Black Mirror VII: Obsidius on steroids!

jeffwhitfield

Well-known member
Finally finished this sucker today! Took a while with this one. Had a debacle over some REVV builds and ended up with some store credits on the PCB Guitar Mania site. I had already built an Obsidius Preamp but really wanted something closer to a Darkglass Microtubes B7K. Picked up a Black Mirror VII board and waited for it to arrive, which was in October. Once I got it, I started planning the build but held off on ordering parts due to an announcement of a few mods that add a couple of settings from the B7K Ultra.

Finally got around to building it a few weeks ago. Build went pretty smooth. After getting the main stuff on the board, I plugged it in to test it out. Everything worked for the most part....but the Drive was acting funny. Distortion worked only for the first 30-40% of the pot. Dropped out after that. Replaced the op-amps, which helped and got it to where it wouldn't start dropping out until 80-90%. Played with the op-amps and I think one of the sockets was being finicky. Once I made sure everything was seated well seems the Drive pot started to work better.

Last thing is the Ultra mod that adds a few switches for the selection of Hi-Mids and Lo-Mids frequencies. I opted for the 168 Hz (100n) and 500 Hz (10n) options for the Lo-Mids and 1.55 kHz (3300pf) and 3.3 kHz (680pf) for the Hi-Mids. This is about as close as I felt I could get to the original B7K options. Mods worked well and do add quite a bit of flexibility. Might play with different caps later on with a custom breadboard or something. Still damn good as-is though.

Once I put everything together, I noticed that I messed up the enclosure design a bit. Seems I got the Grunt and Ultra-Hi switch labels mixed up. Didn't have any labels set for the mods so I just added a label there too. This is my own personal pedal so no biggie. Not anything I plan on selling so no harm, no foul.

Sound-wise, this ended up being a really, really great pedal for me. I bought a Darkglass Vintage Deluxe v3 to compare it to. I'm very surprised at just how close the Black Mirror is to it. Granted, the options aren't quite the same but still very comparable and highly flexible. The drive character is different with the Vintage. Like many reviewers have said, it's warmer than the B7K...which is certainly the case with the Black Mirror. I was surprised that I ended up liking the Black Mirror more though. The drive has a richness about it that the Vintage doesn't have. Just feels like I can get it to cut through a mix easier. Definitely more modern sounding...but with a few tweaks it can get quite mellow and warm. Maybe not quite like the Vintage...but close enough.

Overall, I'm very happy with this preamp. I'll be returning the Vintage and sticking with the Black Mirror as my bass preamp of choice. :D

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jeffwhitfield

Well-known member
Very cool! What does the blend do? Did you try DI?
The Blend controls the mix of the clean and drive tones. EQ gets applied to both but you can control how the drive is effected with the Grunt and Ultra-Hi switches.

DI works well. It just takes the output and spits it out with a balanced signal that can be dropped into any board. I probably won’t be using it but kept it in the build just in case.
 

csipete

New member
Finally finished this sucker today! Took a while with this one. Had a debacle over some REVV builds and ended up with some store credits on the PCB Guitar Mania site. I had already built an Obsidius Preamp but really wanted something closer to a Darkglass Microtubes B7K. Picked up a Black Mirror VII board and waited for it to arrive, which was in October. Once I got it, I started planning the build but held off on ordering parts due to an announcement of a few mods that add a couple of settings from the B7K Ultra.

Finally got around to building it a few weeks ago. Build went pretty smooth. After getting the main stuff on the board, I plugged it in to test it out. Everything worked for the most part....but the Drive was acting funny. Distortion worked only for the first 30-40% of the pot. Dropped out after that. Replaced the op-amps, which helped and got it to where it wouldn't start dropping out until 80-90%. Played with the op-amps and I think one of the sockets was being finicky. Once I made sure everything was seated well seems the Drive pot started to work better.

Last thing is the Ultra mod that adds a few switches for the selection of Hi-Mids and Lo-Mids frequencies. I opted for the 168 Hz (100n) and 500 Hz (10n) options for the Lo-Mids and 1.55 kHz (3300pf) and 3.3 kHz (680pf) for the Hi-Mids. This is about as close as I felt I could get to the original B7K options. Mods worked well and do add quite a bit of flexibility. Might play with different caps later on with a custom breadboard or something. Still damn good as-is though.

Once I put everything together, I noticed that I messed up the enclosure design a bit. Seems I got the Grunt and Ultra-Hi switch labels mixed up. Didn't have any labels set for the mods so I just added a label there too. This is my own personal pedal so no biggie. Not anything I plan on selling so no harm, no foul.

Sound-wise, this ended up being a really, really great pedal for me. I bought a Darkglass Vintage Deluxe v3 to compare it to. I'm very surprised at just how close the Black Mirror is to it. Granted, the options aren't quite the same but still very comparable and highly flexible. The drive character is different with the Vintage. Like many reviewers have said, it's warmer than the B7K...which is certainly the case with the Black Mirror. I was surprised that I ended up liking the Black Mirror more though. The drive has a richness about it that the Vintage doesn't have. Just feels like I can get it to cut through a mix easier. Definitely more modern sounding...but with a few tweaks it can get quite mellow and warm. Maybe not quite like the Vintage...but close enough.

Overall, I'm very happy with this preamp. I'll be returning the Vintage and sticking with the Black Mirror as my bass preamp of choice. :D

View attachment 21648
View attachment 21649
I made mine last week. I have the same problems with the distortion. How did you fix that? I tried to replace the ic4 with another kind of opamps, but when i want to turn the level, the blend and the distortion pots to the max. at the same time its dying.
 

jeffwhitfield

Well-known member
I made mine last week. I have the same problems with the distortion. How did you fix that? I tried to replace the ic4 with another kind of opamps, but when i want to turn the level, the blend and the distortion pots to the max. at the same time its dying.
Try switching out the J201’s. I socketed mine and switched them out with a different set. That seems to make a difference.
 

fig

Village Idiot
Still looks great! Did you happen to take any measurements on those 201s?
I'm also wondering about the CD4049. Some of those have been reported to be noisy by a certain Circuit Wizard known to grace these here parts?
 
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jeffwhitfield

Well-known member
Still looks great! Did you happen to take any measurements on those 201s?
I'm also wondering about the CD4049. Some of those have been reported to be noisy by a certain Circuit Wizard known to grace these here parts?
I haven't but I probably should. When this issue was happening to me, I did some probing but couldn't figure it out. My best guess is that the circuit is rather finicky about the clippers so having the right 201's is probably it.

This one doesn't use a CD4049...just some TL072's and TL074's. I wondered if it was due to some bad TL072's so I tried switching those out too.
 
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jeffwhitfield

Well-known member
Still looks great! Did you happen to take any measurements on those 201s?
I'm also wondering about the CD4049. Some of those have been reported to be noisy by a certain Circuit Wizard known to grace these here parts?
NM. I'm an idiot. There is a CD4049 in the circuit. :p
 

csipete

New member
Try switching out the J201’s. I socketed mine and switched them out with a different set. That seems to make a difference.
I switched out the j201s with several pairs, but the problem was still there. I went to another store and bought another (but different made) 4049 chip and it sounds perfect. I cannot belive that there can be that kinda difference between the same sort of chips.
 

jeffwhitfield

Well-known member
I switched out the j201s with several pairs, but the problem was still there. I went to another store and bought another (but different made) 4049 chip and it sounds perfect. I cannot belive that there can be that kinda difference between the same sort of chips.
Whats the exact part number? Just tried all my CD4049UBE chips and none of them work. I’m thinking I have the wrong 4049. 🤪
 
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jeffwhitfield

Well-known member
Jeff,

That's why I initially asked. @Chuck D. Bones wrote something about the newer date code chips being noisy. (y)
Yeah, and I assume that the 4049 is what is mostly responsible for the drive given that it's sandwiched between one of the TL072 stages. If that's the case then these new 4049's are kinda borking things. Might mean some biasing is required. Ugg! Really don't wanna! :p
 

csipete

New member
Whats the exact part number? Just tried all my CD4049UBE chips and none of them work. I’m thinking I have the wrong 4049. 🤪
cd74hc4049 were bad, and now a cd4049ube is good.
And there is another idea: yesterday i tested it with a 9 volt battery (and works fine), so it is possible that my boss adapter is not enough for this circuit. But IDK. :)
 
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