Blog Comments

  1. Micky's Avatar
    The above modifications are pretty much common knowledge, but one of the aspects still haunts me, day after day.

    You see, this type of pedal is inherently noisy, that is, there is a fair amount of hiss when you activate the circuit. One of the things I usually do with BOSS pedals that still allow for modifications is change the op-amp from the stock choice, to one more suited to the task.

    One of my go-to choices is the Texas Instruments NE5532. Here is a link to a Monte Allums site where he provides a very nice section and describes several op-amps in detail. http://monteallums.com/pedal_mod_parts.html#ops Here is what he said about the 5532:

    NE5532 - Made by Texas Instruments. Very similar tone-wise to the JRC4558D and RC4558P. This is a more Hi-Fi, lower noise chip than both the JRC4558D and the RC4558P. I really like the tone and gain of this chip. In some ways I like it better than a JRC4558D or RC4558P. Rich, smooth gain with nice overtones. This is a very popular chip with pedal modders.

    The reason this is my go-to chip is simply because of the low noise. I especially like this chip in the GE-7 equalizer pedal because if the low noise, (high signal to noise ratio as well as the incredibly low noise floor) and the way it corrects a deficiency in the OEM chip, where lowering one setting can actually INCREASE the noise in the pedal.

    In this particular application, it is the lowest noise op-amp that you can reasonably obtain that will still fit in the pc board as designed. The Dual Inline Package (DIP) is an old-school design that does not lend itself to close component placement such as some newer smd designs that have incredibly low noise, and when the design is right, can offer some unbelievably low noise floors. With the design of the OS-2 you really don't have a lot of choices, and you need to work with what will fit. Even the 1/2 watt resistors I used were actually too big, and I needed to install them vertically because I did not have 1% metal film resistors in 1/8 or 1/4 watt sizes.

    Another thing not many will notice (mainly because I did not go into detail about the replacement components I used...) is that I replaced a couple electrolytic caps with monolithic dipped caps. You can get away with this about up to 1uf or so. The smaller metal film caps used in BOSS pedals are incredibly inexpensive, and with time, their values tend to drift a bit.

    Anyway, if you were looking for sound clips you are gonna be disappointed. None will be found here. Sorry. Just take it for a fact the pedal sounds better and is much quieter. Actually the biggest change had nothing to do really with any of the components I changed. It had to do with cleaning the 30-some year-old pots that had become scratchy and irregular. I sprayed them (with waaaaay too much) DeOxIt cleaner and lube, and then had to wipe up the excess lube after the pots had dried a bit. The 12mm pots with knurled shafts used (4-in-a-row) are difficult to find, although I found a source for the smooth shaft ones. If I had some small knobs with set-screws I would have just changed them out rather than try to bring them back to life. Anyway, with the lube they should be good for another 30 years or so.

    Feel free to contact me if you have questions, I can be reached at mcorrow@gmail.com
  2. Micky's Avatar
    You can see by comparing the last 2 photos above, many of the mylar caps have been replaced such as C27, C20, C17 and others. Some of the electrolytics have been replaced as well, with ceramic/mylar/poly (or whatever) dipped caps. As long as the value is under 1u you can generally get away with this, especially in lo-voltage circuits such as this.

    The modification kit I purchased for this is the Fromel Electronics out in Seattle. This kit is a good start to make a mediocre pedal into a very good pedal. Beyond this kit I have chosen to make additional modifications and replacements, to get things into a bit of a customized for my situation type of sound. You can see the kits for pedal mods here: https://fromelelectronics.com/collec...pedal-mod-kits and they have many other products as well. Although the kit I purchased was complete, the instructions were geared towards advanced builders, you can do it yourself or have them mod your device. I felt the lack of a step-by-step listing should really discourage many pedal modders.

    The mod kit I purchased is very similar to the mods I found here:

    https://www.roboticbeast.com/modific...-la-boss-os-2/ These show some very detailed photos outlining the various component replacements he made, I needed to translate it from French.

    The schematic (basic one anyway is here: https://0x4c.files.wordpress.com/2018/10/os-2_orig.png

    Some op-amp information and links here:
    https://www.cycfi.com/projects/six-p...-amp-shootout/

    http://www.ti.com/lit/ds/symlink/opa2134.pdf

    https://www.rcscomponents.kiev.ua/da...4ufguygf43.pdf

    https://pdf1.alldatasheet.com/datash...I/M5218AL.html
  3. Francis's Avatar
  4. RiverRat's Avatar
    Thanks man, I appreciate it. The rectifier is a 5Y3. Glad you’re getting some good tones from it finally. You kinda got me in the mood to build something for myself. I have a chassis I can recycle. I already put in an order with Mouser for the resistors and signal caps.
  5. Micky's Avatar
    Whatever it is it sounds fantastic! I didn't pay too much attention to it, all I really remember is that it was a nice big bottle 6L6, and I had already tried a couple others. I can't even remember what rectifier I had, all the printing seems to be worn off, whatever the combination is it sounds great. Thank you again, without your eagle eyes I would have never gotten this running again.

    I tried a new trick with it today, more about that later after I figure it all out...
  6. RiverRat's Avatar
    That was actually a 6L6GB I sent. You should get a little more break up with it - kinda like a 5881 but more big and round, if that makes any sense.
  7. cornhusker86's Avatar
    Glad you like it. Play the shit out of it!!!
  8. Micky's Avatar
    Time to finalize this entry in the blog!

    After an agonizing wait, Alan finally shipped the amp back to me. I will bet anything he was having a blast testing this thing out!
    He was kind enough to send along some extra tubes, and since this is a single-ended 8-pin design, just about anything left over will fit and work. I know I couldn't wait to try all the odds-and-ends I had laying around. Every goddam one of them sounds great in this little amp.

    What amazes me is how quiet this thing is. Just the slightest bit of hum, and you need to put your ear up to the speaker to hear it. Of course it is a different story with a guitar plugged in and the amp turned up all the way. OH- You should notice that this amp goes to 12. That is 2 more, int it?

    Having just received the amp a day early, I haven't had a chance to try different guitars yet. I also wanna plug in a pedal or two, but so far things are working great. Hard to believe it is only a 5-watt amp. So far I like the 6L6GC big bottle in it...
  9. coyotesgator's Avatar
    Update! Update!
  10. cornhusker86's Avatar
    I play it often. Sounds great! A boost pedal is all I use with it. Too much dirt overwhelms the speaker. A 10" will give you more choices. The 5 watts is perfect for what I use the amp for.
  11. Micky's Avatar
    OMG! I love it!

    Like I mentioned, it is almost identical to the Champ 5F1 circuit, so I will bet that it sounds glorious! I have built-in a couple mods into mine already like the larger OT (15W) and @RiverRat has already tried several different finals in it. I am looking for a very specific tone from it, most notably Joe Walsh type of mid gain creaminess.

    Do you use this amp a lot? Is it your carry anywhere go-to amp? How does it fare with pedals?
    Sorry for all the questions, but I need an amp I can throw in the back of the truck easily and cart around, something that doesn't weigh too much but still cranks a bit. The GA-5 or 5T is a cool little package, but in my Champ I decided to get a custom-made 10" cab that I think might be a good compromise. I just hope with all the upgrades that it is not too heavy...
  12. cornhusker86's Avatar
    Micky,

    I have one of reissue versions of the Gibson;




    I replaced the weber speaker w/ an eminence patriot 820H. Sounds great and now the bottom end stays together at full volume. Not a lot of choices for 8" speakers. I bought the damn thing more out of curiosity than anything else. After having it for a year now, I doubt I'll ever sell it.
  13. Micky's Avatar
    So, apparently the Gibson GA-5 is just about the same circuit. I think they called it a Skylark, but anyway it came in several different configurations just like the Champ went thru.

    I am itching for one of these, but I fear it is so much like the Champ it won't be worth it. I love the simplicity of it, but this GA-5 is a SS rectified model, and I will bet it has a bit more clean headroom as well. I am pretty sure the GA-5 is the amp Marty McFly cranked in the beginning of Back To The Future...
  14. RiverRat's Avatar
    I with I could crank it. Living in an apartment, I have to be careful. I did crank the volume all the way for a minute and lightly brushed the strings on my SG. It’s a magical experience for sure. If I had the cab, I might not be in too big a hurry to send it home. I gotta build one of these. I have a 1x12 combo cab if I can find a chassis to fit it.
  15. Micky's Avatar
    Yeah, I have been beating myself up over it for a while now, but now that Alan has saved the day I think I will take some time and relax with a big grin on my face. It is not the first time I have let the smoke outta something, and I imagine it won't be the last. Remind me to post about the time we vaporized a pie tin with a Ham Radio amplifier...

    Now all I need to do is convince Alan to wire it for 16-ohms and send it along. I can see him now with a smile on his face cranking out old Aerosmith tunes...
  16. coyotesgator's Avatar
    Don't beat yourself up about it Micky. Sooner or later we all let the smoke out of something.

    Nice save Alan.
  17. RiverRat's Avatar
    The amp is up and running and sounds GREAT! Since it has iron that’s rated for up to 15 watts, I’ve been playing around with different tubes. I have a GE 6L6GB that sounds big and round. I’m probably going to send it with the amp.

    I checked the power tube socket and noticed that it didn’t have anything soldered to pin 1. I put a jumper wire between pin 1 and the cathode at pin 8, so now this puppy can run EL34’s and the old metal can 6V6 and 6L6 tubes without the danger of touching the can and getting a nasty shock. Cool!

    I love the 5F1/5F2A circuit. It’s simple and sounds huge for what it is. I hope the owner is happy with it. I would be.

    New transformers:


    With an EL34:
  18. Micky's Avatar
    Time to fess up...

    The amp is almost done, but there was a slight detour along the way.
    After mounting the board, and insuring everything was soldered, I fired up the amp.
    Kind of a strange humming, but it didn't look too bad, and the humming was inline as I turned up the volume.
    My wife called me from the other room, and I got up and went to see what she wanted.

    I came back just a few moments later, and I could not believe all the smoke coming out of this tiny amplifier.
    Apparently I had something terribly wrong, and now I had let all the smoke out.
    The smoke filled the house and started setting off smoke alarms. I turned off the amp...

    After opening all the windows in the middle of a cold winter night, the smoke finally cleared.
    I looked inside the amp, and something had gotten very hot, and had dripped out onto the base of the combo.
    Why hadn't the fuse blown?

    Then I found out why... The fuse below is still good.



    It is an MDX 5A, slo-blo 5 amp. Why had I installed a 5-amp fuse in a 2-amp holder?
    Apparently I am dyslexic or something, as I didn't even think to re-check it before turning it on.
    I had been working on it on the dining room table, where all my test equipment is downstairs.
    (this incident has inspired me to modify/install my variac in a new enclosure...)

    I was so disgusted with myself I threw the amp downstairs behind a pile of other stuff I had screwed up.
    I tried and tried to forget about it, and thought I had succeeded...
    That is, until I started to clean out the junkpile downstairs.

    I was looking for items to sell at a flea market, and looked long and hard at the amp.
    I have already invested over $450 into it, and thought about what it might be worth as scrap.
    Parting it out might recover about half of it, but I knew I would take a hellova loss if I did.

    I was kinda sure I had let all the smoke out of the transformers, which was really sad.
    These were nice ClassicTone transformers, plus I was sure some of the caps were gone as well.
    I thought about trying to diagnose things, but each time I picked up the amp I got more disgusted with myself.

    In steps @RiverRat to the rescue. I had something he wanted, so we worked out a trade.
    He agreed to diagnose the amp, and I agreed to send what he wanted.

    So finally he confirmed what I feared the most, that the transformers were shot.
    About $100 later, he has new transformers and should be installing them soon.
    Maybe if he reads this it might inspire him to chime in about his experience with this little amp.

    Hopefully he can ship it back soon, and I can provide some final photos of this beautiful little thing.

    Then come the modifications...
  19. DirtySteve's Avatar
    I forgot about this blog section. Cool to see pics!

    I honestly don't know what this blog thing is all about. Why not just post this on the main forum? I can't even give you a "like".
  20. S÷ulcaster's Avatar
    Good luck Micky,
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