Author Topic: Little Gem MKII not working on the BB  (Read 21561 times)

Kipper4

Re: Little Gem MKII not working on the BB
« Reply #60 on: September 12, 2016, 06:13:42 PM »
Rename it the Tupperware?

Ferris wheel. Geez.
Mexican radio receiver with a pill bottle Ariel ?
Pictures please.:)
"Duck_Arse
otherwise, you might end-up with SOIC or gullwings, for surface mounts."


Smoke me a Kipper. I'll be back for breakfast.

Grey Paper.
http://www.aronnelson.com/DIYFiles/up/

PRR

Re: Little Gem MKII not working on the BB
« Reply #61 on: September 12, 2016, 11:08:30 PM »
> Electro-static from the neighbor's ferris wheel?

I just heard a story, that a traveling ferris wheel, foldable for travel, folded-up while people were on it, triggered by smart-phone radiation or somesuch.

What have you got to lose? A leg? A life? A plastic container?
  • SUPPORTER

duck_arse

Re: Little Gem MKII not working on the BB
« Reply #62 on: September 13, 2016, 11:11:14 AM »
mount the metal jack on some etched PCB. mount the copper-less pcb to the metal chassis (4 bolts/rivets), with a hole bigger than the jack so it doesn't contact. whoosh-kah (as kipper tries to say).

or just do what Paul tells you. twice now.
"i have it exactly like that"

Ben Lyman

Re: Little Gem MKII not working on the BB
« Reply #63 on: September 13, 2016, 12:01:04 PM »
thanks guys, for now I am going to try the plastic box. It already has two holes in the lid slightly larger than a jack but I used some oversized washers to make them stick.
I have no idea what these boxes came from but they appear to be some kind of waterproof electronic device enclosure with two buttons on top





"I like distortion and I like delay. There... I said it!"
                                                                          -S. Vai

Ben Lyman

Re: Little Gem MKII not working on the BB
« Reply #64 on: September 13, 2016, 01:34:00 PM »
I kinda rushed through the assembly so it's not much to look at but it works exactly as the ROG schematic shows, no volume knob, I have the DPDT gain boost switch on both 10uF caps and I added an extra switch to add one 10uF cap for a lighter gain boost.

« Last Edit: September 13, 2016, 06:19:48 PM by Ben Lyman »
"I like distortion and I like delay. There... I said it!"
                                                                          -S. Vai

Ben Lyman

Re: Little Gem MKII not working on the BB
« Reply #65 on: September 14, 2016, 10:04:33 AM »
what's the best way to add a volume pot without sacrificing the max output?
Data sheets show a 10k b/t buffer and IC's but there's a loss of maximum volume, I'm guessing because there is always 10k going to ground no matter what.
"I like distortion and I like delay. There... I said it!"
                                                                          -S. Vai

Phoenix

Re: Little Gem MKII not working on the BB
« Reply #66 on: September 14, 2016, 10:08:38 AM »
Replace the 10k jfet source resistor with the 10k log pot, and connect the 220nF cap to the wiper of the pot instead of the resistor/source junction.
You're correct about why it drops the volume, a 10k load is too much on the jfet source follower.

EDIT:
Could also use a larger value pot like 1MEG after the cap (in the same position you had the 10k pot presumably), as that will not load down the jfet so much, and also has the benefit of not having a DC voltage across it, so you won't have a scratchy volume control.
« Last Edit: September 14, 2016, 10:16:22 AM by Phoenix »

Ben Lyman

Re: Little Gem MKII not working on the BB
« Reply #67 on: September 14, 2016, 10:42:33 AM »
Thanks Pheonix, sounds like a plan. I had thought about trying a 1M pot but I thought maybe the sweep would be weird. I'll give it a try anyway, then maybe a reverse log and see how it reacts.
I also like your idea of replacing Q1s r with a 10k pot. cool thanks.

What about building a preamp onto the front end with gain, volume, and tone? Can that just be added right onto the buffer input?
"I like distortion and I like delay. There... I said it!"
                                                                          -S. Vai

Phoenix

Re: Little Gem MKII not working on the BB
« Reply #68 on: September 14, 2016, 11:12:34 AM »
Keep in mind that replacing the 10k source resistor with a volume pot may result in a scratchy volume control due to DC being present on the pot, as I noted in my edit to the previous post. It may or may not be objectionable, try it and see.

The input impedance of the LM386 is typically 50k for both the inverting and non-inverting inputs, you're driving two in parallel, so the load on the pot would be ~25k. That's definitely low enough to mess with the taper of a 1MEG pot. If you used something like a 100k linear pot, that will not further load down the source follower to any significant degree, but matches up nicely with that ~25k load as a tapering resistance to give you an approximately logarithmic response.
This would not effect a 10k pot placed in the jfet source, as the following load (~25k) would not load it enough to taper it, so you would be best to use a log, not linear pot in that position.

If you made a preamp with tone controls and clipping you could omit the buffer, as the preamp itself would be a buffer - it's just there to prevent loading your guitar too much. Other circuits such as the Smokey amp load the guitar on purpose as part of their tone, that is why they don't include the input buffer.
If you put in a passive tone stack at the end of you preamp you may need a buffer in between it and the power amp though, as 25k is a pretty low load impedance - depends what and how you try to implement.
You wouldn't want much gain/output level from a preamp, because the LM386's already have a gain of 20, or 200 with the boost caps engaged. You've already got the 10uF boost capacitors on a switch though, so that will make experimentation easier.

Another option for gain control would be to add a pot (10k would be a good choice) wired as a variable resistor in series with the boost caps. You could do this for both LM386's with a dual gang pot, or you could do it on just one of the LM386's for asymmetrical distortion.

Hope this helps.

Ben Lyman

Re: Little Gem MKII not working on the BB
« Reply #69 on: September 14, 2016, 12:00:22 PM »
Hope this helps.
Tremendously! thanks
"I like distortion and I like delay. There... I said it!"
                                                                          -S. Vai

Ben Lyman

Re: Little Gem MKII not working on the BB
« Reply #70 on: September 15, 2016, 01:57:41 AM »
I'm learning from experimentation as well as the info from you all.

TS-9 in front, sharing the same daisy chain 9v adapter works with the amp in "un-boosted" mode. Boost switch ruins it.
TS-9 on it's own battery into the amp works in all modes.

So I guess I would have a problem building a preamp into the amp because a 9v 1-Spot won't provide juice for all of it?

I could build another LG MKII without boost switches and build in a preamp because it sounds great with the TS9 on all the time thru the clean setting, gives me 3 controls, gain, level, and tone. It is also way louder when using the TS-9 as the source of tone and volume into the clean LG MKII.

TS9, simple as it is, still seems like too much for me to want to add to the LG MKII though.

The ROG Tonemender looks like a possibility too, but it's just a clean booster with tone controls and I'm not sure how that would work out with the boost switches either:
Tonemender schematic http://www.runoffgroove.com/tonemender.png
Tonemender html http://www.runoffgroove.com/tonemender.html



"I like distortion and I like delay. There... I said it!"
                                                                          -S. Vai

Phoenix

Re: Little Gem MKII not working on the BB
« Reply #71 on: September 15, 2016, 02:50:54 AM »
TS-9 in front, sharing the same daisy chain 9v adapter works with the amp in "un-boosted" mode. Boost switch ruins it.
TS-9 on it's own battery into the amp works in all modes.
A genuine 1 Spot has more than enough current available to run both, can you describe what you mean by "ruins" it? No output at all? Unpleasant distortion? Choppy/gated sound? Oscillation/squeal?

So I guess I would have a problem building a preamp into the amp because a 9v 1-Spot won't provide juice for all of it?
That's jumping the gun a bit, first we need to figure out what's causing the incompatibility when running both the LtlGemII and TS-9 off the same power supply.

Ben Lyman

Re: Little Gem MKII not working on the BB
« Reply #72 on: September 15, 2016, 09:38:09 AM »
Cool, thanks Pheonix. Unpleasant, gated, choppy is pretty accurate. I'll try to make a demo vid later showing how the boost switches affect the combo.

Edit:
it seems to be sounding fine, go figure.
I must've been doing something wrong late last night, maybe a bad cord or something, I dunno.

The other effect I really like in front of the amp is a sort of Electra type OD that I made a while back
« Last Edit: September 15, 2016, 10:05:57 AM by Ben Lyman »
"I like distortion and I like delay. There... I said it!"
                                                                          -S. Vai

Ben Lyman

Re: Little Gem MKII not working on the BB
« Reply #73 on: September 16, 2016, 02:13:57 AM »
Still working after an hour of loud use today with the TS9 cranking it up. Definitely loud enough to use with my band through my 2x12" cab.

I got out my TDA2822 and checked the data sheet. It is a lot easier to do the bridge thing with a single IC like this, worked first try on the BB, no noises or anything bad.
There is a schematic on the data sheet for bridged mono output. I added a 2n5088 buffer with a 22nF input cap and took out the 4.7uF, replaced the 10k pin 7 to ground with a 10k pot.

Here's a link to the data sheet, the schematic is down at page 4/11:
http://www.st.com/content/ccc/resource/technical/document/datasheet/9e/18/f7/cd/2e/b8/43/62/CD00000134.pdf/files/CD00000134.pdf/jcr:content/translations/en.CD00000134.pdf

Its very loud and clean,it looks to me like theres no way to adjust gain like on the LM386? But I think because of the simplicity, its a good candidate for a preamp.

Where would you adjust tone if you wanted a little more treble out of it? Its kind of bass heavy
"I like distortion and I like delay. There... I said it!"
                                                                          -S. Vai

anotherjim

Re: Little Gem MKII not working on the BB
« Reply #74 on: September 16, 2016, 03:59:44 AM »
I'd use a coupling cap into the chip. It has 100k input impedance, so in the 4.7nF to  22nF range to cut bass.
Try a big muff tone control. It will be lossy, but can be set to give some mid-scoop similar to a traditional tone stack.
Croeso i Diystompboxes.

If they didn't hear you then you didn't say it.

Ben Lyman

Re: Little Gem MKII not working on the BB
« Reply #75 on: September 16, 2016, 11:39:13 AM »
Thanks Jim. I think this is what I have now. For R3, is it possible to use a 100K pot because I think it will increase the volume even more?
And then, put the BMP tone stack right after that going to Pin7?

"I like distortion and I like delay. There... I said it!"
                                                                          -S. Vai

anotherjim

Re: Little Gem MKII not working on the BB
« Reply #76 on: September 16, 2016, 03:50:00 PM »
Hi Ben,
You do have a base bias on Q1?
I don't think 10k should be loading it that much, but sure 100k could work (there's 47k pot in the radio application in the data).
Bass limit cap would be between emitter and vol pot. If pot=100k, it would be about 1/10th of the range I suggested above - but it's working into 50k (the pot and chip input impedance in parallel).
To run a tone stack, the front end should have some gain - copy an LPB1 for the front end - that should do it.

Or if you have some J-fet, use a Fetzer stage. Then you can claim tube sound ;)
If true polarity bothers you and the pre-amp is inverting, you only have to swap the wires for the speaker jack to put it right.
Croeso i Diystompboxes.

If they didn't hear you then you didn't say it.

Ben Lyman

Re: Little Gem MKII not working on the BB
« Reply #77 on: September 16, 2016, 04:59:28 PM »
Awesome! Thanks again Jim. Yes forgot the bias, I'm using a couple 220K like this, corrected schematic:


I tried it with an A100k vol pot, so far it's good. I also put a 22nF cap at the input to the buffer base, and another 22nF at the emitter to volume pot... is that weird? It just seems to cut some of the lows that way, it's still not perfect but getting close.
« Last Edit: September 17, 2016, 03:08:47 AM by Ben Lyman »
"I like distortion and I like delay. There... I said it!"
                                                                          -S. Vai

Ben Lyman

Re: Little Gem MKII not working on the BB
« Reply #78 on: September 17, 2016, 03:09:15 AM »
It sounds great with the BMP tone stack, LPB-1 as a booster is working. It didn't take kindly to a TS9 or RAT until I put the buffer back on. I really like it now, very loud, tone is bright or dark as needed and sounds great with pedals. I went back to the 10k volume pot just because. What about all those caps? Can C11 4.7uF go? Anything else that should go? Or something missing?
Here's the updated schematic:
"I like distortion and I like delay. There... I said it!"
                                                                          -S. Vai

anotherjim

Re: Little Gem MKII not working on the BB
« Reply #79 on: September 17, 2016, 05:09:42 AM »
Both sides of C11 are ground referenced, so you should be able to lose it, although making it smaller is another opportunity to cut bass overall.

10k volume is loading down the tone control. 100k will give a lot more back. With those tone values, you have high/low shelving control, but no mid scoop. That's fine if it suits your sound.

You shouldn't have to put a buffer in front. It has similar impedance to the LPB, and having no gain, shouldn't be doing anything for you. If anywhere, the buffer can go after the tone. Then you can have 10k volume without loading the tone stack so much.

I would try putting power filtering RC on the pre-amp supply. You don't want supply ripple fed into the preamp, especially not now it has gain. This may also be key to why you're getting interaction with some other pedals. The C doesn't have to be very large - 10uF? and the R can be larger 470R?.
Croeso i Diystompboxes.

If they didn't hear you then you didn't say it.