Pete Cornish - NG-2

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Re: Pete Cornish - NG-2

Postby palelight » 22 Jan 2019, 00:40

andy-h-h wrote:
sopapo1 wrote:Ok, thanks, I was thinking that the most convenient thing to do is to make the bias asjust with a pot, and put it in the outside with de others controls like in the ng3 version...any posible cons to it? More noise?
Its something that I always think, that using a pot instead of a good metal resistor for the critical task of biasing it will add noise, given the nature of the pots...


I've tried it with an external 50k pot, and it was far to sensitive to be really useful (the internal 50k trimmer is also very sensitive). I'm planning on trying this with a resistor or two to set a range for the pot, and hopefully reduce the sensitivity and get a more workable range. The extremes of the biasing range for my germanium are 8k to 40k. Outside of this it either doesn't work or is completely pointless. Silicon is more forgiving.


If you end up using some fixed resistors, please share how you make out (and what values you end up using). I'd like to try it out.
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Re: Pete Cornish - NG-2

Postby andy-h-h » 22 Jan 2019, 13:23

Hey PaleIight,

I've worked it out in my head and have a modified layout ready to try. Will let you know what I end up with after I've tested it properley. Resistors will no doubt vary depending on transistors used in the last stage.
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Re: Pete Cornish - NG-2

Postby sopapo1 » 24 Jan 2019, 16:14

the bias adjust with the trimmer (or pot) is better done entirely by ear? or around a reference voltage....
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Re: Pete Cornish - NG-2

Postby andy-h-h » 24 Jan 2019, 21:50

Hello,

Bias by ear as there are no reference voltages available (at least none that I know of) + personal taste will come into play when doing this. When biasing on the bench with a scope/FFT, I found it easiest to bias with the sustain and drive at lower settings first, and then check again with high gain. When I found something that looked and sounded good at both ends of the spectrum, it also sounded good and gave a wide useable range when I plugged the guitar in.
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Re: Pete Cornish - NG-2

Postby andy-h-h » 26 Jan 2019, 07:44

EXTERNAL BIAS POT

I ended up using a 4.7k resistor with a 25k pot for the external bias. Gave a nice range. Works well on the board I made which is using germanium transistors for Q 4 & 5. Naturally the bias range will be transistor dependant.

So resistor from the junction of Q4 collector and Q5 base, to bias 1. Bias 2 to the power rail.

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palelight (27 Jan 2019, 07:26)
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Re: Pete Cornish - NG-2

Postby palelight » 27 Jan 2019, 07:26

andy-h-h wrote:EXTERNAL BIAS POT

I ended up using a 4.7k resistor with a 25k pot for the external bias. Gave a nice range. Works well on the board I made which is using germanium transistors for Q 4 & 5. Naturally the bias range will be transistor dependant.

So resistor from the junction of Q4 collector and Q5 base, to bias 1. Bias 2 to the power rail.


Much appreciated! I'll give it a try.
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Re: Pete Cornish - NG-2

Postby andy-h-h » 27 Jan 2019, 11:41

Should look something like this. It is possible to trim this down a couple of rows too if you want to move a few things around, and the 100uf cap is optional, as is the power diode, as you could just take power from the Cornish Buffer layout that IvIark has nicely provided on guitar effects layouts.

And this is just a work-a-like based on the Nugget Fuzz. No claims that this is a real NG-3.
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Re: Pete Cornish - NG-2

Postby sopapo1 » 28 Jan 2019, 20:51

I just realized that in the old pic ungooped of a cornish ng in the first page (more that ten years ago¡¡¡ :lol: :lol: ) there is a third board with an ic in it instead of the usual buffer+effect ¿¿?? what is? also, very surprised of the perf... :hmmm: the blue capacitor and the resistor is maybe something related to reject RF or protection for shocks???
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Re: Pete Cornish - NG-2

Postby andy-h-h » 29 Jan 2019, 01:37

I've seen that pic too. The third board with the IC might be another buffer, or possibly even a power inverter to run PNP transistors. I think a buffer is way more likely, but you never know....

The blue cap is a link to ground. You can find more details on this by looking at the G2 schematic, as it included in the jack wiring. I read somewhere this helps with noise filtering / interference.
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Re: Pete Cornish - NG-2

Postby palelight » 29 Jan 2019, 23:39

andy-h-h wrote:I've seen that pic too. The third board with the IC might be another buffer, or possibly even a power inverter to run PNP transistors. I think a buffer is way more likely, but you never know....

The blue cap is a link to ground. You can find more details on this by looking at the G2 schematic, as it included in the jack wiring. I read somewhere this helps with noise filtering / interference.



There's a few pics of very early NG fuzzes floating around (gooped and non-gooped), both with the IC and perf daughterboards. By later versions (the standard grey series), the ic and daughterboard are gone. I'm more inclined to believe it was a power inverter, I think some early examples were definitely sporting some PNP transistors (pure speculation based on the transistor casing). Later NG's sport pretty standard TO92 transistors (assume BC549 or similar), likely doing away with the need for a power inverter. Pete's pedals are usually laid out very practically from a design standpoint (if not space conscientiously). The buffer is directly adjacent to the input for example, the fact the ic board was directly in front of the power plug makes me think it was related to that. Again, just a guess.

I've never seen a Pete C pedal use an opamp buffer, P2/G2/SS2 etc. all use the standard bootstrapped fet buffer, going well back into examples from the early 90's (the Guild Brian May Box etc.). But you never know I suppose.
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Re: Pete Cornish - NG-2

Postby andy-h-h » 30 Jan 2019, 08:25

palelight wrote:
I've never seen a Pete C pedal use an opamp buffer, P2/G2/SS2 etc. all use the standard bootstrapped fet buffer, going well back into examples from the early 90's (the Guild Brian May Box etc.). But you never know I suppose.


That's a very good point. I might have to try building a PNP version now.
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