Monoprice 5 watt chassis removal

[JSMac]

Has anyone here pulled the chassis from one of these? It should be simple. It has the typical four screws on the top and one on each side. with those removed the chassis moves up and down but something is keeping it from sliding out.

I thought that maybe the faceplate was attached to the cabinet so I removed the nut's that secure the controls. No go. Then I found a pic of one that was removed and saw that the faceplate should pull out with the chassis.

Any clues?

 

[doof]

It's been a while since I took the chassis out of mine, but if I remember correctly, it really was just the 6 screws. I think I had to give it a good push to actually remove it as the deformed steel around the screw holes of the chassis was getting caught on something in the cab. But with the rear panel removed, everything should just push out towards the rear.

 

[JSMac]

That's what I was thinking. I tried a little prying to free it from any material around the mounting holes but no luck. I'll see if I can get something thinner in there. Maybe a table knife. Definitely feels like it is is still mechanically attached and not just wedged between the top of the baffle and the cab.

 

[Chiogtr4x]

Has anyone here pulled the chassis from one of these? It should be simple. It has the typical four screws on the top and one on each side. with those removed the chassis moves up and down but something is keeping it from sliding out.

I thought that maybe the faceplate was attached to the cabinet so I removed the nut's that secure the controls. No go. Then I found a pic of one that was removed and saw that the faceplate should pull out with the chassis.

Any clues?

Just curious as I own this amp. ( a Christmas gift to myself)

Why do you want to take the chassis out?

 

[JSMac]

I got it. It took more prying and tapping than I was comfortable with but it did come out.

 

[JSMac]

Just curious as I own this amp. ( a Christmas gift to myself)

Why do you want to take the chassis out?

I'm going to experiment with some mods. I learned that the negative feedback loop uses a 220 ohm resistor. I'm going to experiment with different values. Maybe start with a more typical 22k ohm like a Champ uses.

Them I'll compare it to the tweed Champ circuit and see if I want to change anything else.

 

[doof]

I put an NFB switch in mine, and modified the 22k resistor in the NFB circuit. Using an ON-OFF-ON DPDT switch I have values 22k, 46k, and the centre position disconnects the NFB. It's a fun mod that makes a noticeable difference right away, but also increases the background hiss quite a bit. Still, I totally recommend doing it.

 

[JSMac]

Cool, thanks. Just waiting for my wife to get done giving piano lessons then I'll experiment with the values that you mentioned.

 

[Tarkus60]

Cool ...keep us updated. I love mine. I did change my valves out to a vintage GE and ELectro harmonix.

 

[Maguchi]

Has anyone here pulled the chassis from one of these? It should be simple. It has the typical four screws on the top and one on each side. with those removed the chassis moves up and down but something is keeping it from sliding out.

I thought that maybe the faceplate was attached to the cabinet so I removed the nut's that secure the controls. No go. Then I found a pic of one that was removed and saw that the faceplate should pull out with the chassis.

Any clues?

I know they've gone up in price a little, however I paid like $115 for a new one a coupla years ago. So they're kinda like disposable to me. Rather than take it apart, I'd toss it in the trash and buy a new one.

 

[JSMac]

I know they've gone up in price a little, however I paid like $115 for a new one a coupla years ago. So they're kinda like disposable to me. Rather than take it apart, I'd toss it in the trash and buy a new one.

Except that I like to tinker and what better amp to do that on than one that me cost $114?

 

[JSMac]

Well, so much for the internet. After watching a vid on the NFB mod I went to work. Changing the value of the resistor or taking it out of the circuit completely made zero difference.

A little research found that the 220 ohm resistor shown in the video is not part of the NFB circuit. It is for protection at the external speaker jack and should be left in place. I must say that the placement of it didn't look right. why would it be mounted on the same board as the output jack? But, I continued anyway.

The actual NFB resistor in the Monoprice 5 is 33K. Good enough for me. I'll resolder the 220 ohm R and call it good.

I need to get better at following PCB circuits without a layout. Or better yet, I should quit messing with that stuff and stick to point to point construction.

Anyway, no harm done and beware the net.

 

[JSMac]

FYI, I found a nice schematic that someone drew. It clearly shows a 33K in the NFB loop and the 220 ohm across the extension speaker jack. Wish I would have found that before I followed the erroneous advice that I found online and wasted a bunch of time.

No one to blame but myself.