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Old 15th November 2012, 06:44 PM   #12691
udailey is offline udailey  United States
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Quote:
Originally Posted by flg View Post
I would like to comment that a typical toroid will pass likely the whole audio band albeit not flat, thru it's primary - core and secondary windings if that's what the line has to offer. What I just read makes it sound like a 50-60Hz bandpass filter which it is far from
Of course, but what he describes is a hum which is often 50 or 60hz depending where we live. Thats what I was responding to. Then turn all the frequencies to DC and filter.
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Old 16th November 2012, 05:11 PM   #12692
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Hi, it seems i have had an internal ground loop, but it is gone forever now, thanks to :
The Leach Amp - Part 2

If you are sure that the hum is due to an internal ground loop, the procedure for breaking this loop is as follows:
  1. Turn the amplifier off and wait for the power supply to discharge. Do not perform this procedure with the amplifier on.
  2. Cut the wire to the central ground on the input side of one circuit board.
  3. Solder a short circuit jumper wire between the ground lugs on the two input jacks.
  4. The circuit board with the cut ground wire is now grounded back through its input ground lead to the ground of the other circuit board. Use an ohmmeter to verify the new ground connection before turning the amp back on.
This eliminated my F5's hum completely Thanks to everyone
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Old 19th November 2012, 05:05 AM   #12693
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Post some pictures tolikas. That way the thread is must more helpful.
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Old 20th November 2012, 07:46 AM   #12694
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Tried to search this giant thread but must lack the talent to do it right. A probably dumb pair of question here.

Background, I have been using an F2, Papa built, on my full range augmented system for a few years and have loved it. I just bagged a "factory" F5, which I have wanted for a long time. I put it on the Full range speakers just to test it for function but fell for the sound BIG TIME. But the bass enhancement the F2 brings is gone re: the F5's damping factor of 80.

Questions - will loading the F5 output with resistors (in the style of the F1) do horrible things to the sound or the equipment? If not, is the said resistor placed across the output terminals of the amp? Or similarly across the speaker terminals? I'm thinking non-inductive wirewounds of perhaps 15 ohms 10 watt. These speakers are around 100dB/w/m so there will not be much current.

Sorry to invade a knowledgeable DIY forum with such ignorance, but I know your advice will be solid. Unrelated, RIP SemiSouth. Sniffle.
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Old 20th November 2012, 08:04 AM   #12695
Zen Mod is offline Zen Mod  Serbia
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put resistor in series with speaker ( resistor between positive amp out and positive speaker post)
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Old 20th November 2012, 08:39 AM   #12696
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Originally Posted by Zen Mod View Post
put resistor in series with speaker ( resistor between positive amp out and positive speaker post)
Thank you! Most grateful. My wirewound parts bin is long empty so off to Mouser I go.
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Old 20th November 2012, 10:22 AM   #12697
AndrewT is offline AndrewT  Scotland
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Try a series connected 1r0 and if that is too much (speaker Q too high) then add extra 1r0 in parallel to the first.

Alternatively start at the other end.
Try 0r1 and add extra series 0r1 until the speaker Q rises to the value you like to hear.
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Old 20th November 2012, 01:42 PM   #12698
6L6 is offline 6L6  United States
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Quote:
Originally Posted by 4345owner View Post
Tried to search this giant thread but must lack the talent to do it right.
Nope, it's not you, the forum software search function is basically worthless.



Quote:
I'm thinking non-inductive wirewounds of perhaps 15 ohms 10 watt.
Way too much resistance. That will make all the damping of the F5 go away, and kill it even more. Let's look at what AndrewT says -

Quote:
Originally Posted by AndrewT
Try a series connected 1r0 and if that is too much (speaker Q too high) then add extra 1r0 in parallel to the first.

Alternatively start at the other end.
Try 0r1 and add extra series 0r1 until the speaker Q rises to the value you like to hear.
(By the way, 1r0 is 1.0 ohm, and 0r1 is .1 ohm . With 100db speakers, 3 or 5 watt resistors will be fine. )

He is saying to start with 1 ohm, and make it less resistive (adding a parallel 1 ohm will make .5ohm) or starting with .1 ohm and adding, in series, more .1 ohm until you get the bass tuning you prefer.

Quote:
Sorry to invade a knowledgeable DIY forum with such ignorance, but I know your advice will be solid.
No apology necessary! We salute you with your quest for factual information, instead of audiophile hearsay...
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Old 20th November 2012, 04:46 PM   #12699
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My wild guesses were based on my previous setup. My attempt here was to create a Thevenin equivalent of the F2's current source configuration, which Nelson had written was the angel gifting the F2 (and my speakers) with its enhanced bass response. The F2J (mine) as well as the F2 is published as using three parallel three watt 47 ohm resistors; my geriatric brain figured a 15 ohm 10w piece.

My full range speaker is a Hammer Dynamics Super 12, a twelve inch unit with wizzer, and can usefully employ to good effect more damping than a smaller Fostex or Lowther, which is to say still hardly any, having been designed for .7 watt 45 amps. It sounds great on the F2J but I like the sound quality from the F5 much better. I am one of those "if it is on the recording I want to hear it" guys, so the F5 is heaven sent and heaven inducing for my listening. I wanted my cake and still wanted to eat it - the bass - too.

In any case, that is the ignorant process that hatched my ignorant estimates. BTW, if I need another F5 I will certainly build it. Between the boards and the enclosure you guys have essentially produced a kit amp. The stock F5 has more power than I could ever use, so I wouldn't need the enhanced versions. To paraphrase Mr Pass, did I mention I love the sound?

Last edited by 4345owner; 20th November 2012 at 05:09 PM.
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Old 20th November 2012, 05:13 PM   #12700
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I encountered enough people with the F1 (including reviewers) who seemed
dazed and confused by the notion of output loading, which is ok, unless they
are unwilling to try it to get the right output impedance for their speaker.

From experience, I figured that the maximum output impedance anyone will
want is probably 16 ohms or so, and so I put that in as a default value.

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