The Hybrid Class A amplifier

[gaborbela]

Hello
I would like to know if someone have successful ever built these amplifier ?
http://digilander.libero.it/essentia...id_circuit.htm

I'd like the simplicity of the amplifier but my friend warn me he built these amp couple years back and at the firs power up it did blew up .
For me a bit somehow unbelievable these circuit can work with vertical mosfet but also lateral mosfet in Class A mode with out any parts need to be exchange.
You can read that on the bottom under the sign PCB & KITS
Also for Class A he calculate the x-former the same voltage like to the Class A/B . He calculate the power supp. voltage after rectification by 1.4DCV . That is unbelievable with these high bias .
If the amp biased in 3A /or 4A/ channel you can't get more than 1.2DCV after rectification under load . That mean if I use 25V transformer will give me under the load around 30VDC not 35VDC . Am I wrong ?
Usually the need different circuit for lateral and vertical power mosfet ? Something fishy with these schematic .
Probably the guy didn't put up the right schematic , because he sell PC boards , kits for the amp ? But in that case He supposed to warn the people the schematic posted is not with the right values !
Please if someone built these amp successful let me know .
Also would you please comment the sound of the amp .
Greets

[lineup]

I have seen something similar.
.. of course .. because I have seen so much in all years in audio

In one borebely Headphone amp.
A Hybrid Tube/MOSFET Headphone Amplifier
by
Erno Borbely
Special Article, pdf:
http://www.borbelyaudio.com/special_articles.asp
http://www.borbelyaudio.com/pics/405borbely2506.pdf

Good luck with this one.
Even for loudspeakers, Tubes can make good sound & great amps.
Headphones can really shine in pleasant HeadPhones amplifiers.

yours, Line 'linie' Lineup

[ilimzn]

Originally posted by gaborbela
Hello
I would like to know if someone have successful ever built these amplifier ?
http://digilander.libero.it/essentia...id_circuit.htm

This schematic keeps appearing over and over and has been discussed before on this site, at length (search???). The amp as drawn has several problems which may well result in smoke. Even when te errors are corrected, the general idea is not a very good one. For starters triodes are not pentodes, MOSFETs, bipolars - the input stage will always be unbalanced in this topology. Not to mention that the operating voltage for the tubes is too low to get enough current to drive MOSFETs, that the MOSFETs are asked to dissipate way too much, that the output wil clip asymetrically, that the current source is designed so it is not thermally stable, and in fact it's biassing is fitered wrong so it may blow up on startup, taking your speakers with it...
As usual, do not believe everything you find on the internet, even if there is someone selling kits of it.

[gaborbela]

Hello
Thank you for your reply .
OK I pas these amp .Even I like Hybrid design but probably there is better design out there .
Greets

[ja2dhc]

My hybrid amp is described below(sorry in Japanese).

http://ja1cty.servehttp.com/mosfet/mosfet2.html

The current of MOSFET is 1.5A and voltage is +/-16V. Therefore
thermal dissipation of each MOSFET is 24W (16Vx1.5A). I used a forced
air cooled heatsink for a pair of MOSFET(top and bottom ones).
Therefore each heatsink handles 48W(24W+24W). If MOSFET operation
assumed 35V, 3A(105W/each MOSFET). very big heatsink is required.

The outlooking of my amp is seen below.

http://ja1cty.servehttp.com/mosfet/FET-outside.jpg

[lineup]

Originally posted by ilimzn
This schematic keeps appearing over and over and has been discussed before on this site, at length (search???). The amp as drawn has several problems which may well result in smoke.

Ilimzn
Think you are very right.I have heard this before .. the last time I did see this Borbely Amp in forum.
So it must be changed to be safe.

Originally posted by gaborbela
Hello
Thank you for your reply .
OK I pas these amp .Even I like Hybrid design but probably there is better design out there .
Greets

gaborbela
you and your freind has some intestesting Hybrid ideas.
The idea is good. I would like to wsee more of Tube + MOS + BJT Class A amplifiers.
Which are properly tested and does not smoke.

If anybody else has some better similar great idea
than I be a Happy Lineup

thanks gaborbela.
Dont give up Hybrids
Your friend from sweden: 'linie' Lineup

[sajti]

Szia Béla,

I don't recommend this amplifier. There are some problems with it.

1st: R13-C4. This filter takes the hum, and rail noise into the amplifier circuit.
2nd: The mosfets has large input capacitance, and the tubes low current is not able to drive them easily.

Sajti

[gaborbela]

Szia Sajti

In Hungarian
Igen valoban valaki meg epitette ezt az erositot es az elso probara felrobbant .
Szoval nem erdekel egyaltalan .Konyu lett volna megepiteni mert a nyakrajz adott hoza de ha nem mukodik csak vesztegetem az idomet es a penzem vele .
Koszi a tanacsodat
Udv Gabor

In English
Yes one of my friend did built these amp and at the first try it blew up .
Even it would be easy to try it because it has the layout I don't want to wast my money and time with it .
Thanks for the advise
Greets Gabor

[gaborbela]

Hello ja2dhc

Post #5
My hybrid amp is described below(sorry in Japanese).

http://ja1cty.servehttp.com/mosfet/mosfet2.html

The current of MOSFET is 1.5A and voltage is +/-16V. Therefore
thermal dissipation of each MOSFET is 24W (16Vx1.5A). I used a forced
air cooled heatsink for a pair of MOSFET(top and bottom ones).
Therefore each heatsink handles 48W(24W+24W). If MOSFET operation
assumed 35V, 3A(105W/each MOSFET). very big heatsink is required.

The outlooking of my amp is seen below.

http://ja1cty.servehttp.com/mosfet/FET-outside.jpg

It is a really nice simple well design amplifier . I Google the power mosfet unfortunately hard to find part .At least not in North America .
These is a lateral mosfet or vertical .
It is possible to replace it with 2SK type of Hitachi or Toshiba or may be with IRFP mosfet .
Thanks for the schematic .
Greetings

[Arnulf]

Originally posted by sajti
1st: R13-C4. This filter takes the hum, and rail noise into the amplifier circuit.

How do you filter your HT supply ?