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Old 12th June 2009, 05:55 PM   #3971
udailey is offline udailey  United States
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Okay, I saw a guy posting about modding his amp (forget which one, some super commercial brand) by removing some resistors and replacing them with precision current sources. He used LM334 TO-92 packages with current setting resistors in place of a few resistors. Claimed it was great for improving the cymbals sound.
What do you guys think? Hogwash or room for experimentation?
I dont know if this was used in the signal or not, wish I had bookmarked the page.
Uriah

Okay, I found the reference
http://www.drmaudioht.com/BASIC_M1_CurrentSource.htm
Not as I remembered it but its interesting anyway.
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Old 12th June 2009, 06:13 PM   #3972
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Default F5 + quad

Quote:
Originally posted by bobodioulasso
Isn't the F5 able to drive loads lower than 8 ohms and so, to reach twice its power?
May be this could explain why Nelson oversized the transformer.

Have anyone of you nice people tried the F5 with the ESL-63 or the original Quad electrostatic?
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Old 12th June 2009, 07:20 PM   #3973
udailey is offline udailey  United States
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In the manual Nelson says:
"In spite of the thermal compensation in the circuit, you should assume that there will be drift as the heat sink temperature
rises, and you will need to readjust the values over the course of an hour or two. Usually it is best to start out bias
adjustment low, at maybe 0.4 mV across R11 and R12 until the amp is warmed up a bit"

Is the drift because P1 and P2 drift in resistance as they warm up from the heat of the heatsink? If not, why?

Uriah
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Old 12th June 2009, 07:35 PM   #3974
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You start around 0.4 V, not mV.

The drift is due to temperature change in the semiconductors.

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Old 12th June 2009, 07:40 PM   #3975
udailey is offline udailey  United States
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Thanks Mr. Pass. And thanks for the clarification on .4V vs .4mV, thats a pretty big difference.
Uriah
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Old 13th June 2009, 08:06 AM   #3976
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Quote:
Actually, I'm using 500VA transformer for my F5 . . .
I usually double this rating for a 2x100w class AB amp (bottom in multi-amplification). Though, who will use F5 on a 2 ohm load? Is'nt the limiting current circuit set too low for this ( i do not remember, as i do not use any)?
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Old 13th June 2009, 08:18 AM   #3977
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by bobodioulasso
"I'm using 500VA transformer for"

I usually double this rating for a 2x100w class AB amp
1kVA for 100W+100W ClassAB is unusually high. I don't think there are many here who would recommend that VA to W ratio and few builders who would follow that advice.
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Old 13th June 2009, 09:22 AM   #3978
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It is only sensible to do if you have 100W/8Ohms amps that doubles and doubles each time you divide the load by 2, i.e 200W/4Ohms, 400W/2Ohms and so on.
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Old 13th June 2009, 09:25 AM   #3979
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Quote:
Originally posted by AndrewT
1kVA for 100W+100W ClassAB is unusually high. I don't think there are many here who would recommend that VA to W ratio and few builders who would follow that advice.
I do not give any advice, just telling what i do.

For a 2x 100w/8 ohms capable of 2x400w/2 ohms i do not think i oversize so much the transfo rating. ( See commercial P.A. products)

In the case of the F5/2ohms capable, of coarse , it would be oversized.

As a rule of thumb, when Nelson recommends 600Va, i prefer to follow his instructions rather than to loose myself into uncertain calculations.

Though, Nelson's well known generosity, certainly allow us some margin in our transformer rating choice ( depending on availability and price).
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Old 13th June 2009, 09:31 AM   #3980
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Quote:
Originally posted by R-K Rønningstad
It is only sensible to do if you have 100W/8Ohms amps that doubles and doubles each time you divide the load by 2, i.e 200W/4Ohms, 400W/2Ohms and so on.
That's what they call "High current amplifiers".
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