Covington Fireplace Ultra Treble Booster Trace

[anotherjim]

The pot will be noisy as it will change the DC conditions for the transistor. Usually, volume & tone pots are isolated by capacitors from the DC levels of amplifiers, but that can't be done with this configuration.

[nickbungus]

Thanks Jim.  Shame.  Could I not put a fixed value resistor (or jumper) where the pot should be and then just put a pot on the output for volume control?

Strangely, with the pedal engaged I was getting a crackle when using my guitar volume pot too.  This could just be the guitar pot although I wasn't getting this when bypassing and I've never noticed it before on this guitar.

[Gus]

Nick

Read the last part of reply 33 for a way to add an output volume like a RM uses

[nickbungus]

Thanks Gus.  On post 33, you have two options which sort of confused me. 

Which do you recommend and I will build it.  Sorry, I'm a bit thick.

Thanks.

[anotherjim]

I'm afraid blocking caps don't cure noisy pots, but without them, you might see your speaker cone being kicked all over the place as you turn the control.
But it can be a sign the blocking (aka coupling) cap has a leakage path around or inside it. Easy check for an input or output cap is to measure for any voltage other than zero on the socket tip.

[nickbungus]

I designed this as part of a discussion for another thread but its worth adding the image to this one too.

[skycef07]

hi do you have wiring diagram for programmable looper for 6channel?

[skycef07]

i found this on google

[Bolty_Guitars]

Hi,

Sorry to butt in on this older thread but it seemed so relevant that I thought it was better to post on this one rather than start a new one.

I've been fascinated with the red special since a young age and I've now got myself an AC30 and a BM guitar. Rather than spend $150 on a pro made booster I thought I'd try the "Brian May Treble Boost", and this "fireplace Covington" version of it. I've now completed both examples and have some questions!

The main differences between the two schematics are the additional 1M resistors which are doing nothing and then there's a pull down resistor (150k) and a 4n7 cap to ground on the output of the Fireplace Covington one.

Does this 150k resistor and 4n7 cap do anything? As both boosters sound practically exactly the same! I was planning to etch a PCB as opposed to Veroboard and wanted clarification before setting to work!

Thank you very much in advance.

Bolty.

[nickbungus]

I've made a much smaller pcb layout for this.  I just cloned what I saw and there were some odd resistors and caps in parallel but for the sake of mojo, I've kept them in but obviously they can be omitted.

Board size is 43mm x 20.5mm   (I dont understand inches)


            
C1   22pf                                      
C2   47uf                                  
C3   10nf                                  
C4   47uf                                      
C5   1nf                                  
C6   47nf            
C7   4n7        

R1   4K7        
R2   100ohm
R3   100K
R4   1M   
R5   120k
R6   1k
R7   22k
R8   2k2
R9   1M
R10   150k
R11  6k8

VR1   10k      
      
Q1   BC182      

[Bolty_Guitars]

That's a great layout, so thank you for that.

(I work in mm as well as inches Nick as I'm UK based  )

[Bolty_Guitars]

Just out of interest also: this Brian may booster/Fireplace booster sounds remarkably like a very famous 1983 TB don't you think?

[nickbungus]

I'm pretty sure it's a clone of the tb83.  I think the extra parallel resistors were added by Greg Covington to try and reduce switching noise but I'd love to open an original and find out.

[crillev]

@Nickbungus.
Hi,
Looking at your latest PCB from Feb 27, it seems to me that VR1 pads are missing.
Or are you giving us the option to use R11 or VR1 in the place for R11?
Cheers / Chris

[nickbungus]

Good question.   I've replaced it with the 6k8 fixed resistor as you noticed.  Yes you can put the pot there but it's noisy when you adjust. I've been adding a 10k pot at the end of the signal.  This can be seen on the vero layout.

[Bolty_Guitars]

Question for Nick!

If I wanted to create an "insane" booster, and by that I mean one which uses this circuit but has a shed load more gain, would I reduce the resistance of the 6K8 resistor going to the collector leg or would I reduce the resistance at the 2k2 on the emitter?

[nickbungus]

Dont ask me, I dont have a clue!!  I can barely tie my own shoelaces.

Serious, sorry, I dont  understand it.  I just like soldering and making layouts.  I can understand a schematic and can convert it to a layout but thats about it.

Hopefully, some other kind fellow on here can help?

[Cozybuilder]

Question for Nick!

If I wanted to create an "insane" booster, and by that I mean one which uses this circuit but has a shed load more gain, would I reduce the resistance of the 6K8 resistor going to the collector leg or would I reduce the resistance at the 2k2 on the emitter?

Look at Gus' reply #33 first. You can reduce the 2K2 on the emitter (R8) and adjust the collector to give a proper bias (DC gain is about VR1/R8). You can also reduce R6 (1K) to get a stronger input signal- depending on pickups you will probably increase distortion though. This could be tamed somewhat by replacing R8 with the outer legs of a C1K pot and placing the 47uF cap on the wiper. If the 1K resistance is too low, add some between the pot and ground.

[Bolty_Guitars]

Thank you - I've checked reply 33 just now. I've already done away with the potentiometer VR1 and made it a fixed 6.8k resistor. I'm not sure I understand what Gus means by "you can replace R10 with a 100KA on top of a 47k" - isn't that just making near enough 150k as per R10 originally?

[Cozybuilder]

R10 is the 150K just before the output jack. By replacing it with an A100K pot on a 47K to ground (lug 1 to the 47K, lug 3 to the transistor collector, lug 2 to the output), you have the same max volume potential, but the ability to turn the vol down.

If you leave the VR1 in place at the collector to 9V rather than replacing it with a fixed 6K8, you can tweak your bias, which is important when playing with different emitter resistors.