Masco MAP-120N

[baddog]

Perfect as always Enzo. I just wanted to make sure i didnt screw it up



thanks again to everyone
keith

[Dave Curtis, dB AudioTech]

Perfect as always Enzo. I just wanted to make sure i didnt screw it up



thanks again to everyone
keith

I'll add that if you increase the C9 or C10 cathode bypass caps, you may end up with too much bass, so like Enzo said, stick with 10uF there.

-DC

[baddog]

Thanks to everyone

I ordered new caps from Just Radios and cant wait to install them. It sounds pretty cool now and it can only get better. I think i might have a blown speaker though. When im in the high gain channel with the amp cranked i gan get a ringing ghost note at the 14th fret on the G string after i strike the note and stop . the speaker apears to be a newer blue fender 10" speaker .I did notice that the paper looked wavy near the dust cap on the back side instead of smooth. I dont now of this is normal or if the mounting surface is uneven . Any thoughts?

thanks again
keith

[Dave Curtis, dB AudioTech]

If the speaker is mounted too tight, it can warp the frame. Try either loosening it a bit, or unmounting it and see how it sounds. If you have another speaker cab, see how it sounds through that.

-DC

[Mars Amp Repair]

In the 'olden days', I always felt they used the smaller value caps they could get away with for cost but sometimes more for space. The caps (as you can see) were quite a bit bigger than they are today. Size/value was more an issue in the cap-can's or multi section caps like this amp seems to have, too.

Why they used 'oddball' values like 8uf, I don't know. That might have been what was 'common' then.

I agree that you certainly could use 10uf caps for all those filters. In the pic from schemo heaven, it looks like one of those multi section caps is just dangling.

glen

[baddog]

Hi everyone

Thanks for all of the advice. I changed C6,7,8 to 20uf and C9,10 to 10uf and it sounds great. I also changed the .005 caps to newer ones except the old square ones . The ghost notes are gone and now i get a rolling stones , beatles sound when cranked. the only problem i have is i still get static through the volume pot , when i crank the amp all the way up the static seems to go away somewhat. I ordered both audio and Lin 500k pots . What should i use in this amp audio or Lin ?

blues rock lives

Keith

[Dave Curtis, dB AudioTech]

the only problem i have is i still get static through the volume pot , when i crank the amp all the way up the static seems to go away somewhat. I ordered both audio and Lin 500k pots . What should i use in this amp audio or Lin ?

blues rock lives

Keith

Have you cleaned the pots, yet? Radio Shack has Caig products, last I checked... Deoxit, then MCL. If you've cleaned them and they're still scratchy, replacing is quick and easy (audio taper in this case), but the pot can often be repaired. A small tweak of the contact fingers that rotate on the worn carbon track inside can make an old pot new again. Over the years those contacts wear a groove in the track, causing noise as it's turned. If you're careful, you can move them just a tad to a new spot on the carbon track. It can be done without taking the pot apart, but it's more difficult.

Or just change it, but not before cleaning the old one.

-Dave

[baddog]

Hi

The noise coming from the amp is more of a buzz that gets louder when i turn the amp up but when i turn the amp up all the way the buzz mostly disapears . what could be causing this ? I did try cleaning the pots because they where scratchy when i bought the amp. it did clean up the scratchiness. I did install a grounded cord on the amp also.

thanks
keith

[Dave Curtis, dB AudioTech]

Sounds like a ground loop. Changing the pot won't help this. See this article: http://www.geofex.com/Article_Folder...nd/stargnd.htm

[baddog]

Dave

So the basic idea here is to remove the grounds from the chassy and have them meet a comon point. can you look at the schematic for this amp and let me now what i should hook to a common grounding point


thanks
keith

[Mars Amp Repair]

If this amp has not been updated to a 3prong grounded ac cord, have you tried turning the AC cord around in the socket?
]
You might just be dealing with the basic non-grounded chassis issue.

If it already has a grounded cord, then of course this idea won't apply. glen

[baddog]

HI

I have updated the amp to a three prong plug. I just soldered the line and the common to the places that i removed them from in the amp and put the ground to the chassy. I think that is correct.

thanks
keith

[Dave Curtis, dB AudioTech]

Dave

So the basic idea here is to remove the grounds from the chassy and have them meet a comon point. can you look at the schematic for this amp and let me now what i should hook to a common grounding point


thanks
keith

Here's a good read:
http://www.aikenamps.com/StarGround.html

[Dave Curtis, dB AudioTech]

HI

I have updated the amp to a three prong plug. I just soldered the line and the common to the places that i removed them from in the amp and put the ground to the chassy. I think that is correct.

thanks
keith

The hot incoming AC lead should be soldered to the rear of the fuseholder, then a wire from the other fuseholder terminal to the switch, then out of the switch to one tranny lead. The neutral solders directly to the other tranny lead.