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Old 11th February 2012, 12:08 AM   #1
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Default Improving a FirstWatt-built F4

I understand I'm treading on shaky ground, but here goes.

Would there be any degradation in SQ if I replace the 47.5K input-load resistors with 100K or 150K resistors? I ask because each preamp channel will be driving two F4 channels plus a 67K-input channel of a subwoofer amp for a net of 17K-odd Ohms. That moves the filterpoint of the preamp's output-coupling cap to about 4.5Hz, about an octave higher than I'd like, and I prefer not to have to buy and install more expensive Teflon-film caps.

Thx in advance.
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Old 11th February 2012, 02:10 AM   #2
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No degradation. Pick any value that amuses you. Probably 1Meg is OK.

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Old 11th February 2012, 02:19 AM   #3
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Originally Posted by Nelson Pass View Post
No degradation. Pick any value that amuses you. Probably 1Meg is OK.

TYVM.
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Old 11th February 2012, 02:23 AM   #4
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Originally Posted by Nelson Pass View Post
No degradation. Pick any value that amuses you. Probably 1Meg is OK.

TYVM. 220Ks get me to 1.9Hz.
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Old 11th February 2012, 08:20 PM   #5
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Default Improving a FirstWatt-built F4--question #2

Probably I'll change them all to 100uF/50/std. pol. BlackGates bypassed with 1uF SoniCap Platinum (Teflon-film) caps.

But first, I'll listen (before improving parts) for as long as this compulsive tweakist can stand before turning on the soldering iron.

---------------------------

From an e-mail exchange:

Sure. If you like. They can be smaller, no problem.

np


----------------------------

From: Jeffrey Behr
Sent: Friday, February 10, 2012 5:06 PM
To: 'Nelson Pass'
Subject: FirstWatt F4--capacitors 1 and 2

I know you're a busy man, but perhaps you didn't see this, and I'd really appreciate your help:
1. Would it make sense to replace Cs 1 and 2 (in new-to-me, FW-manufactured-last-fall amps) with something like BlackGates?
2. Could they be any smaller…say 100uF or 150uF…and still work correctly? I have plenty of 100uF BGs so I could make them all (8 caps in 2 amps) 200uF caps.

TYMV.


Jeffrey Behr, Phoenix, AZ USA
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Old 14th February 2012, 11:14 PM   #6
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Old 27th February 2012, 08:51 AM   #7
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Nice picture, Jeff !
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Old 28th February 2012, 04:40 PM   #8
flg is offline flg  United States
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Quote:
Originally Posted by jeffreybehr View Post
I understand I'm treading on shaky ground, but here goes...
Wowwa, cool, go for it dude!!!
But?
That's all???
Hey, I don't suppose I'm hi-jacking if:
I propose 1A minimum/Comp. FET Pair???
How about if we dump the Fairchild/IRF devices and go to 2SK1530/2SJ201???
Along with that, we should just put those Rs in the right area with .2-.22??? .1-.15 if you have balls(eggs-huevos, or matched FETs etc.)???
I suppose we need to work on that TL thingy for proper bias???
So do you want classA?// We'll Lower the 24V rails to 19-21V rails??? (a 15-0-15 0r 16-0-16 xfmr)...
I just thought those would be improvements???
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Old 28th February 2012, 05:13 PM   #9
Gyuri is offline Gyuri  Hungary
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Hm, I think I would leave it alone, as is.
Rather, I would build another one.
But I only say this.
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Old 28th February 2012, 08:17 PM   #10
Zen Mod is offline Zen Mod  Serbia
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possible improvement is to make it dual mono ( another toroid + another rectifier+filter block) ;

puttin' laterals instead of IRFP's will not gain much ( if anything) ;

I made somewhere schm of biasing for lat's for someone

I'll try to find it in my PC Arc

edit - found it
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File Type: gif F4 for laterals - bias concept.GIF (56.7 KB, 181 views)
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