Hi,
I've recent bought an used amplifier, MAC Audio 4000D, 4x150W 4om, and i am a bit concerned about something.
If i set the gain by multimeter, i get different values between ch 1 and ch 2.
For example i've set gain for ch1+ch2 24.13V, multimeter cables in ch1, and i measure 25.47 V on Ch.2. So a difference of 1.34V in the output.
I've set gain for ch 3 + ch 4 and they bot stay the same 23.94V set on ch3 and ch4 also got 23.94V (equal)
Also, if i touch the Full/LP/HPswitch the amp kind of goes to the other setting. For example if it's in HP and i touch the switch (but not moving to select) it switches to LP (being the nex select position), but only touching or moving a little little bit with a screw driver's head.
Is this a thing to concern for getting different power to ch 1 and 2?
Should i get back to the seller and sort things out probably if he agrees to get my money back?
Thanks
I've recent bought an used amplifier, MAC Audio 4000D, 4x150W 4om, and i am a bit concerned about something.
If i set the gain by multimeter, i get different values between ch 1 and ch 2.
For example i've set gain for ch1+ch2 24.13V, multimeter cables in ch1, and i measure 25.47 V on Ch.2. So a difference of 1.34V in the output.
I've set gain for ch 3 + ch 4 and they bot stay the same 23.94V set on ch3 and ch4 also got 23.94V (equal)
Also, if i touch the Full/LP/HPswitch the amp kind of goes to the other setting. For example if it's in HP and i touch the switch (but not moving to select) it switches to LP (being the nex select position), but only touching or moving a little little bit with a screw driver's head.
Is this a thing to concern for getting different power to ch 1 and 2?
Should i get back to the seller and sort things out probably if he agrees to get my money back?
Thanks
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That's a difference of 1/2 decibel and inaudible.
The difference could be from variations in the two sections of the potentiometer... or from differences in the precise values of corresponding components between the two channels.
If the other two channels are precisely the same, it's random chance and very rare.
The difference could be from variations in the two sections of the potentiometer... or from differences in the precise values of corresponding components between the two channels.
If the other two channels are precisely the same, it's random chance and very rare.
I've seen this difference for example in JBL GTO 75.4 i've had for a couple of weeks but didn't cared about it because a mate wanted the amp so i've gate it to him since it had less power and not so great signal ration and THD
Ch 3 and 4 are dead spot on 23.94V both.
Ch 3 and 4 are dead spot on 23.94V both.
Read the following page, specifically the section you'll find by doing a ctrl-f search on the page. search for:
It may look like the curve in Figure R4-7
Potentiometers – Basic Principles – Passive Components Blog
Potentiometers are FAR from perfect.
It may look like the curve in Figure R4-7
Potentiometers – Basic Principles – Passive Components Blog
Potentiometers are FAR from perfect.
Thanks, maybe also being a little older amp and used by multiple people can get a bit loosy.
My new amp (even though it's a low budget Edge Amp) is very stiff.
I'm curious just what these voltages actually are that you are measuring and how you are coming to a conclusion that the levels are different.
Are they AC signal voltages across a test load impedance or something else?
Are they AC signal voltages across a test load impedance or something else?
That has nothing to do with the potentiometer tracking, it's just the damping grease that's been pushed out in the older pots. When new they feel stiff, as they get use the grease moves and is pushed out.
