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hot tubes
Silver Member
Canada
162 Posts |
 Posted - 04/18/2009 : 16:08:59
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by changing R2 to 1M , what does that do ?
does it have an overall effect on the tone ?
thanks |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 04/18/2009 : 16:22:24
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Not really. R2 is the base bias resistor for the input buffer (Q1). What increasing it to 1M will do is lower the operating point of Q1 giving less headroom on the input. I haven't tried it, but it might lower it so far that you will get clipping in that buffer - maybe adding some interesting tone.
What are you trying to achieve? |
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hot tubes
Silver Member
Canada
162 Posts |
Posted - 04/19/2009 : 23:14:35
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they talk about this on a few mods that i have seen on the net .
just wonding what its for .
i assume that each change of a mod does somthing etc.
thanks |
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cctsim
Silver Member
United Kingdom
418 Posts |
Posted - 04/20/2009 : 01:09:23
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Increasing R2 will give you a higher input AC impedance, which means less loading of the previous pedal/stage etc, and more presence.
Personally, I could hardly notice any difference when I changed R2 from 470k to 620k (as in Keeley 5* GE mod). |
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hot tubes
Silver Member
Canada
162 Posts |
Posted - 04/20/2009 : 05:31:45
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i 'm just looking for changes to the SD 1 that help keep the
core tone the best it can be. so would you just omit this change
the R2 TO 1M ??
THANKS
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 04/20/2009 : 05:38:52
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I can't see how the change to 1M is useful, so I'd suggest skipping it.
One important thing to do with an SD-1 is stop the bleed. There are a number of approaches to this, and one is to "harden" the 4.5V rail. This has been proven to be a good approach which still maintains the essential tone of the beast.
zentropa and I figured this one out last year:
1) R18 = 10k
2) R19 = 10k (measured to match R18 as closely as possible)
3) C11 = 100uF
4) Add a new capacitor across C11 - a 1uF ceramic or monoblock (not electrolytic or polyester)
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Edited by - Laurie on 04/20/2009 05:43:01 |
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hot tubes
Silver Member
Canada
162 Posts |
Posted - 04/20/2009 : 15:35:01
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for R18 and R19 , are you saying make sure you measure with a meter
and get 2 resistors exactly 10K , its that critical i take it !
thanks for this info  |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 04/20/2009 : 20:15:09
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| They don't have to be exactly 10k - they have to be as close to exactly equal as possible (eg if they were both 9.8k it would be fine). |
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hot tubes
Silver Member
Canada
162 Posts |
Posted - 04/21/2009 : 21:24:52
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| when do you see or hear this "bleed thru" on the SD1? |
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cctsim
Silver Member
United Kingdom
418 Posts |
Posted - 04/24/2009 : 19:57:27
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quote:
Originally posted by hot tubes
when do you see or hear this "bleed thru" on the SD1?
In bypass mode, with the DRIVE control set 10 o'clock or higher, if you can still hear the overdrive then your unit has the bleed-through problem.
Needless to say that you need a clean set up amp. |
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zentropa
Gold Member
USA
837 Posts |
Posted - 04/25/2009 : 18:36:04
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it also colors the tone of pedals placed after the sd-1 in the pedal chain.
for example, a DS-1 sounds differently when placed after an SD-1 (that is in bypass mode with the drive high) than before it.
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SD 1 QUESTION ?
