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This is the 2nd Boogie 57 in a row and I have the same problem with the second one after not being able to figure out why the 1st one is acting up. IT SOUNDS GREAT. Don’t’ get me wrong, it’s just not right. The gain pot goes from clean tone to max gain with the lightest turn CW. Based on forum chats and help, I swapped the B1M pot for a B500k, A1m and now has a C1m and they all act the same. Also, Q3 won’t bias as intended, won’t come down to 6v. Also, Q3 and Q4 bias voltages go up and down with the gain pot, but Q1 and Q2 do not, just an observation if it matters. I’m still going to use these in my prototypes, but I’d like to find out why this is happening and if anyone had these issues. Thanks!!!
Hi Robert,
Do me a favor and replace only R11 with anything from 3.3k to 4.7k
Let me know how that works please.
Barry
Good morning Barry. I swapped out the R11 on both builds and all of the transistors are happily biased at 5.6v. When tracing the circuit I did notice R11 was 39k, higher than the other legs going to ground through a 1k8. Did we find a mistake? I used 3k9 thinking that was the intended value? IDK, but much better range for the voltage.
The gain still goes from 0 to crazy at 8 oclock… But I don’t care about that for my build. Who plays a High gain Mesa Dual Rec with the gain down anyway? hahaha.
Again while biasing, I see the gain control affects the voltage, so I figured to obviously bias the transistors at max gain and trim the resistance to 5.6
Let me know if that is wrong. I’m new to biasing voltages in my builds. And hey, thanks! good products. Good support. I always enjoy opening my pcb orders and seeing a smiley face on a free foot switch board or a buff n blend. I always include some swag in my build shipments.
I believe that is the case for the voltage issue. Noted and upgrading.
I would Bias at half the supply voltage and only go up from there as needed.
Now for the 2nd problem.
Try lightly tacking on a 1M resistor connecting lugs 1 and 3 of your B500k Gain potentiometer. I say lightly tack because you can try other values using a Parallel Resistance Calculator. That should give you a value of about 330K (test with your DMM). Let me know how that works out for the Gain range. Keeping in mind this is a high gain circuit as well as a circuit to suit different types of pickups.
I will, if what I’m describing is not supposed to be. I’m still semi new at this. I follow recipes and instructions to cook and build. I am still studying the how and why things are used and what values. I test my circuits here in the lab with a loaded BOSS loop station playing loops and tracks through a marshall 15w combo amp. I’m just here thinking there is little difference in the sound past 8 oclock. It’s more like 7 oclock. I’ll put the 1M in and see what’s what. I was happy with it as is. But let’s see…. Thanks again.
I bridged a 1M over 1&3 and I swear it’s exactly the same. I notice no change one the pot is past MIN. Touch it the slightest bit and that’s the gain for the rest of the sweep. Maybe it’s me, my ears, or my inexperience in high gain circuits. I thank you for the help, We found R11 listed wrong, so that’s a win! Let’s call it even. hahaha. You’re a very decent dude.
Yah can’t stop this process when we are nearly finished and about to have a major breakthrough 🙂
This could also be some of the best stuff you learn this year. So if you will indulge me…
I need you to answer 2 questions:
- Did you confirm by putting a DMM set to Ω on lugs 1 & 3 with the Gain pot turned up full using a 1M resistor in parallel across lugs 1 & 3 that it indeed measures near 330K or .330M.
- I would like to confirm what you mean by 7 and 8 o’clock. To me 7:00 would be the furthest counter clockwise you can go. 8 o’clock would just be a pinch of a turn more than that. 4:00 would represent Full Up.
Update Note: When testing the POT value, the pot must not be connected to the board. If you know you have this wired correctly based on the image below then you can skip the testing step and proceed if you wish.
Mod Finalized:
To expand on the Gain Pot Mod simply add-on another resistor this time in series with Lug 1 going to the main board Pad 1 (note board silkscreen 1) anything from 8.2k to 10k should do nicely.
Make sure you are doing this mod to a B500K pot and not a 1M Pot. The numbers would all be wrong otherwise.
Here is a nice image I made up for this.
Final thoughts and questions:
I will assume you have been testing with a high gain humbucker pickup?
Test with same pickup and see what you notice. Any changes?
Test with a single coil pickup. What happens?
You can use the clock analogy to answer as long as 7:00 is full counter clockwise and 4:00 is Full Up.
One Last Mod: Drop that 3k9 value down to 100 Ohms or any Ohm value you have near that. Thoughts?
Thanks again for testing this out for me and responding with your findings. The answers will be important to a 2021 revision.
The B500 GAIN pot with a 1M resistor in parallel across lugs 1 and 3 will only measure 330K Ohms if the pot is removed from the circuit. If it is in the circuit, the reading will include the resistances of R6 and R5. Just disconnect lugs 1 and 3 before measuring.
Hi hey and hello. Thanks for further including me in the trials for the new and improved V2. Now, recapping a few details. I missed that you specified the Gain pot as B500K. I had replaced and built another with a B1M and C1M. Did you want me to use a 500K and bridge a resistor? Or change the resistor value to go with the 1M Pot? 2M resistor on the 1M pot? Double the 1M r with a 500K pot… Simple resistor math? That’s 1…. As far as my clock references, I apologize. 7:00 is off and …. wait. 4:00 is full on? Well that’s not symmetrical. On the opposite sides of 6 o’clock, 7 goes with 5 and 8 goes with 4. haha. I’ll meet you in the middle. If you say 7 o’clock is min, then 5 o’clock is max. I looed up some nerd stats to help myself out with that. I found that a typical pot has a shaft turn range to almost 300 degrees. That’s about between 5 o’clock and 7 o’clock. So with that… With Gain at min, using the original B1m pot with and without the R1M, as soon as you move the pot from 7 o’clock, by the time I get to 8 o’clock, my ears hear no difference past that all the way up to max. Again, maybe just me and my ears. Also, because you also mentioned pickups, I’m not actually testing this in a real playing situation. I have channels of prerecorded tones and riffs being played in a loop pedal into the 15w marshall combo amp. I will do a few things with it and plug in at home as well if that might actually matter. I’ll swap out the resistor and pot as recommended but curious… Does the insight from Wilkie change what you wanted me to try? Let me know either way. I’m getting on this now.
This is fun, thanks.
So, here we go. I am learning and swapping resistors. using 2 B500k pots for comparison. 500k pot with R1M across 1&3 gives me 280k, with R9.1k off leg 1 gives me 290k. Another 500k pot with the R1m gives me 290k. I used 2 pots as they have been known to swing within their tolerances. So, trying to get 330k on the meter, We’re doing this with the pot OFF of the pcb? Because mine are off, should it be wired up? IS that what the extra R on the 1leg is helping achieve? Or should I get that resistance with the pot off? Because if so, I needed R33k between lug 1 and the pcb. FYI. Will be trying both in the mean time.
When installed, the pot with 9.1k on lug 1 reads 260k across 1&3. but I don’t think we were looking for this value. This also doesn’t have a very noticeable change in gain, sounds like less gain overall. I liked it as a high gain monster earlier. But will keep on …
The other pot with the 33k on lug 1 also reads 260k across 1&3 too. That must be the circuit affecting the reading. But this was the one that got me 320k/330k between 1&3 when OFF the board. And also has little noticeable change up and down the gain pot. I’m going to bring 1 back to the original circuit and keep 1 for further trials.
Barry I’ve got the V1 board if you need me to build it let me know and I’ll get to it, just msg me any components you want socketed etc
Yes I meant 5:00 as full up and yes it is fun IMHO.
So I am confused a bit here. You are saying that there is no difference between the Wiring Diagram Mod I made above and just attaching a B1M pot stock? Details on that specific change between stock and my mod as shown in the diagram is what I need to know. Details on the Pot value only needed to be close to verify the 1M worked correctly, nothing more. It appears good to me.
If there is no change or very little change between my Mod and Stock (I would have expected a real change) then take the 3k9 value on the board and drop it to 100R or something close to that. After doing that Bias the circuit again to 5v. or do I mean 4v (kidding).
After doing that update me on the change regarding just dropping that value while still utilizing my Pot mod.
@Billy: more heads are always better than one. I think you get what I am going for here. Build everything stock except for R11 (make that near 3k9) and make the Gain Pot (B500K). After testing that try adding a 1M resistor to the Gain Pot. What are the results? If needed further reduce the value of R11 to 100R. Results?
Has anyone tried using an A500K or A1M pot for GAIN? I wonder if the AUDIO taper that starts out with a slower resistance change might improve the change in gain as the rotation increases? Just my thought.
That is a good thing to try after I get some more info on his build.
I am getting all this new information at the same time.
This circuit will be featured in an upcoming DC movie and the guy that built it up for his studio did this:
His final comments are:
3k9 becomes 100 K
Gain P1 becomes 300k ( with cross parallel resistor)
Leg 1 has 8.2k resistor before going back to pcb
Awesome sound
This is his rig for the DC movie (release date is July 29, 2022) which includes all GuitarPCB projects.
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