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Hello again!

So I've built a Mimosa with the bass mods, but the compression doesn't seem to be doing very much and I get a lot of clipping (especially on lower notes). LED, on/off all work fine and the level and blend knobs are working properly.

Adjusting the trimpot, I can only get a max value of 0.92v on the middle transistor pin, well shy of the suggested 1.5-1.7v.

I've already reflowed all my solder joints (since taking the below pics), with no change in sound or voltage reading.

My transistors are 2N5457G, does the "G" denote a different pinout or something?

And finally, since I have bulk components but I had to "locally source" the (bass mod) .33n caps: I believe I ended up using ceramic disk instead of film caps in positions C1, C2 and C3. Does that make a difference?

You may have installed incorrect value caps. The instructions note that C1-C3 should be changed to 330nf or 0.33uf film (334), not 0.33n. Using 0.33n (330pf) would cut a ton of bass signal from the signal path. The instructions also note that the 330n caps should be included with the kit. From step 6: "To modify your Mimosa kit for use with a bass guitar, change the capacitors highlighted in blue to the .33u provided in your kit."

If the 334 caps were not included in the kit, I would email BYOC and they'll send you some.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

Sorry, that was a typo. I know they're .33uF. The caps I used say "334" on them. I just got the PCB, not the entire kit, from BYOC. All the other components I have bulk. Sorry if I wasn't clear on that.

Anyway, C1-C3 caps don't look like regular film caps - if they're ceramic disk, would that make a difference?

I don't have 334 film caps, but I have higher values. Would that work?

The cap composition doesn’t matter for operation.


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MasterDelayer/Reverbrador/Ampaholic/TopJacker

Ok, so my capacitors are fine, then. Thanks!

I'm thinking the overall bad sound is somehow related to my voltage reading on the transistor. What might cause that?

What type of diode do you have in D1? It doesn't look germanium, it looks like a 4148. I don't know this circuit that well, but my understanding is the germanium diode is critical to operation (different fwd voltage).

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

Germanium 1n34a, according to the packaging. Is it a possibility they're mislabeled?

http://www.nteinc.com/specs/original/1N34A.pdf

I'm really at a loss here as to what might be going on:

I've tripled checked every resistor and cap (including electrolytic caps), I've resoldered every joint, I've measured the diode to confirm it's germanium with a forward voltage of exactly .3V. Could it be a bum transistor or IC? Is there a way to check them?

My IC is a Texas Instruments MC3403N. The transistors are 2N5457G. Do the respective "N" and "G" suffixes mean anything important?

Any help would be greatly appreciated. I've been throwing myself into learning about circuits, but I'm still very much a noob. Does the low voltage reading at Q2 point to any specific problems? Thanks again!

Did you reflow all of the solder joints? Many of them don’t look like they flow through the solder pads. After 7 or 8 years old building, I occasionally screw some up still.


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Pedal building is like the opposite of sex. All the fun stuff happens before you get in the box.

It looks like you got the PCB from us, but sourced your own parts. Where did you get the 2N5457 from?

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*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

The transistors are from Tech Express, part number: TET2n5457, purchased through Amazon.

On them are printed the following, exactly as written:
FBC27
2N
5457

Uh-oh. That's exactly what's printed on the counterfeit 2N5457 that I just clipped out of my Lazy Sprocket 2.0 per Keith's post here: viewtopic.php?p=482557#p482557

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A problem with JFETs would explain a lot: My only other build with this batch was a BYOC Tremolo, and while it sounds pretty good I do hear a hair of clipping.

Has BYOC had problems with them? A few months ago I made an Echo Royal (from a full BYOC kit, no sourcing of my own) with some issues:
http://www.byocelectronics.com/board/viewtopic.php?f=20&t=56680

Did your kit come with 2N5457 JFETs or did it come with J113 JFETs?

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

I had to look: the Echo Royal kit came with J112, so I'll have to explore that further once I've solved this Mimosa mystery.

We did it! It was definitely bad transistors: swapped in new ones and it cleaned right up, compressing as it should. Next I'm going to try replacing them in my Tremolo.

My only other question is, I seemed to need to set the bias pretty high to notice compression: 2.00v seems to be a sweet spot. Any thoughts on that?

Thanks again! I'm really looking forward to my bassist trying it out at rehearsal next week.

EDIT: I was playing like a wimp at first, so I didn't notice that the poor thing is still clipping. The compression is much more noticeable wit the new transistors, but anything on the E or B of my 5 string bass introduces a nasty buzz, especially if I play with any amount of aggression. I tried fooling with the bias pot, but it actually clips on ANY setting, also with the blend all the way down. This tells me I'm clipping early on in the signal chain, before it hits whatever is doing the compression (bypass mode is still totally fine). Any suggestions welcome.

It only clips with my bass (an active Spector), not with my guitars (passive pickups), so clearly the hotter signal is causing the clipping. Is this normal for an OS clone? Is there something I can modify to totally eliminate the clipping, even when I'm playing aggressively?

It may be possible to run the Mimosa at 18V—if so, that may increase your headroom.

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Thanks, everyone who helped!

I finally got it perfect - once I replaced the bum transistors, the problem was that my bass was just outputting a PREPOSTEROUSLY hot signal. I actually have two Spector basses: a Korean and the aforementioned Czech model. The latter is equipped with a TonePump preamp that really needs to be dialed back via a trimpot. The pedal worked great for my Korean (has a different preamp), so I just dialed the Czech to a similar level and voila! Works like a charm and sounds great! I've tried a few other active basses through it and they all sound awesome. Thanks again!