Does anyone care to ask an amplifier designer a technical question? My door is open.

@musicpod 

Slew rate. Some people feel that this is a significant amp spec. Would you please give your thoughts on the importance of slew rate.

Slew rate is another way to look at the power bandwith of an amplifier. The Jadis 200 had horrible slew rate (intentionally it seems) and this 200 watt amplifier could make less than 5 watts at 20Khz.  It was not broken!

Like any spec, some manufacturers will focus on this and get a geat number. If the amp can make full power without turning the sine wave into a triangle at 20Khz then thats good enough. 10V/us is enough though you will see numbers much higher. 

At what db level do you consider a speaker efficient? At what level inefficient?




Would it be possible to provide context to where Mr. Levinson may have been coming from regarding the 400-watt optimum power level?

I have discovered in speaking with many audiophiles that almost everyone has way too much power and too much gain. People overestimate their listening level typically by 10 dB which means they are using 1/10 the power they think they are using.

I will not advise anyone on power unless they know their speaker sensitivity and have a Radio Shack or better SPL meter. Quoting listening level without and SPL meter is pure foolishess. 

The range of listening levels is much wider than the range of speaker sensitivity. Therefore one must know their listening level. I would be really impressed if someone quoted their peak voltage at the speaker terminals. So far this has not happened. 

Mr Levinson does not design amplifiers. However his engineers have made everything from 25 watts to whatever. Where he comes up with 400 watts I have no idea but I would say thats is a crazy high number for most people. 

@unreceivedogma

The triode mods actually have more power somehow. I know Jon put a tiny little transformer in there somewhere, he explained what it is for and that it’s not in the output circuitry but I’m not technical enough to remember.

I have built both triode and pentode Futtermans with the same tubes you have and I cannot agree that triode has more power.

 I did triode for simplicity in a low power Futterman I offer with a built in Autotransformer. It does about 3 watts into 8 ohms direct but 30 watts into any load via the Autoformer. I plan to make more OTL/autoformer amplifiers. Including the Autoformer in the amplifier feedback loop is far better than having it outside the loop. 

Did you happen to see the measurements before and after?

There are several builders offering fancy cabinets for the classic speakers like the 604. Who can say what a piece of fine furniture should cost? Of course for that money there is better sound to be had.

I would like someone to tell me why spend big bucks on cone speakers when there are better technologies. 

Hello Roger

Many people believe that SET tube amplifier give more mid range magic than Push pull tube amplifier.

Do you agree on the notion as designer of tube amplifier?

If so, could tell me why it is so?

thanks in advance

Thomas

Hello Roger, I've purchased your tubes several decades and liked the quality and longetivity.  

Funny how people denigrate my Marantz 7T although I only use it for 78 rpm phono stage.  It sounds much like a 7C.

My Dynaco ST70 on my second system has magnificent bass as it was modified from its ultralinear design to a voltage regulated design (taking off the 2nd transformer tap).  Added very large storage cap, ss rectification but kept the tube for soft start.  Just a wonderful low powered amp.

My friends and I have found some early ss receivers with low power are superior to higher power receivers in the same line.  E.g. Yamaha CR 620 is superior to the CR 1020 and higher power receivers.  The Sherwood 7100 is superior to the 7200 and 7300.  They have fewer stages on the low powered units.  I use the Yamaha for video/audio systems although a friend uses them on his Legacy Focuses.  Even the Sherwood brings out great low and tight bass on Legacy Signature IIIs (its shocked the seller when I used it to audition them).

I really like your answers on many of this forums questions.  

There only place where I strongly disagree is in the use of premium fuses.  My amps had standard fuses replaced by SR Blue fuses.  The difference in SQ was very substantial.  The manufacturer of my big amps went one step further and replaced his fuses with circuit breakers.  Now his amps sound nearly identical (we can't tell the difference) from my amps with the SR blue fuses.  He is a huge skeptic and this is his only tweak to his system.  

I'd like to know what you opinion is of the VAC IQ (continuous autobias) amplifiers.  They sounded great wherever I heard them and they appear to be conventional designs well executed.  They must have good impedance outputs to make them adaptable to drive many types of speakers.   

I heard those Jadis amps on new Magico speakers (maybe the S3 or Q3).  I wondered why the highs were rolled off and soft sounding.  Probably due the loss of power in the highs.  Terrible sounding.  

Many people believe that SET tube amplifier give more mid range magic than Push pull tube amplifier.

The reason for this is because most SET amps act like tone controls. Here is a typical, response graph of a set amp into a very easy Kanton simulated load. It’s the wavy line.
  Here is the Jadis SE 300B monoblocks.
Fig.1 Jadis SE300B, frequency response at 1W into 8 ohms (top at 10kHz) and into simulated speaker load (right channel dashed, 1dB/vertical div.).
https://www.stereophile.com/images/396JADFIG1.jpg

Note: how much higher the 700hz to 2khz (midrange) is compared to the rest, there’s your midrange emphasis and your tone control response.

The straight line is what it does into a fixed 8ohm resistor,, which no speaker is.

Cheers George