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SLO-100 Clone - To PCB or not...


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9/14/2000 3:50 AM
Jeff Stapleton
SLO-100 Clone - To PCB or not...
Hey guys,  
 
I have a hombuilt SLO-100 and have been having annoying hum problems since I finished it. I have done the star ground thing, etc.  
 
I have started to think about completely redoing it to be pretty much an exact clone of the real SLO-100 (only 50 watts). I have a number of pretty detailed photos of the innards, including closeups of the boards.  
 
So, I pose a few questions:  
 
- How difficult would it be to do a copy of the PCB's with the identical layout?  
 
- If not doing a PCB, assuming I would use a phenolic board and either turrents or rivets, how possible would it be to still duplicate the layout, but substitute wires for traces (seems tough)?  
 
- I have never done a PCB. Is this a huge deal or what? Are there others here that would be interested in a PCB for the SLO?  
 
Thanks,  
 
Jeff
 
9/14/2000 1:42 PM
Joe L

quote:
"- How difficult would it be to do a copy of the PCB's with the identical layout?"
 
 
A full copy with an etched pcb is possible but is going to take some work laying out because of all the pad spacing. You will need to get the components in and doing some measuring or just photographically copy the existing board pics and bend the leads to fit the spacing of the pads.  
 
quote:
"- If not doing a PCB, assuming I would use a phenolic board and either turrents or rivets, how possible would it be to still duplicate the layout, but substitute wires for traces (seems tough)?"
 
 
Been there, done that! It's a piece of cake. I just took the clearest pic of an SLO pc board that I had and corrected it for perspective and scale and used it as a drill pattern. I glued the pic to a sheet of fiberglass and drilled holes where all the pads were except for where a wire was connected to a pad right next to a component in which case I just put one rivet and shared it between the component and the wire. I have already traced out the pcb so I knew what went where so it was just a matter of adding the rivets, components and wires between pads. It doesn't make the best looking board but its easy to do and should outlive us :)  
 
The amp I used this circuit board in is the Bassman/SLO clone. I was able to easily wire in the board even though the pots are on the opposite side from where a real SLO has them. The wires are a bit longer but I had no problems whatsoever with stability. I only have a couple of shielded wires in the preamp and the only hum I have problems with is noise from the switching circuit in Clean mode althought it is way less than what my still factory Marshalls do at stage volume.  
 
If you trace out the SLO pcb, you will find that they use a buss type grounding scheme. The ground trace starts under the two 10uF supply caps and works it's way from front end to PI exiting at the power supply end of the board. I was able to quieten down my version some by running separate wires for a few subsections. That was easy to do with the rivets and due to the fact that I kept all wiring except the switching on top of the board. It wasn't the best for looks but it's all rock and roll anyway :).  
 
quote:
"- I have never done a PCB. Is this a huge deal or what? Are there others here that would be interested in a PCB for the SLO?"
 
 
It's not terribly hard, but I wouldn't mess with it unless I was building a bunch of amps and I have the design as _I_ am going to build it, totally debugged. Even though I used the exact physical layout of the real thing, I still was able to improve on the grounding and the parts layout around V2 on my version. I'd hate to give up the ability to mod the layout once the board is wired in.  
 
Are you sure you can't get any more hum out of that thing? Did you try running a separate transformer for the LDR supply like we have discussed in the past? I still feel that using the filament windings in double duty as the LDR supply prevents you from being able to fully balance the filament AC and causes hum. My Marshall/SLO is almost dead quiet and it has a separate transformer, the Basman/SLO isn't and shares it.  
 
Good luck with it Jeff!  
 
..Joe L
 
9/14/2000 6:30 PM
Jeff Stapleton

Hey Joe,  
 
I guess you have a new email address!  
 
I read your reply to me, and I wonder if you could sent me the newest board layouts for your SLO that you were referring to. I agree that a PCB would be a pain.  
 
Now, considering you put the board into a pre-existing chassis, did you have to change the board size, or did you make it identical in size to the original SLO?  
 
I'm also assuming you did not make a power supply board, correct?  
 
Any pics and layouts would certainly be mucho appreciated.  
 
Basically I'm at the point of seriously thinking my layout is causing some coupling, and I think the tone may suffer as a result of the dual tone stack arrangement. I am considering a complete rebuild, new chassis, no tube recto, single tone stack, original switching scheme, etc., and using the original SLO layouts, including the bus grounding and bussed filaments.  
 
Thanks man!
 
9/14/2000 10:40 PM
Joe L

quote:
"I read your reply to me, and I wonder if you could sent me the newest board layouts for your SLO that you were referring to. I agree that a PCB would be a pain."
 
 
Already done by email.  
 
quote:
"Now, considering you put the board into a pre-existing chassis, did you have to change the board size, or did you make it identical in size to the original SLO?"
 
 
I tried to make it the correct size, but it's just guesswork working with a schematic. Since I knew the exact size of the LDRs, I used them to get the scale of the board and corrected the perspective and resized using Paintshop Pro.  
 
quote:
"I'm also assuming you did not make a power supply board, correct?"
 
 
Hehe, you know me :) I just used the Bassman power supply board and adjusted capacitors and resistors to give me the correct voltages.  
 
quote:
"Basically I'm at the point of seriously thinking my layout is causing some coupling, and I think the tone may suffer as a result of the dual tone stack arrangement. I am considering a complete rebuild, new chassis, no tube recto, single tone stack, original switching scheme, etc., and using the original SLO layouts, including the bus grounding and bussed filaments."
 
 
Sounds like a lot of work! Are you going to reuse your transformers or buying new ones?  
 
I think if you have any coupling problems, it will be at the section between V2a and V2b. And if you do like I did and move the plate resistor, coupling cap and grid resistor to the tube socket, most of your coupling problems will go away. That area is hot as hell with p/p signal levels of ~150vac and anything you can do to move it away from everything else is going to improve the tone and bleedover into the clean channel. My Mid control was very critical and peaky until I made the modification even on the amp with the same layout as the real thing.  
 
 
..Joe L
 
9/14/2000 7:36 PM
Jeff Stapleton

Joe,  
 
Another thing: after examining the SLO closeup pics, they only show 3 200uF/300V caps. I can't figure this out. The schem calls for 6 total. What's up with that? These are not some weird multi-section caps, are they?
 
9/14/2000 9:23 PM
Craig D

Jeff,  
 
I am preparing to build a SLO clone. I was planning on doing the dual tonestack thing as you have done.  
You think this is causing some tonal problems? What are you experiencing?  
 
I also thought that there were just 3 filter caps, until I read the description at the bottom of the page on Joe's site. The other 3 caps are under the board. You can see the leads where they come through the top of the power supply board if you look closely.  
 
see ya  
 
Craig D
 
9/14/2000 10:42 PM
Joe L

Craig is right of course, there are 3 more caps under the power supply board.  
 
..Joe L
 

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