Asheville, North Carolina ‘s Home Theater and Audio specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

It can’t get bigger!

Now there’s an opening line that if this were not a public blog I would just have to add my own punchline to. But…

My friend Larry Borden, editor at the audio website Dagogo, sent me a note just in the nick of time. I was sitting at my desk trying to figure out how I could help people get a really clear view of what we’re discussing in this series; the importance of power supplies in amplifiers. And yesterday I posted a picture that was pure simplicity. Here it is again.

I repost this picture for a good reason. It helps explain something rather profound about amplifiers.

We all think that amplifiers take the small and enlarge it (amplify it) to something larger. And they do. Except… and this is where Larry’s brilliant insight comes into play.

Let me quote Larry:
“Over the years I came to the realization that the biggest misconception is that an amplifier actually makes the electrical signal “bigger.” Once I explained that this is not possible per se, they could then follow the metaphor of a water valve. One that concept was grasped, they would have an “aha moment” regarding the importance of the power supply.”

Okay, I know that’s confusing so let’s step back a moment. Imagine our amplifier valve as that of a water faucet. The power supply is the reservoir of water. We know from that image the faucet cannot make more water than what is available from the reservoir. In fact, the valve can only let what’s in the reservoir out or stop it from flowing. It cannot make more. So yes, an amplifier takes a small signal and makes it bigger – but not bigger than what’s available in the power supply. The valve can only make something smaller than the power supply is capable of providing. It is, after all, a valve.

So now let’s move to the example of an amplifier powering a loudspeaker. We all know that amplifiers have power ratings: anywhere from 1 watt to 1000 watts. What is the gating item that determines the output power of an amplifier? Is it the valve or the power supply? If you guessed power supply, congratulations, you win the prize. Ignoring some of the practical limitations we engineers face when designing equipment for a moment, the difference between a 100 watt power amplifier and a 500 watt power amplifier is not the valve (amplifier) but the power supply. Take a 100 watt amplifier, replace its power supply with one 5 times more powerful and you have a 500 watt amplifier. Plain and simple.

Yes, yes, let us not pollute our understanding of these basic ideas with details such as: bigger heatsinks, stronger valves, etc. I am not trying to help you design a new amplifier.
Amplifiers can only make what their power supplies offer smaller, never bigger.

So why do we call them ‘amplifiers’ when, in fact, they are only valves? For the same reason a small turn of the faucet can release a huge and powerful stream of water. It amplifies the small force into the bigger force but – and here’s the key – never bigger than the power supply.

And never better than the power supply. Let that be your food for thought and our starting point for tomorrow’s discussion.

Asheville, North Carolina ‘s Home Theater and Audio specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

Try this on for size

The best chef in the world would have trouble turning out a great meal with poor ingredients. So it is with amplifiers.
The ingredient of an amplifier is power. The chef is the amplification ‘valve’. If either the ingredients or the chef are subpar the music suffers.

Ever notice what happens when you try and spiff up something that started out poorly? For example, if I have a lousy source like a cheap turntable, the best phono preamplifier I have cannot help it sound as good as if I had started with a better source. And so it is with the dance between power supply and amplifier.
Look at the diagram I have included. Note how the power supply feeds the box labeled ‘amp valve’. The amp valve is the amplifier circuitry itself. But note something important. The valve (whether solid state or vacuum tube) has no ability to do anything other than act as its name implies: as a valve. It cannot generate anything and it is completely dependent on what the power supply sends its way.

This is the essence of what we’ll be going over in the next few days. Simple as it may seem, you’d be surprised how many people do not understand the interaction between the source and the modifier. In this case the supply and the valve. It’s my goal to help walk us through this very important subject.

Asheville, North Carolina ‘s Home Theater and Audio specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

We’re not engineers

Several of my readers have written me expressing concern on the course we’re embarking upon; learning about power supplies. For, as they have said to me, we don’t know what a power supply is and we’re not too sure if we should care. We just want good sounding stereo equipment.

Good thoughts and I appreciate the dilemma. One doesn’t necessarily have to know the difference between a 4 cylinder and an 8 cylinder engine to appreciate the virtues of a car. But in the broader sense we, as music lovers and Audiophiles, need a certain level of savvy to understand the difference between a receiver and separates, a boom box and a component audio system. Even the most uninformed among us probably knows what a DAC, turntable, loudspeaker, power amplifier are. And who among us does not recognize the difference between a tube and solid state product? Many do not give themselves adequate credit for their knowledge.

I think it important to dig a bit into the workings of things so that we may understand better what to expect when we play music though our equipment.

Let me attempt to simplify things for those struggling with the understanding. We can break the components of a stereo system into sub groups easily:
• Sources
• Amplifiers
• Loudspeakers
• Connecting interfaces

We can easily eliminate the last two on the list for who among us does not understand that loudspeakers make the sound in our rooms and cables connect things together?

That leaves sources and amplifiers and today we are focusing on amplifiers. Within any amplifier, whether it be a pre or power, we find only a few basic elements of the system:
• Power supply
• Valves (either solid state or tube)
• Inputs/outputs
• Sometimes a volume control element

I am assuming we all understand inputs and outputs since who among us cannot connect a stereo system to play music? And turning up and down the volume is a rather basic tenant of any stereo, one easy to understand.

That leaves us with only two great mysteries:
• Power supply
• Valves (either solid state or tube)

We’ll go slowly and in depth on these two subsystems tomorrow.

Asheville, North Carolina ‘s Home Theater and Audio specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

Trick questions

I asked a fundamental question in yesterday’s post. If the power supply of a piece of equipment is not in the signal path, how could it have an affect on the sound?

The question, of course, is a trick one. For the power supply IS in the signal path as much or perhaps more than the amplification circuitry itself. I started the conversation with this ‘trick’ question because I wanted to engage those who still believe in this often used misconception. What’s interesting to me is how many folks just kind of take for granted the role the power supply takes and assume it is separate and not a ‘real’ part of the signal path. I recall years ago getting into heated debate with an engineer who told me it was as obvious as the nose on my face that power supplies and amplifiers are independent systems that, when the power supply is appropriately designed, hasn’t any bearing on the sound quality. The conversation went something like this:

“The signal is modulated by the amplifier and that signal passes only through the amplification circuitry. As long as the power supply is adequate, there should be no difference from one to another.”

“Yes,” said I, “but if you look at a schematic you’ll note the power supply is in series with the amplifier’s output. It’s fed from that supply.”

“True,” he said, “but note that the power supply doesn’t move and its only job is to remain a rock solid source of power for the amplifier to work on the musical signal. As long as that supply is steady, regulated and clean, there can be no difference in sound between various types.”

So perhaps that’s a good place to start our discussion; the role power supplies play in our circuits. What does a power supply actually do? A power supply replaces that that could be handled by a battery. Batteries are DC (direct current), stereo circuits require DC but what comes out of our home’s wall sockets is AC. Remembering back to our prior discussions on the difference between DC and AC, we’ll recall that AC is like a battery – only it changes from plus to minus 50 or 60 times a second (depending on the country you live in). AC is used without conversion for lightbulbs, heaters and motors and not much else. Anything we stereo buffs would be interested in requires conversion to DC before its useful. So, the first task of any power supply is to convert the AC into DC and this is where the trouble starts. But I digress.

Primary function of a power supply is converting AC to DC.

Secondary function of a power supply is to make the DC as clean and free of AC as possible.

Tertiary function of a power supply, to provide the appropriate voltage levels the preamplifier requires.

Tomorrow we look even closer.

Asheville, North Carolina ‘s Home Theater and Audio specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

Hearing what’s not there

I am often asked why power supplies make a difference in audio electronics. For, after all, it’s the power supply and it is not in the signal path. Being outside the signal path suggests that a well designed power supply should be sonically invisible, as if it were not even there, yet the opposite is true.

Perhaps we’ll spend some time exploring this very subject.
Let’s start with the obvious. The power supply for a power generating product, like a power amplifier, makes a sonic difference for a number of reasons. Chief among them is the ability to deliver enough power to not starve the loudspeaker’s needs. When the music gets loud power is required to drive the loudspeaker and that power comes from the amp’s supply. It would then seem obvious that a supply that’s less than adequate would have some sonic issues if it simply ran out of power.

Clipping, strained sound, etc. would be rather obvious effects.
But what happens if you compare the sonic results of two power supplies of equal strength driving the same amplifier? Would they sound the same if their topology was very different and neither caused any obvious signal damage? The short answer is no, they would not and the reason they would not is fundamental to answering our question of how something not in the signal path could affect the sound your hear.

Tomorrow we’ll start to take a look at this intriguing question.

Asheville, North Carolina ‘s Home Theater and Audio specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

Technology’s lineage

We gave a couple of Sprout integrateds to relatives for Christmas this year. They were thrilled. What they really were excited about is Bluetooth. The capability to stream from their phones to their home speakers seems a miracle to many not daily involved in the industry. That’s always been interesting to me. I find it cool as well, but more of a novelty than something I would do on a regular basis.

And I always wonder if my reluctance in one area of new technology is due to my getting older, stuck in a bygone era or rather something different. On the one hand I am involved in creating some of the newest and most innovative products in stereo, yet on the other hand, I still question some of the new technology: fad or here to stay?

I’ll give you an example from a different point of view. Our general manager’s 13 year old daughter Mandi announced she wanted a turntable. Out of the blue, she wants the ‘new thing’ her friends are excited about. Of course, a turntable is anything but new to those of us reading this blog, but to her group it’s new, fresh and fun. I guess the point of all this centers around the idea that the appeal of different technologies isn’t a clear linear progression one can map. Their acceptance seems to vary with the moment to suit the tastes and expectations of those using them and without regard to their lineage.

Now where did I store that old Muntz 8-track?

Asheville, North Carolina ‘s Home Theater and Audio specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

If doing the right thing fails…

So let’s imagine you’ve taken my suggestions, done all you can to fix a ground loop hum issue at its source and you still have hum.

What then?

Then you have to take a different path: break the ground loop. To do this you will need to ‘unground’ the offending piece of equipment. This can be accomplished in any number of ways depending on what country you live in. But here’s the thing. You must know it’s not recommended to unground a product from the wall socket. Why? In the unlikely event a connector or wire with live voltage should get loose in the chassis it could be dangerous. Lethal, in fact. So this is one reason we suggest you fix the problem of the different ground in the first place.
But I have seen many instances where this is not practical. In those cases I sometimes remove the ground pin from the power cable or use a simple ‘cheater plug’, available at most any hardware store for this very purpose. Once connected back in the system, the offending unit is still grounded, but it’s grounded through the connecting cables. It’s not up to code and it is not advised the YOU do this. Legally I cannot and should not encourage you to do such a thing and I won’t. In fact, don’t.

One thing you can try is to use a ground loop buster which claims to be effective and safe. Click here. I haven’t any experience with this because I live a dangerous life on the edge. I take all sorts of risks. It’s just in my nature.

If one of the components in my chain has a ground loop issue, it’s almost always the power amp. I am not sure why this is, but that’s been my experience. If I can’t fix the ground then I cheat this plug and leave every other piece of equipment in the system grounded. This solves the hum problem by ‘floating’ the power amp, relative to ground. The power amp is, in fact, grounded. Only, instead of being grounded through the third prong on your AC socket, it’s grounded through the connecting cables to the preamp’s ground, which is connected to the third prong ground on your AC connector.

But don’t listen to me. Certainly do not do what I do.

Asheville, North Carolina ‘s Home Theater and Audio specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

Ho, Ho, Ho

It’s Christmas morning and I wanted to say happy holidays to everyone of you. Thank you for all you do for the community, for music, for putting smiles on people’s faces.

I like this time of year. I like it because it’s a time when we are drawn together in the spirit of friendship. A time of bonding.
I try and reflect on all the good things I have in my life and you, my friends, are among the best.

Thank you.

Asheville, North Carolina ‘s Home Theater and Audio specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

Isolation

I mentioned one of the biggest offenders of hum creation in our systems through a ground loop comes from the cable TV connection. If you have satellite TV like Direct it’s not a problem, but if you’re connected to the cable and that is connected in your system at any point, chances are good you have a ground loop. Remedying it at the source is the best way to solve the problem. I typically recommend a CATV isolation transformer but I also make that suggestion with a cautionary note. Most CATV isolation transformers have a price to pay because of their limited bandwidth: poorer picture quality for higher speed HD signals.

Reader Gary Gallo came up with a better solution, one that does not come with such a price to pay.

CATV grounding can be a menace to audio systems and, as you point out, isolation transformers can be a problematic solution due to the losses involved.

A better solution is to use a capacitive isolator. All you need are a pair of 2.2nF capacitors – one in the signal line and one in the ground line. When terminated with a 75-ohm load, the isolator provides a low-loss signal path in the RF region while appearing very high-Z at the line frequency and the low-order harmonics likely to cause buzz. I’ve attached a schematic and a photo.

The F-connectors and capacitors can be housed in a small plastic project box, such as a Hammond 1591L, Digi-Key #HM100-ND. The capacitors should be film types with a rating of 250 VDC / 140 VAC, in countries where the line voltage is nominally 120 VAC. I used Epcos metallized polypropylene, Digi-Key #495-1279-ND. A 630 VDC / 400 VAC version is also available, Digi-Key #495-1318-ND.

Insert the isolator between the cable TV outlet in your A/V room and your CATV or DVR box. That way, your A/V system is also isolated from your cable modem. For those who can’t build one themselves, Jensen Transformers offers an excellent capacitive isolator, VRD-1FF (www.jensen-transformers.com). It’s actually the only product Jensen makes that isn’t a transformer.

I suggest checking the AC voltage difference between your cable TV ground and power line ground before adding the isolator. It only takes a small difference in potential to cause hum in your audio system, but if the difference is more than a few volts, I suggest finding the root of the problem. A CATV isolator should not be used as a band-aid to cover up a potentially dangerous situation caused by improper or failed grounding of your CATV line or your house electrical system (I once saw a difference of 50 VAC due to a failed cable TV ground!). If in doubt, call a licensed electrician and/or your cable TV company. But, even with all grounding up to code, I always use a capacitive isolator in my CATV line.

Simple, effective, yet shouldn’t present a compromise to your TV picture.

Thanks Gary.

Asheville, North Carolina ‘s Home Theater and Audio specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

Fixing ground loops

We’ve been discussing how to identify a ground loop. Now it’s time to fix what we’ve identified as a problem. But let me warn you of a couple of things: reread what I have written about identifying them (make sure it actually IS a ground loop), secondly, the cure can be dangerous if not done properly.
To review. There cannot be a ground loop with only one piece of equipment. It takes two. The difference in ground potential between the two (ground being at a different level for each) is what causes the hum. Further, you can have one piece of equipment in a many-piece set that is at a different level, while all the others are at a proper level. You will still get hum.
To remedy the ground loop we must do one of two things: find the source of the ground difference and correct it (that’s the best way), or float the offending piece of gear from the others.
Here’s a good example. The most common ground loop problem comes from a cable TV. Their grounds are rarely at the same level as our home’s grounds (although they are supposed to be). Connect the little CATV connector to, say, a cable TV box that is also connected to your stereo or home theater system and bingo! You’d got a ground loop. Remove the CATV connector and the hum goes away (so too does the picture). So, how do we fix this? One quick example is to use a TOSLINK optical cable between the cable TV box and the stereo system, if your system has a DAC. This works because the optical cable cannot have a ground problem since it is optically isolated from the system. Here’s another, less desirable way: use a cable TV isolation transformer between the input CATV connector and the cable box. This works for isolation and hum elimination, but with modern high speed internet and cable streams you might lose some quality. These are just a few examples.

But now let’s say we have only a pure audio system, yet we still have hum. We suspect a ground loop because of two facts we’ve discovered: the hum is a higher pitched buzz relative to a low smooth hum (I have placed audio examples here) and the two suspect pieces are plugged into different AC outlets. Our first task is to narrow down the offending piece. This is where we want to use our method of elimination, starting at the loudspeaker again. Remember? Connect the power amp to the loudspeaker making certain you haven’t any inputs on the power amp – here I am being very literal. I don’t mean no signal present. I mean, NO INTERCONNECTS attached. Even without a signal our grounds would still be attached. Is there hum? If there is, you have a problem specific to your power amp, one requiring you to return it to the manufacturer for repair. No hum? Okay, now connect the preamplifier with the same restrictions. NO INPUTS. Hum? No and you start adding inputs in one at a time till you find the culprit. Hum, yes? Then you must find out if that hum goes up and down with level of the preamp. If it does, it’s not a ground loop. If it doesn’t, it may likely be.

Let’s leave of till tomorrow the next steps (I don’t like the posts getting too long).