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Old 16th May 2013, 12:49 AM   #11
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Thanks Russell,

By the way, I note that you used 220R feedback resistors in place of the 100R nominal ones, to slightly boost the gain, and that you also removed the current limiting portion of the circuit. This is also what I intend to do on my build (which is currently queued behind my DAC completion). How did that work out for you?
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Old 19th May 2013, 06:26 PM   #12
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Originally Posted by LucasAdamson View Post
Thanks Russell,

By the way, I note that you used 220R feedback resistors in place of the 100R nominal ones, to slightly boost the gain, and that you also removed the current limiting portion of the circuit. This is also what I intend to do on my build (which is currently queued behind my DAC completion). How did that work out for you?
That amp still needs a case to put it in and the power supply caps. Have all other parts and sinks. The F-5 I have up and running is a standard F-5, dual mono. Got side tracked with the F-5 turbo group build, but have every intention of finishing the no limiting/220 ohm feedback. Some say not much difference but more gain, I think that was Buzz, sorry if I am remembering wrong, I saw one report that they thought it messed with the bass, but they were having other problems. Nelson and Zenmod suggested it, how could you go wrong I figure. I could always change it back I guess.

Russellc
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Old 24th May 2013, 03:34 PM   #13
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Originally Posted by Russellc View Post
That amp still needs a case to put it in and the power supply caps. Have all other parts and sinks. The F-5 I have up and running is a standard F-5, dual mono. Got side tracked with the F-5 turbo group build, but have every intention of finishing the no limiting/220 ohm feedback. Some say not much difference but more gain, I think that was Buzz, sorry if I am remembering wrong, I saw one report that they thought it messed with the bass, but they were having other problems. Nelson and Zenmod suggested it, how could you go wrong I figure. I could always change it back I guess.

Russellc
Didn't Nelson suggest a bit more than that? I remember this particular advice he gave, to somebody wanting to use carbon resistors instead of metal film, in order to soften the unyielding hardness of the amp. Papa Pass suggested 2x 3w 200r (=100r 6w) for R5/R8 in place of 2x 3w 100r (=50r 6w) plus:

22r in place of 10r for R1/R2...plus:

1 Ohm fo R11 & R12 in place of 0.47 Ohm.

Don't ask me why...the result was found very pleasing to the poster, who commented:

"Yep, Yep, amp runs a little cooler(perhaps 8-10 degree farenheit) and the "tight fist" now has a velvet glove! I found the original spec a bit dry and etched in sound relative to my Dynaco st70 - accurate and detailed but lacking a bit of body or warmth. The new feedback seems to be definitely a step in the right direction."

Having said this, my friend Lorian has made the same complaint initially, only to retract it after burn in, which opened up both bass and warmth, so best wait before implementing resistor value changes. Mr Pass sure knows what he's doing!
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Old 24th May 2013, 04:45 PM   #14
AndrewT is offline AndrewT  Scotland
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I am pretty sure that using a resistor with a very high tempco in the feedback circuit will sound different.
I don't want a bad copy of the input signal sent to my speaker.
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Old 25th May 2013, 11:14 PM   #15
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I am pretty sure that using a resistor with a very high tempco in the feedback circuit will sound different.
I don't want a bad copy of the input signal sent to my speaker.
What do you recommend?
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Old 26th May 2013, 08:07 AM   #16
AndrewT is offline AndrewT  Scotland
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Almost anything except carbon composition and if carbon film, then guaranteed by design and build and specification to perform as a resistor and not as an NTC/PTC
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Old 29th May 2013, 12:42 AM   #17
alazira is offline alazira  United States
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What do you recommend?
If you want to use carbons, perhaps at the gates. I believe Peter Daniel built his with some Rikens there.
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Old 29th May 2013, 01:22 AM   #18
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For the record, I have no desire to use carbon anything in my F5.

But when faced with a builder that suggested it to "warm up" the sound of the amp, NP suggested instead a few (metal film) resistor changes that are interesting, and not merely 100r to 220r R5/R8, but also the other changes I posted. I wonder if changing only R5?R8 could cause any issues....
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Old 7th June 2013, 01:32 AM   #19
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Originally Posted by LucasAdamson View Post
For the record, I have no desire to use carbon anything in my F5.

But when faced with a builder that suggested it to "warm up" the sound of the amp, NP suggested instead a few (metal film) resistor changes that are interesting, and not merely 100r to 220r R5/R8, but also the other changes I posted. I wonder if changing only R5?R8 could cause any issues....
Yes, remember taking notes about Nelson's suggestions to the poster wanting to warm up his F-5 while reading this gigantic thread when I initially built. There were several resistors changed up, I didnt follow that route as some others felt it might be a bit much "warming up." My amp never struck me as needing "warmed up" (maybe because of the IRF outputs?) just a little more gain.

Russellc
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Old 7th June 2013, 01:59 AM   #20
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Originally Posted by LucasAdamson View Post
For the record, I have no desire to use carbon anything in my F5.

But when faced with a builder that suggested it to "warm up" the sound of the amp, NP suggested instead a few (metal film) resistor changes that are interesting, and not merely 100r to 220r R5/R8, but also the other changes I posted. I wonder if changing only R5?R8 could cause any issues....
look at F5 turbo. there is no changes other then R5-R8. this will raise the gain from 15.5db to 22db.
regarding carbon. i use allmost only carbon composit in my F5(exept feedback resistors and source resistors). and i like it.
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