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Old 3rd January 2018, 04:11 PM   #561
marconi118 is offline marconi118  Germany
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Quote:
Originally Posted by Zen Mod View Post
more of good engineering practice ....... 300k + 100K pot for biasing net

1k gate stoppers I understand it is too high, but for biasing net why 300k is too high? It isn't in the signal path. What is the highest value you recommend? And reasonable value of coupling cap? My dac is rated 2vrms on a 10k load
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Old 3rd January 2018, 04:28 PM   #562
rco3 is online now rco3  United States
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Originally Posted by xrk971 View Post
In the critical feedback resistor, a carbon film vs metal thick film reduced H3 relative to H2.
Thick film resistors are cermet (ceramic and OXIDE), not metal film. The same confusion was perpetrated in that other thread as well. Thin film = metal film, thick film != metal film. Now you are telling people that a metal film resistor caused your H3 when it was a thick film - please do not perpetuate misunderstandings.
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Old 3rd January 2018, 05:38 PM   #563
needtubes is offline needtubes  United States
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Even more interesting... Perhaps xrk will try a true metal film in that position?
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Old 3rd January 2018, 05:48 PM   #564
ratbagp is online now ratbagp  United States
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Originally Posted by ratbagp View Post
Since the subject of gate stoppers has come up, I have a question about R2, 221 ohms. When I build tube amps I would normally use a carbon composition resistor which is non-inductive as grid stopper on a tube. Since I am not knowledgeable about transistors, is a metal film or carbon film ok on the gate of a mosfet?

ray
I suppose my underlying question is whether gate stoppers for mosfets should be non-inductive.

ray
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Old 3rd January 2018, 10:17 PM   #565
xrk971 is online now xrk971  United States
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Quote:
Originally Posted by rco3 View Post
Thick film resistors are cermet (ceramic and OXIDE), not metal film. The same confusion was perpetrated in that other thread as well. Thin film = metal film, thick film != metal film. Now you are telling people that a metal film resistor caused your H3 when it was a thick film - please do not perpetuate misunderstandings.
Yes, sorry about that but I meant metal oxide thick film. I have not tested metal thin film SMT but bet that it would be fine, which is why I said thick film resistors.

Thin and thick film >> Resistor Guide
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Old 11th January 2018, 01:41 PM   #566
marconi118 is offline marconi118  Germany
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Which could actually sound better, especially on widebanders and compression drivers. Build it and listen, try reversing speaker connection an listen again. You are in for a surprise.
for cmpression driver 600Hz upwards, better bulb or inductor?
I con't care about voltage swing or efficiency as I need only 1W of output power
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Old 11th January 2018, 02:56 PM   #567
xrk971 is online now xrk971  United States
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Inductor will allow more headroom so even if you only need 1W, the distortion will be lower. So it depends on what you want as THD figure. I measured 0.2%THD at 1w into 8ohms with an inductor. It was quite a bit higher with just a resistor.
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Old 11th January 2018, 04:40 PM   #568
indra1 is offline indra1  Indonesia
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Originally Posted by marconi118 View Post
for cmpression driver 600Hz upwards, better bulb or inductor?
I con't care about voltage swing or efficiency as I need only 1W of output power
I can not tell you for sure because :
- My taste and "sound better" definition could be similar, but could be totally different than yours.
- All compression drivers are not built the same way.
- All inductors are not built the same way.
- Mr. Pass explained about some amount and negative phase of second harmonic distortion has a signature he preferred. For some people, but not all, a bit higher distortion (not too much) of an amplifier actually sound better. 6L6 has a youtube video here.
- The late Eduardo de Lima of Audiopax published a white paper claiming that when single ended amplifier (like the MoFo) is used with a widebander (like your compression driver) connected at a certain polarity, measured distortion at listener position is lower compared to a very low distortion amp. But a lot worse distortion when speaker polarity is reversed.

A lightbulb does not cost a fortune, why don't you try it first. You can always try the inductor later if you don't like it. In my experience, light bulb load gives more "air" while inductor gives more "slam" with "a little subdued high". But I tried with nemesis type circuit and my diy inductor is made with non oriented core, not a real good quality one. However, nobody can guarantee that a certain inductor with better specification or more expensive will sound better to me on my setup in my listening room. Our Mr. MR tried a lot more options compared to my very limited experience, perhaps he could chip in his experience.

In short, "better" is a very complicated issue. Simply try it and have a good diy journey, it's a fun journey for all of us.
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Old 12th January 2018, 07:13 AM   #569
Vix is offline Vix  Yugoslavia
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Nothing wrong with lightbulbs, except that you may need high wattage ones that are getting a bit more diffucult to obtain (leds everywhere), and/or you may find that a higher psu supply is needed, since for a proper headroom, you will want to drop around 2/3rds of the supply voltage through the lightbulb, and 1/3rd across the mosfet. With 19 v supply, it won't be enough for anything useful, but you can try. That also means readjusting the voltages on drain/source...
See what a DeLite-MoFo looks like
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Old 12th January 2018, 08:16 AM   #570
marconi118 is offline marconi118  Germany
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I have the same light bulbs, 1000W 220v
will try with 19v PSU, 12V on the bulb, 7V on the IFRP, it will bias around 0.8A

And thanks to the trick of reversing polarity!
It means that the distortion will change if I output referenced to the + or the - ?
Parallel to the bulb will sound differently than parallel to the IRFP?

my compression driver is JBL 2446
for the bass (2226) I plan to use F4 buffer, for bedder damping factor
Directly feed from DAC, no preamp, 2.2V RMS is plenty for high sensitivity speakers.

Next I will replace bulb by 2.5mH air core inductor and compare
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