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Interesting.  Glad you got it sorted out.

Yes, me too! I thought I was losing it because I couldn't find anything physically wrong with the build.

I did some more experimenting and tried a couple of late '90's Yugoslavian Ei brand and an unknown brand of old stock tube that has "Britain 12AX7A/ECC83" stamped on it. Both are longer plate tubes similar to the old German Telefunkens. Huge volume boost with these.

There's something about how the circuit is designed that favors certain tube types. The Russian one that is commonly available and worked well is an EHX 12AX7EH that has the short dual parallel plates. I settled on the old stock "Britain" tube because it provided the most output; about 20%-ish more than the EHX. The Ei tubes were good as well, but I liked the sound of the Britain tube better.

I'm curious to find out what tubes are used in the actual B.K Butler pedals. I wonder if anyone in the forum has one that they could open and find out? 

So, I discovered that the pedal is sensitive to different types of tubes. The Chinese 12ax7 that I was using wasn't allowing enough gain to get the pedal above unity in HI/LO mode. When I swapped it for a Russian version, there is a significant gain boost from both sides of the EQ and the issue is fixed. 

Just finished the Archibald '22 build. Sounds amazing except when I switch from EQ to HI/LO mode there is a huge volume drop. Even when the level is at max I can only get about 3/4 perceived unity gain in that mode. EQ side has plenty of output. I've already checked all the component values and such. Any hints on where else I should start checking?

FYI - I saw the thread regarding a bad J201 possibly causing issues. I have a batch of 20+ year old NOS and 2N5457 that I could swap but just wanted to see if the brain collaborative had any other ideas before I do so.

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.....

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.

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?

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. 

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.