Konnichiwa,
Well, a HV FET with Transformer will sound nothing like a 300B, you would need to add a lot of loop feedback around the stage to get the gain and output impedance down.
I think a Pass Zen with the feedback cranked up and gain down to near would be close, when combined with a suitable valve line stage. No OPT needed.
As said, the closest sonic equivalent in SS is Hiraga's l'Monstre, it was designed to be a SS 300B Amp....
Sayonara
grataku said:
Well, a HV FET with Transformer will sound nothing like a 300B, you would need to add a lot of loop feedback around the stage to get the gain and output impedance down.
I think a Pass Zen with the feedback cranked up and gain down to near would be close, when combined with a suitable valve line stage. No OPT needed.
As said, the closest sonic equivalent in SS is Hiraga's l'Monstre, it was designed to be a SS 300B Amp....
Sayonara
The case is that valve (tube) and MOSFET are different devices in their nature. High input impedance of both leads to idea just to copy valve topology to mosfets. This is not the correct approach. Always try to utilize advantages of different devices and build tailor-made topologies for them, do not simply try to copy valve topologies to solid state devices.
Hi Pavel and Thorste,
I'm happy to read that You agreed on some points, hence if against me!
The thread is devoted to the search of a solid state amplifier that sound good like a 300B, but at a fraction of the price, mainly avoiding the output transformer and using low voltage caps.
I built and debugged 5-6 solid state amplifier and every time instead of an amplifier I get a power oscillator.
I have two scope (one 20MHz and occasionally a Tek 2Ms/s), an audio generator and a precision attenutor. I made a Lm1875 gainclone two years ago, following teh National application note and I had lot of stability problem and sound was nothing exceptional, so I turn back to tube amplifier (I do not know why but these sounds good since the first power on).
In the gainclone case, I used a SLA battery, as suggested by Thorsten, and also in case of a TA2024 amp I used a cheap 12V house alarm battery, much cheaper and performant that for example the huge battery of capacitor of Hiraga's 8W.
The schematic proposed by the two Pavel are surely good, but without a well designed PCB are beyond my skills.
The Hiraga 20W wasa a good candidate I taken into considartion some years ago, but lot of trouble to found the exact components.
Apart from the Gainclone suggsted by Thorsten, I like the East germa amplifier, simple and cheap. I'm little worried by all the compensation network it has.
An updated replica of this amply may worth the effort.
Any other opinion welcomed.
I'm happy to read that You agreed on some points, hence if against me!
The thread is devoted to the search of a solid state amplifier that sound good like a 300B, but at a fraction of the price, mainly avoiding the output transformer and using low voltage caps.
I built and debugged 5-6 solid state amplifier and every time instead of an amplifier I get a power oscillator.
I have two scope (one 20MHz and occasionally a Tek 2Ms/s), an audio generator and a precision attenutor. I made a Lm1875 gainclone two years ago, following teh National application note and I had lot of stability problem and sound was nothing exceptional, so I turn back to tube amplifier (I do not know why but these sounds good since the first power on).
In the gainclone case, I used a SLA battery, as suggested by Thorsten, and also in case of a TA2024 amp I used a cheap 12V house alarm battery, much cheaper and performant that for example the huge battery of capacitor of Hiraga's 8W.
The schematic proposed by the two Pavel are surely good, but without a well designed PCB are beyond my skills.
The Hiraga 20W wasa a good candidate I taken into considartion some years ago, but lot of trouble to found the exact components.
Apart from the Gainclone suggsted by Thorsten, I like the East germa amplifier, simple and cheap. I'm little worried by all the compensation network it has.
An updated replica of this amply may worth the effort.
Any other opinion welcomed.
Hi,
Then you definitly want the Hiraga l'Monstre or similar.... This website may be of use:
http://home.tiscalinet.ch/cooltune/Projects/Megalith01.htm
Ciao T
plovati said:
Then you definitly want the Hiraga l'Monstre or similar.... This website may be of use:
http://home.tiscalinet.ch/cooltune/Projects/Megalith01.htm
Ciao T
PMA said:
yes, there are countless differences between a mosfet and a tube. However, that difference is considerably smaller than those between a bjt and a tube, or a laser (a light amplifier) and a tube, or a pump (a pressure amplifier) and a tube, etc.
The point is that just because they are different, it isn't sufficient to say that one cannot use them in similar ways.
I would argue that for most of audio applications, mosfets make a good substitute for tubes. sure, they aren't going to perform identicially (Heh, even a tube-for-tube substitution will not perform identically). But the modifications needed to get them to work will be consierably less than if you had used a water pump there.
I have used a transformer loaded SE bjt class a amplifier before and most recently tried a mosfet version as well. They do work, not as well as I would have thought.
the problem is limited power output as you will need to run high idle current through the transformers and they don't like to be driven by a DC source.
a better compromise is either a Susan-Zeus styled PP amplifier, or a LTP loaded with a transformer (Pass experimented with that). I have done both and I like Susan's better for its simplicity.
the problem is limited power output as you will need to run high idle current through the transformers and they don't like to be driven by a DC source.
a better compromise is either a Susan-Zeus styled PP amplifier, or a LTP loaded with a transformer (Pass experimented with that). I have done both and I like Susan's better for its simplicity.
Hi tlf,
could you elaborate on your mosfet amp?
I was thinking to run a 500volt high power mosfet biased at ~90 mA using a luhndal 1693 (I think) and the output transformer which I have somewhere downstairs.
What kind of powers were you talking about?
I built Hiraga amps and though they sounded really good they where very hard to get stable and the DC offset was bad at startup. Ok, I didn't get the right output trannies and didn't wait for the new moon for testing etc, so it's probably my fault.
After that I build some of Pass balanced amps and they were leaps and bounds better both in terms of stability and sound.
could you elaborate on your mosfet amp?
I was thinking to run a 500volt high power mosfet biased at ~90 mA using a luhndal 1693 (I think) and the output transformer which I have somewhere downstairs.
What kind of powers were you talking about?
I built Hiraga amps and though they sounded really good they where very hard to get stable and the DC offset was bad at startup. Ok, I didn't get the right output trannies and didn't wait for the new moon for testing etc, so it's probably my fault.
After that I build some of Pass balanced amps and they were leaps and bounds better both in terms of stability and sound.
this amplifier is only 8W but with mosfet more powerful, you must be able to have more power and more bias current !
http://perso.wanadoo.fr/jm.plantefeve/Gibouin.html
at place of capacitor, you can put a transformer
An externally hosted image should be here but it was not working when we last tested it.
http://perso.wanadoo.fr/jm.plantefeve/Gibouin.html
at place of capacitor, you can put a transformer
An externally hosted image should be here but it was not working when we last tested it.
grataku said:
Mine was a 56vdc powered SE MOSFET idled at 250ma. the output transformer is a 220v/46v power transformer.
the only problem I had was humming of the output transformer, which I attributed to the high DC current.
I think your has a much better chance of working out, as you aren't running at as high of an idle current. However, finding the output transformer might be difficult.
Konnichiwa,
This sort of thing:
http://www.bonavolta.ch/hobby/en/audio/2sk135se.htm
Remember, a Mosfet is basically close in electrical behaviour to a penthode, not to a triode and as the Mosfet does not have a screengrid terminal you cannot "triode connect" the Mosfet.
If you run it open loop the output impedance is going to be very high.
So you need probably to use source degeneration to get the transconductance more linear and then looped feedback to get the gain and output impedance sensible.
You will retain the rather drastically high and very voltage (and thus signal) dependent input capacitance, which makes the driver circuit rather harder to design than when using an output valve.
So, have fun, but expect to work hard on getting this right.
Sayonara
grataku said:
This sort of thing:
http://www.bonavolta.ch/hobby/en/audio/2sk135se.htm
Remember, a Mosfet is basically close in electrical behaviour to a penthode, not to a triode and as the Mosfet does not have a screengrid terminal you cannot "triode connect" the Mosfet.
If you run it open loop the output impedance is going to be very high.
So you need probably to use source degeneration to get the transconductance more linear and then looped feedback to get the gain and output impedance sensible.
You will retain the rather drastically high and very voltage (and thus signal) dependent input capacitance, which makes the driver circuit rather harder to design than when using an output valve.
So, have fun, but expect to work hard on getting this right.
Sayonara
Thanks guys,
and I thought I was doing something original! 😉
The opt I plan to use is for se use so it has a gap in the iron to make it work alright with dc.
I plan to drive it with a high biased mosfet follower. I agree it's going to be tricky.
and I thought I was doing something original! 😉
The opt I plan to use is for se use so it has a gap in the iron to make it work alright with dc.
I plan to drive it with a high biased mosfet follower. I agree it's going to be tricky.
Thorsten,
I'm studying about the East German amplifier You proposed.
This is close to the classic Lin 1956 amplifier, included the tharmistor based polarization (but Lin used Germanium transistor, much difficult to thermal stabilize).
What does means the different simbols used for resistor? In fact there are some with one slash bar ie R49 R53), some other with two (R40 R42) and others with a sort of alpa (R59 and R60).
I see lot of comsensation and equalization network, is this amplifier a trouble sources? You said You'd repeired lot of them: what weere the most common trouble?
In the meanwhile I'm back on Hiraga 20W. There are some version with western common transistor (MJE or 2N series)?
Thank You
I'm studying about the East German amplifier You proposed.
This is close to the classic Lin 1956 amplifier, included the tharmistor based polarization (but Lin used Germanium transistor, much difficult to thermal stabilize).
What does means the different simbols used for resistor? In fact there are some with one slash bar ie R49 R53), some other with two (R40 R42) and others with a sort of alpa (R59 and R60).
I see lot of comsensation and equalization network, is this amplifier a trouble sources? You said You'd repeired lot of them: what weere the most common trouble?
In the meanwhile I'm back on Hiraga 20W. There are some version with western common transistor (MJE or 2N series)?
Thank You
Konnichiwa,
IIRC (this is now long ago) this signified the power rating.
Not really a troble-source. Most of the transistoirs used where not ideal for the jobs they did, especially the output transistors where way to slow, so the whole Amplifier had to be slowed down.
I posted this one merely for curiosity, not as suggestion to build!!!!
Hiraga 20W is better to build.
Dead electrolytic capacitors. This was the most common trouble with east german gear in the 1980's which was more than 10 Years. I repaired many TV's, Radios and Amplifiers where I had to replace ALL electrolytic capacitors in preference to actually finding the dead ones! Especially the old white plastic case ones one had to pull like rotten teeth wherever encountered!
Sayonara
plovati said:
IIRC (this is now long ago) this signified the power rating.
plovati said:
Not really a troble-source. Most of the transistoirs used where not ideal for the jobs they did, especially the output transistors where way to slow, so the whole Amplifier had to be slowed down.
I posted this one merely for curiosity, not as suggestion to build!!!!
Hiraga 20W is better to build.
plovati said:
Dead electrolytic capacitors. This was the most common trouble with east german gear in the 1980's which was more than 10 Years. I repaired many TV's, Radios and Amplifiers where I had to replace ALL electrolytic capacitors in preference to actually finding the dead ones! Especially the old white plastic case ones one had to pull like rotten teeth wherever encountered!
Sayonara
Upupa Epops said:
Yes Pavel, Thank You. I think that yours amplifier is surely a very good one, professional and rock solid. I'm little bit worried that the project is beyond my actual skills, I'm evaluating pros and cons of the proposed schematic, with some more attention to the simpler ones.
Unless You have a ready made PCB...
RCA 25W
Just for curiosity, this is a proposed 25W amplifier taken from RCA Audio Amplifier Manual 1979:
[img=http://img357.imageshack.us/img357/443/rca25w9ba.jpg]
seems very similar to East Germany amp, but with modern transistor. Rated data were:
25W /8ohm
25W /4 ohm (with BDX33A BDX34A)
14W /16 ohm
TDH 0,15 % max from 0,1 to 20W
If someone interested I've also the THD vs Pout graph.
Just for curiosity, this is a proposed 25W amplifier taken from RCA Audio Amplifier Manual 1979:
[img=http://img357.imageshack.us/img357/443/rca25w9ba.jpg]
seems very similar to East Germany amp, but with modern transistor. Rated data were:
25W /8ohm
25W /4 ohm (with BDX33A BDX34A)
14W /16 ohm
TDH 0,15 % max from 0,1 to 20W
If someone interested I've also the THD vs Pout graph.
So seems that Hiraga's project are the best candidate for a solid state equivalent of a 300B amplifier.
What about this one:
http://www.hilberink.nl/amps/amps7.htm
I'm referring to the second diagram, fully simmetric design.
What about this one:
http://www.hilberink.nl/amps/amps7.htm
I'm referring to the second diagram, fully simmetric design.
Konnichiwa,
You realise both diagrams are MC pre-preamp stages?
And Mr. Hilberinks "improvements" on Hiraga should be considered with a good pinch of salt. I personally would not like a "riped" design, for one.
Sayonara
plovati said:
You realise both diagrams are MC pre-preamp stages?
And Mr. Hilberinks "improvements" on Hiraga should be considered with a good pinch of salt. I personally would not like a "riped" design, for one.
Sayonara
Yes, I'm referring to the topology of the amplifier. It is interesting and can be used for more powerful amplifier, isn't it?
Konnichiwa,
I suppose so, but the amplifier has close to 0Ohm input impedance and even as MC pre-pre stage it does not strike me as particulary good an idea. BTW, in case it is not clear, this is a simple rail symmetrical folded cascode. The source must provide all the current that is eventually available to the current/voltage resistor (2K).
Using the folded cascode over Hiraga's circuit substites one coupling capacitor for multiple active components, bad deal if you ask me.
Sayonara
plovati said:
I suppose so, but the amplifier has close to 0Ohm input impedance and even as MC pre-pre stage it does not strike me as particulary good an idea. BTW, in case it is not clear, this is a simple rail symmetrical folded cascode. The source must provide all the current that is eventually available to the current/voltage resistor (2K).
Using the folded cascode over Hiraga's circuit substites one coupling capacitor for multiple active components, bad deal if you ask me.
Sayonara
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