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Old 19th April 2002, 06:11 PM   #101
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Question It is not....

Anybody can get an amp to work with a spice model, reality places other costraints on the design. Iq has nothing to do with current limit. At over 17 watts dissapation, an IRF 510 won't last long. Mosfets oscillate without gate resistors. Like I said, a man has to know his limitations.... I have posted pictures of two amp designs, a modified Aleph 3, a jfet buffer, and several very good passive preamps. Do your guinea pigs do spice modeling also?

H.H.
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Old 19th April 2002, 07:51 PM   #102
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Anybody knows any amps that work when builded but not when simulated?
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Old 19th April 2002, 08:06 PM   #103
Geoff is offline Geoff  United Kingdom
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Harry

"It was not in jest that I said that the JLH topology shares some resemblance to that of the Aleph series. "

Your comment hadn't escaped me, I just wanted to gather my thoughts before responding. Yes, there are similarities in that both utilise an active current source.

The JLH circuit modulates the current source from 0 to around 1.4 times Iq dependant on the input voltage level. The Aleph current source is superior in that it modulates from 0 to 2 times Iq dependant on the output current thus taking into account impedance and phase variations in the load.

I have spent a lot of time during the past couple of days (as a result of this thread) reconsidering the action of this output stage. Despite Doug Self's assertion in his 'audio power amplifier design handbook' that Tr2 is an output emitter follower with Tr1 acting as a voltage controlled current source, I have come to the conclusion that Tr1 is the output amplifying device with Tr2 being an active current source. Had it not been for Self's book I might have come to this conclusion a long time ago.

"Everybody simulates..... doesn't anyone actually build something?"

Simulation is a useful tool to aid the understanding of how circuits work but I agree that it is no substitute for building things (provided that you have access to suitable test equipment so that the results can be validated). Unfortunately, at times certain other factors come into play. The time spent answering email queries generated from a website or posting at a discussion forum can leave little available for anything else. Not to mention the lack of available finance due to unemployment :-(

Geoff
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Old 20th April 2002, 12:40 AM   #104
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Dear H.H. ,

You do understand that I wasn't serious in my reply? I like your repies, even when they are ... hmmm ... rather strong .. (I haven't got the right word for it) .. I'm not really critisizing you..

I hope you do find it interesting that the whole amp simulates more lineair while each of the four actice component seems less linear ... give me something to think about ..

Goodnight,
thijs

Geoff and H.H. ,

I wish I could build every amp I simulate, money and time dictates otherwise
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Old 20th April 2002, 01:08 AM   #105
FBJ is offline FBJ  United States
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Hey tschrama-
You said you built the 10W JLH, have you hear and will you upgrade to the 15W?
As far me I am going to get the input transistors matched for the 8W amp from borbely audio but I am having a hard time finding the other transistors. I can find all the transistors for the 10 W or 15 W JLH amp in Mouser catalog but there is so much info to read about the JLH amps that it might take me a while to choose which amp to build.
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Old 20th April 2002, 08:05 AM   #106
sonnya is offline sonnya  Denmark
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Quote:
Originally posted by Geoff
The JLH circuit modulates the current source from 0 to around 1.4 times Iq dependant on the input voltage level. The Aleph current source is superior in that it modulates from 0 to 2 times Iq dependant on the output current thus taking into account impedance and phase variations in the load.

I have spent a lot of time during the past couple of days (as a result of this thread) reconsidering the action of this output stage. Despite Doug Self's assertion in his 'audio power amplifier design handbook' that Tr2 is an output emitter follower with Tr1 acting as a voltage controlled current source, I have come to the conclusion that Tr1 is the output amplifying device with Tr2 being an active current source. Had it not been for Self's book I might have come to this conclusion a long time ago.
Geoff [/B]
You are right about you conclusion. Tr2 is currentsource. You could very easy remove Tr3 connection to Tr5 and turn Tr2 and Tr5 into a "passive" currentsource and the amp would still work but with less currentcapability.

Sonny
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Old 20th April 2002, 10:02 AM   #107
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Hi FBJ,

I will not upgrade my JLH10watt to 15 watts or DC coupling. I don't think I need the extra power and I consider the AC coupling OK for now...but maybe in the future..? The great advantage of the JLH10wattes is that there's so much experince with en internet publications. Like the tips I got for other output transistors.. I'm gonna ghet them!! However it would be very interesting if somebody build something else this time and tells us his experiences...

goodluck,

Thijs
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Old 21st April 2002, 03:20 AM   #108
FBJ is offline FBJ  United States
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Sounds OK tschrama.
I was trying to get an idea of what direction to go in. And you sounds like you KNOW what you LIKE. I just moved and it will take me a while to get myself setup again and I don't see myself finishing anything for a while but I can start collecting parts.
Maybe I will try batties for the 8W Monster. Mr. Borbely supplies me with all my JFets and he has battery PS for his preamps.
When I get something together I will post some pictures.
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Old 23rd April 2002, 12:53 AM   #109
Kevinbd is offline Kevinbd  United Kingdom
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Default Some Questions on the linsley hood amp

Hello,

Just wondering if some of you can help me.

In the 1969 design, which uses the 2N1611/MJ801's transistors what is the feedback rate?. Due to the lower gain of this driver i suspect the feedback rate is lower than the 1996 design.

Regarding the output capacitor, what is the critical parameters? Obviously handling the current is one. Could i use a high capacitance film cap for example?

I have seen an AC coupled amp use a bipolar but not any with films. Not sure about this one.


KD
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Old 23rd April 2002, 11:40 AM   #110
Geoff is offline Geoff  United Kingdom
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KG

Are we talking about the same amp here? The original JLH Class-A used 2N1613 and MJ480 (MJ481 for supply rails above 30V).

So far as the output capacitor is concerned, you will not be able to use a film type unless the amp is only driving a tweeter at frequencies above 2.5 to 3kHz. The output capacitor forms a high pass filter in conjunction with the load impedance and to achieve a suitable -3dB frequency for full range use (<10Hz), the capacitor size is such that the only feasable type is an electrolytic.

With an output capacitor of 2400uF and an 8ohm load, the corner frequency is just over 8Hz. If the amp was only feeding a tweeter, the capacitor size could be reduced to 12uF which would give a -3dB frequency of a little under 1.7kHz with an 8ohm load. This size of capacitor could be a quality film type.

A bipolar electrolytic is not required in this position since there will always be a dc bias across the capacitor due to the single supply rail.

Geoff
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