Hi Masters,
I´m glad lifting the OD-entrance theme again on stage. Because I think that this is a very sensitiv questione for - at least - new Dumble clone builder.
From which side (low/high plate, 100/250/500k trim, ...) ever you look at this interesting theme, you always come back to the "original" values as digged out of an original HAD Dumble.
hans-jörg wrote:Hi Masters,
..............you always come back to the "original" values as digged out of an original HAD Dumble
.Hans-Jörg
You're absolutely right !!
More often than not, you end up with the original values. Guess the point is not to stray too much from the original values, if you want the 'original' tone from a given circuit e.g. #102, #124 or #183. These designs simply WORK. Max once wrote that HAD's amps are designed for studio and stage work - not for home use - This is so true.
The advise to new builders would be to build a given amp as close to the original design (as per Tony's layouts) as possible - blueprinting so to speak. AND allow a good long break-in time AND the right preamp tubes.
However, if you want to customize a D-amp to fit your particular style or instrument, it does makes sense to mod the amp a little bit - after break-in period.
Forgive me if this question doesn't apply to this exact ODS version but is all of this 'load' also in parallel with the 1M Clean Master volume? Seems like it to me but I'm just getting back into this obses...er...hobby.
Per the last schemo of my only ODS attempt I have a whopping 470k (partially bypasssed) + 200k + 25k pot + 4k7 to ground...but I'm still not sure if that ~700k is in parallel with the 1M Clean Master.
Early brewers were primarily women, mostly because it was deemed a woman's job. Mesopotamian men, of some 3,800 years ago, were obviously complete assclowns and had yet to realize the pleasure of brewing beer.
I do not have a #124 build. I do have a boatload of other non HRM builds. None have the 346K trimmer, but the 220K into 100K trimmer. They soudn and feel spectacular!
So, 346K may be nice, but nothing worng with 100K either! Just make sure to set it well.... I like 25-26K from ground with high plates.
Fischerman wrote:Forgive me if this question doesn't apply to this exact ODS version but is all of this 'load' also in parallel with the 1M Clean Master volume? Seems like it to me but I'm just getting back into this obses...er...hobby.
Per the last schemo of my only ODS attempt I have a whopping 470k (partially bypasssed) + 200k + 25k pot + 4k7 to ground...but I'm still not sure if that ~700k is in parallel with the 1M Clean Master.
In the HRM case you would take into consideration V1b coupling cap (C) the CL master/ OD entrance network/ and the grid resistor (R)..The response would be down -3dB at X hz relative to the midband gain. It would drop with a -20dB/decade slope as the frequency is lowered,forming a high pass filter
Tony
" The psychics on my bench is the same as Dumble'"
I believe it's safe to say that this type OD entrance would only work (or work best) on a low plate w/ low value (5uf) bypass caps like 124..
Tony, are you referring to V2 cathode caps (5uf) only, rather than V1 (10uf) as on #124?
Cheers,
Paul.
I was most concerned w/OD side..But you have a point and we all know 124 has the goods.. I have a 124 w/ 250k trigger 250k drive (5uf throughout) that I like very much....The testing I've had with altering the OD entrance trigger on high plates (5uf throughout) and I always went back to the traditional on those for reasons I mentioned..
BTW ..A 346K pot set @ 26K is going to sound much different than a 100k set @ 26k..Try it..
Hope this helps!!
Tony
Last edited by talbany on Tue May 31, 2011 10:31 pm, edited 6 times in total.
" The psychics on my bench is the same as Dumble'"
dogears wrote:I do not have a #124 build. I do have a boatload of other non HRM builds. None have the 346K trimmer, but the 220K into 100K trimmer. They soudn and feel spectacular!
So, 346K may be nice, but nothing worng with 100K either! Just make sure to set it well.... I like 25-26K from ground with high plates.
My recently completed ODS is very close to a #124, low-plate, OD entrance is 220k into a 100k trimmer that is set around 24k to ground. Sounds great, and the available range of OD tone is very broad. This was my point above... the value of one part (within reason) is not going to make or break an amp, and the "best" value for any particular part depends upon the context. It's been said before and earlier in this thread: start with a known baseline and then explore from there. And, I'll add that a good place to begin exploring is to try different tubes in the preamp and PI locations ;^)
Forgive me if ive got it wrong here, but I seem to remember in the #124 notes that the real #124 had its OD trim set at @100k to ground. On my build I have 220k into a 500k pot paralleled with a 1m resistor (gives @320k) and I cant get anywhere near 25k to ground.......I think its set at @ 105k from memory. Sounds great to my ears.
With the total load resistance putting the final touch on the character of the clean output per the discussion above, the trimmer setting is the next item in the chain. To my mind it determines the minimum amount of distortion for the OD channel, and works in concert with the Drive/Level and Volume/Ratio controls to vary the combination of gain and distortion from the OD stages.
You are correct, 100k to ground is the setting that was noted. That would be about 18% of the Cl2 output, whereas 24k with the 100k trimmer would be 7.5%... not as big a discrepancy as it might seem at first.
Guys, the 100K low plate amps, in some of the real ones I have seen/heard of, have the trimmers set at about 2X the setting of the high plates. Remember, the low plates have less gain.....
dogears wrote:Guys, the 100K low plate amps, in some of the real ones I have seen/heard of, have the trimmers set at about 2X the setting of the high plates. Remember, the low plates have less gain.....
Wow, this is interesting! And it stands in stark contrast to the setting I find most useful in my amp (around 12k), and also apparently to something Gil had found some time ago in his own low-plate amp discussed here http://ampgarage.com/forum/viewtopic.ph ... hlight=15k
Unless I'm misunderstanding the 2X comment, Scott...which I'm interpreting to mean "high plate amps had settings around 25k, but low plate amps around 50k."
So now I'm really wondering what is different about my classic low plate amp.
I have a friend in Canada with a low plate amp. He measured the trimmer and it was over 50K from ground. Untouched since Dumble set it.....
Also, my friends high voltage Music Man amp with low plates had the trimmer set about halfway in the pics.
greiswig wrote:
dogears wrote:Guys, the 100K low plate amps, in some of the real ones I have seen/heard of, have the trimmers set at about 2X the setting of the high plates. Remember, the low plates have less gain.....
Wow, this is interesting! And it stands in stark contrast to the setting I find most useful in my amp (around 12k), and also apparently to something Gil had found some time ago in his own low-plate amp discussed here http://ampgarage.com/forum/viewtopic.ph ... hlight=15k
Unless I'm misunderstanding the 2X comment, Scott...which I'm interpreting to mean "high plate amps had settings around 25k, but low plate amps around 50k."
So now I'm really wondering what is different about my classic low plate amp.
dogears wrote:Guys, the 100K low plate amps, in some of the real ones I have seen/heard of, have the trimmers set at about 2X the setting of the high plates. Remember, the low plates have less gain.....
Yes, good point. With the volume and EQ controls set the same, a high-plate (220k, 150k) amp would have ~38% higher voltage gain at the OD entrance than a low-plate amp... wouldn't explain all of the difference, but a good chunk of it.
Another part of the equation to this would be when selecting a value pot for OD trigger...Consider where the wiper is set in the trace..Lower settings of the pot you have larger series resistance, which effects the high end frequency response...100k set 50k will be brighter than say the 346 set the same being darker or some might consider it smoother.. Thought I would mention..
Tony
" The psychics on my bench is the same as Dumble'"
