Removing low end mud

[daz]

If you followed the last thread i started, i recently I found that putting a 120k resistor on the wiper of my master pot allowed my amp's true tone to come thru at low volume. Much like putting a treble bleed in a guitar, without it my tone was like mud at the volumes i use it at most of the time. Why a resistor on the wiper seems to do the same as a treble bleed cap i have no idea. It answered a lot of questions i had such as why i found the amp much too soft and muddy with NFB and had to add a pot to dial it out mostly.

So now the amp is gawd awful bright and i then find using a ton of NFB (33k on the 16 ohm tap) is now not only usable but necassary. The amp sounds great like this, however i spent some time making changes that worked well with this "new" amp. Like 820R for cathodes on V1 A&B where before 1.5k worked best. Now 1.5k seems too metallic while 820R sounds smooth and rich. Grid stoppers now help, tho i've come to feel on V1B it sounds better w/o still.

So heres the question, and at the risk of driving potential replies away, i gotta tell you i've tried most of the typical stuff. But the tone is great now cept for one thing.....the low end is now rather muddy. The note attack is soft and indistinct. Sounds good with a hyper gain courtesy of a clean boost, but the cleaner i go the more obvious it is. It has that wooliness to it and it remains no matter how still i make the PSU, and if i drop couplers any lower the amp becomes too thin. Upping the slope R is a not go for the same reason. the amp is bright enough, so removing lows doesn't seem like the answer, it seems like the just need to be tightened some other way if possible. But i have no ideas for that so I have thought of lowering couplers really low anyways and try and beef the tone back up later in the amp, but i tried a resonance in the NFB with no success and can't think of anything else. Any ideas? Heres the latest schematic...
http://i24.photobucket.com/albums/c39/dazco/amp2.jpg

[Chuck H]

I covered this in another thread on this amp. But I'll sum it up again. all parameters are relative. That is, for example, you changed back to the lower preamp voltage having ultimately decided it was better. Well, now that you've altered a bunch of stuff, higher preamp volts may un-muddy the bottom end. It's important to "get" that just because something sounds good or bad in one amp doesn't mean it will be that way with every amp, or set of surrounding parameters. So now might be a good time to try raising the preamp volts again. But just a little. Last time you threw them right over the top at first which can make for a poor perception of the effect. If you had never tried pepper on your fried eggs and someone said "You've got to try it. It's great." Dumping a tablespoon of ground pepper on your eggs might convince you that you don't like pepper. Also...

changing ALL the preamp cathode resistors to 820 may have had an initial affect that you liked. But everything is a tradeoff. By doing that you've cut the effect of your .68uf bypass caps. Ergo, more relative bass in your preamp. Also, in the later stages you will be clipping assymetrical with a majority of saturation clipping. This is going to be very warm and smooth with more 2nd order harmonics. The flatter clipping of cutoff is important for odd order harmonics. That's where the spice comes in. You need this if you want any crunch to your tone. The flatter clipping of cutoff can also add an edge to the clipped bass frequencies. Making the LF seem more defined. For V1a the biggest difference will be in the effect of the bypass cap. For the following stages the difference is both the effect of the bypass cap and the nature of the clipping. I would try 1K for both V1A and B or change just one or the other back to 1.5k. That and a little voltage tweak should give you some stuff to play with.

[daz]

You nailed the cathode thing Chuck. Not that i read this and tried it, but i tried i earlier (along with many other values/combos) then again just before i read this. The first time i went with one 1.5k and one 820R on V1 it didn't do anything much. This time it was nite and day, but only because of another change i made which affected everything. In fact, i think i found the biggest improvement i have found in a long time. And it makes sense that it's something i haven't messed with much at all to this point. By the way, the schematic i posted is no longer accurate if thats not already apparent Anyways, I had been beating my head against the wall all morning and i went for a walk to get my daily exercise and i often think about what i can do to he circuit as i'm walking. It hit me that i haven't done much of anything with the 3rd stage for a few reasons, but i HAVE in the past tried larger cathode resistors only to find the tone got bland and lifeless. While walking it hit me.....what if i i try a 1.5k again but get the lost gain back by using a 220k plate R? It made sense for several reasons, so i got back and tried it. That was the magic bullet. I actually wasn't trying that just for the low end issue, but that and best tone overall because i figured once the balance is right everything including the lows would fall into place. I figured there needed to be a change in V2A, something that would just change the dynamic a lot and i thought that would do it. It did, and big time. After that it was simple to tweak other things because the tone was no longer flawed and just needed fine tuning. Took me a few minutes. I changed a few things including the cathode thing you mentioned, and it just nailed it when i tried 1.5k on V1A and 820R on B. The opposite sounded no where near as good. It was nite and day, and i could tell things are in much better balance overall because now things like that make big difference. When things are out of balance, little things make much less difference and often are hard to tell good from bad. Oh, and i played with the voltages but i'm leaving it lower.

Anyways, i think i'm done ! At least for this latest excursion into amp tweaking. I will play it a few days and if I still love it at that point, i'll replace the chassis in the cab. I hate to sound too excited because if i haven't yet caused the boy who cried wolf reaction yet, that would likely put me over the edge. But honestly, i can say w/o reservation at all, this is easily the best it's ever sounded AND felt. And by the way, that test i've mentioned before i use to see how good the tone is doing.....hit the B string at the 10th fret with average gain and see how well it sustains....this is the best it's ever been. I always hope it will begin to feed back and swell into a higher octave, but it never does till i crank the gain all the way, and even then often not. Now it does that with much less gain than it took before, about 2:00 on the gain pot. For me a great sign, as if the tone didn't tell me that already. Bass is now good and the feel is amazing. Everything feels like it's in balance. Hopefully i won't touch it again for a long long time.....pray for me Chuck.

I covered this in another thread on this amp. But I'll sum it up again. all parameters are relative. That is, for example, you changed back to the lower preamp voltage having ultimately decided it was better. Well, now that you've altered a bunch of stuff, higher preamp volts may un-muddy the bottom end. It's important to "get" that just because something sounds good or bad in one amp doesn't mean it will be that way with every amp, or set of surrounding parameters. So now might be a good time to try raising the preamp volts again. But just a little. Last time you threw them right over the top at first which can make for a poor perception of the effect. If you had never tried pepper on your fried eggs and someone said "You've got to try it. It's great." Dumping a tablespoon of ground pepper on your eggs might convince you that you don't like pepper. Also...

changing ALL the preamp cathode resistors to 820 may have had an initial affect that you liked. But everything is a tradeoff. By doing that you've cut the effect of your .68uf bypass caps. Ergo, more relative bass in your preamp. Also, in the later stages you will be clipping assymetrical with a majority of saturation clipping. This is going to be very warm and smooth with more 2nd order harmonics. The flatter clipping of cutoff is important for odd order harmonics. That's where the spice comes in. You need this if you want any crunch to your tone. The flatter clipping of cutoff can also add an edge to the clipped bass frequencies. Making the LF seem more defined. For V1a the biggest difference will be in the effect of the bypass cap. For the following stages the difference is both the effect of the bypass cap and the nature of the clipping. I would try 1K for both V1A and B or change just one or the other back to 1.5k. That and a little voltage tweak should give you some stuff to play with.

[Chuck H]

cancelled post

[daz]

Latest...
http://i24.photobucket.com/albums/c39/dazco/amp3.jpg

[Gingertube]

Low end mud is controlled by limiting the amount of bass energy passed to successive stages. This is best done by reducing the interstage coupling cap value. For an example, look at the Trainwreck Express circuits, between stage 2 and the final preamp stage (stage 3) the coupling cap value is 2n2. When I built my last Trainwreck Clone I read the cap code wrong and put a 22nF in there, this was immediately obvious from the mud it produced. Changing the cap for the "correct" 2n2 fixed the problem.

You can get some control of this by reducing cathode bypass caps to lift the half boost frequency but these give you a shelving response whereas the coupling cap gives a genuine 6dB/octave roll off and is therefore usually better.

Use the cathode bypass caps to give you harmonic emphasis.

Trim off agressive top end edge with caps across the anode load resistor.

Cheers,
Ian


Cheers,
Ian

[R.G.]

See "The Technology of the Tube Screamer" at Geofex.com for another view of how this is done.

When a distortion stage is overdriven, it distorts more at the frequencies with the biggest volume. Cutting bass cuts the amount of distortion at low frequencies, which is usually perceived as "muddy". Cutting treble makes the results less sharp and biting.

Filtering after distortion cuts away some of the created distortion products. Most commercial distortion products - amps and pedals alike - use some combination of these tricks.

[daz]

Thanks guys. I get all that and have lived by it. Look at the schematic in my last post. .68uf V1A&B cathodes, a .0047uf for the first coupler and the the PI input. But i gotta tell you i've gone further than that and at that point is when things get downright plinky thin. I've tried a .0047 for the second coupler with that result. Gone as low as 1000, then 2000pf on the 1st one. But if i go low enough it kills everything. And it's not that there too much lows.....even if i make the tone super tinny with small caps, the lows still sounded fuzzy even when theres hardly any low end ! Maybe like RG says, it's gotta happen early. But when i go super low on the coupler value there, i can't find a way to fix this tinny result later on in the amp. Anything i've tried doesn't get it back. Plus, at this point the amp sounds so good anything i change ruins it.

Now that said, it now sounds much better since i started this thread. But it could still use better low end, tho it's always been like that to the degree it's at now. It's just than nothing seems to get rid of the wolly fuzzyiness 100%.