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I’m just getting back to this…
The mentioned 3k9 becomes 100k is what? The R11 we messed with earlier?
Yes R11
I’m still messing with it got a couple more pot / resistor combos to try when I’m finished work and I’ll report back
Built stock
I tried A,B, 1M A, B, C 500K, and A and B 250K
R11 from stock 3K9 then 10K, 12K, 47K, 68K, 100K and 1M
The best result I found with the values I had on hand
A250K (actual resistance was 219.4K) with 100K at R11
although all other values from 12K to a 100K with an A250K made gain more gradual but I definitely thought 100K sounded best with the least amount of tone change and a more gradual change over the gain pot range
I’d advise some resistance from gain lug 1 to ground it being wired as a voltage divider as you’d expect when completely CCW volume drops a lot
When I get a moment I’ll try a 300K pot and 100K at R11
I looked at other layouts most used an A1M pot with 3K9 at R11 some advised trying an A1M with 12K but it didn’t make it more gradual to me
* tried an A500K with paralell 1M actual resistance 312K and R11 at 100K
I didn’t think there was a lot of difference to the A250K
Rack mount heaven! Are these all your designs adapted for studio use?
Guys, thanks for all the comments and amazing diligence in problem-solving.
I’m due to build this in awhile and will bear the mods in mind in case I experience similar problems to Robert’s. But I’ll surely socket the transistors as Barry advises. Non-SMD 5457s are getting rare and precious as we know and I have a fairly limited stash. Boogie 102 or 113 doesn’t sound quite as cool as Boogie 57.
Best, M
@mybud Yes that is all GuitarPCB in a rack-mount design and interestingly is being used in a studio in LA for an upcoming DC movie this July.
I do have many transistors available.
So, have we eliminated the resistor across 1&3 of the gain pot? And the resistor off of leg 1 is still a 10k?
No if you’re using a 500K you’d still put the 1M in parallel across lugs 1 and 3
R11 yes 100K
Lug 1 of the gain pot needs some resistance to stop it cutting audio level when fully CCW
8K2 was suggested
Note I tried a few different pot values and tapers and R11 values detailed above
Now if I’d read all comments fully I’d have seen Barry already detailed what the DC movie guy did and noted he’d already put resistance on lug 1
What I tried confirms what the DC movie guy did will work
If you use an A250K gain pot then you wouldn’t need the paralell resistance across lugs 1 and 3 if you use an A500K then put a 1M across lugs 1 and 3
Make R11 100K and add 8K2 to lug 1 and you’ll be good to go
Here’s a wee pic my test set up for info
No, A250K works fine
It definitely made a difference across the gain pot range but what I would say is it’s a gain monster so you wont notice much difference nearer the middle of the range and using your guitar volume also has an affect as you’d expect
I just tried again with a A250K pot actual resistance 248K this time I measured the resistance on lug 1 to 2 fully CCW where the signal is as clean as you’ll get it and level doesn’t drastically drop out, it read 5.5K so lug 1 resistance anything between 5K5 to 8K2
Thanks Billy for testing all of that for me. I will add the resistance to the new circuit board and I will experiment but I will likely go with the A250k for a Pot value for the Gain control. I can also make this information available in the old build document as well. That way we don’t just have a Gain monster (stock) that goes from 10 to 11 only.
In your opinion using the A250k Billy did you still have plenty of that heavy duty Gain tone if needed?
Yeah definitely a gain monster
You can still go to major sustain approaching feedback sounds with guitar volume cranked up
I’d checked other layouts most of which suggested A1M with R11 at 12K but that didn’t make a lot of difference the gain range was still bunched up
I found very little difference between the A250 and 300K pots with R11 at 100K to me it was slight, the 250K I thought gave the least difference in tone
With some of the other values bass increased around halfway for a small portion of the range but with a 250K tone remained constant throughout the pots rotation
It’s down to personal preference but both the 250 and 300K worked well try both but as I say not a lot of difference gain is more gradual up to halfway but you can still hear a difference after halfway it’s just not as obvious
You could experiment with the resistance on lug 1 I tried 4K7 which was fine to me then decided to measure the resistance between 1 and 2 where level dropped out which as I said was 5K5
I’ve sent some clips on spacebook messenger
Stock values
Pot change only to A250K
Pot A250K and R11 100K
How are we on the Transistor biasing through all of this? I still have Q3 at 8v, that’s as low as it will go with the trim at min.
My Q3 is biased at 8.4v and works fine the source resistance change will affect it a little, 1, 2 and 4 biased to 5v and Q5 to around 8v
You’ll notice Q3 and 5 have no source bypass cap so gain is set by Q1, 2 and 4 making them important to bias at 5v ish
I’m happy. Are WE happy? Yes I noticed The biasing. 8.4 exactly! Sounds great. The A250k pot was the way to go for the gradual gain. I’m glad I asked in the first place. I feel like family now. Now as far as Version 2.0 is concerned, We can rename it the Robert Jay’s Boogie 57, Right?… Hahahaha. Gentlemen. Thank you. This Boogie 57 is going in my next Signature Sound Series Metallica Box. Should pair well with a Tube Screamer circuit for some James and Kirk tones.
Not much of a plug as much as sharing the link, but if you’d like to see where my GuitarPCB parts and boards go…
https://www.facebook.com/KillDozer-Pedals-By-Robert-Jay-112534230887383
Just keeping you guys in the loop. What a great build./ We are so happy with what we pulled off. The boogie 57 really cranks. Thanks!
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