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Old 4th May 2012, 08:10 AM   #791
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I'm very curious how this is going to evolve. How about the other usual suspects: IXTH6N50D2 and SJDP120R085?
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Old 4th May 2012, 11:23 AM   #792
Pano is offline Pano  United States
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Sure, you could use other MOSFETs. They don't even have to be depletion mode, they just have to be biased properly to drop the same voltage as the resistor or bulb.

One problem I'm finding is thermal - it takes some time to settle. Until the temperature settles, the DC offset drifts. That's not good for the speaker. The amp will probably need some sort of DC servo or DC protection circuit - and that's going to be about 5X more complicated than the amp. We shall see.
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Old 6th January 2013, 07:12 PM   #793
Pano is offline Pano  United States
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I finally got back to this after a busy year. Now trying with Nichrome wire in place of the light bulb. I'm attempting a low voltage version.

These IXTH20N50 sure do seem to need a lot of bias current to get any decent voltage swing. As anyone else found the sweet spot for bias?
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Old 27th February 2013, 01:01 AM   #794
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Pano - I really need to come up and audition some of your stuff and take a look at your delite amp. I keep coming back and looking at this amp as a future build (too many project right now).

In any case, since I have nothing really to add to this thread - Good luck!

Ben K.
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Old 3rd March 2013, 01:55 PM   #795
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Default DELITE improvements

Here is my small contribution: a new connection of C3, the speaker and the 0V terminal. This allows a great improvement in the ripple rejection, without altering any of the other sound settings.

Click the image to open in full size.

The improvement depends on the current and voltage of the circuit. The improvement also strongly depends on the resistance of the filament of the bulb.

Another thing I found is that if you choose a filament resistance equal to about twice the lower speaker impedance, frequency response is much flatter and pleasant. The impedance of a speaker tends to fluctuate between a minimum and a maximum value typically about 400 to 500%. Choosing a filament resistance equal to twice the minimum expected impedance value, ensures that the power dissipation in the speaker minimally varies between extreme frequencies of the spectrum.

I give an example: if the speaker impedance varies between 4 ohms and 16 ohms (between a frequency close to fs and about 10 KHz or more) and choose Rfilament = 8 ohms: Power at minimum impedance (about 200 to 600 Hz ) is only 0.51 dB greater than the power in a high impedance (near fs and 10 KHz or more).

Click the image to open in full size.

Unfortunately this leads to a lower efficiency and less control of the low end of the frequency.

regards

PD: Check the polarity of the capacitor C4 (depending on how you connect your preamplifier). R1 can be changed to the opposite side, if you want. The 0V connection can be left as in the original scheme, if you want, too.
Attached Images
File Type: gif diegomj1973 DELITE modification.gif (14.0 KB, 324 views)
File Type: gif Example of dB relative vs. Rfilament and Zspeaker.gif (32.0 KB, 325 views)

Last edited by diegomj1973; 3rd March 2013 at 02:20 PM.
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Old 3rd March 2013, 02:12 PM   #796
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I am little lost,
C3 seems to be of wrong polarity. C4 seems fine.

Also, the ground connection after PS would seem to keep the thing from powering up.
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Old 21st March 2014, 04:43 PM   #797
OllBoll is offline OllBoll  Sweden
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Soon when my R085 arrive (Thanks Tea-Bag!) I'll start building this little amp:

First I thought to use a single device per channel which should net me about 8-10 W into 8 ohm. I remember Nelson talking about that he likes to use these devices at 20-30W and since I will have enough JFETs for it I thought I could parallel two and do this:

Now I just need a sanity check if there is something dumb in the schematic =)

If I've understood correctly the degeneration works as output resistors so I won't have to add extra series resistance. My question is if there is any problems of both JFETs sharing the same current source which in my case is the big 193V inductor.

If this proves to be a bad idea then the plan is to use a single device like the second pic.

In the end the idea is to do 2x paralleled amps for the mids and then 2x single device amps for the tweeters, and those amps will have smaller inductors =)

EDIT: Though when you think about it's probably easier to just use one and push it to 40-45 W. If in 3 years one of them fails I still have 2 spares and when those also fail there will probably be a newer and more shiny transistor to use instead =)
Attached Images
File Type: png De-Lite Choke Parallel.png (265.5 KB, 141 views)
File Type: png De-Lite Choke.png (199.6 KB, 88 views)

Last edited by OllBoll; 21st March 2014 at 05:11 PM.
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Old 23rd March 2014, 01:42 AM   #798
OllBoll is offline OllBoll  Sweden
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Hmm, I think the 10k resistor & bias should be on the left side of the gate stopper resistor and not on the right. And when I think about it: As the R085s aren't perfectly matched then shouldn't it be better to have a cap to each of them so the bias of one can't leak onto the other one?

Last edited by OllBoll; 23rd March 2014 at 02:06 AM.
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Old 23rd March 2014, 04:44 AM   #799
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1) Naaah, it's fine.

2) Naaah, it's fine.

You can do it either way.

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Old 23rd March 2014, 10:50 AM   #800
OllBoll is offline OllBoll  Sweden
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Quote:
Originally Posted by Nelson Pass View Post
1) Naaah, it's fine.

2) Naaah, it's fine.

You can do it either way.

Nice!

Another thing I've wondered about dissipation and reliability:

If we take say the R085 or similar device and push it to 40-45W with generous heat sinking. Is it that you expect it to fail after say 5 years or is it that if you produce 100 amplifiers you expect a few of them to fail after say 5 years?

EDIT: I think I found you clarifying that a while ago: I take it this is true today too?

Last edited by OllBoll; 23rd March 2014 at 11:02 AM.
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