Dano's FKR - built, works, but maybe I need to debug??

[ACS]

Hey all, I've been lurking around here for ages, soaking up the knowledge and getting ideas... 

Finally got the time to do my first pedal build (have built loads of other kits in the past - but never anything from scratch) and chose Dano's FKR (http://www.beavisaudio.com/Projects/FKR/archive/BAR_FKR_Mark_2_Build_Documentation.pdf) as his instructions were so good!

So it's all built up, and lo! I actually get sound out of the other end (gotta admit - I was a bit surprised with that, as my soldering skills aren't what they used to be!).  HOWEVER...

The clipping is.... well... Odd.  Sounds fine most of the time, but the decay has a definite 'shelf' - almost a gated effect - as the signal drops off.  This is more pronounced on the higher gain settings, and more pronounced with (for the example) the LED clipping.  Interestingly, if I strike a note, and then turn the level pot down, there comes a point where the volume seems to actually increase - and then the gated effect disappears.  Wierd or what?!

So, having never used and original ProCo Rat before - is this just typical of the pedal, or does this indicate a fault?  I've taken some voltage readings from the LS308, and was surprised to see several pins up around 20V.  Again, is this normal?

Hope you guys can help me out!  I've got the pedal building bug now...

Aidan

p.s. I have actually emailed Dano for help already, but didn't get a response (which is quite unlike him) - I'm assuming he must be on holiday or something!

[petemoore]

So, having never used and original ProCo Rat before - is this just typical of the pedal, or does this indicate a fault?  I've taken some voltage readings from the LS308, and was surprised to see several pins up around 20V.  Again, is this normal?
  Impossible with a 9volt supply...

[ACS]

So, having never used and original ProCo Rat before - is this just typical of the pedal, or does this indicate a fault?  I've taken some voltage readings from the LS308, and was surprised to see several pins up around 20V.  Again, is this normal?
  Impossible with a 9volt supply...

yeah, funny that.  I'm the first to admit I don't know a huge amount about what's actually going on in the circuit, but it definitely struck me as odd...  Will double check with the mm when I get home tonight...

[ACS]

Ahem.  Yes, well it does help if you select the right V setting - ie V DC not AC...  I always was good at first impressions...

What I meant to say was the LM308 pin readings are:

1 - 8.60V
2 - 4.70V
3 - 2.30V
4 - 0.00V
5 - 0.00V
6 - 5.18V
7 - 9.37V
8 - 5.30V

[ACS]

...and battery is brand new at 9.47V

[ACS]

So have double checked all cap orientations and R values and it seems to check out.  Any thoughts please guys?  Or is this simply a case of 'that's how it sounds'?

Thanks in advance
Aidan

[dano12]

Dano? Holiday? No such luck!

Did you build off the layout in the PDF?

What you are describing is not kosher--it should not gate under any settings.

We'll figure it out.

[ACS]

Yep, direct off layout.  Only 'possible' difference is that I've used 3mm LEDs rather than 5mm as that's what I had lying around...  Everything else is as per spec.

Sound wise, apart from the first post, some other things I've noticed while fiddling in the past couple of days:
* there's very little audible difference between the symmetrical and asymmetrical clipping modes.  Is this normal?
* there's a big volume jump up from the diode clipping mode to the LED/Mosfet modes.  Again, is this normal?
* It's possible to get a non-gated sound by turning the drive down to 'a point' where the distortion kind of smooths out (as above).

Do those pin readings look right to you?

So then, where to start?!

[raulgrell]

Meh, my guess would be that the chip is faulty. Switch it out, see what it sounds like.

[ACS]

Interesting - is there anything that points directly to this, perhaps in the V's?  I'm learning all the time here...

I have double and triple checked all components for correct value and orientation, and am happy I have not made any errors.

Below is an image of the populated main PCB if it's any help.

I really hope that someone can help get this sucker sorted - it's driving me mad!

[dano12]

Below is an image of the populated main PCB if it's any help.

I can't see anything obvious. I wouldn't recommend ceramic caps throughout, (I use film caps, except for the 33pf which is Mica) but I don't think that would cause issues. Probably the two most obvious suspects are the chip and the output buffer FET. I'd replace those and see what happens.

[wampcat1]

are you sure you are using a 1m for r5?

[ACS]

Yes, R5 def 1M.  Tx.

Have now noticed that the stack of 1N34A's that I got, whilst all labelled as 1N34A on the packets are in fact labelled 1N60P on the diode itself!  Never trust a mail order supplier...  Haven't changed them yet, but will at some stage soon.

However... I got a new opamp as suggested (couldn't get another LM308 cheaply and easily so decided to throw in a $2 TL071 instead) and when I took the LM308 out I noticed that pin 8 was broken half way down!  Turns out the socket I had was sh1t and pin 8 wasn't making contact, so soldered a new socket in and i now works far better!!  Thanks for all help and advice guys!

I can definitely hear the difference between the two opamps, so will have to play around a bit and see which I prefer...  I can definitely hear that Rat 'yowl' with the LM308 tho...

I've still got a slight gated effected on the diode clipping stage, but I think this is now most likely due to the wrong diodes.  Comments?

One question though - there are quite large volume differences in the various mods - is this usual?  Loudest is 'unmodded', LED OD is next, LED clipping next, Mosfet clipping next, diode clipping last...  Normal?

Thanks guys - a happy ending to my first full build!  And huge kudos to Dano for a great design 

Cheers mate.

[wampcat1]

Yes, R5 def 1M.  Tx.

Have now noticed that the stack of 1N34A's that I got, whilst all labelled as 1N34A on the packets are in fact labelled 1N60P on the diode itself!  Never trust a mail order supplier...  Haven't changed them yet, but will at some stage soon.

However... I got a new opamp as suggested (couldn't get another LM308 cheaply and easily so decided to throw in a $2 TL071 instead) and when I took the LM308 out I noticed that pin 8 was broken half way down!  Turns out the socket I had was sh1t and pin 8 wasn't making contact, so soldered a new socket in and i now works far better!!  Thanks for all help and advice guys!

I can definitely hear the difference between the two opamps, so will have to play around a bit and see which I prefer...  I can definitely hear that Rat 'yowl' with the LM308 tho...

I've still got a slight gated effected on the diode clipping stage, but I think this is now most likely due to the wrong diodes.  Comments?

One question though - there are quite large volume differences in the various mods - is this usual?  Loudest is 'unmodded', LED OD is next, LED clipping next, Mosfet clipping next, diode clipping last...  Normal?

Thanks guys - a happy ending to my first full build!  And huge kudos to Dano for a great design 

Cheers mate.

that'll do it.
yes, different diode choices will have an effect on volume if you don't do other changes along with it, normal for that.
bw