3K74 resistor?

E

Eschmidt

Member
Hello!
I’m looking forward to building the new Breakroom overdrive (Keeley 1962x). Looks straightforward enough outside of one thing. One resistor is labeled as 3K74. I’m fairly new to pedal building but I haven’t seen this before. Is it appropriate to use a 3.7K resistor, or would I need an actual 3K74? They don’t seem to be common. Any help would be appreciated!
 
Eschmidt, even if you ordered specifically a 3k74 resistor, the tightest affordable tolerance is 1%.
Maybe there's tighter tolerance 3k74 resistors out there, but we're not trying to blow up a Space X project, just blow up a guitar signal.

Your 1%-tolerance 3k74 could measure as high as
3k7774​
or as low as
3k7026.​


Alternative to Robert's resistors in series idea...
... if you've got a couple 7k5 you can run them parallel to get even closer at 3k75 — assuming the values are spot on 7k5 without drifting 1%-tolerance.




How important is that small of a percentage?
Not enough to make a special order if you've got 3k7, which at 1%-tolerance could measure as high as 3k737.
 
You won't hear the difference with 3k6, 3k7, 3k74 or even 3k9.
Take into account that we don't know Vp of the transistor. A different Vp value means a different drain resistor value (trimmer), which also somehow affects the frequency response of this stage.
Below - frequency response of the 1962 input stage. Same transistor, four different source resistors, "trimmer" adjusted to keep the 4.5V drain voltage.
1750742486982.png


And here - four diffent transistors (Vp -0.7V, -0.64V, -0.74V, -0.87V), 3k74 source resistor, "trimmer" adjusted to keep the 4.5V drain voltage.
1750742752120.png


As you can see, the source resistor value has less influence on the output signal than a specific transistor.
 
still, I 'don't see the reason of those specific values, there is no cap across the source resistor, so the real difference it's not in the frequency response but in the stage gain, you want more gain pick a 3K3, you want more headroom pick a 4K7
 
Here's a little page that describes the E series of preferred numbers fairly well:

Resistor Values E6 E12 E24 E48 E96 E192

AnaLog Services, Inc. provides services to the oil well, water well, and mineral logging / wireline industries.
www.logwell.com

374 is part of the E96 series, which corresponds to a 1% tolerance.

Guitar pedals don't generally need that tight of a tolerance, though. Folks like getting fancy sometimes.
 
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