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Colorsound Power Boost Clone

Andy Betts

Hi guys,

 

Newbie to electronics.... so please be gentle with me :-)

 

I'm planning on reproducing a clone of the famous Colorsound Power boost, and have gathered together various bits and pieces to help me do this...... My intention is to clone the original PCB layout. I had originally posted some questions regarding the transistors and I had a lot of helpful info being passed back to me.... Thank you. I'm now at layout stage, and have happened across an issue with the schematic, either that or i have done something wrong in the schematic in Eagle.

 

IAt the moment I just can't get my head around what's wrong. I'll give you as much information as possible so here goes.........

 

below is the schematic that I'm working from......

 

 

 

Image

 

I've copied this faithfully into eagle, here is the Eagle reproduction

 

Image

And here is the board layout in Eagle from that schematic

 

 

Image

 

 

next we have a mirrored image of the actual PB PCB layout. I've scribbled onto it the location and value of the various components..... This was my aid when laying out the PCB in Eagle.

 

 

Image

 

 

I'm looking at the 2 4k7 resistors R8 & R9 on the Eagle schematic, on the board photo I've highlighted a track in yellow, on the schematic it would appear this is not correct. On the schematic it shows that track going to U$6 however on the actual board photo it's going to U$7.

Also on the photo the trace from the 22uf cap U$13, is going to resistor R8 and NOT R9 as it shows on the schematic.

 

The photo is correct, that we do know as this was from a working power boost from around 1970 and it's the same board layout they're using for the expensive reissues...... The schematic shows some issues but I can't get my head around what changes are required on the schematic to correct them.

 

I've been advised by the guy that wrote the schematic that the 2 resistors R8 & R9 are the wrong way round, if I swap around the two resistors R8 & R9 that will make the trace for pin 3 of the bass pot incorrect. At the moment the trace for pin 3 of the bass pot goes UNDER R8 to connect the top of R9... If I swap the resistors around that connection won't be correct. See the updated image below with the added trace for pin 3 on the bass, going to the top of the R9 resistor.... This is correct, however the other end of the R9 resistor should be going to U$7 according to the board but the schematic is saying it must connect to U$6 which isn't correct to the original board layout.

 

Also the negative end of U$13 according to board layout should connect to R8.... But the schematic is saying it's got to connect to R9.

 

The resistors are in the correct place when you look at the other connections and where they're going........ Something is not correct according to the original board layout.....

 

 

 

  • 0

    I think you just need to mirror the bass pot so that pin 1 connects where pin 3 is and vice versa. Then you'll be able to place and route the resistors like the original. (The CW arrow on the pot needs to face the input signal from U$5 like the one on the treble pot does.)

     

    It would be a good idea to connect pins 1 and 2 of the 'volume' pot on the schematic. I can see you've done it on the layout, but if you do it on the schematic too it won't flag it up when you come to do error checks on the board.

  • 0

    Many thanks for the speedy reply Jon,

     

    Firstly, pins 1 & 2 on the volume pot...... Agreed. Forgot that on the Eagle schematic, it's on the original. I'll sort that when I get home.

     

    Secondly your suggestion regarding mirroring the bass pot....... If I mirror the bass pot and swap the pins around won't that screw up the connections at pin 1 going to U$8 and R8. At the moment those connections are identical to the board photo, that's where my confusion is. The connections at the top of R8 & R9 are correct to the photo, so i don't understand why the connections at the bottom are incorrect unless the schematic is wrong to the photo. Also the original board used the same pots for both bass and treble.... Therefore the pins are in the correct place as per the original board.

     

    I think the schematic needs tweaking..... At the moment it's not correct to the photo of the board.

     

    I think i'll make copies of both the schematic and PCB eagle files, and have a play and see what I come up with...... If I get something that looks right i'll post the schematic for your perusal.

  • 0 in reply to Andy Betts

    Imagine you swap 1 and 3 on the schematic. The physical placement of those pins on the PCB stays the same. So you'll rotate U$8 through 180 degrees on the layout to get its pins into place and physically swap R8 and R9. Then it will route as the original.

     

    The schematic has the clockwise rotation of the pot wrong.

     

    An alternative way to swap it is to leave the pinning of the pot alone and connect R8 to U$13 and R9 to U$5. That achieves the same thing except that the schematic, once you've straightened it out, will have the idents for R8 and R9 swapped. You can do it that way too because of the symmetry.

     

    Make a copy of what you've got now and then try it and see.

  • 0 in reply to jc2048

    Aaaaaaaaaahhh... I see what you mean. Let me have a look tonight, and i'll let you know how it goes. I had a suspicion there was something wrong with the schematic, and I'm a newbie.

     

    I know the photo is correct... It has to be so there had to be something wrong with the schematic.

  • 0 in reply to jc2048

    Jon, tried mirroring the bass pot to switch the pins on the schematic..... it didn't make any difference at all. U$8 is NOT polarised so wasn't affected by me switching the pots pins... consequently neither were R8 & R9 they are the same value. i'll try your other suggestion of changing the connections in the schematic.

  • 0 in reply to Andy Betts

    Jon, I have now finished re-laying out the schematic.... I removed all the pertinent connections and then methodically connected them one at a time referring to the photo all the time. I now have a PCB layout that is exactly the same as the original board.... however to get there the schematic looks messy. Here they are....... Let me know your thoughts regarding the schematic etc

     

    image

     

    image

  • 0 in reply to Andy Betts

    If you mirror R8, R9, U$8 and the bass pot, swap the positions of R8 and R9, and untangle the nets, you'll get this

     

     

    image

     

     

    which is back to the conventional way of drawing Baxandall's tone control.

     

    The 4.7uF for U$10 rolls off the bass response below about 100Hz for the level response (bass pot halfway). If you want the bass response to extend flat further down you'd need to up the value to 10uF or even 22uF. Whether it's a problem, I don't know. It looks like it certainly would be for a bass guitar if the lowest open string is E1 (41.2Hz). It would also have a bit of an effect on a six-string guitar if the lowest open string is E2 (82.4Hz). [I'm unsure about the notes and frequencies there - I'm sure you know more about guitar tuning than I do.]

  • 0 in reply to jc2048

    Thanks Jon, once again for your time with this..... All the way this is a learning curve for me and I appreciate all you're doing to help :-)

     

    Anyhow, onto the issue in hand. I re-laid out the schematic as you've suggested.... Here is what it looks like:

     

    image

     

     

     

    And it worked........ Many thanks Jon for your time, I've learned a lot. :-)