IM distortion

[Bob-I]

I'll consider it...I've seen other unexplainable, strange things happen when changing a ground point. I once had an amp go into major squealing oscillation when I added a small value cap from signal to ground. But this happens at all volumes...if anything it improves when I crank the amp.

I certainly want to track this down but I definitely don't want to get into the dog chasing it's own tail thing by just changing things willy-nilly. I've used a lot of restraint to not mod this thing to hell and back like I often do...only to have to make a new board because the old one looks so bad and ultimately go back to 'stock' or very close to it. I already did that to 3 previous homebrews.

I wouldn't call this "will nilly". The screen modulating the plates is a common issue causing ghosting like you describe.

[dogears]

Here is a recent HRM clip (with BM setup). This is really smooth to my ears, not perfect yet, but I prefer this to my years of non-HRM clips. Plus it feels better to me as a player. HRM is harder to dial it in, but when you do

http://www.scottlernermusic.com/2007/AlthraxBlues.mp3

Keep at it, you'll get it!!

[Fischerman]

Sounds great as usual Scott. Mind posting your settings for that? I'm almost embarrassed to ask that...I would hope that after all these years I can at least dial in an amp. But I can go from low CL vol/High-ish Drive to high CL vol/Low-ish Drive and all points in between and while they do sound different...they are all similar in terms of 'OD quality' and these issues are there at all times.

Bob, What I meant was...I don't want to start changing things without at least some 'good' reason to do so. What you describe may very well be the problem but I would prefer to find/diagnose the problem and then fix it...instead of just throwing 'fixes' at it until one happens to work. And as I mentioned above...Clean sounds good even when loud...OD exhibits these same 'problems' even at very low volumes so I didn't think what you were referring to could be this issue (which is not to say my amp doesn't have this issue to some degree).

[Tonegeek]

I think i have a similar issue with my 50 watt HRM BM which I will address next time I have the chassis out. I get a ghost note on double stops (clean, or OD). the worst offender is playing a C# on the D string. I will be checking my tubes first though because It seems like this behavior just slowly came on in the last month. Could be a filter cap i guess but the suggestions about the grounds are worth exploring too. My grounds all go to the buss wire with one chassis ground at the input. My chassis carries no current. I have separate grounds from each filter node to the buss (stock precision PS - 50uF OT center tap filtering total). The OT goes to the isolated speaker jacks and then there is a 20 gauge wire to the buss (only needed if using neg. feedback). I am using a resistor instead of the choke at the moment.

BTW- on the schematic Fischerman posted, are the HRM tweaks something Dumble did or is this owner mods? I am referring to the slope trimmer, the .001 > 270k series and the 500ka pot.

The .0047 into the OD network seems like it would kill a lot of bass tones in OD but then again I only have 1uF on OD2 cK.

[ayan]

Here is a recent HRM clip (with BM setup). This is really smooth to my ears, not perfect yet, but I prefer this to my years of non-HRM clips. Plus it feels better to me as a player. HRM is harder to dial it in, but when you do

http://www.scottlernermusic.com/2007/AlthraxBlues.mp3

Keep at it, you'll get it!!

Excellent clip Scott, as usual!

I can qualify what I mean by smoothness. I have already posted this link, but here it goes again:

http://www.youtube.com/watch?v=zP5i-zmhhsw

If the playing style incorporates vibrato, use of feeeback and a lot of dynamics in the picking, I don't think any HRM amp can touch a non HRM, period. Those amps have a lot more gain on tap and have two things going on against them: they don't crunch well, and sound not-so-good if one approaches them with a heavy hand. I have seen that hundreds of times when people have plugged into my amps. Someone had said the non HRM amps were a bit like a tube screamer, and to me the analogy is valid.

If one is going more for more a horn phrasing approach, without incorporating as many of the "blues elements" I mentioned above, I can totally see the HRM working very well. But make no mistake, it's hard to make those amp sustain, and they are a lot pickier when using anything but humbuckers (and they tend to not like the neck pickup). As devastatingly good as Scott's clips are, they are not what I call "super smooth." Larry Carlton's clip above is "super smooth," Ritchie Blackmore tone in Machine Head is "super smooth," etc.

If I had to find an analogy for the HRM amps, they are more along the lines of a Rat pedal, with the option of not having the midrange hump, though. You can get them to sound real good, but they are a whole different animal than a TS-808. Speaking of the Rat, I find John Scofield's tone with a Rat similar in some ways to an HRM amp...

Cheers,

Gil

[Bob-I]

Bob, What I meant was...I don't want to start changing things without at least some 'good' reason to do so. What you describe may very well be the problem but I would prefer to find/diagnose the problem and then fix it...instead of just throwing 'fixes' at it until one happens to work. And as I mentioned above...Clean sounds good even when loud...OD exhibits these same 'problems' even at very low volumes so I didn't think what you were referring to could be this issue (which is not to say my amp doesn't have this issue to some degree).

I understand completley. Ghost notes tend to jump out with distortion. It simply may not show up with the clean tone at any volume but jump out at you as soon as the signal is clipped.

[Fischerman]

BTW- on the schematic Fischerman posted, are the HRM tweaks something Dumble did or is this owner mods? I am referring to the slope trimmer, the .001 > 270k series and the 500ka pot.

The .0047 into the OD network seems like it would kill a lot of bass tones in OD but then again I only have 1uF on OD2 cK.

TG,
The mods are either stuff I did or stuff I've read about others doing. The slope trimmer is something I often do...I mark the 'stock' resistance before I install it and if set to the stock resistance it's just like a resistor (albeit perhaps a cheap one). The .001/270k treble bleed is something I had seen discussed here. I think Gil has used it in the past. I originally used a 1M-L pot and a .002 cap but switched to the .001 cap and then dialed it in, pulled it, measured it and used the nearest value resistor. I was surprised how much I had to turn down that 1M pot to get a significant amount of hi-cut. The 500K-A HRM bass pot is what I consider just good common sense. That tonestack has the oh-so-common 'jump' from Bass OFF to Bass ON early in the sweep...a linear pot just makes it worse and a 1M pot is too big (for my amp that is). With a 500K-A HRM bass pot my bass control never goes above about 4 or so (using a numbered Fender 1-10 knob). It seems that log trimmers are much more rare than linear trimmers so maybe that's why HAD used linear there...plus some people like a lot more bass than me. The .0047uF extra cap for the OD really cleaned up the low end but I can get every bit of the lows back using the HRM bass pot. It seems that adjustments like this early in the preamp affect the 'flavor' of the distortion more and adjustments made later (especially if after the distortion...like the HRM pots) affect the frequency balance more while not affecting the 'flavor' as much. At least that's my take.

Gil,
I use a lot of left-hand vibrato but I'm not sure I can say I have a lot of picking dynamics. Not sure about the heavy hand...probably though. I don't have a horn phrasing approach. I have a Vintage Rat and several Tubescreamers/clones. lol, I like them both...but I haven't heard a Scofield tone that I liked very much (haven't heard that much...not fond of what sounds like mindless noodling to me...I just don't 'get' Sco)....but I can listen to Coltrane noodle all day.

[Bob-I]

http://www.scottlernermusic.com/2007/AlthraxBlues.mp3

Nice phrasing. I like the way it breathes and builds. The legato is very trumpet like in the attack of each note. Being a would be sax man (I'm still working at it after 40 years ) I don't like the lumping of "horn" into one bucket. Sax an trumpet have very different attack envelopes, sax being more flowing, trumpet being more staccato. You're mostly attacking like a trumpet, with an occasional reed like flurry.

Overall I love this one, I enjoy your playing a lot when you build a piece like this

[Tonegeek]

BTW- on the schematic Fischerman posted, are the HRM tweaks something Dumble did or is this owner mods? I am referring to the slope trimmer, the .001 > 270k series and the 500ka pot.

The .0047 into the OD network seems like it would kill a lot of bass tones in OD but then again I only have 1uF on OD2 cK.

TG,
The mods are either stuff I did or stuff I've read about others doing. The slope trimmer is something I often do...I mark the 'stock' resistance before I install it and if set to the stock resistance it's just like a resistor (albeit perhaps a cheap one). The .001/270k treble bleed is something I had seen discussed here. I think Gil has used it in the past. I originally used a 1M-L pot and a .002 cap but switched to the .001 cap and then dialed it in, pulled it, measured it and used the nearest value resistor. I was surprised how much I had to turn down that 1M pot to get a significant amount of hi-cut. The 500K-A HRM bass pot is what I consider just good common sense. That tonestack has the oh-so-common 'jump' from Bass OFF to Bass ON early in the sweep...a linear pot just makes it worse and a 1M pot is too big (for my amp that is). With a 500K-A HRM bass pot my bass control never goes above about 4 or so (using a numbered Fender 1-10 knob). It seems that log trimmers are much more rare than linear trimmers so maybe that's why HAD used linear there...plus some people like a lot more bass than me. The .0047uF extra cap for the OD really cleaned up the low end but I can get every bit of the lows back using the HRM bass pot. It seems that adjustments like this early in the preamp affect the 'flavor' of the distortion more and adjustments made later (especially if after the distortion...like the HRM pots) affect the frequency balance more while not affecting the 'flavor' as much. At least that's my take.

I like the flexability of the slope trim and the post HRM high cut seems like a useable mod too. You are right about the bass trim control- mine has a very narrow useable range. thanks

[greiswig]

The OT center tap node and the screen node use the same ground wire and ground near the PT.

I'd seperate these. Ground the OT CT near the PT, the screen near the tube sockets.

I'm trying to figure out of this is my problem, too, regarding the "fizz" over the OD tone. My D'Lite has *all* of the grounds at the bottom of the PS filter cap/res pairs on a common bus for the PS circuit board, which then all go to a lug near the master volume.

Is the attached diagram the way you guys are describing the better way? Any other grounds that I should think about looking at?

[Bob-I]

I'm trying to figure out of this is my problem, too, regarding the "fizz" over the OD tone. My D'Lite has *all* of the grounds at the bottom of the PS filter cap/res pairs on a common bus for the PS circuit board, which then all go to a lug near the master volume.

Is the attached diagram the way you guys are describing the better way? Any other grounds that I should think about looking at?

That looks correct. IMHO though, this will prevent ground loop hum. I honestoy don't know what the fizz problem is, sorry.

[greiswig]

I'm trying to figure out of this is my problem, too, regarding the "fizz" over the OD tone. My D'Lite has *all* of the grounds at the bottom of the PS filter cap/res pairs on a common bus for the PS circuit board, which then all go to a lug near the master volume.

Is the attached diagram the way you guys are describing the better way? Any other grounds that I should think about looking at?

That looks correct. IMHO though, this will prevent ground loop hum. I honestoy don't know what the fizz problem is, sorry.

Thanks, Bob. Since I don't know what intermodulation distortion sounds like, I guess I wonder if that might be my problem. If this grounding helps, I'll take it.

Part of the issue, though, is that this seems to be a very common problem among D'Lite builders. Searching the archives for topics about buzz, fizz, distortion, oscillation, etc. reveals a plethora of people who have noticed what seems to be (by their descriptions) like what I am getting. And the vast majority of those threads dead end without a solution.

[mdroberts1243]

...BUMP...

Fischerman, Where are you now with this issue? Did you isolate it and find a root cause for the IM/Ghost Notes? I'd like to reduce this in my own BM build.

Bob, What I meant was...I don't want to start changing things without at least some 'good' reason to do so. What you describe may very well be the problem but I would prefer to find/diagnose the problem and then fix it...instead of just throwing 'fixes' at it until one happens to work. And as I mentioned above...Clean sounds good even when loud...OD exhibits these same 'problems' even at very low volumes so I didn't think what you were referring to could be this issue (which is not to say my amp doesn't have this issue to some degree).

I understand completely. Ghost notes tend to jump out with distortion. It simply may not show up with the clean tone at any volume but jump out at you as soon as the signal is clipped.

[Fischerman]

Fischerman, Where are you now with this issue? Did you isolate it and find a root cause for the IM/Ghost Notes? I'd like to reduce this in my own BM build.

Nowhere really. I've tried some things here and there but none of them are addressing the 'problems' with my amp. I think I'm through trying to cut bass* and tweek the gain structure...none of those tweeks do ANYTHING for all the fuzzy/buzzy shit I hear. In fact, they almost make it worse because all the good stuff has been sucked out of the tone...leaving only the trash. Just yesterday I had cut a ton of bass in the OD section and it was sounding pretty crappy (PAB ON)...then for the hell of it I flipped the Mid-boost ON which would usually make it way too bassy but...it sounded much better.

The whole purpose for my amp was to even see if I would like the Dumble sound since I can't play a real one nor any clones. My amp is not a good representation to go by but just from what I have learned I don't think an ODS is the right amp for me (nor is the Express). I'm just a heavy-handed Marshall guy I guess. I really LOVE to dig in when I play and I need an amp that will let me play as hard as I want with my right hand (like SRV hard) with no penalty. Tag's 'Politician' thread on TGP pretty much sealed the deal...until stelligan came along and posted his awesome clip.

* - I went so far as to add a 1000pF blocking cap before the OD entrance AND use another 1000pF cap between OD1 and OD2 (PAB ON)...still fuzzy/buzzy.

[mdroberts1243]

I had thought your main issue was with the lower harmonics/IM, not buzz/fuzz. My own build doesn't have any buzz or fuzz per se, but when you play up the neck you can get this harmonic overdrive blooming which can sound quite musical but it is something that in general you'd want to keep under control... and that's what I want to target.

Heisthl said his was due to the NFB being off or reduced, but I think it is apparent on mine with 'normal' presence settings.

BTW, I did drop the bass a bit going into the overdrive on mine, but that provided a subtle bass cut and wasn't really trying to address any buzz.

Fischerman, Where are you now with this issue? Did you isolate it and find a root cause for the IM/Ghost Notes? I'd like to reduce this in my own BM build.

Nowhere really. I've tried some things here and there but none of them are addressing the 'problems' with my amp. I think I'm through trying to cut bass* and tweek the gain structure...none of those tweeks do ANYTHING for all the fuzzy/buzzy shit I hear. In fact, they almost make it worse because all the good stuff has been sucked out of the tone...leaving only the trash. Just yesterday I had cut a ton of bass in the OD section and it was sounding pretty crappy (PAB ON)...then for the hell of it I flipped the Mid-boost ON which would usually make it way too bassy but...it sounded much better.

The whole purpose for my amp was to even see if I would like the Dumble sound since I can't play a real one nor any clones. My amp is not a good representation to go by but just from what I have learned I don't think an ODS is the right amp for me (nor is the Express). I'm just a heavy-handed Marshall guy I guess. I really LOVE to dig in when I play and I need an amp that will let me play as hard as I want with my right hand (like SRV hard) with no penalty. Tag's 'Politician' thread on TGP pretty much sealed the deal...until stelligan came along and posted his awesome clip.

* - I went so far as to add a 1000pF blocking cap before the OD entrance AND use another 1000pF cap between OD1 and OD2 (PAB ON)...still fuzzy/buzzy.