Clipping transistors in opamp distortipn designs

[dist]

Hi. This is my first post here. I havent realy had the time to poke around in this forum yet so maby this has been adressed before.
And by the way, im Norwegian, and my english suck so bear with me.

So i read some where that when conecting base and emiter of an pnp transistor together it acts as an diode, never gave it mutch thougt til an local "have it all shop" you know the ones that sell everyting but food, had a sale on transistors.

Im vorkin on an simple opamp distortion and decided to buy a cpl of transistors and try it in my design. And wow. I've just tested some bc 327-25 transistors as both hard and soft clipping "diodes" and its mutch more transparent than any diode ive ever heard. Eaven with numetal amounts of clipping i can hear every note. And it cleans up realy nice. On the neck pu of my strat i have an sd mini humbucker with paralell/splitt/series sw on the coils and ulike any higain ditortion ive ever heard  i can realy tell the difference. eaven at hi gain settings.  CAnt wait to "gain stack" thise things in an dual op amp design im workin on.

On the other side, the sustain is bad. gotta work on that. Anny ideas?

[phaeton]

Hi dist.  Welcome to the forum.  Your English seems fine to me 

When you say the sustain is 'bad', does that mean it has less sustain than when bypassed?  If so this could be a biasing issue.

Is this opamp distortion you're working on an old design or one of your own?  If you have a schematic handy we could take a look for you.

 

[brett]

Hi
thanks for your interesting post.

On the other side, the sustain is bad.

Extra sustain is usually achieved by increasing the gain.  Gain between 100 and 500 is usually good.
cheers

[dist]

Well the schematic is kinda floating on the internett. I've used the distortion + / DOD 250 as an startingpoint and is modifying it as i go.
I made a PCB layout with eagle with two pads for soft clipping and two pads for hard clipping, wired it to a dpdt on on toggle SW. the toggle SW it then wired to a jack so that i easily can switch diodes ans listen to them in both soft an hard clipping position.

I also have  pads ready to ad an extra PCB with a tone pot. Think I'll  be making some sort of bi muff style tone controll.

I think the sustain issue is in the rest of the design, and not in the transistors. And since they are doing the job of a diode the do not need to be biased.

Its really interesting to be able to change diodes quickly. I'm also using an a/b box type of thing to A/B test different diodes. Only problem now is. I CANT DECIDE WITCH TO USE. They all sounds good. In their own way

[Paul Perry (Frostwave)]

I'm also using an a/b box type of thing to A/B test different diodes. Only problem now is. I CANT DECIDE WITCH TO USE. They all sounds good. In their own way

That's why they make 12 position switches 

[dist]

Yea. I could use two of them. One for each side of the diodes, and switch them from hard to soft. That would give me a total of... Manny possible sounds...   

I'm gonna ad an fx loop to my dist box for extra eq and maybe other effects i only wanna use with distortion. All on in one stomp. Like a built inn loop box.  I can Even use it to feed two different amps. One for clean and one for the distortion...

[WGTP]

Do you know what the clipping threshold of the transistors is??? If it is high, around 2v, like LED's, it is not going to compress as much as if it is low, around .3v, like with GE diodes.   

[dist]

I have no idea.
Dint get any datasheet.
Only thing written that came with the transistors say es this

transistor BC 327-25
pol pnp
p tot:0,8w

Max values
Vceo 45V
I c:0,5A

typ val
hfe:160/400
fT:100MHz

And i don't have a clue to what Anny of it Menes

[petemoore]

  I like to get clipping elements in on a 2 way switch and try 'em out for a time or two.
  So I just put the 1rst diodes config in 'semi-permanent' [like somewhere besides soldered through the board], but reliable place, then socket the diode configuration on the other side of a SPST or SPDT switch.
  If I find a socketted config. I prefer to the semi-permanent ones, I'll swap their positions, try something different in the sockets...try 'em out again for a time 'er two.
  This is partly due to the reason that I have lots of RS DPDT toggle switches floating around that were once used as TBypass, but were replaced with stompswitches.