Amp build for a first time builder?

[yoyohomieg5432]

ok the board is complete as far as what i can do without the remaining parts. the pics i attached are about 20 minutes before i finished. there were a couple other things i soldered on and i cleaned up those long wires on the back as well as trimmed up all of them throughout the entire board.

i also realized after taking this one of the caps was soldered on wrong. i fixed that afterwards

[yoyohomieg5432]

i have a question with the bassman layout. when looking at the inputs, are these from the perspective of looking at the outside of the amp? or if the chassis was face down and looking inside? the circuit board itself is from a perspective of looking face down, but I'm not sure for the input jacks. based on teh perspective i could be soldering the 1M resistors to the input jack with of channel '2' or '1'

another problem.. there's supposed to be a .1uF 200V cap for the presence that i don't have.. i have an extra .1uF 600V cap but the excel sheet says this is for the bass cap? im not seeing where this goes.

[tribi9]

You should clip off the ends of the components. If you do need to do any rework, (And believe me, you will) It will be a major pain in the ass to remove them from the board with ends angled the way it shows on your underside of the board pic.

[martin manning]

Can you post top and bottom side pictures of your board as it is now? I see a couple of things that don't look right, but maybe they are among the things you fixed.

[yoyohomieg5432]

Can you post top and bottom side pictures of your board as it is now? I see a couple of things that don't look right, but maybe they are among the things you fixed.

Martin, the person that has been taking pics for me isn't home now. I probably wont be able to get new pics til tomorrow. What else do you see? The only thing I fixed was the polarity on one of the capacitors (in parallel with the 47k)

[martin manning]

i have a question with the bassman layout. when looking at the inputs, are these from the perspective of looking at the outside of the amp? or if the chassis was face down and looking inside? the circuit board itself is from a perspective of looking face down, but I'm not sure for the input jacks. based on teh perspective i could be soldering the 1M resistors to the input jack with of channel '2' or '1'

In the layout the top and bottom panels are shown as seen from inside the chassis. Or in other words it's as if the chassis were opened out flat.

[yoyohomieg5432]

i have a question with the bassman layout. when looking at the inputs, are these from the perspective of looking at the outside of the amp? or if the chassis was face down and looking inside? the circuit board itself is from a perspective of looking face down, but I'm not sure for the input jacks. based on teh perspective i could be soldering the 1M resistors to the input jack with of channel '2' or '1'

In the layout the top and bottom panels are shown as seen from inside the chassis. Or in other words it's as if the chassis were opened out flat.

ok, so to double check, i'm soldering the 1M to the inputs of channel 1?

and a few pages back we were talking about mounting the tube sockets. you said that mojo should include hardware for this. and that i should use #6 and #4. all i have from mojo is this:

- "4-40 x1/4"
- "6-32 x 1/2" screws. it says they are for copper head baffle
-they gave me a bunch of 8-32 keps nuts but no screws...

can you explain what #6 and #4 is? If i go to the hardware store to get these they will be labeled #6? What length should i get?

[martin manning]

Can you post top and bottom side pictures of your board as it is now? I see a couple of things that don't look right, but maybe they are among the things you fixed.

Martin, the person that has been taking pics for me isn't home now. I probably wont be able to get new pics til tomorrow. What else do you see? The only thing I fixed was the polarity on one of the capacitors (in parallel with the 47k)

Here's a view of the board from the bottom. The two jumpers running transverse to the long dimension of the board from B+2 and 3 to the 4k7 dropping resistor are missing on yours. Also, I didn't see any electrolytic cap mounted the wrong way in the posted pic?

The 1M are on the #1 input jacks on channel 1 and channel 2, the ones closest to the open side of the chassis. Remember you can temporarily attach the jacks and pots on the outside to have better access. When you do that the 1M will go on the jacks closest to the closed side of the chassis so when you flip them over to the inside they will be in the right place.

Small screws are sized by a number in the English system. A #4 screw is about 3mm, and a #6 is about 3.5mm. You will find these in the hardware store, and they may be labeled 4-40 and 6-32. The 40 and the 32 are the number of threads per inch. I like 3/8" length to mount the tube sockets, but your steel chassis might be thin enough to use 1/4" for the 9-pin sockets.

[yoyohomieg5432]

Can you post top and bottom side pictures of your board as it is now? I see a couple of things that don't look right, but maybe they are among the things you fixed.

Martin, the person that has been taking pics for me isn't home now. I probably wont be able to get new pics til tomorrow. What else do you see? The only thing I fixed was the polarity on one of the capacitors (in parallel with the 47k)

Here's a view of the board from the bottom. The two jumpers running transverse to the long dimension of the board from B+2 and 3 to the 4k7 dropping resistor are missing on yours. Also, I didn't see any electrolytic cap mounted the wrong way in the posted pic?

The 1M are on the #1 input jacks on channel 1 and channel 2, the ones closest to the open side of the chassis. Remember you can temporarily attach the jacks and pots on the outside to have better access. When you do that the 1M will go on the jacks closest to the closed side of the chassis so when you flip them over to the inside they will be in the right place.

Small screws are sized by a number in the English system. A #4 screw is about 2mm, and a #6 is about 3mm. You will find these in the hardware store, and they may be labeled 4-40 and 6-32. The 40 and the 32 are the number of threads per inch. I like 3/8" length to mount the tube sockets, but your steel chassis might be thin enough to use 1/4" for the 9-pin sockets.

the 10u cap in parallel with 47k had opposite polarity to that in the schematic.

the two wires you are talking about i added after the pic was taken.

you may have missed this above, but i mentioend that i'm missing the .1uF 200V cap for the presence knob. i said i had a spare .1uF 600V from mouser that i'm not sure what is for. Can i use this for the presence? The spreadsheet says its for the bass cap but i'm having trouble locating where this would be used

[martin manning]

Judging from the size, it looks like the bass cap you installed on your board is a 0.1uF. No problem using the 600V for the presence cap. I had that on the Mouser list because it was a change from the Fender layout. Mojo may have shipped you a 0.1 for that location. If you don't have an extra 0.02uF then that is probably the case.

The diagram below shows the tone stack and PI in layout and schematic views with the parts we are talking about identified. These are some of the most-tweaked components in a guitar amp circuit of this type, and there are many of them that use this tone control and long-tailed pair inverter. Note that the presence pot is part of the PI tail in this version.

[martin manning]

A comment on your under-board wiring: Don't position the wires so that they pass directly under other eyelets. If they do, you run the risk of melting the insulation and causing a short when you are soldering leads from the top side. Also, move the 10uF bias cap away from the B+ eyelets. Maybe it's not as close as it looks, but its metal case could be common with its negative lead, and you don't want to accidentally melt through the plastic sleve.

[yoyohomieg5432]

A comment on your under-board wiring: Don't position the wires so that they pass directly under other eyelets. If they do, you run the risk of melting the insulation and causing a short when you are soldering leads from the top side. Also, move the 10uF bias cap away from the B+ eyelets. Maybe it's not as close as it looks, but its metal case could be common with its negative lead, and you don't want to accidentally melt through the plastic sleve.

hey Martin, that's a good point about the wiring, didn't think about that much. there should be a bit of slack so i can push it out of the way a bit.

went to radioshack today, they didn't have the pots i needed so im just going to build it with the pots i have now. down the road i can fix it if i don't like it as you said.

[martin manning]

Yes, it looks like you can probably just push those wires and the one cap over a bit. Radio Shack doesn't have much anymore, and the selection seems to be shrinking every year. There is no issue with the pots not working or affecting the sound in any way, just a different knob position to get a given effect, and maybe a bit more touchy to find what you are looking for.

Got your hardware? Figured out exactly what parts you still need?

[yoyohomieg5432]

Yes, it looks like you can probably just push those wires and the one cap over a bit. Radio Shack doesn't have much anymore, and the selection seems to be shrinking every year. There is no issue with the pots not working or affecting the sound in any way, just a different knob position to get a given effect, and maybe a bit more touchy to find what you are looking for.

Got your hardware? Figured out exactly what parts you still need?

i was going to get the screws today. i did the mouser order a few days ago but i picked the cheapest shipping option (economy shipping) and the predicted delivery date isn't til around the 5th for some reason. Hopefully it will be here sooner, the first mouser order was here within like 3 days but i did fedex ground and not economy shipping.

i've started wiring the potentiometers. i didn't do it outside like you said and now i see why that is much better to do. what's your advice as far as connections between the circuit board and pots. should i secure the board into the chassis then try to solder or just kind of lay the board on the bottom and solder to it?

[martin manning]

I've had pretty good results with the economy shipping, but I've noticed that the package takes a circuitous route, and the delivery time probably depends upon your location wrt the depot(s).

Some people like to attach all of the "flying" leads to the board first, mount it in the chassis, then route the leads and solder them to the chassis-mounted components. This means you have to make them long enough to get to where they're going, so you might have to lay the board in the chassis and roughly route the leads before cutting them to length. The leads that come from under the board will have to be done that way. If you have a limited amount of wire, you don't want to leave too much excess length either.

You can also mount the board with only the under-board leads attached, and solder the other leads to the pots etc. first, and then route them to the board, cut, strip, bend a hook in the end, and solder them to the eyelets. I do it this way frequently, but sometimes I need a third hand or use a weight to hold the lead down tight to the board while I solder it.

This chassis is pretty cramped so it might make sense to attatch most of the leads to the board first, but in the guide I suggested soldering the input leads to the input jacks first, since they are going to be hard to get to in that corner.