alexc

runoff Groove umble build
« on: December 08, 2018, 03:54:24 AM »
ANyone else done on of these ...

runoff Groove's 'umble'    pedal preamp implementation of classic tube amp 'pre' section ...

http://www.olcircuits.com/olc_umble.html

I got my pcb going properly today and wow!zer  - did it knock my socks off.

Biased it up quite basic like, the four fets are common unmatched   ..   j201  ... the Vp is reasonably similar across the set and the bias up quite close, at the 'source' pin   ..   +0.82V to +0.90V. No probs 'centre biasing' the 'drain' pin with 100K trimmers.

ANyway - yep, it's all there ... huge dynamic range, even with a standard 9V battery supply. 

I was playing it into my 'tube bass amp' head and '15" pine box' and it was huge. 

The tube amp is single ended and I like to run it at low power quite clean ..  it's a big sound that you don;t mess with! It can be a little-bit light on the delicate 'treble' ..  I think it 'takes' boosting pedals quite well, taking a lot to ruffle it's gravitas.

But this modest circuit transformed it into a raging beast  ... 

Fairly quiet, schmutz wise, with maximum on the 'touch sensitivity' tweaky-tweaky thing,  like I've never known before.

....

ANyway, I'm just putting it in an alu box .. but again, I'm amazed at what 4 fets and some thoughtful approaches to historical circuits can achieve ... for quite low cost.

I'm really interested to hear how it will sound with some solid state power amps, like those tiny modern types  :)

I'm ordering another similar pcb, just to see how it integrates into  my   rack of  'franken-modules'  ..  I think it's worthy of inclusion!

Thinking  to add a line amp for recording  and some small amp module .. 

:) 
« Last Edit: December 08, 2018, 09:14:44 PM by alexc »
I ping therefore I am


midwayfair

Re: runoff Groove umble build
« Reply #1 on: December 08, 2018, 10:23:07 AM »
If you ever get the itch to do a second one, look around for the old aquataur site. He did some fantastic mods to this circuit. If you can't find it(I think it went offline at some point) if you dig up my Snow Day OD I used his miniature compression circuit in there for the same reason.

ROG have come a long way with their circuits since they made this. Their newer stuff (especially the Britannia) sounds much better through solid state stuff. I've used the Britannia direct for recording a couple times and it's on par with most decent digital emulators but sounds a little better when distorted.
I'm Jon. Myself's music and things I make: jonpattonmusic.com. My band: www.midwayfair.org. [Disclaimer: PCBs of guitar pedals I've designed are sold by Madbean, 1776 Effects, and JMK PCBs.]

alexc

Re: runoff Groove umble build
« Reply #2 on: December 08, 2018, 05:10:24 PM »
Thanks for the tips!  I am looking at the Britannia next.

This 'umble' pcb from OLC is years old ..   the current ones are more developed, which is great to see.

The circuit , made of 4x  j201 jfets in the 'fetzer valve' style is really interesting to mess with. Next one, I remember to put in sockets for the fets to do some fet-rolling :)

I love the realism of the sound - and it can get very mean sounding,  but not too 'fizzy' like some overdriving schemes ...

I'm looking forward measuring this little pcb once I have it put together with a box ..

Still working thru the 'different' eq stack  ..  the 'umble' part  but it does seem to have an all-powerful 'mid' control ....  more like a 'roar' control  :)

These little boards are a great way to hear what these different tone stacks sound like.

Next up



I ping therefore I am

alexc

Re: runoff Groove umble build
« Reply #3 on: December 08, 2018, 09:15:10 PM »
And I do have a project in mind for a rechargable, battery powered combo amp in mind ... it's been on my mind to do one for years.

The batteries are much better these days. I have to do refresh to find a suitable powerpack for +12 to +18V supply with a few amps behind it.  If I can find a 'charge controller' to suit, it can be plugged into main supply, all the better.

I'm thinking a solid 30Wrms or so, probably stereo, of 'class T'  power .. with a fan.

Pine box, nice and modern drivers for hifi ..

Some brass plate frontages for the different modules   ....  sort of a larger 'pignose' done the way I want.

I had a little one as my only git-amp when I 'travelled' ..  I thought then that one day, I would make a good sounding one.
« Last Edit: December 08, 2018, 09:49:04 PM by alexc »
I ping therefore I am

alexc

Re: runoff Groove umble build
« Reply #4 on: December 17, 2018, 03:58:50 AM »
Having a more detailed look at this tiny but powerful best of a pcb  ....

I started with the basic 'centre bias' -ing of the 4 fets with a 9V battery supply. 
I did a simple setup by ear with my 'test strat'  to get a basic sound, as clean as I could and reasonably flat-ish.

Then I hooked it up to REW and optimised each bias in sequence for lowest THD at the output. 
Then I variously tuned the last 3 fets to find any improvements.

I get basic figures of something like 4.5% thd for fet_1 mostly h2   .....  to 18% thd at fet_4 output, complex thd spectra ....  this pcb is quite a high output for a pedal.

I'm just looking at the noise and dynamic range - it kind of maxes out at around 60dB of signal-to-hum margin with a good sized amount of 50Hz that I'm still looking at. 

Not sure where it's coming from ...  there's no mains anywhere nearby and I know my analyzer setup is super low noise. I haven't really spent time with effects pedals and REW, but it is interesting to see the differences with battery powered stuff.

The test setup is batter powered, input is sourced from an 10K-10K isolating/debalancing transformer and outputs are connected to a 20K load.

I'm ordering another pcb to do it properly  ...  this one was just a curiosity from spare parts  :)
I ping therefore I am

L´Andratté

Re: runoff Groove umble build
« Reply #5 on: December 17, 2018, 04:39:43 AM »
Never did the Umble, but did a ROG Ginger and Azabache, and both are among my favourite and most used circuits I ever build. Especially Ginger on bass, very dynamic, a lot of subtlety.

For battery voltage monitor check out maxim 7663 and 7665 combination in the Max7665 datasheet, maybe it´s interesting to you, I stumbled upon it, checking out 18650 battery packs for more firepower...
Strictly amateur since 1973...

Jarno

Re: runoff Groove umble build
« Reply #6 on: December 17, 2018, 06:35:56 AM »
I did build the umble, and a few other circuits, but for my basses it had not enough headroom, and I could not find the sweetspot very well, it was either clean or distorted, none of that creamy warm tube distortion (but then, maybe this is not to be expected from such a simple circuit). I think I did also try higher power supply voltage, it has been a while. The concept is promising though, maybe something with a better biasing scheme to allow for JFET variation, driven off of dual rails to get more headroom.

Edit:
Now I remember, I liked the Umble for guitar. The thing I wasn't so enthousiastic about was the ROG Flipster, that wasn't able to cope with the output of my basses (admittedly, they are all active basses).
« Last Edit: December 17, 2018, 06:41:34 AM by Jarno »

midwayfair

Re: runoff Groove umble build
« Reply #7 on: December 17, 2018, 11:37:54 PM »
Not sure where it's coming from ...  there's no mains anywhere nearby and I know my analyzer setup is super low noise. I haven't really spent time with effects pedals and REW, but it is interesting to see the differences with battery powered stuff.

Is it boxed up or on a breadboard? Because it could be environmental.
I'm Jon. Myself's music and things I make: jonpattonmusic.com. My band: www.midwayfair.org. [Disclaimer: PCBs of guitar pedals I've designed are sold by Madbean, 1776 Effects, and JMK PCBs.]

alexc

Re: runoff Groove umble build
« Reply #8 on: December 18, 2018, 01:04:57 AM »
Is it boxed up or on a breadboard? Because it could be environmental.

Most definitely so .. environmental!  Not boxed yet, just a pcb module with screened and shielded short pieces of cable for the 5x pots and 2xjacks.

I've been messing with the grounding scheme of the controls and jacks ... I think I've got it stable, I mean it sounds pretty right with a git amp - titanic gain with some schmutz ...  tamer gain settings and it's quite nice.

..

So - yep.  It's all about environmentals ... box, switch, jacks, wiring, pots 

....  then the little pcb module and circuit and parts.

I thought I'd get a modern pcb version with the same guy's  bypass-led pcb  and some of the proper pots from 'small bear' before boxing and painting  :)

I'd also like to try some fets I have left over from the 1176 exploits  .. :) 

.....

Apart from finishing up a  nice pedal, I want to get a better feel of the details of battery-powered  stuff  ... hum wise  ...  both from 'ground' and 'induced' from the environment.

After all these years, I still wish I could figure out why when I 'ground' myself to the circuit, hum drops 3dB or more.

I mean, am I some great source or sink of electrons that it should make a difference ?  But yep - it does!

....

It took me a good many years to finish going thru all my gits electronics,  getting all the switching, pots, jacks and grounds working properly and quietly.

Many 'name' brands, thru the years that I've bought, had dismal wiring and noise issues ... stock.

It's amazing what good parts, wiring and some serious shielding/screening    ... can do.
« Last Edit: December 18, 2018, 01:07:59 AM by alexc »
I ping therefore I am

 

Related Topics

  Subject / Started by Replies Last post
18 Replies
4383 Views
Last post November 06, 2005, 04:53:23 PM
by Hayman
12 Replies
3241 Views
Last post December 23, 2005, 09:32:16 AM
by ciminosound
11 Replies
6140 Views
Last post February 18, 2006, 11:15:52 AM
by Gus
2 Replies
6109 Views
Last post May 20, 2006, 12:20:26 AM
by neverlistentome