Author Topic: PorkBarrel volume drop: SOLVED!  (Read 359 times)

UncleLarry

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PorkBarrel volume drop: SOLVED!
« on: December 24, 2021, 02:14:14 PM »
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.
« Last Edit: December 26, 2021, 04:11:16 PM by UncleLarry »

jimilee

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Re: PorkBarrel volume drop
« Reply #1 on: December 24, 2021, 03:36:52 PM »
Did you measure or make sure all of your resistors are the right values? Thatís an easy mistake to make, apparently after 10 years. Donít ask me how I know.


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UncleLarry

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Re: PorkBarrel volume drop
« Reply #2 on: December 24, 2021, 04:01:11 PM »
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

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Re: PorkBarrel volume drop
« Reply #3 on: December 24, 2021, 04:53:18 PM »
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.  ::)
Thatís the unfortunate starting point. Check the color bands and make sure theyíre the right values. The original didnít have a pull down resistor, I know sometimes that pulls a little signal.


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UncleLarry

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Re: PorkBarrel volume drop
« Reply #4 on: December 24, 2021, 08:25:22 PM »
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?
« Last Edit: December 24, 2021, 11:32:28 PM by UncleLarry »

thomasha

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Re: PorkBarrel volume drop
« Reply #5 on: December 25, 2021, 04:26:31 AM »
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.
« Last Edit: December 25, 2021, 04:30:12 AM by thomasha »

UncleLarry

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Re: PorkBarrel volume drop: SOLVED!
« Reply #6 on: December 26, 2021, 03:52:18 PM »
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 15k and voila, unity gain! :D

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

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Re: PorkBarrel volume drop: SOLVED!
« Reply #7 on: December 26, 2021, 05:16:16 PM »
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.
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UncleLarry

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Re: PorkBarrel volume drop: SOLVED!
« Reply #8 on: December 26, 2021, 05:40:32 PM »
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.....