By popular demand, and because....

[Dave H]

there seem to be only a few people here who use mobile devices to connect to MEF

That's because we are dinosaurs Steve I have absolutely no interest in computers. A computer is just a tool to me. I still have an xp desktop which has been running my schematic and pcb layout programs for over 15 years. I use it for the big screen. I'm not going to draw a schematic or track out a pcb on a mobile phone. If it ain't broke don't fix it.

[daz]

Is there a particular collection of electronic symbols you use?

Thanks!

Steve A.

I made most of it but not the transformer or tube symbols and possibly one or 2 other things. Those i copy and past from other schematics. The things i drew i just draw once and each time i need to add one i just copy and paste it then use the move tool to move it exactly to where i want it. Copy and pasting is what makes the work less then extremely tedious and long.

[The Dude]

...... Does anyone know if there a mobile site or app for MEF? Thanks!

Steve,

It's a mixed bag. I sometimes use it and sometimes not, depending on the device and how I plan to use the forum. There are some things better and some worse. You'll have to try it, but FYI, at the bottom of this page, there is a box that says "vB4 Default Style". If you click the arrow next to it, there is an option for "Default Mobile Style". That may or may not help you.

[daz]

Anyone wanna tell me if they can see anything in my schematic that might be causing the following symptom? It sounds like a excessive amount of squishy feel in the attack and i suspect theres still some blocking happening or starting to. Along with that i get this effect thats really obvious playing single notes on the wound strings up near the 10-12th fret and higher. It sound like locking because you hit a note and you hear some brightness in the attack but then it becomes very dark and sustains and hold sustain indefinitely but sounds like theres a blanket over it. But it's very obvious the initial attack had normal EQ and it sounds normal for a split second till the tone just goes dark and muddy. It sounds like some form of blocking like if you hit an amp's input with to hot a signal from a clean boost and the initial attack sound normal then goes to mud. This happens even with the gain knob at noon which is not a lot of OD at all.

I tried upping the 10k grid stopper to 47k then 100k and it does help but it then loses the tone and it also sounds like the issue is still there somewhat. tried a small coupler but the tone then get thing and the issue still seems to be there. Seems like it's some other issue beside too hot a signal but causes a symptom of just that.

[daz]

double post

[SoulFetish]

Anyone wanna tell me if they can see anything in my schematic that might be causing the following symptom? It sounds like a excessive amount of squishy feel in the attack and i suspect theres still some blocking happening or starting to. Along with that i get this effect thats really obvious playing single notes on the wound strings up near the 10-12th fret and higher. It sound like locking because you hit a note and you hear some brightness in the attack but then it becomes very dark and sustains and hold sustain indefinitely but sounds like theres a blanket over it. But it's very obvious the initial attack had normal EQ and it sounds normal for a split second till the tone just goes dark and muddy. It sounds like some form of blocking like if you hit an amp's input with to hot a signal from a clean boost and the initial attack sound normal then goes to mud. This happens even with the gain knob at noon which is not a lot of OD at all.

I tried upping the 10k grid stopper to 47k then 100k and it does help but it then loses the tone and it also sounds like the issue is still there somewhat. tried a small coupler but the tone then get thing and the issue still seems to be there. Seems like it's some other issue beside too hot a signal but causes a symptom of just that.

[ATTACH=CONFIG]41031[/ATTACH]

Daz,
Do you have a scope? With an oscilloscope, blockin can be easy to diagnose; thereby confirm or eliminate as the cause.
Do you know what to look for?

[daz]

Daz,
Do you have a scope? With an oscilloscope, blockin can be easy to diagnose; thereby confirm or eliminate as the cause.
Do you know what to look for?

I did, but it lasted about a year then the tube apparently went south It was old anyways. Not about to buy another, but i was just wondering if anything looks suspect on the schematic. The trannys are heyboer 18 watts by the way.

[Malcolm Irving]

In the second edition of his pre-amp book (pp 171-176) Merlin discusses some benefits of using a cooler bias on the LTP-PI. Might be worth trying a 1k to replace the 470r on the cathodes of the PI.

[Chuck H]

That does sound like blocking. Could also be an oscillation induced problem. A good reason to suspect blocking (sans scope) is that you are deriving all your clipping from a single triode stage. Too much squashing of the wave form at one single stage. Making the problem worse is the amount of resistance in your HV rail. Basically, V3a is sitting there happy as a clam and ready to amplify whatever comes it's way. That's why you hear the initial attack as normal. It takes several milliseconds for the voltage to sag at V3a once current starts. This darkens the tone and reduces V3a's ability to handle incoming signals. This is somewhat abated by the previous stages also sagging, but not entirely. So with that sag in voltage V3a clips harder and sounds darker. I'm not saying any of this is a problem or flaw. It's how tube amps clip and we love the sound. Too much of it at one stage can sound bad though. I remember having similar issues with my first mod project. A Marshall 1959 reissue that I cascaded the stages on. Not "unlike" you're schematic. If I tried for too much clipping the tone got compressed and buzzy. I struggled with a happy medium between the amount of gain I wanted and the amount of tonal detriment I could tolerate. And, like you, I continued to experiment with the circuit hoping to eliminate this compromise. But I never did. I did make it as good as I thought it could be, for me that is. That's what you're doing. But in your travels just understand that you're at a point where you're making tradeoffs in tonal properties with every change. That is, you can't always improve one tonal aspect without detriment to another at this point. That's my experience from a very similar perspective.

That doesn't mean you shouldn't keep trying It's just time to go next level and learn to accept the limitations of the circuits. That means learning more about the actual circuits and what affect their operation. I didn't think you ever wanted to take it that far though.

[daz]

Thats what I was afraid of Chuck. I have always felt that it takes 4 stages to get a decent amount of gain w/o compromises. But i'll keep trying anyways. Seems like lowering the amount of gain available takes a lot of the richness away. Also, i keep the bias at 17.5 mA at the 1 ohm resistors but last nite it hit me to check it and i found it was at over 20. Not sure how it got there but i wander if thats part of it.I doubt it because i thing i have checked it since i first noticed this but not sure. I think i need to add that bias circuit you posted for me asap just to remove that as a suspect if nothing else.

Malcom...i gibe that a try too.

EDIT: i tried doubling the value at V3's cathode to 1.6k. Seems to help without killing the tone. But because i like the tone at a certain point in the gain pot;s rotation due to the .001uf bleed cap on the pot, the tonal balance is now different. If not for that maybe it would be good like this. I thought of disconnecting the pot and measuring the in/out lugs then putting a R/C filter with that resistor value and a .001 in front of the pot. But then i would have to try and make the pot;s tonal balance at less than 10 the same as on 10 by picking the right treble bleed setup so it doesn't add anything. I never found that easy to do but it may be ok since the pot will now reside closer to 10 than before since it has less gain.

[daz]

Chuck, what i noticed screwing with values today is if i lower gain at or before the 3rd stage it helps, but no matter how low i go within reason, even tho it improves the issue is still there to a lesser degree. So at this point i'm thinking it's likely NOT blocking. Maybe you were right to mention oscillation, but how can i look for that?

[Chuck H]

Chuck, what i noticed screwing with values today is if i lower gain at or before the 3rd stage it helps, but no matter how low i go within reason, even tho it improves the issue is still there to a lesser degree. So at this point i'm thinking it's likely NOT blocking. Maybe you were right to mention oscillation, but how can i look for that?

Scope

Seriously. It can be almost impossible to pinpoint a parasitic even with a scope because it's one radiant emission affecting a lead acting as an antennae.?. Sometimes the affects show most in places where the problem isn't. The scope is able to actually see the parasitic in the affected wave form and see things like analogous hashy spikes and blips from one point to another that can help location.

One way to see if it's a parasitic artifact might be to take a .0022 cap and connect one end to ground. Then connect the other end to point along the signal path. If any test stops the problem you probably have a parasitic oscillation and that behavior may be a consequence. Remember though that just because placing the cap in a circuit affect the problem, that doesn't mean that's where the problem is.

[daz]

So the cap trick tells you there IS PO but has zero indication as to where? Is this mainy a lead dress issue or components that in circuits that shouldn't be close mounted to close together? O tried moving leads around an hour ago and i swear it affected the harmonic content in a good way, tho it didn't affect this issue.

Scope

Seriously. It can be almost impossible to pinpoint a parasitic even with a scope because it's one radiant emission affecting a lead acting as an antennae.?. Sometimes the affects show most in places where the problem isn't. The scope is able to actually see the parasitic in the affected wave form and see things like analogous hashy spikes and blips from one point to another that can help location.

One way to see if it's a parasitic artifact might be to take a .0022 cap and connect one end to ground. Then connect the other end to point along the signal path. If any test stops the problem you probably have a parasitic oscillation and that behavior may be a consequence. Remember though that just because placing the cap in a circuit affect the problem, that doesn't mean that's where the problem is.

[Chuck H]

So the cap trick tells you there IS PO but has zero indication as to where? Is this mainy a lead dress issue or components that in circuits that shouldn't be close mounted to close together? O tried moving leads around an hour ago and i swear it affected the harmonic content in a good way, tho it didn't affect this issue.

If moving leads affected the tone then you DO have invisible crosstalk happening in the amp. And I know from experience that this can actually be a good thing. I remember a case where moving an OT 180* on a corner screw changed the tone of a build from pedantic to hairy in a good way. Unfortunately that same amp had oscillation issues that caused a crackle on certain notes when under heavy overdrive. It's a slippery slope and a fools game to try to exploit that sort of thing. Apparently Ken Fischer (of TrainWreck fame) was someone who had refined this application for his design. And it went a long way in immortalizing his circuit. I, OTOH, design specifically to avoid it completely now because it's too much of an unknown quantity to manage for the number of designs I tinker with. Anyway, my point is just that the phenomenon is real. But you shouldn't count on it unless you're Ken Fischer.

Yes, the cap will tell you if, but not where. One helpful hint I can offer is that a parasitic oscillation results from a positive feedback loop. That is, two like phase circuits are communicating via the empty space between them. So you can often spot things about a layout that might be suspect. Like two wires that must cross or are near in the design being of different circuits and like phase. That or if there are any shared grounds or filter connections that carry like phase circuits, these can also be suspected. I never share grounds for like phase circuits. It's deeper than that, and I've learned some of the nuance needed to avoid problems, but even a broad understanding of the matter can help a lot in tracking oscillation problems.

Hope this helps.

[daz]

yeah, it does help, thanks. Sorta reinforced what i have seemed to notice about the random nature of things that create a tone and that it's at least partially a crap shoot with PTP amps. I did some of this tonite. For example, because it started out as a 18 watt and is radically different now, the only place to put the components for the NFB and at the PI was to put them near the gain stages and run a long wire to the presence pot. So i made a longer wire that allowed me to run it down low below ass the stuff it was near to before. I then started moving small signal wires out of the way of plate wires and all that sorta stuff. Net result seems to be about the same as far as whatever the issue is, maybe a little better, but the tone is better then ever with swirling harmonics like it's never had. Use a strats neck pup and single notes and double stops and all that SRV kinda stuff up the neck sounds as alive as his tone did. nearly like having a phaser on or such. It's really just what i am always after. So thats the good news. But the bad news is i have learned that you cant touch the thing once you get the tone right or chances are it will go away. So now i'm afraid to screw with it anymore. But i need to clean up all the tacked in stuff from experimenting so i'll probably lose it when i do that. If not i may just live with the tradeoff, tho its not problematic bad. I guess thats one good thing about PCB amps....if they nail a tone with PCB they can recreate it over and over blinfolded.

If moving leads affected the tone then you DO have invisible crosstalk happening in the amp. And I know from experience that this can actually be a good thing. I remember a case where moving an OT 180* on a corner screw changed the tone of a build from pedantic to hairy in a good way. Unfortunately that same amp had oscillation issues that caused a crackle on certain notes when under heavy overdrive. It's a slippery slope and a fools game to try to exploit that sort of thing. Apparently Ken Fischer (of TrainWreck fame) was someone who had refined this application for his design. And it went a long way in immortalizing his circuit. I, OTOH, design specifically to avoid it completely now because it's too much of an unknown quantity to manage for the number of designs I tinker with. Anyway, my point is just that the phenomenon is real. But you shouldn't count on it unless you're Ken Fischer.

Yes, the cap will tell you if, but not where. One helpful hint I can offer is that a parasitic oscillation results from a positive feedback loop. That is, two like phase circuits are communicating via the empty space between them. So you can often spot things about a layout that might be suspect. Like two wires that must cross or are near in the design being of different circuits and like phase. That or if there are any shared grounds or filter connections that carry like phase circuits, these can also be suspected. I never share grounds for like phase circuits. It's deeper than that, and I've learned some of the nuance needed to avoid problems, but even a broad understanding of the matter can help a lot in tracking oscillation problems.

Hope this helps.