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Hybrid Circlotron Amplifier with only 3 components on the signal path

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#4
DF96 said:
The "signal path" is a concept which, as normally used, is meaningless. I can see at least 8 components which could affect the signal, quite apart from the power supply.
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This is true!

I am considering only the main components: tube, interstage transf. and mosfet.

If I compare this project to others this is a not common design, also my PF2007 system is more complex because need the output capacitor.
PF2007: the system

I see as large influence in the sound the cathode capacitor that I cannot eliminate but it can be considered an advantage because you can use it to modify the sound.

Some candidates are:
1) Sanyo OS-Con - very neutral but a little bit too hard
2) ELNA Cerafine - very smooth, good to lay normal CD
3) ELNA Silmic II - less smooth of Cercafine but still too much

In my last GM70 SE dc coupled
GM70 amplifier with Fiat transformers
I have got a good benefit using a led ( in the optocoupled) instead of cap/res. on cathode but here I cannot apply it because the low frequecny band will be too much compromised.
 
#7
In my test 2SK1058 are much better than BUZ900P.

The minimum distortion with BUZ900P is at the bias point 30V DC and 900mA at any output level.

Using the 2SK1058 the minimum distortion is at the bias point 30V DC and 1600mA and the level is 60-70% less than BUZ with the same input stage.

You cannot use IRF types and 2SK1529 because these need a thermal compensation circuit.
 
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#12
P.Lacombe said:
...please : power supplies (Three !) (ie electrolytic capacitors).

Circlotron always include capacitors in signal path.

That's life ! 😛
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This is a common myth about Circlotrons. The filter caps in the power supply are not coupling caps (anymore than filter caps are in a conventional amplifier circuit) and have little effect on the sound. You can have a direct-coupled input and a direct-coupled output. No caps, if you want.
 
#15
Bigun said:
I disagree, the signal current in a Circlotron flows through the power supplies and since it can't flow through rectifiers that are most of the time off the current flows through the psu filer capacitors. We can debate their impact on the sound, but they are in the circuit, IMHO.
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If you want to understand the Circlotron, the thing to do is to look at how the DC currents flow through it. One thing you see right away is that there is no signal path through the power supply. If you don't see how that works, its probably because there is an incorrect assumption about what the current paths actually are.

You can build the Circlotron with no filter caps at all, and it will work passably well. If the filter caps could be considered to be coupling caps also, this would not be possible.
 
#18
atmasphere said:
You can build the Circlotron with no filter caps at all, and it will work passably well.
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No. But it will be quiet at idle. I had once (in 1983 when I worked briefly as an audio engineer in Philharmonics) such a problem with German Wermona Regent-1000 amp during concert: bass guitar sounded dirty. After the concert I run on stage, opened the amp, and found one filter cap unbolted by vibration (it had negative polarity on body).
 
#19
Bigun said:
You're gonna have to draw me a picture 'cus I see the signal current going through the power supply - both of 'em.
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Sure. This is the basics of what anyone interested in a Circlotron has to know. In the rather simple schematic, we see a CF-coupled triode amplifier. The load is the the cathode resistor so I depicted it with a loudspeaker symbol.

The power supply is conventional and so is depicted by a box. In this case I have drawn it so that the cathode load goes to ground as does the power supply. The input is the grid. As you can see, no capacitor in the power supply of this example can also be construed to be a coupling capacitor.

However it is also obvious that there will be DC current through the load. How do we get rid of this? By building an equal circuit that has current flow through the load in the opposite direction.

Now the circuit I drew is exactly 1/2 of a Circlotron. Add the other half and you have the whole thing. You can have one side at ground if you want, but if you do so the driver circuit has to be designed to take that into account.

By adding the second half, which is identical to the first, we don't somehow change the function of the supplies. They behave exactly the same way that they would as if the circuit was single-ended.

If you do not want to ground one side (which is nice if you want to use a balanced driver circuit) then you have to reference the circuit to ground in some way so that the circuit is completed when input voltages are applied to the grid. The usual technique to install a pair of resistors on either speaker terminal that go to ground. These resistors are not critical in value but should be the same value, and something of high enough resistance so that they are an insignificant load. In our amps we use 600 ohms but they could be 100 ohms or 1500. They can be regarded as being in series with the input signal on the grid. By floating the circuit in this fashion, the filter caps maintain exactly the same operation and relationships to the rest of the circuit that they did before.
 

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