Giaime said:
Not far off. In most CCS, the drain is the business end, and as a CCS, we want the source impedance there to be as high as possible. The drain is also usually the terminal which is brought out to the case. When you put the device on a grounded heat sink with a nice high dielectric constant thermal insulator (e.g., mica), you form a capacitance to ground from the drain. And it can be a pretty significant capacitance. That severely compromises the desired high source impedance, getting worse at higher frequencies.
Hi all,
I choose this topology for few reasons:
I've been always a fan of Class A amplifiers.
My favorite amplifier, up to now, is the Nelson Pass's Aleph 30 clone I built some years ago.
I never finished it: during a listening session, with the amplifier open on my workbench, I made a bad short-circuit on the left channel board, and the channel literally exploded... I never replaced the channel, too much work.
By the way, the large Heatsink you can see used in my tube amplifer prototype was part of the Aleph 30 clone.
When I decided to build my tube amplifier I searched the web for information, until I found the "parallel feed" topology.
I was already thinking about a SE amplifier with a CCS on top (this is the topology normally used by my previous SS amplifiers), and I fallen in love with "para-feed"; I do not know why, but my "instinct" told me that such a topology was MY topology.
Next has been to decide which CCS to use: a tube CCS needs too much voltage to me, so I decided to go with a SS CCS, that can have a voltage as low as 10V.
In this case using a relatively "low" B+ voltage of 600V I can have, on the KT88s plate, up to 590V.
Ciao,
Giovanni
I choose this topology for few reasons:
I've been always a fan of Class A amplifiers.
My favorite amplifier, up to now, is the Nelson Pass's Aleph 30 clone I built some years ago.
I never finished it: during a listening session, with the amplifier open on my workbench, I made a bad short-circuit on the left channel board, and the channel literally exploded... I never replaced the channel, too much work.
By the way, the large Heatsink you can see used in my tube amplifer prototype was part of the Aleph 30 clone.
When I decided to build my tube amplifier I searched the web for information, until I found the "parallel feed" topology.
I was already thinking about a SE amplifier with a CCS on top (this is the topology normally used by my previous SS amplifiers), and I fallen in love with "para-feed"; I do not know why, but my "instinct" told me that such a topology was MY topology.
Next has been to decide which CCS to use: a tube CCS needs too much voltage to me, so I decided to go with a SS CCS, that can have a voltage as low as 10V.
In this case using a relatively "low" B+ voltage of 600V I can have, on the KT88s plate, up to 590V.
Ciao,
Giovanni
About my CCS:
The Drain pin of the mosfet (the one connected to the mosfet case) is connected directly to the B+ rail; that means that if it introduces some capacitance, this will be added to the PS filter capacitance, since it is connected between B+ and ground.
The "business" end of my CCS (the one that goes to the output tubes) is the source one, and the capacitance on this side is near zero.
The heatsink is of course insulated from the mosfet drain, and firmly connected to ground.
In case of a short-circuit between the mosfet case and the heatsink, you simply have a short-cicuit between B+ and ground... so the protection fuse on the PS (I always place protection on PS, I hope you make the same) will blow avoiding any danger.
An example: Imagine a "traditional" amplifier, wired point-to-point: at a certain point the B+ wire disconnect from the output tubes and touch the chassis... What happens? exactly the same than could happen to my amplifier if the mosfet short-circuit to the heatsink.
About output transformes:
I too use toroidal power transformer, I'm used to use such a transformer for my job, and they have an extremely wide bandwidth and frequency range.
For what I can heard, they sound great.
THIS is a link to an italian page with an amplifer using a toroidal transformer as output.
Ciao,
Giovanni
The Drain pin of the mosfet (the one connected to the mosfet case) is connected directly to the B+ rail; that means that if it introduces some capacitance, this will be added to the PS filter capacitance, since it is connected between B+ and ground.
The "business" end of my CCS (the one that goes to the output tubes) is the source one, and the capacitance on this side is near zero.
The heatsink is of course insulated from the mosfet drain, and firmly connected to ground.
In case of a short-circuit between the mosfet case and the heatsink, you simply have a short-cicuit between B+ and ground... so the protection fuse on the PS (I always place protection on PS, I hope you make the same) will blow avoiding any danger.
An example: Imagine a "traditional" amplifier, wired point-to-point: at a certain point the B+ wire disconnect from the output tubes and touch the chassis... What happens? exactly the same than could happen to my amplifier if the mosfet short-circuit to the heatsink.
About output transformes:
I too use toroidal power transformer, I'm used to use such a transformer for my job, and they have an extremely wide bandwidth and frequency range.
For what I can heard, they sound great.
THIS is a link to an italian page with an amplifer using a toroidal transformer as output.
Ciao,
Giovanni
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