DIYstompboxes.com

Hi All

As mentioned on another post, I recently repaired a Covington Fireplace Ultra Treble Booster for a friend.  While I had the pedal I took some gutshots with a view to do a trace.  Never done it before so I thought it would be good fun!

I do have a couple of questions but here are some images of where I am currently.

(http://www.dirtmonkey.org/cov/IMAG1127.jpg)
(http://www.dirtmonkey.org/cov/IMAG1125.jpg)



This is what I'm seeing but the signal path doesn't seem right and neither does the powering of the transistor.

(http://www.dirtmonkey.org/cov/CovingtonTB.jpg).

Lastly, I have a couple of mystery cap values:
(http://www.dirtmonkey.org/cov/MysteryCaps.jpg)

I'm guessing the 2A102G is a 1n but the .01K 50/100 one has me baffled.

The circuit does seem very similar to the Greg Fryer Treble Booster (http://3.bp.blogspot.com/-4oHazSc9raE/UUmpFRFwv7I/AAAAAAAAAgw/sL0s6upmmxg/s640/Greg+Fryer+Treble+Booster+Deluxe+Schematic.jpg).

I'm pretty sure that's .01uF:

http://www.diystompboxes.com/smfforum/index.php?topic=76079.0

102 should be .001uf.

The .01 is just a .01uf.

Brilliant.  Cheers guys.  Caps sorted.  A 1n and a 10n (0.001uf and a 0.01uf).

Does the trace look right?

Like there's a 100ohm resistor between the 9Vdc and the signal out?  Also, I'd expect the transistor to be a bit more directly linked to the power?

Without knowing enough, I just feel there's a mistake somewhere on my trace.

bungus - I don't think the "out" should connect to the 9V via a 100R, it don't sit right, somewhere. can you draw the circuit out for us? liberal use of the ohm-meter is allowed.

can we see the pot wiring/off boards as well?

Cheers Ducky.

It doesn't look right to me either and I'm an idiot.  I did intend to draw it out properly and then create a PCB layout but the fact that my trace doesn't look right is making me hesitant.

I'm pretty sure I am missing something (or I've added something) in the copper trace.

you draw it, we'll poke at it (also, like idiots). then worry about the pcb.

Okey dokey ducky.  I'm actually starting to suspect I've got the pads labelled wrong.   I'll go over all the images I took.

I did a trace on this, and have the following:

(http://i1362.photobucket.com/albums/r688/russrutledge/DSCN3082_zpsnj04sylj.jpg)

Thanks Russ

That's excellent

C6 and C7 are definitely the same value.  Unfortunately, the values had been worn off but I was going with 47ufs

47uF for C6 gives a low pass filter knee of 33.9 Hz, while a 100uF would give 15.9 Hz- I think either is fine. Probably anything from 1uF on up would make you happy at C7.

Thank you for posting the photos, these were nicely done. On the way home now (India trip), I plan to bread this one too ;D

What jellybean are you using please?

the transistor is a BC-scribble-C, isn't it? what's going on with the 1M's and shadows? more wierdness.

Unsurprisingly given its name it's basically a Brian May Treble Booster http://www.diystompboxes.com/smfforum/index.php?topic=27422.0 (http://www.diystompboxes.com/smfforum/index.php?topic=27422.0)

I've built at least 4 times great circuit the BM treble booster and to my ears bc182 sounds best
Thanks

If  Cozybuilder schematic is correct

I will be nice

Is the 6.8k a bias control? is it external?
A better place to adjust bias is the 2.2k because it is cap bypassed gain is going to be about the same with different values because the emitter resistor is bypassed by a big enough cap value. You can adjust the C value to R selected

OR the 100k from 1k(base) to +9VDC because this should  change the input resistance only a little with different transistors of about the same hfe/beta range you could try a 68K or 82K with a 50k trim in series

The 1meg input is not needed there is a 120k

C4?

The 6k8 is a pot and its labelled Gain
(http://dirtmonkey.org/cov/1.jpg)

How is the gain potentiometer wired?
Is it a variable resistor like Cozybuilder trace?
Or does it have the wiper going to Switch?

Whoops, I forgot to take an image but I can tell you its a 10k Linear pot with a 22k resistor between Pins 1 and 3 to give 6k8.

(http://dirtmonkey.org/cov/CovingtonTB2.jpg)

The left pad was connected to Pot pins 1 and 2 and the right pad was connected to pin 3.

So it is wired as a variable resistor?
Why would someone want to connect the C to 9VDC when the control is set to 0 ohms.
Did someone work on the effect before you worked on it?

Any other pictures of the PCB on the web of other builds?

I don't think this has been modded in any way or played with.

The guy who owns it says it's his favourite treble booster but he clueless to what is inside.

Doesn't the schematic show the C attached by 100k to 9v?

Now the way this TB is wired is different it seems if the trace is correct the 10K is a variable resistor in the collector leg in parallel with a 22k?  They could have just used a 10k then the BIAS/GAIN CHANGE would be even greater. 0 to 6.8k vs 0 to 10k

Using a fixed resistor across the outer lugs make no sense to me, adjust the circuit to the potentiometer value you are using.  I will start a thread.

I suppose all I can do is make it and see what happens.

Anyway, I've knocked up a schematic and a copy of the layout to test.

(http://dirtmonkey.org/cov/schematic.png)

(http://dirtmonkey.org/cov/layout.png)

(http://dirtmonkey.org/cov/transfer.png)

Ref Name   Value
C1           22pf
C2           47uF
C3           10n
C4           47uF
C5           1n
C6           47n
C7           4n7
Q1           BC182
R1           4k7
R2           100ohm
R3           100K
R4           1M
R5           120K
R6           1K
R7           22K
R8           2k2
R9           1M
R10          150K
VR1          6k8

drop R4 and R9 (1M), they are both being swamped by 120k|150k. we don't really believe in mojo that much, do we? and make sure (make sure) of the bc184 BC182 pinout, it comes in the dreaded "L" variant.

http://pdf.datasheetcatalog.com/datasheet/MicroElectronics/mXuzsyu.pdf

I'm getting the feeling that opinion is, the person(s) who designed this didn't really know what they were doing?

I take it R4 is there to eliminate pop from switching?  Duck, what do you mean by 'being swamped'?

well, if you parallel 1M and 150k, which dominates the resulting resistance? it comes out a lot closer to 150k than to 1M, so the 150k has "swamped" the 1M.

you check that transistor pinout yet?

Thanks Ducksbum.

I think I've got some BC182s (https://www.fairchildsemi.com/datasheets/BC/BC182.pdf).  I was going to socket and see what sounds best/works anyway.

Are we absolutely sure the pot has 1&2 common? If true, and it certainly looks that way, how does the original behave? 'cause I'd expect min resistance to not only zero the output but greatly increase current consumption, although the increased voltage drop over the 100R supply filter will turn the Tr toward off - but maybe not enough.
Under DC conditions, there's the 2k2 emitter resistor to limit the current safely, but AC signal present will dump the supply via the collector-emitter to ground thru the 47u emitter bypass -  only the 100R in the supply is limiting that. Surely it's a battery killer?

Honestly, I'd put a minimum 470R (or even 1k) in series with the pot at the collector end for a little current limiting without changing the sound too much. Or the extra R at the supply end if you don't mind it not going to total silence (and when do we actually use a pedals volume knob as an off switch?)

Those extra 1M input and output resistors can be left out as Duck's says. A makers trick to catch out blatantly direct copies?
As if we would!

Hi Jim.  Thanks as always for your input.

Blatant copy!  That's exactly what I'm trying to achieve.  The lad I fixed it for really loves his so I said I'd clone it while I had it and make him (and myself) a (blatant) copy! :)

The pot definitely had 1 & 2 common.  The output is zero when set to min.  I never tested any current consumption.

Quote from: anotherjim on December 07, 2015, 09:37:28 AMUnder DC conditions, there's the 2k2 emitter resistor to limit the current safely, but AC signal present will dump the supply via the collector-emitter to ground thru the 47u emitter bypass -  only the 100R in the supply is limiting that. Surely it's a battery killer?

You ignore 47 uF of filtering capacitance post the "R". The circuit will suck up current from the path of least resistance and for a moment this current is limited only by capacitor's internal resistance. 100R only comes in play after some amount of energy is sucked dry from the capacitor and the parallel energy source is no longer swamped by a lower impedance source of energy. I would suspect it's not just a battery killer, it propably kills that transistor on a regular basis too.

The tapering... well, it obviously must work as some sort of "volume" control so overall gain should ideally change in logarithmic manner. Someone can probably calculate better than me how linear vs. "makeshift" logarithmic pot behave as variable collector resistances. Because it's not just a resistive attenuator for output signal, but also affects stage gain, the most ideal  taper function (for -consistent- gain/loudness control throughout the dial's range) is probably somewhat special.

Nick- While you have it on breadboard, why not simply connect the wiper to C6, and the pot with 22K across 1-3 as you described, with 1 to V+ and 3 to Q1C, using the VR as a 6K8 volume control?

Make VR1 10K forget about the 22K  gives a greater range of the strange gain/bias control.  Remember 6.8k is lower than 10k
Get rid of the 1megs and C1 they are a waste

You can make the collector a fixed 6.8k and change  R10 to a 100KA on top of a 47k, Or try a 100KA or 220KA volume

Or wire it like a RM with a 10KA in the collector leg, wiper as the output with a 3.3k emitter resistor

Nick, what was the repair you had to make to it? Was it the transistor?
I understand you want an exact clone, but expect some variation between builds. This is a highly interactive circuit. If the original transistor is good -  try to match it's Hfe for the copies.
Ok, that volume control. It would probably never be used at minimum resistance, so you avoid the potential for damage from that. Hmmm, if you use a chicken head knob, you could fit a pin in the case top to stop the control turning to minimum ;)

The repair was very simple, a wire had come away from one of the pot lugs.  That was why I wanted to understand the role of the resistor across the pins.

The pedal would be useless with the pot at minimum as sound doesn't pass.  Sorry, I don't have the pedal anymore to check the Hfe.  I was just going to try a few transistors.  I've got a few BC182s as well as some potential substitutes.  The plan was just to see what sounds best.  Looking at the datasheet the BC182 can have an Hfe within the range of 125-500, so another lesson learned.  I should have checked that.

Question, do you think this pedal has been designed by an amateur? 

I was expecting it to be a 99.9% copy of a schematic easily available online but this seems to have some of the best on here scratching their heads.

Possibly amateur or else a pro who doesn't like anyone giving their design a once-over so it got missed. Peer review is a powerful check and a hallmark of a truly professional undertaking IMHO.

I try to resist "this all wrong" rants. If everything was done by the book, we wouldn't have much else of anything.

I would not worry much about the transistor hfe
If you look in another thread I posted a screenshot of a sim

When I tried different transistors in sims the voltages did not change much from 2N2222 to 2N5089 so most to92 etc package NPN Silicon transistors should bias up with not adjustment needed.  I added a bias note to the sim because I often build with an external bias control to change the sound

Note the use of a 2.2k emitter and a 22k base to ground and 101k base to +9 that makes a more stable bias because of the lower resistance values in the voltage divider bias.

So I've built my 100% replica and it seems pretty much exactly the same as 'original' I had.  It doesn't quite sound as dirty but I had my amp at a low volume because my boys are asleep.  I might try a few different trannies as an experiment if I get the same results with the amp driven harder (Vox AC4).

I subbed the 47nf for a 56nf (I've got some 47nfs on order so I may change this if anyone thinks it will make a difference).

Interestingly, the pot is crackly when adjusting.  This was also true of the original I had.  I just used a 10K pot and didn't bother with the resistor across the pins to give me 6K8.

I etched another board at the same time so I'll do another build, this time experiment with the suggestions from you guys. 

Any further suggestions are more than welcome too.

Just a quick update on this one.  I haven't got round to messing with this too much but my 100% clone (despite the unnecessary resistors and weird pot wiring), sounded amazing once I cranked my VOX AC4.  On my last post I said it didn't sound dirty enough at low volumes but the cranking of the amp made a great difference.

I'd go as far as saying its my favourite treble booster and I have built most of them that are available through the power of Google.

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.

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.

Nick

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

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.

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.

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

(http://dirtmonkey.org/cov/DragonAttack.png)

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

(http://uploads.tapatalk-cdn.com/20160315/33d4ad8a027e54759e1e3faab4729ebf.jpg)



i found this on google

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.

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)

(http://i1067.photobucket.com/albums/u424/nick_james8/V2_zpstaxgtuo6.png)
            
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      

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

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

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

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.

@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

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.

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?

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

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?

Quote from: Bolty_Guitars on March 14, 2017, 07:58:14 PM
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.

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?

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.

Just to chip in a little bit of extra info that might be of interest to those here - I found a photo online of the inside of a Cornish TB-83 and although the circuit is of course hidden, there is one component on display which appears to be a rectifier diode.
I'm sure this makes no difference to the sound and is probably just to prevent a reverse voltage from a wrongly corrected battery, but for those of us who want exact details, hopefully this is of interest.
Here's the pic:
https://www.google.co.uk/search?q=inside+a+cornish+TB83&espv=2&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiplZnCiqHTAhUIIMAKHbxjAYYQ_AUIBigB&biw=1280&bih=906#imgrc=q27oWUGxxenGbM: (https://www.google.co.uk/search?q=inside+a+cornish+TB83&espv=2&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiplZnCiqHTAhUIIMAKHbxjAYYQ_AUIBigB&biw=1280&bih=906#imgrc=q27oWUGxxenGbM:)
or here:
https://reverb-res.cloudinary.com/image/upload/s--n_bh0Lo5--/a_exif,c_limit,e_unsharp_mask:80,f_auto,fl_progressive,g_south,h_620,q_90,w_620/v1470947841/wtbbn4nzwild5wouzxjp.jpg (https://reverb-res.cloudinary.com/image/upload/s--n_bh0Lo5--/a_exif,c_limit,e_unsharp_mask:80,f_auto,fl_progressive,g_south,h_620,q_90,w_620/v1470947841/wtbbn4nzwild5wouzxjp.jpg)

Also I managed to reach Greg Covington online and although he was of course reluctant to give away the schematic, he did say that his 'Ultra' booster was an attempt to get his boxes closer to being identical to the TB-83 - before he eventually gave up and took the Cornish apart to discover he was only one component's difference to it.
No mention of what that component was exactly but I'd bet Nick's efforts here are as close as you will find to a real TB-83.

Cheers guys

Nice work.   Surprised he didn't give you the schematic.   He doesn't sell anymore and he was once in the same boat as us.   I've never been sure about the ethics of tracing but he's done it so i can't understand why he hasn't helped.

Yes, kind of my thoughts too - however, although he doesn't strictly build any more, he is still offering to build one-offs for those that contact him as he did with me.
Seems he'd rather still 'keep his hand in' as it were, so I guess I can understand why he wouldn't share his schematic  :-\

Perhaps it's because he'd spent so much time and effort building/modifying them 'blind' and got so close on his own without tracing, just listening and tweaking. Who knows.

Maybe I'll have another bash ha ha

If you want the schematic, just google it, you can find the schem as well as the board !

I've never seen the Cornish schematic.   The Fryer one is easy to find.   .  Pease share a link Alfafalfa

Hi Alfafalfa,

Glad you have found the Cornish schematic, even better the board, a lot of us on here have been searching for it for ages. Please do share the link so others can benefit.
Thanks

(http://www.reactiongifs.com/r/weeds.gif)

Man, has nobody opened up a Cornish yet?  Seems like by now someone other than Greg Covington would have done it!...   :icon_lol: