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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

The "Valvolozzo" - SE amp with torroids

I decided to open this discussion 'cause I saw some strange/interessant schematics in "elettronica flash", an italian magazine.
The "valvolozzo" is a SE amp with torroid output transformers, by Diego Barone.
He uses normal torroids(220V-12V 100VA for EL34 and 8ohm, 220V-9V 100VA for 4ohm) and a cap and a choke for eliminate DC.
ECC82 as driver, with a configuration which introduce a distortion so that can be added with the final distortion to attenuate it.
The power tube is EL34.
There is also a mosfet for 3 pouprose:
1)filtering better the supply
2)driving EL34 with low impedance
3)force the ECC82 to work in a load exclusively made by R7-R8

The schematic:
[IMGDEAD]http://www.studioerosbarone.it/diego/jpg/Valvolozzo.jpg[/IMGDEAD]

You can see a distortion of 2% in the graphics of his web page:
Barone


What do you think about? :D
 

ThorstenL

Previously: Kuei Yang Wang
Konnichiwa,

TheGatesOfFate said:
What do you think about? :D

Well, the Amplifier is pretty generic parallel feed. The use of mall toroidal mains transformers as parallel feed outputs or PP Outputs is hardly new, these transformers clearly are a compromise solution and regardless of nominal power level (core) only suitable for low powers. Thypically a 1:4 to 1:8 derating is neccesary for audio service, so a 230V RMS primary really should not be pushed past 75-115V AC for audio service.

Also, for a parallel feed output transformers mains torroids often have rather low inductance, leading to a very large required coupling capacitor. Further, the anode load choke chosen is rather too low in value for good LF performance.

The frontend is a Kimmel mu Follower, but with the addition of a load on the lower valve to make it distort more than neccesary. This cancels some 2nd harmonic of the output stage and increases the 3rd harmonic level, thus making the amplifier measure better, but sound subjectively actually more distorted than without cancellation.

This kind of thing is nice for experiments in cheap audio, but ultimatly the quality available is limited. So by all means build one if it must be cheap to make more than anything else.

Sayonara
 
Re: Re: The "Valvolozzo" - SE amp with torroids

Kuei Yang Wang said:
Konnichiwa,
This kind of thing is nice for experiments in cheap audio, but ultimatly the quality available is limited. So by all means build one if it must be cheap to make more than anything else.

Sayonara

Yes I know,
Barone in his web-site tells about a cheap amp for cheap experiments...
Also the other projects are in strange philosophy.
The "ibrid" with IGBT:
[IMGDEAD]http://www.studioerosbarone.it/diego/jpg/HYBRID1.jpg[/IMGDEAD]

or the 2A3 SE with mosfet(and 1% thd):
[IMGDEAD]http://www.studioerosbarone.it/diego/jpg/MAD2A.jpg[/IMGDEAD]

and many suggestions for plasma tweeter.

;)