The Hybrid Class A amplifier

[Wavebourn]

Whatever...

Put both out of sight and play them through the same speaker - you won't "taste" the difference. Pretending that you can is fine though.

Carry on.

To "taste" the differences a good direct record of acoustical instruments and/or human voices is needed made by good microphones in a nice reverberating environment. No EQs, no gates/compressors, no artificial reverberation must be involved. The point is, you must compare amp/speaker sound with real natural sound.

 

[gaborbela]

Hello da2dhc

Thanks for your answer .
Some more questions .
Did you match the power mosfets ?
I have at home at least 20PC orig Toshiba 2SK1529 and at least 40PC IRFP240 & some IRFP150N.
I did look up the data of the mosfet what U use , I don't know if is lateral or vertical mosfet (I think that is very important). It doesn't have any info about .I guess is vertical mosfet .I'm not an expert of mosfets . I will check aggain .
Also I have to look which mosfet is closer to yours the Toshiba or the IRFP .
I like the simplicity of the amp , I believe it produce great clear sound .
What type of preamp U use to drive your amp or there is no need for preamp ?
Please let me know .
May be I will give a try to your amp .
Greets

 

[Wavebourn]

Hi Gaborbela;

no need to match MOSFETs. One of them works as a source follower (on top), another one works as a current source for it (on bottom). It is not important is it lateral or vertical MOSFET, since current is defined by resistor in source and voltage on gate that is set by a trimpot. The higher is the value of that resistor in source, the more it is stable thermally. Also, a forced air cooling helps.

 

[gaborbela]

Hello Wavebourn

Thanks for your answer ! I really appreciate it .
I have one more question .
In the power supply I think He uses 3PC relay .Do I have to use those if I case if I use large heat sink for cooling not air forced cooling .
I hate the noise of the fan.
Please let me know .
Thank you very much .
I see you an expert about tube stuff , I did visited your website .

Greetings

 

[ja2dhc]

Hello da2dhc

Thanks for your answer .
Some more questions .
Did you match the power mosfets ?
I have at home at least 20PC orig Toshiba 2SK1529 and at least 40PC IRFP240 & some IRFP150N.
I did look up the data of the mosfet what U use , I don't know if is lateral or vertical mosfet (I think that is very important). It doesn't have any info

I recommend 2SK1529 because of TO-3P package. My MOS FET of
FS22SM-12A has conventional lateral construction in it. Due to SOURCE
FOLLOWER usage, Vertical/Lateral does not make sense.

No matched pair MOS FET's are required as Wavebourn says.
A forced air cooling is mandatory required. I used PC CPU use FAN
heatsink with half voltage applying to the motor coil resulting FAN
noise is reduced to the level of unnoticeable at a music listening
room.

 

[Wavebourn]

He uses relays for 2 purposes: to delay speaker connection, that is necessary until output voltage sets up. Without such delay speaker will thump when you power on your amp. And second, he pre-charges big capacitances of filter capacitors before connecting them to rails, to decrease a surge current, otherwise notebook power supplies may think they are shorted up and shut down themselves.
Yes, you can use big heatsinks. But a current source I would improve in such case to prevent thermal run-away.

 

[gaborbela]

Hello ca2dhc
I would like to have a question.
These is about the LF441CN IC . Do I have to connect the # 1 & 5 of the IC ?
I started the PC board lay out , I don't want to make mistake .
Please let me know .
Thank you very much
Greetings

 

[ja2dhc]

Hello ca2dhc
I would like to have a question.
These is about the LF441CN IC . Do I have to connect the # 1 & 5 of the IC ?

Hello, Thanks so much to build a hybrid amp. Pin #1 and #5 are
designed for an adjustment of offset voltage. According to the datasheet
of LF441CN, the maximum offset voltage is only 0.5mV which may
be outputs to the speaker terminal. I don't think 0.5mV makes the
speaker broken or bad impact to the sonic. You can keep open #1 and #5.

For your information:

*Make sure thermal coupling between MOS FET and heatsink.
*Make sure to select enough thermal capacity of heatsink with FAN.
*You can change the top tube from 6688 to your tubes on-hand.
*Make sure to adjust bias VR. It has some time delay due to the filtering
capacitor(47uF) near Zener Diode. Turn VR slowly.

My power supply schematic is shown in the below URL. I use a pair of
Notebook PC AC Adapter (16V, 4.5A rated).

http://ja1cty.servehttp.com/mosfet/FET-Power.png

I am looking forward to hear from you about GOOD SONIC by the amp.

 

[gaborbela]

Hello
Thanks for your answer
Do I have to use the relay or is enough if I use a soft starter for the power supply .
If I have to use relay what type of relay do I use .I have at home some 12V type with 5pin I don't know if I can use them ?
Thank for sharing with me your power supply . OK I didn't connect the #1 & 5 pin of the IC.

Greets

 

[gaborbela]

Hello
I little more work done on the PC board .
I'm planing to use large heat sink instead air forced heat sink .
I do not like the noise of the fans .
I have large heatsink . Do i have to use a preamplifier or I can connect direct to the CD player using a blue velvet Alps pot.

Greets

 

[ja2dhc]

Hi ! very quick response, gaborbela

Do I have to use the relay or is enough if I use a soft starter for the power supply.

If a "soft starter" is used, relays are not needed but it depends on
the characteristics of "Soft Start". I recommend you to reserve a space
of relays for a back up in a case of necessity. The relay which you showed
can be used for the purpose if coil voltage is adjusted to 12V from +16V
rail by a resistor in series.

I'm planing to use large heat sink instead air forced heat sink.
I do not like the noise of the fans.

One of my friend challenged no FAN heatsink. He reported me that
50cm x 50cm x 10cm one is needed. If you use FAN's driven by half
voltage of the rating, enough air flow and silent operation can be obtained as I am now doing.

 

[ja2dhc]

Do i have to use a preamplifier or I can connect direct to the CD player using a blue velvet Alps pot.
Greets

My amp has enough voltage gain of 28 times from the input terminal to
the speaker output terminal therefore no preamplifier is needed. You can
connect CD player directly.

 

[gaborbela]

Hello
Thank you
I'm still working on the layout , I do with my hand .
One more question .
Only the three pin have to connected the LF441CN IC ?
My fried ask what about pin #4 and #7 .
I do after the schematic .
In case if I have to connect those pins please let me know .
Thank you
Greetings

 

[ja2dhc]

My fried ask what about pin #4 and #7 .

The pin #4 and #7 are connected to the rails of +/-16V.
Please refer to the attached photo.

#7: +16V
#4: -16V

Don't forget by-pass capacitors of 0.1uF-10uF near by the IC
as shown in the photo.

 

[gaborbela]

Thank you very much
Greets

 

[revintage]

Hey ja2dhc,
I like your coolers. Just bought a pair of Alpine Pro for my choke-loaded hybrids. E180F is also a very good choice.

But I am not sure SF is the way to go. Better to make a MOSFET behave like a triode as DF and give some gain.

Will come back with a schematic when the circuit(6H30+4:1 IT) is tested.

Why bother with +/- supplies. It is almost the same if the "second" capacitor is from output to speaker or from ground to minus. If going singlesupply it could be better to use a P-channel SF with the CCS on top. This way PSRR should be no problem.

 

[Wavebourn]

But I am not sure SF is the way to go. Better to make a MOSFET behave like a triode as DF and give some gain.

Why, and what's the reason?

I would add one more BJT in a current source to make the whole thingy more temperature stable, that's it.

 

[gaborbela]

Hello
Finally I finish the layout for these amplifier .
I made it by hand so if you use it used for your responsibility .
It was not tested so it can have some mistakes etc . I would be not responsible in case if U use it and cause any damage to you .

Greetings

 

[ja2dhc]

Will come back with a schematic when the circuit(6H30+4:1 IT) is tested.

Good Morning Folks from Japan, now entering to the rainy season here.

My schematic was not my original design. I found below URL of Sajti's
one year ago and was deeply impressed about its design philosophy.

http://www.geocities.com/ResearchTriangle/4055/

I modified it to adapt my parts and embeded my preferences to get
my sonic. Following lists my comments.

SF or DF of MOS FET ?
SF cancels its own sonic of FET because of self NFB and has below
benefits.
>> No voltage gain, (I can enjoy DRIVER's tube sonic taste. I like tube)
>> Effectively reducing input big capacitance (Good Freq. response)
>> High PSRR
>> Enough Damping Factor without overall NFB
>> Whatever kind of MOS FET can be used because of no dependency
of FET own sonic. (If DF, we must be careful to select MOS FET,
such as vertical/lateral construction depending on own sonic taste)

Now I am enjoying to listen 6688(E180F) sound but want to see
your schematic of (6H30+IT) when it will come up.

 

[gaborbela]

Hello ja2dhc
Good morning , for me good night , I just go to sleep now .
Did you ever com paired your amplifier with another DIY amplifier or some better quality from the store?
My fried doesn't like the schematic because the IC between the tube and the mosfet .
I said I still I give a try .
He said is to complicated schematic , but I'd like it .
Right now I have some another amps to finish after I start these .
Thanks one more time for your help .
I like the high voltage on the tube .
What size of transformer use for the power amp section .
300VA is enough?
I hope yes because that is I have at hand .
I will buy some Russian military tubes .
May be some carbon type resistors .
Right now I'm curious to what kind of schematic will come up revintage .I hope he shares with all of us .
The finale layout with the parts marked on .

Greets