Help with brian may treble boost capacitors needed!

[To The Moon]

So I'm building a Brian may TB from tagboardeffects' layout, and I'm wondering which capacitors are critical to keeping the sound true to the design. Particularly the two electrolytics going from 9v to ground - are those just filter caps or will they mess it up if I only have say... 68uf polarized caps to work with? I've built a bunch of stuff, I just have no idea what does what in this circuit and which components need to stay true to the schematic for it to function right! So some help would be nice 

[To The Moon]

Also, what would be a good transistor for this? I've got MPSA18, 2n3904, 2n5088, PN2222a, 2n5089, BC108, and BC109 all ready to go... Totally not familiar with the BC239 used with this circuit and I just dunno what to use instead.

[antonis]

http://www.diystompboxes.com/smfforum/index.php?topic=27422.0 

Try different transistors and listen...

[smallbearelec]

So I'm building a Brian may TB from tagboardeffects' layout, and I'm wondering which capacitors are critical to keeping the sound true to the design. Particularly the two electrolytics going from 9v to ground

Find a schematic and build it on breadboard before you commit to solder; what pleases your ears might turn out to be Not the "classic" parts list. The electrolytics have little or no effect on the tone; two are for power supply decoupling (I don't understand why a single 100 mf. was not used) and the other is emitter bypass to raise the stage gain. The value of the 6.8 nf (.0068 mf.) input cap (start with any good-quality polyester-metal film) Does matter a lot; various ways to select and vary it are common. The choice of transistor type (germanium or silicon) and gain also have an influence.

[To The Moon]

Okay cool, thanks. Also the little 10pf caps, can I just leave those out? Or if I wanted to would I jumper? I'll be running on battery power and I can add them later if so...
This layout looks a little more compact and also makes it look like I could just leave that cap out for now. No jumper as it would dump my signal to ground, right?

[smallbearelec]

Okay cool, thanks. Also the little 10pf caps, can I just leave those out? Or if I wanted to would I jumper?

Don't jumper where the caps are...Just leave them out and see if the build sounds OK without. I would be surprised if they were really needed.

[To The Moon]

Sounds great without! A tiny bit of presence added but I dunno if that's because my Vox still has the bright cap - which I'll be removing anyways. Thanks!

[nickbungus]

Hi

Just to put my 2 pence worth in, I've built nearly every TB that's available on the WWW and I'm convinced  this TB-83 clone is the best:

Sounds amazing through my Vox Ac30.  I traced it from a repair for a friend.  I'd love to see the schematic for a genuine TB-83 though.

I keep meaning to do a Vero layout for this but hate Vero too much!

[duck_arse]

the two 10pF caps are in series for a total of 5pF on the tagboardeffects layout. there is a 4p7 cap at C2 on the paulinthelab layout, performing the same function. do you have the pitl C2 fitted?

[To The Moon]

I just did it without c2. Sounds terrific still. Next time I put in an order I'll get some 4.7pf caps and toss one in to see if it really did anything.

And I wanted to build a TB-83! But I can't find a schematic or vero layout anywhere.

[Kipper4]

Some reading for you


http://www.diystompboxes.com/smfforum/index.php?topic=112790.0

[cab42]

I just did it without c2. Sounds terrific still. Next time I put in an order I'll get some 4.7pf caps and toss one in to see if it really did anything.

And I wanted to build a TB-83! But I can't find a schematic or vero layout anywhere.

I'm on a TB quest at the moment. I'll be happy to make a vero layout of the TB-83. I think there was a schematic in Nicks link. However it might take a few days, though.

[cab42]

Okay, using Nicks schematic from the link a few posts above, it looks like the Covington TB can built using Paulinthelabs Greg Fryer TB vero with a few changes. Component names are from the layout. Note that the two 1M's and the 22p can be left out according to the thread Nick links to. Unless, off course, you want to make an exact copy. Read the thread, lots of good info.

A 100R resistor is added in series with 9V. It could be placed off board or by adding a new row above row A, connect 9V to the new row and place the 100R between the new row and row a.

Leave out C2

Place a 1M resistor from b7 c7

Add a column to the left of column 10 and add a 1M resistor from row h to row b (or piggyback it on R8)

place a 22p capacitor from a3 to b3

change C1 to 10n (or make the input cap switchable)

Replace R7 with a jumper wire

Change R8 to 150K

Peplace R6 with a 10K pot with a 22K between pin 1 and 3 and pin 1 and 2 connected (or just use the 10K with pin 1 and 2 connected)

That's it (I think)

Have fun. Let me know if anything doesn't look OK.

[To The Moon]

Okay, using Nicks schematic from the link a few posts above, it looks like the Covington TB can built using Paulinthelabs Greg Fryer TB vero with a few changes. Component names are from the layout. Note that the two 1M's and the 22p can be left out according to the thread Nick links to. Unless, off course, you want to make an exact copy. Read the thread, lots of good info.

A 100R resistor is added in series with 9V. It could be placed off board or by adding a new row above row A, connect 9V to the new row and place the 100R between the new row and row a.

Leave out C2

Place a 1M resistor from b7 c7

Add a column to the left of column 10 and add a 1M resistor from row h to row b (or piggyback it on R8)

place a 22p capacitor from a3 to b3

change C1 to 10n (or make the input cap switchable)

Replace R7 with a jumper wire

Change R8 to 150K

Peplace R6 with a 10K pot with a 22K between pin 1 and 3 and pin 1 and 2 connected (or just use the 10K with pin 1 and 2 connected)

That's it (I think)

Have fun. Let me know if anything doesn't look OK.

Thank you so much! I built another fryer today, I'll go ahead with the cornish in the upcoming week.

Both fryers I made ended up great, one with a PN2222a, one with a 2n4401. The PN2222a is nice and bright, and 2n4401 is just right - perfect amount of harmonics and enough low end to retain the character of my jazzmaster pickups.

[nickbungus]

I've also messed on with the trannies and I would definitely try and get hold of some BC182's.  If I remember rightly the 2n2222s sounded really bright but not enough dirt.   I haven't tried the 2n4401s though.

If you read through the whole thread about the trace, I came to the conclusion that Greg Covington added the 1Ms in an attempt to combat the switching pop but because these are in parallel with other lower value resistors, it was pointed out to me that these are redundant.

I also reckon (as supported by the Youtube Video), that GC traced the standard TB-83 and put in the pot in an attempt to promote the circuit to a TB-83 extra.  Next time I build it I was thinking of using a fixed resistor and then wire a pot on the output in the same fashion as the Paul in the Lab TBs.  With the Covington circuit, there is a very noticeable crackle when you adjust the pot.

[To The Moon]

I'm socketing the tranny, so I'll snag some BC182s soon and swap those in. The 2n4401 is great! Cleans up much better than 2n5089 and 2n3904 did, and any sort of guitar knob/switch crackle was insanely loud with the MPSA18. Don't know why. Also the BC108 sounded absolutely gorgeous but the noise from that thing. It was like a sleep noise generator or something. If the BC182 or BC239c sounds anything like that, but without the crazy noise, I'll be one happy guy. For now though, the 2n4401 seriously is more than just a placeholder, wonderful sound.

[nickbungus]

Here's the Covington/TB-83 in Vero.   I used the old Beavis Audio Treble Booster layout as the basis adding the extra bits and the unnecessary bobs!  I like the slender design as it fits lengthways in a 1590B but also I can cram it onto a side of a 1590BB with my fOXX phaser.

I've built it and it sounds spot on.

[maynut]

Hi Nick,
So, is this the vero for the 100% copy of the covington?  I was trying to follow the various threads about it but got a little lost.
Cheers

[thermionix]

That's weird, R9 and R10 are both in parallel with the pot, effectively making it a 9.285k pot.  That's within 10% tolerance for a 10k pot.  Why bother?

[antonis]

That's weird, R9 and R10 are both in parallel with the pot, effectively making it a 9.285k pot.

Same with R4 & R5, effectively making an 107k anti-pop resistor.. 

Maybe R5 should be moved on the right side of C3 to form a 133Hz HP filter..??
(I'm not aware of the original diagram, so..)