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Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Amplifier Discussion => Topic started by: yeto on September 17, 2015, 10:01:09 AM

Title: What is the purpose of the Red Leds D1 and D2 in the attached schematic?
Post by: yeto on September 17, 2015, 10:01:09 AM
Could someone share the purpose of the Red Leds D1 and D2 in the attached schematic? Is this some type of diode clipping circuit?

Thank you in advance for any help,
yeto
Title: Re: What is the purpose of the Red Leds D1 and D2 in the attached schematic?
Post by: Vitrolin on September 17, 2015, 03:32:48 PM
with a quick look this is my guess.
you should look at two current paths
R6, R5 and D2 is one path and R6, R7 and D1 the other.
the diodes are biased by a very weak current  (9-1,6)/(10k+47k)=157µA
if voltage at D2/R5 rises, then Vforward D2 falls and current decreases. and current through D1 increases, therefore voltage across R7 increases.
were talk small variations to avoid cutoff.

i'm shure someone has a some things add or clarify
Title: Re: What is the purpose of the Red Leds D1 and D2 in the attached schematic?
Post by: yeto on September 17, 2015, 10:18:32 PM
Quote from: Vitrolin on September 17, 2015, 03:32:48 PM
with a quick look this is my guess.
you should look at two current paths
R6, R5 and D2 is one path and R6, R7 and D1 the other.
the diodes are biased by a very weak current  (9-1,6)/(10k+47k)=157µA
if voltage at D2/R5 rises, then Vforward D2 falls and current decreases. and current through D1 increases, therefore voltage across R7 increases.
were talk small variations to avoid cutoff.

i'm shure someone has a some things add or clarify

Thank you. That helps.
Title: Re: What is the purpose of the Red Leds D1 and D2 in the attached schematic?
Post by: galaxiex on September 17, 2015, 11:29:21 PM
I found a discussion thread from 2007 about this amp.

Post #25 and #26 explains about the LED's.

http://www.diystompboxes.com/smfforum/index.php?topic=54524.msg425914#msg425914 (http://www.diystompboxes.com/smfforum/index.php?topic=54524.msg425914#msg425914)
Title: Re: What is the purpose of the Red Leds D1 and D2 in the attached schematic?
Post by: J M Fahey on September 18, 2015, 06:51:21 AM
Well, he actually says that he has no clue, that he "saw them somewhere" , that his amp was oscillating so out of the blue he added it as an attenuator and it helped somewhat, then he was too lazy to pull them out.
Oh well.

EDIT: did you post this very same question in another Forum?

I answered it fully in there, after Merlin and Teemuk, none the less.

When I saw this thread I thought my answer dissapeared, I'm having BIG problems with my ISP provider, but I don't see the other answers so I guess it was somewhere else.

Can you clear this?
Title: Re: What is the purpose of the Red Leds D1 and D2 in the attached schematic?
Post by: DrGonz78 on September 18, 2015, 06:30:02 PM
It was on MEF

http://music-electronics-forum.com/t40377/ (http://music-electronics-forum.com/t40377/)
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