25W Class A amp with Lateral MOSFETs

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acamilicko

acamilicko

Member
Joined 2007
juma said:
I should have named this amp "Therapy" - helping people to stop fearing coupling caps... ;)
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Yeah! Totally agree :)
Such a quality amplifier, amaizing.. Totally forgotten without reason. So simple construction, and so precise sounding amplifier, a lot of details and in the same time pretty transparent - CLASSY AMP!

I've built "mini" variant starting with 200mA bias, and ending up with 500mA - good for these heatsinks. With half of ampere bias it sounds a lot better than low bias, and as Juma says, it shouldn't be less to achieve good sound.

Slim pcb version>
An externally hosted image should be here but it was not working when we last tested it.


Eagle pcb files> http://www.diyaudio.rs/index.php?app=core&module=attach&section=attach&attach_id=38642

More images and process of work here: Projekat: SVAJA - Stranica 6 - Solid State - diyAudio.rs

An externally hosted image should be here but it was not working when we last tested it.


Thanks Juma! :cheers:
 
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F

fireworks

Member
Joined 2010
juma said:
This time I wanted an amp that will combine qualities of my F5 (made with k2013/j313) with a certain seductive gentlenes that comes with good tube amps (member p18 recently made a nice amp with 6C33C that inspired me). Comparatively, I wanted something like F3 but with more control, more gain, more power and insensitiveness to characteristics of source and speakers.
I worked for a few months on it and tried a number of ideas (best candidates were a circlotron with LU1014 and a single rail version of F5 with BJTs at input and Laterals at output) but the buck stopped here:
An externally hosted image should be here but it was not working when we last tested it.

I chose single rail PS becouse it enables using the benign reactive component at the output that makes "sound tailoring" possible.
Transformer is 500VA (2 x 40V AC, one secandary per channel). Cap. multiplier provides smooth and fast source of power (1.5mV ripple at 1.3A). 10mf ELKOs are Siemens Sikorel, bypass are MKC in PS and MKP in direct signal path.
Q1 provides high Zin and Low Z feedback point. Q2 gives all the voltage gain (OLG is about 50dB), it runs on about 7.5mA and that's more than enough to drive a pair of Laterals in push-pull Source follower topology (there are jumpers over Source resistors which are taken off when setting the bias with P2 ; P1 sets the half of the PS voltage at the output).
Here is the 90kHz square wave at the output loaded with Epos 5M (two way, bass reflex, 4 Ohm speaker). CRO was set at 5V/div vertical and 2uSec/div horizontal:
An externally hosted image should be here but it was not working when we last tested it.


Construction looks like this:
An externally hosted image should be here but it was not working when we last tested it.


and the rest of the pictures are here:
Projekat: SVAJA - d


Pass Labs This forum is dedicated to Pass Labs discussion.iayudio.rs
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I'm quite interested in your oscilloscope. It looks old and Russian. :)
Can you tell us more about it?
If you have time maybe you can post a Youtube video where you show it working. I'm sure the "oscilloscope lovers" will appreciate it. :p
 
juma

juma

Member
Joined 2005
G

Guitar.mod

Member
Joined 2006
Dear Juma,

It is a great amp! I was thinking about this topology lately and also about "F5 with bjt input".
You have built both. Some time is passed, so you could tell more objective which one sounds better?

As far as I remember F5 topology amps does not "POP" at power on/off. How about this one, does it "POP"?

p.s. I like output capacitor, because I do not like DC protection with relays.
 
G

Guitar.mod

Member
Joined 2006
analog_sa said:
Do you consider relays more detrimental to sound than caps?
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Relay have other problems:

1. I had problems with relays that made not good (sometimes intermittent) contact after some years of usage. Signal quality degraded at low levels, but with high levels - everything OK.
2. I have seen professional audio amplifiers, that burned very expensive studio equipment speakers, just because the DC protection relay FAILED to open circuit! (the contacts of relay were browned together)

So I thing that capacitor does not have the mentioned problems.
 
G

Guitar.mod

Member
Joined 2006
Yes.
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I was asking seriously...

Pop ? Never ! Just a lot of good rock, jazz and classic.
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Really misunderstood the question...
"POP" means not only music genre. In that context it means "bump" (low frequency output, not healthy to small power speakers) during power on/off.
If it is answered in the topic and that's why You dodge to answer, I am sorry - did not notice.
 
G

Guitar.mod

Member
Joined 2006
acamilicko said:
Slim pcb version>
An externally hosted image should be here but it was not working when we last tested it.
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Nice Work!

p.s. Little note: gate stopper resistors should be as near to the gate as possible.
In Your version - these are as far as possible :(
Also low power signal "GND" shares same trace as power "GND", this practice should be avoided. It should go with separate traces to star gnd point.
 
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juma

juma

Member
Joined 2005
Dear Guitar.mod,
I can not take that question (which of the two good amp sounds better ?) any more seriously - it will always depend on personal preferences, speakers used, etc...What I like better is irrelevant to anyone else - you'll have to gather your own experiences and preferences.

"Pop" is a joke, I thought it was obvious that there is no turn on/off thump.
 
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