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Old 29th January 2013, 08:16 AM   #2681
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Quote:
Originally Posted by AndrewT View Post
If a low powered system is not loud enough then it is wrong to look at increasing gain or increasing input signal to raise the signal sent to the speaker.

It is far better to look at increasing the efficiency of the speaker to give the sound output available from the low power amplifier.
Thank you. My system is not low powered. I've built the high power version with double output transistors.

The problem is that I am not using this power. With the B1 preamp and the volume on max the system is not loud enough. If I use a different preamp with some gain, the system is more than loud enough.

So that is why I'm looking for some gain, but I don't like to ditch the nice sounding B1 or add gain stages to it. Some more gain in the power amp would be great.

MArco
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Old 29th January 2013, 10:46 AM   #2682
Mooly is online now Mooly  United Kingdom
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Uncharted territory but you could halve the value R6 and double the value of C4. That would double the gain. But... you are changing the whole design of the amp... that said it isn't a JLH69 in the true sense anyway.

Why do you feel changing the gain of the amp is preferable to adding gain to the preamp ?
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Old 29th January 2013, 10:57 AM   #2683
Jay is offline Jay  Indonesia
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Originally Posted by deduikertjes View Post
So that is why I'm looking for some gain, but I don't like to ditch the nice sounding B1 or add gain stages to it. Some more gain in the power amp would be great.
You think you need gain . If you don't want to ditch the B1, well, regardless the shunt power supply, DCB1 will most probably solve your problem.
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Old 29th January 2013, 11:20 AM   #2684
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Originally Posted by Jay View Post
You think you need gain . If you don't want to ditch the B1, well, regardless the shunt power supply, DCB1 will most probably solve your problem.
OK, I'll admit: I have a DCB1. Why would that solve my problem?
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Old 29th January 2013, 01:08 PM   #2685
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Originally Posted by Mooly View Post
The gain is set by the feedback factor of R6 and R8 in the circuit in your link (the transistors have no influence). Altering the gain could/would alter the whole character of the amp, its stability margins and DC conditions.
Thank you, somehow I missed your reply earlier.
Could you please elaborate a bit? Are there any guidelines for this, how much gain can be achieved, does anyone have experience in doing this?

I assume it is not as easy as inserting a trimpot in the position of R6 and or R8 and adjusting ..

Thanks, MArco
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Old 29th January 2013, 06:21 PM   #2686
Mooly is online now Mooly  United Kingdom
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It just happens I have the original JLH69 as a simulation and so changing the 220 ohm to 82 ohm was easy to try. That changes the gain from 12 to 33. The raw numbers suggest the THD is lower for the higher gain version. You would have to increase the value of the cap in proportion.
Attached Images
File Type: jpg Original JLH.JPG (193.6 KB, 574 views)
File Type: jpg Hi gain JLH69.JPG (195.8 KB, 497 views)
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Old 29th January 2013, 08:02 PM   #2687
Telstar is offline Telstar  Italy
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It lowers mostly the second harmonic, but at least is not pejorative
As long as it is still stable, it would be a good mod for ppl needing higher gain.
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Old 8th March 2013, 11:35 PM   #2688
JZatopa is offline JZatopa  United States
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Has anyone played around with the 1969 JLH running at higher rail V, say 46V?
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Old 12th March 2013, 11:17 AM   #2689
iperv is offline iperv  Italy
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Wrong post.
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Old 12th March 2013, 11:18 AM   #2690
iperv is offline iperv  Italy
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Originally Posted by DJNUBZ View Post
Has anyone played around with the 1969 JLH running at higher rail V, say 46V?
Yes, I did.
48V@1,7A.

For 4ohm load.
With 2sc5200.
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