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Ok, how about using a multi-meter to check/set bias on MA1's?

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Posted on August 3, 2009 at 13:37:11
marc g.
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 Can it be done and if so, how exactly is it done? What setting should the meter be set at? Just wondering if I can get things set more accurately with a digital meter as I do with the DC offset. Thank you.

marc g. - audiophile by day, music lover by night
RE: Ok, how about using a multi-meter to check/set bias on MA1's?, posted on August 3, 2009 at 19:43:35
baileyler
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Posts: 102
Location: Chadds Ford, PA
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 I am assuming yours is an older version without autobias.

If it is, and is like my M-60 (Mk 1), there is a switch which in the up position is for D.C. Offset, and in the down position is for Bias. I also have a second switch which in the up position is for Operate, and in the down position is for Test. Put a DC ammeter across the speaker terminals, leave the Operate/Test switch at Operate, and push down the other switch to Bias. Your meter will then show the bias.

RE: Ok, how about using a multi-meter to check/set bias on MA1's?, posted on August 4, 2009 at 08:14:14
marc g.
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 Correct. No auto-bias here. These are from 1999 and have the four input tubes.

I'm a bit confused about the switches you refer to on your M60 even though I'm pretty familiar with them as a friend has a pair.

Besides my Standby and Full Power Up switches, there are two other toggles: one for DC offset and the other for the bias. I obviously don't use the DC offset toggle for DC offset as I just use the meter on the speaker terminals. For setting the bias, I have to depress the DC offset toggle followed by the bias toggle before adjusting bias.

Let's see if Ralph chimes in (I asked him to). Thought others might be interested in doing it this way but maybe I'm wrong. Maybe I'll find the built in meter is very accurate?

marc g. - audiophile by day, music lover by night
RE: Put the meter across the speaker terminals, posted on August 4, 2009 at 12:23:55
Ralph
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 And depress the Bias Test switch. Presto- there's your reading.

I usually test and set DC Offset first, if the amp has already been set up.

I must be doing something wrong..., posted on August 13, 2009 at 07:37:50
marc g.
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 I'll have to get a hold another meter (or learn how to use mine better) as I get no reading at all with the meter set to milliamps when checking bias. Also, my DC offset is always 0.000 - which seems too good to be true! Something is amiss here...
marc g. - audiophile by day, music lover by night
Update., posted on November 10, 2009 at 15:10:01
marc g.
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 Learned one has to use the unfused positive post on the meter for bias. Works like a charm now.
marc g. - audiophile by day, music lover by night
If the amp works, posted on August 13, 2009 at 09:08:00
Ralph
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 Then I would check the protection fuse inside the meter!

Blown it was!, posted on August 13, 2009 at 22:08:03
marc g.
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 Couldn't tell the fuse was blown by looking at it as the casing is solid white, but I did substitute it with the spare Radio Shack so thoughtfully included inside the meter and...

Now I get DC offset readings, readings that make sense. Got em' dialed to almost .000 with minor fluctuation.

Bias is a different story as I don't get any readings that resemble the .75 reading I'm looking for... I have to assume I'm not using the meter correctly but will try again tomorrow, with a different meter as well.

marc g. - audiophile by day, music lover by night
Thanks Ralph, appreciate that! (nt), posted on August 4, 2009 at 15:27:22
marc g.
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 .
marc g. - audiophile by day, music lover by night
RE: Ok, how about using a multi-meter to check/set bias on MA1's?, posted on August 4, 2009 at 11:03:04
baileyler
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Posts: 102
Location: Chadds Ford, PA
Joined: January 17, 2007



Here is a photo of the front panel of one of my blocks. They are original M-50s upgraded to M-60 (modified Mk 1).

All I do is push the bias toggle down and measure.

RE: Ok, how about using a multi-meter to check/set bias on MA1's?, posted on August 3, 2009 at 14:23:24
Lew
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Location: Bethesda, Maryland
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 I am absolutely sure it can be done, but I don't know how to do it, since I don't own an MA1. You should ask Ralph. But don't MA1s have a meter on the front panel for this purpose?

RE: Ok, how about using a multi-meter to check/set bias on MA1's?, posted on August 4, 2009 at 08:04:55
marc g.
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Posts: 2336
Location: New Orleans
Joined: October 14, 1999
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  Since: July 8, 2000
 Yeah, there's a meter but just thought a digital readout would be more accurate. I emailed Ralph and asked him to reply here for the benefit of others - if they are interested.
marc g. - audiophile by day, music lover by night

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