I heard this album recently by chance and I bought it staight away.
A very pleasant kind of Jazz music following old italian music themes and styles.
The recording quality is outstanding, dynamic, details, everything....

Enjoy

Gerd

Hello Peter,

no!
Since no part of the circuit has any relation to ground you can connect any SINGLE point of the circuit to ground without changing anything. Except that now any other point of the circuit shows a voltage to ground what does not matter, doesn't it?

Regards,
Gerd   

Hello Coen,

if you drive the amps with a balanced input signal the outputs are floating.
Correction: The output is allways floating, no matter what the input is. There is no relation to the internal ground (- pole of the power supply) nor to earth ground. So you could even hook one output pin to earth ground without problems (what some messurement equipment do when testing on complex load).   

This are the two most important reasons for a balanced design:
1. Symmetry as such to ensure the best protection against any influence from outside.
Think of asymmetric circuit designs with a direct relation to ground. The signal on interconnection cables is directly related to ground since one wire is the grounded shield as well as the ground pin on the mains plug. So the signal might use (and is to a certain extend) the ground wire of the mains as the interconnection between the two connected pieces of equipment. To get best results most expensive mains cables have to be used.
The reduction of even harmonics is a nice side effect that helps a lot to get the best puls response (in my opinion).
2. The circuit I developed in this simplest form is only working on an unipolar power supply. Therefor the output has DC offset. To get rid of the DC a balanced design is the best in terms of sonic result.

Regards, Gerd

Hi Coen,

As with all symmetric (bridged) amplifiers with unipolar power supply there is a DC offset on the output. Between the output terminals the DC is less than 200mV when fully warmed up 40mV. This setting is long term stable since resistors of 0,01% tolerance are used which will have a long term drift of 0,01% in 10 years (Vishay S102C). Even the potentiometer to adjust the DC offset on the output is a military grade thick film metal poti (Vishay 1280G) which I buy at more than 15,00€ excl. VAT per piece.
The amp is long term short circuit proof by design. If one leg fails there will be always a huge overload in this leg and the power supply DC fuse will blow (special fast blow fuse). So in this case there will be only a short low frequency square wave puls of 1/4 of the maximum peak output rating on the output (about 25 Watt).
That should not harm any type of speaker.

Regards, Gerd

Hi Mani,

there are (at least) 2 aspects about bass performance:
1. Low output impedence of the amp to control the energy of the fundamental. Even though your Quad speakers do not have large (cone and coil) mass to move there is energy stored as magnetic energy in the speakers transformer which has to be kept under tight control. This is the same as for dynamic speakers where a lot of people say that the discussion about damping factor is senseless since there is a coil of 0.3 Ohm resistance or more within the dividing network for the bass. And compared to this 0.3 Ohm resistance a difference in cable resistance or output impedance of some 50 milli Ohm or less does not matter. It does, because the magnetic energy within this coil has to be kept under control as well. Its about energy and not only about resistance.  
2. The illusion of a bass as an instrument is the sum of the fundamental and all the other frequencies that makes the natural sound of the acoustic bass or electronic bass guitar or whatever instrument. As long as we are not talking about a single tone generated by a synthesizer the sum of all these frequencies have to be radiated by the speaker accuratly in phase at the right amount of energy. If the amp does not do this job well and is not keeping the speaker well under control in the mid- and high frequency domain, the "bass" woun't be really good. I can demonstate to you the improvement of the bass performance of a small 2-way speaker system in exchanging the capacitor in the dividing network of the tweeter!

I the case of your setup I think it is a combination of both aspects.

As I wrote in an earlier post I stated that the damping of mechanical vibrations improved the bass performance of my amp. This has something to do with aspect 2. The energy of all frequencies of a tone played on a bass a consistend "at the point" at the right time.

This has nothing to do with rated output power, not even with the frequency response plot of an amp. It is again a subject of energy handling in the time domain at every energy level. The amp has to deal with milliwatt or microwatt as accurate as with one, ten or more watt.
And I'm sorry to say but most of the amps can't.

Gerd

Hi,
I have put some plots into my white paper (just in german, but for the plots that does not matter):
http://www.sauermann-audio.de/dokumente/sauermann_white_paper.pdf
But remember music usually has a dynamic range of about 10.
If the amp is fully driven, so that the pulses are at 1% distortion (45 Watt) the RMS level is at about 5 Watt where the distortion is at less than 0,1%.
The amp can be easily overdriven by at least 3dB without audible distortion or compression!
This is due to the circuit design and its' dynamic behaviour.
I would be pleased to give a demonstration.

Gerd

Hi Peter,
thanks for posting that link, but fairaudio did not test the latest revision of my amplifier. There are some anhancements made to eleminate vibrations that have a really significant impact on the sonic quality. The bass gained strenght and dynamic and the entire resolution capabilities of the amp did get better (even though fairaudio rated them extremly good in their test).
There will be another test about the monos comming at "Hörerlebnis" in a couple of month. They will get the amps tomorrow.

Gerd

Hi to all,

I'm very pleased to see that this discussionis starting in this forum. I hope I'll find some time to give replies and comments in time.
Regarding the amps circuit design: On the first look it might have some similarities to Pass' circuits but in the end it differes in total due to one mayor difference which is, that there is constant current flowing through the voltage gain stage.

Hi Coen, You are pretty close but not totally right.
Since there is constant current flowing through the voltage gain stage this stage has an output impedance of some kilo ohms. This stage can not deliver any power or AC current at all.
The current source that is keeping the current through the voltage gain stage constant has a control loop circuit at a current gain of more then 10 million. This control circuit delivers any current the speacer draws in addition to the constant current flowing through the voltage gain stage. Due to the extremly high current gain factor of that controller loop the output impedance of a single current source drops down to as little as 6 to 7 milli ohms. So the symmetric amplifiers has an output impedance of about 15 milli ohms (which no other single stage single transistor amp can deliver).
One big advantage of this circuit design is that the distortion produced is independent of frequency and load impedance. It is just related to the output voltage. The distortion spectrum remains homogenious at nearly any load and frequency change.
But harmonic distortion is not the only aspect that matters. Group delay, phase shift, bandwidth etc. the entire behaviour within the time domain maters much more. And since my amps are very "fast" also at low impedance loads (1 ohm or less) - the current control loop operates at a bandwith of about 1 mega Herz, the amplifiers bandwith is above 300 kilo Herz - the behaviour within the time domain on complex (low) impedence is best.  
But all these electronic technical aspects are not really the main thing. We talk about reproducing the illusion of music. That is what matters. In the end you have to have the feeling that someone real is making music in your room just for you. You have to be able to feel the "puls" of the music the attitude of the artist, his "message".  
I tried to fine tune my amp by various means to give that illusion best. The circuit is only the basis. The next thing is the quality of the parts used and their exact values within the circuit (determined in listening sessions). Then the thermal stability and at last but not least the mechanical attributes. The cabinets of my amps and power supplies are assambled the way to be not sensitive to vibration. Every screw for instance is treated at least twice bevor being mounted. Plates are damped so that no vibration can cause any microphonic effect ....

All of this is responsible for the entire sonic result.

Gerd