Constant current instead of fixed bias?
Moderators: pompeiisneaks, Colossal
-
skyboltone
- Posts: 2287
- Joined: Wed May 10, 2006 7:02 pm
- Location: Sparks, NV, where nowhere looks like home.
Constant current instead of fixed bias?
Anybody horsed around with red-board (led) sourcing for bias current? The HIFi guys are all over this but I don't know if it's too FI you know?
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Re: Constant current instead of fixed bias?
Hey Dan
Our dear (and long-since-banned) friend Gary Moore designed all his amps around using LED biasing, and also used them as his tube life indicating 'BITE' lamps.
Unfortunately he managed to make them all sound awful in the sound clips that were posted, but I don't think that was the fault of the LED biasing!
I'd be interested to hear it properly implemented but there is always the problem that if a tube fails short it will knock out your LED and you'll be SOL for getting through the rest of the gig with just a preamp tube swap.
Our dear (and long-since-banned) friend Gary Moore designed all his amps around using LED biasing, and also used them as his tube life indicating 'BITE' lamps.
Unfortunately he managed to make them all sound awful in the sound clips that were posted, but I don't think that was the fault of the LED biasing!
I'd be interested to hear it properly implemented but there is always the problem that if a tube fails short it will knock out your LED and you'll be SOL for getting through the rest of the gig with just a preamp tube swap.
-
skyboltone
- Posts: 2287
- Joined: Wed May 10, 2006 7:02 pm
- Location: Sparks, NV, where nowhere looks like home.
Re: Constant current instead of fixed bias?
Hey Mister Paul:
I'm going to build up a tested design (for stereo) before I try the technique on a guitar amp. I was planning just the power tubes by the way. Sort of like a HI WATT setup only SS. It's just a current source but I'm sure somebody with better hearing than me will notice some cataclysmic loss of mojo with sand in there......while they hook up their pedal boards.
Thanks, I had forgotten Mister Moore. Kind of forgettable guy eh?
BTW, I've got one of your 6.3VAC to 6.3VDC boards in my Dumbell. Works great. Still have one board, I think I'll stick it in the driver tubes of my HiFi amp.
Dan
I'm going to build up a tested design (for stereo) before I try the technique on a guitar amp. I was planning just the power tubes by the way. Sort of like a HI WATT setup only SS. It's just a current source but I'm sure somebody with better hearing than me will notice some cataclysmic loss of mojo with sand in there......while they hook up their pedal boards.
Thanks, I had forgotten Mister Moore. Kind of forgettable guy eh?
BTW, I've got one of your 6.3VAC to 6.3VDC boards in my Dumbell. Works great. Still have one board, I think I'll stick it in the driver tubes of my HiFi amp.
Dan
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Re: Constant current instead of fixed bias?
I tried a red diode (1.8v) on the first stage of a Champ'ish circuit. Seemed to work just fine. Sound change was subtle, but I can't say for better or worse for the most part. I haven't done any serious A/B's on them because I haven't had the time. 
If you can't be a good example, then you'll just have to be a horrible warning.
Re: Constant current instead of fixed bias?
So Gary Moore was banned from here? That's why he's always at the MEF nowadays I guess.
Re: Constant current instead of fixed bias?
Glad it's working well for you. Now I'm this side of the pond it'll be a lot easier (read: cheaper) to send more over to you if you ever need them!skyboltone wrote:BTW, I've got one of your 6.3VAC to 6.3VDC boards in my Dumbell. Works great. Still have one board, I think I'll stick it in the driver tubes of my HiFi amp.
I think he systematically got himself banned from pretty much every guitar amp forum going. It was a fairly spectacular fireworks display!tubeswell wrote:So Gary Moore was banned from here? That's why he's always at the MEF nowadays I guess.
Re: Constant current instead of fixed bias?
MEF?tubeswell wrote:So Gary Moore was banned from here? That's why he's always at the MEF nowadays I guess.
__________________________________________
Cheers and Beers.
Cheers and Beers.
Re: Constant current instead of fixed bias?
Music Electronics Forum.
-
skyboltone
- Posts: 2287
- Joined: Wed May 10, 2006 7:02 pm
- Location: Sparks, NV, where nowhere looks like home.
Re: Constant current instead of fixed bias?
Well that's good that you done it though. Just try some different colors.echuta13 wrote:I tried a red diode (1.8v) on the first stage of a Champ'ish circuit. Seemed to work just fine. Sound change was subtle, but I can't say for better or worse for the most part. I haven't done any serious A/B's on them because I haven't had the time.
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Re: Constant current instead of fixed bias?
Gary seems to have just about worn out his welcome over @ MEF, and he was banned from the sewatt community quite a while back. Guess it's pretty hard to learn your lesson if you already know everything. 
Back on-topic.... Merlin has a section on diode biasing on his site under his Triode Gain Stage section: http://www.freewebs.com/valvewizard1/gainstage.html
There's a fair amount of examples given if you're inclined to fine-tune your cathode voltages.
Back on-topic.... Merlin has a section on diode biasing on his site under his Triode Gain Stage section: http://www.freewebs.com/valvewizard1/gainstage.html
There's a fair amount of examples given if you're inclined to fine-tune your cathode voltages.
If you can't be a good example, then you'll just have to be a horrible warning.
Re: Constant current instead of fixed bias?
Those LED biased amps sound OK enough on Parisienne Walkways
-
markr14850
- Posts: 204
- Joined: Mon Jun 18, 2007 6:16 pm
Re: Constant current instead of fixed bias?
I'm a bit confused...I was planning just the power tubes by the way. Sort of like a HI WATT setup only SS.
Are you interested in a low impedance drive for the power tube grids - like "MOSFET Follies", or "PowerDrive"?
Or are you considering cathode biasing the output tubes via LED?
Or something else?
Re: Constant current instead of fixed bias?
Dan, an amp I am going to build which is called the Simple Single Ended Amp uses a current regulator.
This is what it uses.
http://ixdev.ixys.com/DataSheet/98704.pdf
http://www.mouser.com/ProductDetail/IXY ... svIA%3d%3d
How this amp uses it.
This is what it uses.
http://ixdev.ixys.com/DataSheet/98704.pdf
http://www.mouser.com/ProductDetail/IXY ... svIA%3d%3d
How this amp uses it.
You do not have the required permissions to view the files attached to this post.
Tom
Don't let that smoke out!
Don't let that smoke out!
-
Andy Le Blanc
- Posts: 2582
- Joined: Sat Dec 22, 2007 1:16 am
- Location: central Maine
Re: Constant current instead of fixed bias?
diode bias is fun, there was a AUDIOEXPRESS articular some time back that
went over a led biased tube pre for computer etc.
you can convert dual triode to diodes, works pretty well.
you can also get some incredible nonlinear distortion. great fuzz tone.
you can also dress a 12au7 as a simple series regulator, why not SRPP?
went over a led biased tube pre for computer etc.
you can convert dual triode to diodes, works pretty well.
you can also get some incredible nonlinear distortion. great fuzz tone.
you can also dress a 12au7 as a simple series regulator, why not SRPP?
lazymaryamps
Re: Constant current instead of fixed bias?
If you are talking about replacing R10 and R20, go for it. In an audio amp it is a great way to reduce distsortion.
In a guitar amp, you will have the minor issue that you can not bypass it with a cap to control frequency response.
If you are talking about replacing R17 and R27 with diode arrays ala RLD amp, it will also work fine since this is a Class A amp.
IIRC, LED Biasing only works with class A.
In a guitar amp, you will have the minor issue that you can not bypass it with a cap to control frequency response.
If you are talking about replacing R17 and R27 with diode arrays ala RLD amp, it will also work fine since this is a Class A amp.
IIRC, LED Biasing only works with class A.