I've done allot of searching and reading here about the OD entrance.
Is the 470k/47p>200k>25k trim>4.7k what everyone uses now? Is this actualy in a dumble or just what people have come up with? In older posts the 220k>100k pot has been used in HRM's as well as others. I'm just interested in how's and why's.
I recall funk saying he did something different that no one else does but wouldn't give any specifics.
I'm convinced that it is a major factor in the character of the OD.
Please post what you are currently using and where you have the trimmer set (resistance from wiper to ground)
if you don't want to be super specific at least drop a hint
I've been curious about this to for a while as well. Is the standard found on HRM schematics based on a de-gooped specimen and if so, was it a standard or possibly an exception (like the 500k in #124)?
"In this world you will find hardship and trials; but take heart, for I have conqured the world."
John 16:33
I don't know if there is an absolute standard but I use the 220/100k trim in non-HRM and sub in something smaller (like a 180K) for the 220k during tweaking - some amps like it most don't. On the HRM I use the 470/47pf into 220k,25Ktrim with 4k7 to ground. As an alternate I have used 120k into a 100k trim after the 470/47pf.
Don't be afraid to sneak in another cap after the relay for less bass.
I originally wired my HRM to the 470k/47p-200k-25k trim-4k7 but I was always at the upper end of the range. dogears made a suggestion to decrease the 200k to 180k and increase the 4k7 to 24k while keeping everything else the same...this just changes the range of the trimmer without changing the load on CL2's output. Now the trimmer seems to have a better range and mine is set at about 40% (I haven't measured the resistance to ground but if I had to guess I'd say it's about 22k+10K=32K which is just slightly more than the max setting with the original arrangement). Note: I didn't have a 24k and used a 22k instead. But I'm still in the tweeking stages so this might change.
EDIT: Also, my extremely limited understanding was that this low gain OD entrance network was designed to be used with the PAB on. Or maybe it's Mid-boost (the note on the schematic just says 'works well with boost' but doesn't say which boost). On my amp, OD with PAB on is the best OD tone followed by OD with Mid-boost on (but not both...the Mid-boost becomes a big bass boost when PAB is on).
I can see how adding another coupler for OD1 might help. My amp originally had a .047 CL2 coupler but I tried a .022 there and liked it a little better. The clean tone did not seem to suffer at all...maybe even a little better. I definitely did not like a 1uF cathode bypass cap on CL2 and went right back to the 5uF.
The low gain network i s indeed in some HRM Dumbles. I have pictorial degooped proof. Also, the amp I measured had the trimmer set to 26K to ground.
The Bluesmaster has a deviation on this theme. Same total load but with a 100K trimmer. 470K into 120K into 100K trimmer. No 47pf cap I believe. Trimmer in the BM I was in had 41K to ground at the trimmer. I think the additional gain is why no 47pf. No 47pf alters the bass response to my ears. That must be why the BM uses a .01uf coupler on CL2.
dogears wrote:The low gain network is indeed in some HRM Dumbles.
Was it in all of the ones you saw? or just some? any deviations?
Also what does that 47pf cap do? does it allow more highs to pass... these parallel filters always mess with my head because I don't know if its a highpass or a lowpass. What is the formula for this type of filter to find the "knee"
I have never seen or heard of one without the lower gain network. Although there could be some.
The 47pf allows highs to pass around the 470k. But, at a very high knee, above the guitar range. To my ear, clipping it out, reduces high harmonics and also adds bass. Somehow, the low knee is effected by the presence of the cap. I like the cap...
yeahyeah wrote:
dogears wrote:The low gain network is indeed in some HRM Dumbles.
Was it in all of the ones you saw? or just some? any deviations?
Also what does that 47pf cap do? does it allow more highs to pass... these parallel filters always mess with my head because I don't know if its a highpass or a lowpass. What is the formula for this type of filter to find the "knee"
