Help Mike!

timhulio · Post by **timhulio** » Sun Feb 22, 2009 7:17 pm

I've been building EH linear power booster for use in something else according to this schematic on Beavis Audio:

And it sounds utterly bad. Like a kinda bad ring mod sound. I've used ceramic caps for the 0.1uF input and output caps, and expensive poly caps and still no joy.
What circuit did you use that sounded best?

Post by **Mike** » Sun Feb 22, 2009 7:23 pm

Blimey! That's bizarre. Do you have it absolutely maxed out or something?

Does it sound like shit if you breadboard it?

The Saltbooster is 820K/100K for the base bias resistors, a 10K collector and a 390 ohm emitter resistor.

I reduced the Emitter resistor to 330 on Fran's because he wanted MOAR power. I up it to 1K when I use it as an output stage for a Harmonic Perculator or similar to tame the raw power. Are you definitely using a known good 2n5088? The coupling caps will be fine anywhere from 47nF up to 200nF depending on how much bass you want to pass.

Any pictures so I can check this? What does your layout look like?
It should sound 100% clean up to max volume, any dirt will be added by the amp you drive.

I just noticed you're building into something else - kill teh 1meg input resistor, you don't need it. It's to de-pop a true bypass input.

What circuit is it in and where is it? I would check you don't have any tracks you need to cut to isolate your booster section from the rest of the circuit.

timhulio · Post by **timhulio** » Sun Feb 22, 2009 7:31 pm

Cheers for that dude. Although I'm slightly more confused now. I tried both 820k and 1M for that top base resistor. I've actually junked the circuit now, pulled the salvagable bits out of it and poured myself a glass of wine. I started-out earlier with a veroboard layout of an eq circuit which called itself an 'all frequency brightener', consisting of a boost followed by a low frequency and high frequency tone controls. The boost wouldn't work at all, so I replaced it with the LPB... nothing... so I sawed the LPB away from the rest of the circuit and ended-up with a the bad ring mod thing. Really odd. I'm going to breadboard the LPB tomorrow and see how I get on.

timhulio · Post by **timhulio** » Sun Feb 22, 2009 7:33 pm

This one. Did my head in!

http://www.freeinfosociety.com/electron ... teners.pdf

Post by **Mike** » Sun Feb 22, 2009 7:34 pm

Hmm

Bad transistor maybe, or just take a break and start again. Once I built an OCD board and it would not work. No sound. Checked every-fucking-thing thrice. All cuts were true - all jumpers current and to the right tracks, no solder bridges connecting tracks that shouldn't be connected. Stared at it for 2 days. Built another one and the chip worked fine in that one. Fuck knows what the problem was, sometimes if you've checked everything it's just time to take a break or start over.

Post by **Mike** » Sun Feb 22, 2009 7:35 pm

BY the way are you around on Friday? I think me, Johno and benwalker and maybe Doog are having some beers in Norf London

Post by **Mike** » Sun Feb 22, 2009 7:37 pm

timhulio wrote:This one. Did my head in!

http://www.freeinfosociety.com/electron ... teners.pdf

Mental.

Scan or make up a layout of that for me and I'll be happy to check it over, there's a bunch of places stuff could go wrong there. I don't like the use of a trimmer to set the booster gain stage, that's just lazy design.

timhulio · Post by **timhulio** » Sun Feb 22, 2009 8:04 pm

I tried the EQ section of this pedal (the bit I sawed-off, ha!) without the boost and it seemed to work okay (just quiet), so I think I'll revist this but use LPBs for the boosty bits. I watched the whole of the Living Daylights just trying to debug the thing, so it was definately time to cut my losses. Like the tagline to that film- "sometimes dead is better".

Yep Friday night drinks would be cool. Where/when?

aen · Post by **aen** » Sun Feb 22, 2009 8:05 pm

I would change the 10k resistor on the collector to 3.3k. 10k makes it sound totally shit, in my experience.

Thats how I did the fat booster, except minus the 1meg pull down resistor mike already mentioned.

I dont know how the hell mike gets a decent osund out of it with a 10k on the collecter. I did it to mine and got the worst fuzz ever.

Post by **Mike** » Sun Feb 22, 2009 8:08 pm

timhulio wrote:I tried the EQ section of this pedal (the bit I sawed-off, ha!) without the boost and it seemed to work okay (just quiet), so I think I'll revist this but use LPBs for the boosty bits. I watched the whole of the Living Daylights just trying to debug the thing, so it was definately time to cut my losses. Like the tagline to that film- "sometimes dead is better".

Yep Friday night drinks would be cool. Where/when?

I know nothing beyond Friday night and a pub in Camden or something? Good Mixer or World's End or whatever, probably right after people get out of work? Watch the pub and we'll make a thread.

Never a problem for me, Aen. Odd.

aen · Post by **aen** » Sun Feb 22, 2009 8:10 pm

Mike wrote:
timhulio wrote:I tried the EQ section of this pedal (the bit I sawed-off, ha!) without the boost and it seemed to work okay (just quiet), so I think I'll revist this but use LPBs for the boosty bits. I watched the whole of the Living Daylights just trying to debug the thing, so it was definately time to cut my losses. Like the tagline to that film- "sometimes dead is better".

Yep Friday night drinks would be cool. Where/when?
I know nothing beyond Friday night and a pub in Camden or something? Good Mixer or World's End or whatever, probably right after people get out of work? Watch the pub and we'll make a thread.

Never a problem for me, Aen. Odd.

Probabaly different brands of transistors. If i do the same hookups with the cheap 2n5088s i get clipping even in my mdified verison. So if I need celan powerz, it's expensive transistors all the way.

Post by **Mike** » Sun Feb 22, 2009 8:13 pm

Yeah that's the only thing I could think of. I use Banzai 2n5088s and they've always been fat and clean.