PorkBarrel volume drop: SOLVED!

[UncleLarry]

Just finished the 2019 PorkBarrel build with the MN3007/3101 chipset. I installed the optional Blend control. The unit sounds amazing with the only niggle being there is about a 10-15% perceived volume loss when the unit is switched on from bypass. Is there a component value that can be changed to give the unit better unity volume between active and bypassed? I did go through and visually double check resistor values and it didn't appear to me that anything was incorrect. Gut shot attached for reference.

[jimilee]

Did you measure or make sure all of your resistors are the right values? That's an easy mistake to make, apparently after 10 years. Don't ask me how I know.


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[UncleLarry]

I didn't measure all of them but I did a "sample test" as I pulled them out of the bag. For example, if the circuit called for five of the same value, I would pull five and check one.

I guess I should go through the board and check each one. 

[jimilee]

I didn't measure all of them but I did a "sample test" as I pulled them out of the bag. For example, if the circuit called for five of the same value, I would pull five and check one.

I guess I should go through the board and check each one. 

That's the unfortunate starting point. Check the color bands and make sure they're the right values. The original didn't have a pull down resistor, I know sometimes that pulls a little signal.


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[UncleLarry]

I went through and checked all the resistor values and all are correct. I also checked voltages on the ICs and and transistors. I used an Ibanez power supply which measures at 8.9 VDC. The voltage readings are within <.5 volt of the ones shown on the chart in the PorkBarrel build instructions except for pins 7 and 8 on IC2 (MN3007) which read 5.32v vs 4.7v on the chart.

Would reducing the values of R9 and R26 in the mix network possibly increase the output volume?

[thomasha]

Hi,
have you tested if the volume drop occurs at every setting?
It could be variations in the BBD gain, but at such low delay times it shouldn't be a problem.

Also, check the caps. Sometimes a large cap somewhere can make things way quieter, like using 100nF instead of 100pf at IC1B.
The transistors name/orientation also. If you used an equivalent transistor it could have swapped pins.

The best way to find a problem in this case is using an audio probe, and tap at some different points of the circuit to see where the volume is dropping the most. I would definitely check levels before and after the BBD.

[UncleLarry]

After doing some probing, I found the volume difference was happening after the mix network for the Blend control. So, I changed the resistors at R9 and R26 from 27k to 10k and voila, unity gain!

Hi,
have you tested if the volume drop occurs at every setting?
It could be variations in the BBD gain, but at such low delay times it shouldn't be a problem.

Also, check the caps. Sometimes a large cap somewhere can make things way quieter, like using 100nF instead of 100pf at IC1B.
The transistors name/orientation also. If you used an equivalent transistor it could have swapped pins.

The best way to find a problem in this case is using an audio probe, and tap at some different points of the circuit to see where the volume is dropping the most. I would definitely check levels before and after the BBD.

[gordo]

Nice.  Glad you got that sorted out.  In the meantime how did you get such cool photos of the caps and wiring?  Looks kinda Blue-Man Group.

[UncleLarry]

Nice.  Glad you got that sorted out.  In the meantime how did you get such cool photos of the caps and wiring?  Looks kinda Blue-Man Group.

I took the gut shot pic through this and cropped it.....