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Old 4th March 2012, 05:13 PM   #1
SoIL4x4 is offline SoIL4x4  United States
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Default Integrated dual mono lm4780

Hello all, I would like to begin by thanking all of the people who contribute valuable information to this site. I would never have reached this point without stalking your build threads. As the thread title suggests I am in the process of building a dual mono lm4780 integrated amp. I am close to completing my enclosure but before I drill the last few holes and wire everything together I have a question. From the attached photo you can see that I am using an extension rod from the faceplate of the amp to the rear to connect the volume knob with the pot. My questions is with the faceplate being aluminum and the shaft being aluminum do I need to electronically isolate the connection of the shaft to the pot? I spent the morning digging through posts about shaft extensions but did not find this brought up anywhere. Is there any chance of noise especially with the proximity of the shaft to the transformers? Am I just overthinking this since many builds have the pot mounted directly to the faceplate.

Here is a little info on the parts
Audio sector boards
Antek an 3222 transformers
Cardass connections
Heatsink usa heatsinks
A pile of scrap aluminum
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Old 4th March 2012, 05:26 PM   #2
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There is no electrical connection between the shaft and the signal-carrying parts of the potentiometer, so no additional isolation is necessary.
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Old 4th March 2012, 06:06 PM   #3
SoIL4x4 is offline SoIL4x4  United States
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Thanks pacificblue. I thought so but wanted to make sure before I made a simple mistake.
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Old 4th March 2012, 10:01 PM   #4
AndrewT is offline AndrewT  Scotland
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Ensure the metal volume control knob is effectively earthed via the chassis.
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Old 4th March 2012, 11:35 PM   #5
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Very nice! the only thing I would change is those tiny power supply caps...try to use more capacitance for power supply. I build the LM3875 from Audiosector long time ago and I try many caps for power supply and they sound way better with at least 10.000uf per rail.

Last edited by lanchile; 4th March 2012 at 11:43 PM.
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Old 5th March 2012, 12:40 AM   #6
SoIL4x4 is offline SoIL4x4  United States
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Thanks Andrew, yes the knob is connected directly to the aluminum extension shaft which rotates on a metal bearing that is directly connected to the faceplate. The entire path from the knob to the star ground is aluminum.
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Old 5th March 2012, 01:14 AM   #7
SoIL4x4 is offline SoIL4x4  United States
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Lanchile, thanks. I am curious about larger caps as I have seen many of other builds that have much larger caps. These are the supplied caps from audiosector(1500uf). Being that this is my first build I don't necessarily know what to expect from larger caps. Deeper bass? Anyway I had planned on using these initially and experimenting later with different values. But, if upgrading now based on the speakers I plan on using would be a good idea then I would rather do it now while it is easier to get at. I will be alternating between two sets of speakers now and maybe another diy pair (I can't decide what, but would like to include diy heil amts) they are klipsch kg4s 4ohm and ess amt monitors 6ohm. Thanks in advance!
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Old 5th March 2012, 02:54 AM   #8
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Quote:
Originally Posted by SoIL4x4 View Post
Lanchile, thanks. I am curious about larger caps as I have seen many of other builds that have much larger caps. These are the supplied caps from audiosector(1500uf). Being that this is my first build I don't necessarily know what to expect from larger caps. Deeper bass? Anyway I had planned on using these initially and experimenting later with different values. But, if upgrading now based on the speakers I plan on using would be a good idea then I would rather do it now while it is easier to get at. I will be alternating between two sets of speakers now and maybe another diy pair (I can't decide what, but would like to include diy heil amts) they are klipsch kg4s 4ohm and ess amt monitors 6ohm. Thanks in advance!
Are the 1500uf caps on the power supply board or on next to the chips? Because I remember when I ordered from Peter Daniel (Audiosector) the power supply caps were really small, I think they were 10uf or so. anyways, With more capacitance you will "feel" the bass. I tested many values from 10uf to 20.000uf per rail with alligator jumpers (easy to change caps) and above 10.000uf I noticed big improvement with bass. if you have spare caps just try with alligator jumpers.

Never mind!!! I just checked it at Audiosector and the 1500uf are on the chip boards. What I would do is lower those 1500uf and use 6.800uf X 4 on the power supply, also I would use .01uf under each diode (power supply), also I would put good quality input caps.

Last edited by lanchile; 5th March 2012 at 03:04 AM.
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Old 5th March 2012, 02:56 AM   #9
AlexQS is offline AlexQS  United States
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I'm thinking of same thing. My audiosector kit is almost done too.

Is it better to jumper-together several smaller caps as opposed to using 1 or 2 big ones?

You're right. P Daniels is still supplying 10uF for power supply and 1500uF caps on amp board

Last edited by AlexQS; 5th March 2012 at 03:03 AM. Reason: Two people post at same time
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Old 5th March 2012, 03:07 AM   #10
AlexQS is offline AlexQS  United States
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BTW SoIL4x4... Meant to say I really like your chassis. Looks like a clean, smart layout. Awesome job! -especially for your first. Let us know how it sounds when your done.
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