[Pneumonic]

That is true, I often use that analogy. Now what happens when an amplifier has the capability of a lot of voltage but runs out of current, which can happen when the load impedance drops? What happens to the devices (tubes or transistors) in this situation?

It is pretty rare though the amp will almost always run out of voltage first.

[Freo-1]

It is pretty rare though the amp will almost always run out of voltage first.

SS amps, OK.  But tube amps, I could see how the amp becomes current limited vs. voltage limited. (Especially a DIY amp).   

[RDavidson]

I do not believe measurements fully describe amplifiers as we hear them. However if all the tests are done, and there are many that are not, we do get a lot closer to what makes a good amplifier.  One should pay attention to John Atkinson's measurements of frequency response alterations with a speaker load. It's the first graph he publishes in every amp measurement. Perhaps that is because he finds it most important also.

I agree with this entirely. The subjective part of reviewing is to help provide a sense of human perspective / analysis / descriptors. We humans listen with our ears (brains) afterall. We can't literally listen to mathematical data. We all know that there are things we humans can perceive that are not measurable by current "standard" testing / data collection methods. The purpose of the measurements is to help inform and perhaps correlate / de-correlate the mathematical (objective data) with what was perceived by the reviewer (the subjective data). This is why it is important to appreciate both data types.....particularly when presented together. Any time I read a Stereophile review, I read the measurements section. I don't fully understand ALL aspects of it, but John Atkinson does a good job of making the meat of the data easy to follow (even if you're a bit of a technical novice).

[Roger A. Modjeski]

It is pretty rare though the amp will almost always run out of voltage first.

Please read what I wrote this morning about current limiting. Perhaps you are unaware that as rail voltage is raised the current limiting becomes more severe. Into a very low load, especially a capacitive load like an ESL, the these limiters kick in at very low levels. A capacitor, or woofer around resonance has a large phase angle where the current and voltage are out of phase. That looks like shorts to the limiters.

I am aware that you have Roger Sanders speakers and amps. I am aware that he has designed his amps not to limit into his speakers. I'd guess he made the amps because most amps will current limit into his speakers.  Please consider that your amps are not typical of what is on the market.

These limiters are real and protect the output transistors. At higher voltages the limiters have to be set lower than at low voltages. I believe you have mentioned you design amplifiers. What are your rail voltages? How do you protect your output transistors?

[Pneumonic]

Indeed, Roger. I agree and understand completely. I have been running <2Ω, C loads for eons. But they are not the norm. Most people employ SS amps which drive speakers with benign, mostly resistive loads. For those many, the amps they employ will tend to run out of voltage before they do current.   

[a.wayne]

Very few amplifiers dont current limit , Roger's amp does current limit at 2ohms, protection is necessary when the  the output stage is undersized. esl's hit their Z-min at high frequencies this takes some of the heavy lifting load off the amplifier , unlike planer magnetics or ribbons their low Z is usually constant for eg....

[Roger A. Modjeski]

Very few amplifiers dont current limit , Roger's amp does current limit at 2ohms, protection is necessary when the  the output stage is undersized. esl's hit their Z-min at high frequencies this takes some of the heavy lifting load off the amplifier , unlike planer magnetics or ribbons their low Z is usually constant for eg....

Are you speaking of Roger Sanders SS amp? Lets make that clear.

[a.wayne]

Yes ....

[Roger A. Modjeski]

This might be a good time to point out that tube amps don't have or need current limiters. This is responsible for their reputation for being able to drive difficult loads like ESLs. Tubes are able to take brief overloads where transistors will short out.

The only way to make SS amps without limiters is to have enough output transistors to survive blowing the rail or power fuses when shorted or overloaded. I note that very few high power amps have enough output devices to use fuses for limiting and even if they do the manufacturer has to rely on the user putting in the right fuse.

A low power, high current amp is the most likely candidate to have fuses and no limiters. However, one has to check on that.

[Freo-1]

This might be a good time to point out that tube amps don't have or need current limiters. This is responsible for their reputation for being able to drive difficult loads like ESLs. Tubes are able to take brief overloads where transistors will short out.

The only way to make SS amps without limiters is to have enough output transistors to survive blowing the rail or power fuses when shorted or overloaded. I note that very few high power amps have enough output devices to use fuses for limiting and even if they do the manufacturer has to rely on the user putting in the right fuse.

A low power, high current amp is the most likely candidate to have fuses and no limiters. However, one has to check on that.

A couple of points of order:

1) I recall most of the Sanders amps are actually made by Coda for Sanders.
2) Nelson's amps are largely high current amps with fused protection.  (Threshold, Pass Labs). 

[Roger A. Modjeski]

A couple of points of order:

1) I recall most of the Sanders amps are actually made by Coda for Sanders.
2) Nelson's amps are largely high current amps with fused protection.  (Threshold, Pass Labs).

It does appear that the Sanders amps are made by Coda from their specs and appearance. What do you know about these amps sonically? reliability and otherwise. They appear to be nicely laid out. I see Coda was formed by Threshold people. They claim no overall feedback, but there is likely some partial. Are there ICs in the front end?

Protecting transistors with fuses is the best way to go sonically.

[Pneumonic]

The Magtech uses 20, 250w, BJT's per side. Rated for 1/3Ω. My Innersound's use 36 per and down to 1Ω. 

[Freo-1]

It does appear that the Sanders amps are made by Coda from their specs and appearance. What do you know about these amps sonically? reliability and otherwise. They appear to be nicely laid out. I see Coda was formed by Threshold people. They claim no overall feedback, but there is likely some partial. Are there ICs in the front end?

Protecting transistors with fuses is the best way to go sonically.

They sound a LOT like the last Threshold series before Nelson Pass left.  In short, pretty darn good.  Coda amps are known to be very reliable, similar to the old Thresholds. 

[Scottdazzle]

I'm coming to this thread late and I see that it's in the All Solid State Circle, but there is an interesting tube amp that is Class A; the Zesto Bia120. I got to hear it a couple times at RMAF 2013 and it sounds as great as it looks. 

[Freo-1]

I'm coming to this thread late and I see that it's in the All Solid State Circle, but there is an interesting tube amp that is Class A; the Zesto Bia120. I got to hear it a couple times at RMAF 2013 and it sounds as great as it looks.

At 12,500 dollars, it darn well better sound good. 

It's products like this that made me go the DIY route.  The sound from these amps are as good as any high end commercial amp. 


 

[RDavidson]

At 12,500 dollars, it darn well better sound good. 

It's products like this that made me go the DIY route.  The sound from these amps are as good as any high end commercial amp. 

Freo, in light of all the previous discussion, you're going to have to send your amps out on tour now (for full review including measurements), since you claim that they sound as good as any high end commercial amp.

[Freo-1]

Freo, in light of all the previous discussion, you're going to have to send your amps out on tour now (for full review including measurements), since you claim that they sound as good as any high end commercial amp.

Commercial tube amp, that is.      (It's a bit tongue in cheek.)

Seriously, tube DIY allows point to point wiring, high quality parts, high quality tubes, iron, etc.  Back in the golden age of audio, lots of stereo buffs were hobbyists, built their own gear by themselves, or had friends help them build.   

[Roger A. Modjeski]

I'm coming to this thread late and I see that it's in the All Solid State Circle, but there is an interesting tube amp that is Class A; the Zesto Bia120. I got to hear it a couple times at RMAF 2013 and it sounds as great as it looks.

I wish people would put a link and perhaps a price for something they want us to look at.    Can you Please

I found it, read the specs. Nothing about damping. Since it claims no feedback I expect the output impedance is rather high. 

[Roger A. Modjeski]

Commercial tube amp, that is.      (It's a bit tongue in cheek.)

Seriously, tube DIY allows point to point wiring, high quality parts, high quality tubes, iron, etc.  Back in the golden age of audio, lots of stereo buffs were hobbyists, built their own gear by themselves, or had friends help them build.

One of the reasons I am moving to the SF Bay area is to teach people to make their own amps. What freo has done is exactly what I would like to see more people doing. In our amplifier "kitchen" we will be developing SS, Tube and hybrid amps. Most of the commercial products have become very expensive due to the general rise in High End pricing. One Stereophile reviewer commented on a show he attended that the entry price for any component was around $20,000.

At the Randall Museum we build a monobloc 40 watt class A cathode biased amplifier for $1200 a pair using good parts, nice wood chassis,
Heybour transformers. I have measured and listened to these and they are great.

[G Georgopoulos]

ok let's see some circuits to explore architectures...