential input stages I built between the head unit/crossover and crossover/power amps did 2 things:

  1. removed any DC offset from either leg of the signal inputs ie managed virtual ground between each bit of gear 
  2. assisted in removing common noise from inputs - essential in noisy car environments - the car this system was installed in was a V8 XY Falcon running a normal distributor and points...noisy from an audio perspective

Home environments are not so demanding - with earth being better defined, and any decent gear having minuscule DC offsets.

Typical standard unbalanced gear can produce great results - although if you generate an earth loop somewhere it can be a total PITA to eradicate.

 

mike

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32 minutes ago, almikel said:

every single amp I've ever looked at the schematic of will run a "differential input pair" of transistors/mosfets whatever

Keep looking then.  Plenty of them don't.  I know it sounds like I am picking an argument, but truly, there's lots of normal single ended inputs to single transistors or valves out there. 

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On 23/10/2020 at 9:18 PM, aussievintage said:

Keep looking then.  Plenty of them don't.  I know it sounds like I am picking an argument, but truly, there's lots of normal single ended inputs to single transistors or valves out there. 

maybe so - power amps that don't run a differential input pair at the input would have a significantly reduced Common Mode Rejection Ratio (CMRR) for noise compared to a power amp that runs a differential input pair at the front end...

 

...excluding the power amps @aussievintage is referring to, mostly every commercial solid state power amp these days would run a differential input stage - it's been the standard input stage for "typical" solid state power amps for several decades...I won't comment on valve amps, or minimalist power amp designs such as Nelson Pass etc...

 

...I completely accept that lots of power amps don't run a differential input pair - but the vast majority of commercial solid state power amps do.

 

cheers

Mike

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On 15/10/2020 at 11:52 AM, JoelG said:

Hi, no, the particular hole was about single ended input(rca) connection that acted like a balanced input but requires a twisted pair IC to work. (Common mode noise reduction) he said that about 25% of amplifiers (usually high end)use this method but it has been overlooked for a long time in the industry.

 

AFAIUI is less common than he makes out.... as he explains, if used with a "standard" RCA cable (a coaxial cable), then it will be ineffective at noise reduction, as it will mix the noise conducted in the outter conductor with the signal on the inner conductor.

 

Any manufacturer wiring an input like this would want to make it very clear to users that they needed to use such a cable.

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20 minutes ago, davewantsmoore said:

 

AFAIUI is less common than he makes out.... as he explains, if used with a "standard" RCA cable (a coaxial cable), then it will be ineffective at noise reduction, as it will mix the noise conducted in the outter conductor with the signal on the inner conductor.

 

Any manufacturer wiring an input like this would want to make it very clear to users that they needed to use such a cable.

 yes, I've never heard of this before watching this video and you would really think it'd be something worth mentioning 😁

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