Output Coupling Caps and Bass response

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Kapo_Polenton
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Output Coupling Caps and Bass response

Post by Kapo_Polenton » Thu Jun 26, 2008 4:27 pm

Hey guys, I've got a really bassy 1987x clone. The normal channel is quite flat and bass intensive and the only way to tighten up the bright channel, was to use a .68uF capacitor in parallel with the 820 R resistor leading off the tonestack. This was ok for a while because I only use the bright channel. However, it sounds great on its own but is not handleling pedals well I find. Boosts and OD's bring out to much mids. It has this bite that annoys the hell out of me yet i really dig the amp on its own. For leads though, its useless. I'd like to neutralize this by looking at areas where I can cut the bass so that I don't have to rely on the .68uf cap. I am using weber trannies from my 6m45p build and I noticed that for his coupling caps, he stuck with the .1u caps as opposed to the traditional .022 u. Would changing these to .1u increase my bass problem? Or should it be opposite? Replacing that one .1u to a .022 to cut bass is what my research would seem to suggest needs to be done. I'm just surprised that the 6m45P when working with the .1u was not excessively bassy at all.

Something def needs to be tweaked as using the standard layout for a 50 watter is getting me oh so close but not quite there.. I am not a transistor snob I decided so i have no problem boosting and using some gain from a pedl, I just want that midrange honk gone when i do.

Any ideas?

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Post by Kapo_Polenton » Fri Jun 27, 2008 12:27 am

Subsequent reading has lead me to beleive that I definitely do not want to change my coupling caps to .1uf but that I might want to change the .1uf on the PI to a .022 as well as go with a 47k resistor for negative feedback to the 8ohm tap. I'll try this first..

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Post by Kapo_Polenton » Fri Jun 27, 2008 12:52 pm

I'll post clips tonight, hopefully someone can chyme in.. also let me know if you hear what i hear.

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Post by Froumy » Fri Jun 27, 2008 4:52 pm

That's supposed to cut some rumble, but will it fix the honk?

To me, the JTM45 pre has a bit less of that mid bark.. Wonder if that spec would suit your pedals better? Completely different beast, though. I'd lower the v1a bypass cap, if you haven't already, and maybe ditch the v2a .68 cap. You could always fool around with your slope/mixer resistors, or try a .002 for the normal channel. Any chance that the ground is lifted on your mid-pot? Just fishing....

Everything is stock, right? Good luck

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Post by 45auto » Fri Jun 27, 2008 5:19 pm

which tone stack is it? the 33/500 is considerably more "middy" than the 56/250
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Post by Kapo_Polenton » Fri Jun 27, 2008 6:29 pm

33/500. The funny thing is that the .68 cap was a necessity to tighten the amp with the negative feedback resistor being 100. I am wondering if going to 47k, i'll be able to ditch that .68 cap. Ground isn't lifted to the mid pot because with an eq pedal on, i can cut the mids and make the pedal and the amp sound like complete $hit. :P

I''ve got the amo open and about to do some minor surgery, I'll report back shortly.

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Post by Kapo_Polenton » Fri Jun 27, 2008 10:32 pm

Alright, here are some clips. Tried to keep levels as close and panning left and right the same way so you can hear what i mean. Maybe using the EQ pedal was a bad choice but any pedal really emphasizes that mid.

I have a 47k NFB resistor and i had to leave the .68uf cap over the 820 resistor because without it the amp is really dark and not as tight. 500pf bright cap, stock values everywhere else based on the layouts for the 1987x that are available here. Bass is on 2, mid 6 , treb 7. The mids can't be at 0 or else it is flat and that hump is still there. Maybe i'll just live with it if nobody has an idea. Sure as hell doesn't sound like everyone elses amp! Maybe the fact that i am using KT-77?

http://media.putfile.com/Stock-NFB47k

http://media.putfile.com/EQPedal-engaged

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Post by Kapo_Polenton » Sat Jun 28, 2008 12:08 pm

I might have to turn this thing into a 2204 with some mods.. its driving me crazy with any pedals on. Bollocks! Frigging midrange just bites through and makes the thing sound soo synthetic. Alnico II, JB, single coil.. doesn't matter, they all do the same thing.

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Post by HEAVIER THAN HELL » Sun Jun 29, 2008 5:21 am

Marshalls ARE midrangey, thats the sound. try the later JCM800 tonestack trick with the 4700pF from the bass pot to ground - that'll scoop the mids some.

(PI mods)... for less bass, you definately want to ditch the 0.1uF caps in the PI and go to 0.022uF

(tonestack mods)... for less low-mids (typical Marshall tone) and more clarity/cut in the midrange, raise the slope resistor to 68k (go as high as 100k, experiment with values) with the treble cap changed to 250pF.

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Post by novosibir » Sun Jun 29, 2008 8:42 am

HEAVIER THAN HELL wrote:(PI mods)... for less bass, you definately want to ditch the 0.1uF caps in the PI and go to 0.022uF

(tonestack mods)... for less low-mids (typical Marshall tone) and more clarity/cut in the midrange, raise the slope resistor to 68k (go as high as 100k, experiment with values) with the treble cap changed to 250pF.
As HTH already suggested, for less bass response I'd also recommend to swap the .1 with .022 - a step in between wouldt be, to keep the .1's, but lower the bias feed resistors from 220K to 100K. That's robbing a tad PI's gain, but gives more clarity, when the amp is dimed.

With the 100K's use a good long plate 12AX7 like Telefunken smooth plate or a Yugo pre war EI, a Tesla (not JJ) E83CC also is working fine in the PI w/lowered bias feed resistors.

A larger slope resistor is reducing the low mid boomyness and I also go there with values of 39K or 47K, sometimes even with 56K, despite the treble cap of 470...500p

Although, a smaller treble cap is reducing the high mids above 1kHz - and, if too small, takes off the needed 'cut through' of the amp in the band context! So be careful by diminishing the treble cap's value.

Larry
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Post by Kapo_Polenton » Sun Jun 29, 2008 11:12 am

Thanks guys, I'll give it a whirl. I found that with the .68 cap removed and my 500 pf treb cap, the amp is tight enough now that I properly soldered my presence .1uf cap in place. I think it was not soldered properly as it now seems to help tighten the amp. So the midrange isn't quite as pronounced but still there when a pedal is on. Essentially, I kind of have that Jake E Lee Badlands tone going... I am going to keep the bright cap as is for the cut but will try some of the other stuff you guys mentioned.

One more thing, did you guys think the amp in my clips sounded normal/indicative of a 1987x? And the pushed sound, does it sound like $hit to you guys?

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Post by wdelaney72 » Sun Jun 29, 2008 1:16 pm

Some time ago, Larry also suggested .047 to be a "happy medium" between .1 and .022. I did this in my last build and like it a lot.
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Post by novosibir » Sun Jun 29, 2008 1:35 pm

wdelaney72 wrote:Some time ago, Larry also suggested .047 to be a "happy medium" between .1 and .022.
Yes, .047 w/ 220K bias Rs or .1 w/ 100K bias Rs are my preferred combination. The 1-st combi is in my DINO amps, the 2-nd in my British Purists now.

Larry
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Post by Kapo_Polenton » Sun Jun 29, 2008 10:47 pm

I went with 56/250, tightened it even more. More clear for sure.. so now it sounds better with a proper balance between high mid and low but with an overdrive pedal it still sounds synthetic to me.. so it can do certain tones for sure. Maybe i should try something a bit more transparent like a micro amp or something but now that the tone is where it should be, I might try tweaking some gain. I wandered over to that blankenship site to hear his vari plexi after hearing Steve Stevens talk about it, listening to the sound clip, how the hell can that thing be stock?? Sound wicked. I need to try and get that..

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Re:

Post by FourT6and2 » Mon Jul 24, 2017 7:28 pm

novosibir wrote:
HEAVIER THAN HELL wrote:(PI mods)... for less bass, you definately want to ditch the 0.1uF caps in the PI and go to 0.022uF

(tonestack mods)... for less low-mids (typical Marshall tone) and more clarity/cut in the midrange, raise the slope resistor to 68k (go as high as 100k, experiment with values) with the treble cap changed to 250pF.
As HTH already suggested, for less bass response I'd also recommend to swap the .1 with .022 - a step in between wouldt be, to keep the .1's, but lower the bias feed resistors from 220K to 100K. That's robbing a tad PI's gain, but gives more clarity, when the amp is dimed.

With the 100K's use a good long plate 12AX7 like Telefunken smooth plate or a Yugo pre war EI, a Tesla (not JJ) E83CC also is working fine in the PI w/lowered bias feed resistors.

A larger slope resistor is reducing the low mid boomyness and I also go there with values of 39K or 47K, sometimes even with 56K, despite the treble cap of 470...500p

Although, a smaller treble cap is reducing the high mids above 1kHz - and, if too small, takes off the needed 'cut through' of the amp in the band context! So be careful by diminishing the treble cap's value.

Larry
novosibir wrote:
wdelaney72 wrote:Some time ago, Larry also suggested .047 to be a "happy medium" between .1 and .022.
Yes, .047 w/ 220K bias Rs or .1 w/ 100K bias Rs are my preferred combination. The 1-st combi is in my DINO amps, the 2-nd in my British Purists now.

Larry
Larry,

What about .047 PI output caps + a lower value for the bias resistors? Like 180K or 150K?

I know raising the PI caps increases bass response. But what does lowering the bias feed resistors do?

I've never heard your Dino or British Purist amps. How does the sound compare between .047/220K and .1/100K?

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