D*A*M - Greasebox GB-83

beedotman · Post by **beedotman** » 22 Apr 2012, 19:22

Yo!

Fresh meat for ya all!

This is just first draft (just wanna do it before Sinner

) and lots of component values need to be confirmed, but more or less this could be it.
Circuit similar to GB-80, but adapted for Si trannies - no darlington pair in first boosting stage, since silicons have enough muscle, and few tweeks to remove silicon harshness and better bias, I think.

Any ideas, thoughts are welcome.

Peace!
b

beedotman · Post by **beedotman** » 22 Apr 2012, 19:25

BTW - D*A*M have started to hide value os components, so it's higher level of difficulty now!

sinner · Post by **sinner** » 22 Apr 2012, 19:44

beedotman · Post by **beedotman** » 22 Apr 2012, 19:56

shit... I missed trace cut after input.

will fix it soon.

phibes · Post by **phibes** » 22 Apr 2012, 20:04

Whoops, my bad... Precision resistors!?

I can agree with him on using the black out vs bright blue from the OCD point of view.

beedotman · Post by **beedotman** » 22 Apr 2012, 21:11

input fixed

phibes · Post by **phibes** » 23 Apr 2012, 06:26

From reading his description, I'm guessing he used a darlington transistor for Q1, works out from eye balling your layout. You could try MPSA14 or a 2N5306 like used in a Scrambler. Did you guess on the values for those black precision resistors? Q2 will be a regular NPN transistor. I'm guessing the 1M resistor is for simulating leakage.

beedotman · Post by **beedotman** » 23 Apr 2012, 07:50

phibes wrote:From reading his description, I'm guessing he used a darlington transistor for Q1, works out from eye balling your layout. You could try MPSA14 or a 2N5306 like used in a Scrambler. Did you guess on the values for those black precision resistors? Q2 will be a regular NPN transistor. I'm guessing the 1M resistor is for simulating leakage.

There's one photo somewhere on D*A*M forum where resistor from +9V rail on Q1B is clearly 470K - maybe one of first units or proto? Will try to find it and post here for reference.
100K to ground is just my guess.

beedotman · Post by **beedotman** » 23 Apr 2012, 07:53

Here it is.
220pF cap value is also confirmed on this pic.

beedotman · Post by **beedotman** » 23 Apr 2012, 08:01

Base to ground resistor could be also higher - up to 470K maybe...

beedotman · Post by **beedotman** » 01 May 2012, 11:39

Thanks to A. I have got few more components confirmed

Q1 is BC547B, Q2 is BC337.

Updated layout attached.

guitarmongot · Post by **guitarmongot** » 05 Jun 2012, 15:51

Hallo. If it´s okay to post here instead of Debug thread...as it is under process( not confirmed.)
I´ve buildt GB-83 from vero above : but I can´t get Q1 and Q2 to bias .
What resistors control BIAS on Q1? Is it the 2 x 470K (ground to Q1 Base and +9V to Q1 base)
or is it 8,2K (+9V to Q1 Col ).
Also 22K (9V to 10K) is that confirmed?
Can´t find a schematic : hope vero above will be ok as a ref...?
Q1 BC547B (hfe 300)
Q2 BC337-40 (hfe 430)

/cheers M

beedotman · Post by **beedotman** » 05 Jun 2012, 18:41

guitarmongot wrote:Hallo. If it´s okay to post here instead of Debug thread...as it is under process( not confirmed.)
I´ve buildt GB-83 from vero above : but I can´t get Q1 and Q2 to bias .
What resistors control BIAS on Q1? Is it the 2 x 470K (ground to Q1 Base and +9V to Q1 base)
or is it 8,2K (+9V to Q1 Col ).
Also 22K (9V to 10K) is that confirmed?
Can´t find a schematic : hope vero above will be ok as a ref...?
Q1 BC547B (hfe 300)
Q2 BC337-40 (hfe 430)

/cheers M

22K is confirmed, here's another pic of the board.
470K on Q1 base to +9V could work fine (You can find pics above with this value), just try to place 470K trimpot in place of Q1 base to ground bias resistor and check what sounds good. And let's us know

Hard to say what are exact values based on pics... 470K was only guess...

guitarmongot · Post by **guitarmongot** » 05 Jun 2012, 18:53

OK Beedotman: you answered when I was away ; busy testing at my workstation..

I must point out : I don´t question your tracing : I´m very glad that you guys do that here at FSB .Thank you .

Also I read at DAM forum : the black resistors are tube shrink covers : "secret black mojo"

And tomorrow I´ll try out your suggestions : but this is what I did today:
I replaced 8.2 K (9V-Q1c) with trimpot (VR1).
22K (9V-10K) with trim (VR2) and 10K (22K-Q2c) with trim(VR3).
I set Q1col and Q2 col to 4.5V with all trims.Then I pluged in my Strat:
and set guitar vol to 7.Set Vol and Int on GB-83 at 12 o´clock.
Played and adjust VR1 and VR2 until I´ll get clean tone without gated buzz.
Thats how I usually do to finally set BIAS on GE FF and Tonebender pedals.
So at guitar vol at full : it´s a full silicon-tonbender with great almost endless sustain
and a lot of volume on tap....: and it´s close to clips on Youtube with orginal GB-83.
Well the odd thing is VR readings:
VR1 : 5.6 K (stock value 8.2K)
VR2: jumper (0.2 ohm) (stock value 22K) ????
VR3 : 2.5 K (stock value 10K).

BC337-40 hfe 430
Q2 col 4.5V
Q2 base 0.6
Q2 emi 0V

BC547B hfe 300
Q1 col 5V
Q1 base 3.8
Q1 emi 3.2V

/cheers M

guitarmongot · Post by **guitarmongot** » 05 Jun 2012, 20:45

A common NPN boost stage would be something like a Rangemaster :
Ground-Q1 base : 68K . 9V-Q1base :470K. 9V-Q1col : 8.2K
Ground-Q1em :4.7K
And with Incap 10nF it gives a basscut filter of 230 Hz...
So a 100K trim in Ground-Q1Base might do the trick ..

Also I have BC337-25 (hfe 300) and BC337-40 (hfe 430) : don´t know if
hfe makes a huge difference in Q2 ?
Gonna try that tomorrow (It´s Swedens National Day : No work..plenty of time to testing....)

/cheers M

phibes · Post by **phibes** » 06 Jun 2012, 04:53

Yeah, like guitarmongot said, a 100K trimmer from Q1's base to ground should be all you need for bias'ing.

beedotman · Post by **beedotman** » 06 Jun 2012, 06:30

You could be right guys!

guitarmongot · Post by **guitarmongot** » 06 Jun 2012, 12:43

Today I put a 500K pot(VR1) in between Ground-Q1Base.
All other values are as shown in Beedotman´s vero above.
Then I adjust VR1 until I got 4.5V on Q1 col.
VR1 is then 260K. Q2 col is 1.2V.
Sounds like a high gain silicon tonbender : unity level at 12" , Int at none..til full..
but don´t clean up as well as it did before, but it doesen´t sound misbiased : just don´t clean up
like a good SI FF...
But again it sounds very close to clips from Youtube (I don´t have a GB-83 to
compare with...)
And it seems to cut away very little base on the input : 260K/10nF gives 61 Hz corner frequency
http://www.muzique.com/schem/filter.htm
So with my combo of trannies : Q1 BC547B (300hfe) and Q2 BC337-40 (hfe 430)
I´ll go with Beedotman´s values from his vero : other than Ground-Q1Base that I´ll change to 260K.
And I think I´ll keep that 25K trim for 22K (9V-10K) for adjusting Q2 col voltage....like a"clean" mod..

Thank you Beedotman for your vero layout and your feedback .

/cheers M

beedotman · Post by **beedotman** » 06 Jun 2012, 13:19

guitarmongot wrote:Today I put a 500K pot(VR1) in between Ground-Q1Base.
All other values are as shown in Beedotman´s vero above.
Then I adjust VR1 until I got 4.5V on Q1 col.
VR1 is then 260K. Q2 col is 1.2V.
Sounds like a high gain silicon tonbender : unity level at 12" , Int at none..til full..
but don´t clean up as well as it did before, but it doesen´t sound misbiased : just don´t clean up
like a good SI FF...
But again it sounds very close to clips from Youtube (I don´t have a GB-83 to
compare with...)
And it seems to cut away very little base on the input : 260K/10nF gives 61 Hz corner frequency
http://www.muzique.com/schem/filter.htm
So with my combo of trannies : Q1 BC547B (300hfe) and Q2 BC337-40 (hfe 430)
I´ll go with Beedotman´s values from his vero : other than Ground-Q1Base that I´ll change to 260K.
And I think I´ll keep that 25K trim for 22K (9V-10K) for adjusting Q2 col voltage....like a"clean" mod..
Thank you Beedotman for your vero layout and your feedback .

/cheers M

Thanks for report, mate!

phibes · Post by **phibes** » 06 Jun 2012, 17:20

Why are you adjusting the trimmer to get 4.5v? Use your ears instead.

D*A*M - Greasebox GB-83 [traced]

DAM - Greasebox GB-83 [traced]