Hawksford

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Jocko Homo

Jocko Homo

RIP
Joined 2002
I agree with Jon's disclaimer. Although Charlie and I have only had the misfortune of knowing each other for >15 years. I'll let you guys decide who has the short end of the stick.

I have "known" of Jon's work for about...........25 years now, I guess.

You may not agree with our positions, but we didn't just make them up 2 minutes before we posted them.

Jocko
 
M

mandat

Member
Joined 2003
I try to reply to janneman's post by quotations.
posted by janneman
[snip] I think that you should not copy Cordell's amplifier exactly, because it's from eighties, [snip]
Hahaha, that says it all, doesn't it! What an insight!
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posted by JonMarch
I built a high power variations on the Cordell circuits (some tweaks and changes to the input stage, and eventually a VERY different MOS output stage) 15 years ago; the final version sounded better than the reference copy I built of his AES paper circuit, and met my client's desires and requirements, but I wouldn't go down that road for myself.
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posted by janneman
Since I grew up with BD139 (which doesn't meet the Vce spec), and the BD239 (which has rather low Hfe), I'm a bit out of touch with the newest devices.
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Originally posted by Heraclitus
Panta rei!
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P.S. My original post has got #14 in this thread.
 
J

JonMarsh

Member
Joined 2002
Something keeps popping up in my head: have you been a technical manager for Audio Technica, if I have the name right, many, many years ago?
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Nope, different guy...


I must have several doppelgangers out there, judging from the "Aren't you ...." that I get... ;)

Audio has been my main work at times in the past, but aside from occasional contract work, I took my career on a side trip into milatary electronics in the beginning of the 80's, then semiconductors in the mid 80s, where I still slave away....

These days in this alter ego I'm just a totally out of control hobbyist... ;)
..... but still an AES member.






~Jon
LivingRoomW_DrvrsSS.jpg
 
thanh

thanh

Member
Joined 2004
Hi Jon! I haven't got much money to build all circuits.I have ever built a amp which use single differential input stage with 2SC2362. It's treble is quite good but i don't like the bass and mid sound of it.
Then, i built a slone's amp with symmetrical topo .I use 2SA1015/2SC1815 for it.Because in my country ,2SC2362 = 4 *2SC2362. It's noisy is high but i prefer the bass and mid sound of it .Can you understand me?
I'm in trouble with short protection circuit .I always look the schematic which have got any distortion .When i have got it, with some transistor at some electronic market in my country i can also have a amp which have the value of distortion about 1E-12 %and more. Because of that reason , i looking for a new technique?
Hi janemen! Are you a beautiful girl?:D
 
fdegrove

fdegrove

diyAudio Senior Member
Joined 2002
Hi,

JC, CH, JH
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Nothing wrong with your English, Thanh....It's the Amway.

JC...It could be John Curl's initials, not sure.

CH : Charles Hansen, I suppose.

JH : actually that one can only belong to Jimi Hendrix but, guess what... Jocko Homo nicked the acronym.

Just kidding....If I'm wrong about it, they'll correct me anyway...They're actually very good at that.

Cheers, ;)
 
J

JonMarsh

Member
Joined 2002
thanh said:
Hi Jon! I haven't got much money to build all circuits.I have ever built a amp which use single differential input stage with 2SC2362. It's treble is quite good but i don't like the bass and mid sound of it.
Then, i built a slone's amp with symmetrical topo .I use 2SA1015/2SC1815 for it.Because in my country ,2SC2362 = 4 *2SC2362. It's noisy is high but i prefer the bass and mid sound of it .Can you understand me?
I'm in trouble with short protection circuit .I always look the schematic which have got any distortion .When i have got it, with some transistor at some electronic market in my country i can also have a amp which have the value of distortion about 1E-12 %and more. Because of that reason , i looking for a new technique?
Hi janemen! Are you a beautiful girl?:D
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Thanh,

I understand that where you live, getting good parts at good prices may be difficult! This may place special limits on what you consider building...

I don't use conventional V/I limiters for short circuit protection anymore; (did use them in the past), instead I use an overload detection circuit outside the signal path measuring voltage and current, and tracking (to the extent possible) device temperature; if I get close to the SOA limit, the supply is "crowbarred" and a magnetic circuit breaker in the primary shuts down. Or the rail fuses blow. I don't really like rail fuses, but use them sometimes. None of these techniques are inexpensive, regrettably. And they require building an output stage with "excess" SOA. But this is also deirable from a signal viewpoint; i.e., if using bipolars, paralleling multipe extended beta bipolars can greatly reduce the open loop distortion and impedance.

Also have a "clip" indicator which compares input and output and triggers LED in the event a difference. This circuit doesn't have to be all that fast, as the amplifier bandwidth is usually only about 150-200 kHz, limited by filters.

Since I only tinker with non interstage feedback amplifiers anymore (NIFA? ;) getting the output stage characteristics as clean as possible is a primary goal. Actually, it's possible to make the output stage work so well that the main source of distortion is still in the VAS amplifier.

These amplifiers are in the 250 watt range @ 8 ohms single ended, and 500W balanced differential. I suspect you may be more interested in techniques for a low power amplifier, perhaps class A?

You mention liking the trebel, but not the bass or mids. In my experience this may mean that your circuit topology is good, but your power supply isn't sufficiently low impedance, especially in the mids and bass.

Look up through Google the old Dynaco ST 416; I built a very similar amplifer using a standard Dynaco 400 Kit and some extra parts about three years before the ST416 came out. It works, makes a very big difference in the midrange and bass.


Regards,

Jon
 
G

ghost_au

Member
Joined 2004
Hawksford error correction

A very nice power amplifier using the Hawksford feedforward error correction scheme was published in 1984 or thereabouts by John Cordell, I have a rather tattered copy of his paper somewhere. This particular amp was notable in the use of cascode voltage amplifying stages throughout, with a dual JFET input and used IRF series Mosfets in the output stage. I have built a version of this and it's performance is exceptional. THD at 20 KHz is below 0.001% and it delivers a slew rate of around 300 V/uS, needless to say the high frequency and transient performance is quite impressive.
 
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