Rdodson":3e82pdhx said:
Remember, the PRESENCE is tied to NFB. So, the higher the control, the LESS negative feedback. So, the amp is not only brighter, but more "alive" as less signal is used to fight the output. Newer designs have separate NFB control (but that introduces its own issues at times). The simplicity of this "Bassman on steroids" circuit allows for that alive "thing" everyone loves about the SLO. Mike wants users to accentuate this by running the PRESENCE high. If you want to chug, then you probably want MORE negative feedback because that tightens things up. Diezel and VHT/Fryette designs have tons of NFB (and filtering) for instance.
Just an FYI. If you are a lead player who loves the expressiveness, run the PRESENCE higher. If you want tight chugness, run the presence lower.
One final point, the higher the gain, the more this is mitigated. If you are a talented lead player with touch, there is some real magic in running the gain at 3.5-4 with the presence high and the treble low (and some volume - the cap is out of the circuit at 4 on the master; run a 25K volume pedal in the loop to tame this but still get out of the squish zone). This is where the amp is at its most expressive. Some may not like it because it will not hide anything set like this, but it will utterly glorify a talented player.
Yes, but it is filtered. Running the pressence wide open, doesn't eliminate nfb in all frequencies. Same for the depth control That is what mesa brought on with the modern mode on the rectifier series. It eliminates negative feedback alltogether not only for bass and treble areas.
Negative feedback keeps thing self ...levelled, tight, clean and controlled. It can be a very good thing. Or make the amp feel overdamped.
If you want to mod the SLO easily and return to stock safely with everything in between you can place a pot as a blocker to the negative feedback in series with the pressence pot, about 1M. That will give variable negative feedback but when taken out of the circuit maxed, it'll be back to stock sound. Because, with the pot out, you have the pressence and depth resistor cap network still in the signal path back to the power amp. With the pot rotated, it blocks the negative feedback as much as you want or completely. Of course pressence and depth will be less effective the more you take negative feedback out. If you bypass it with a relatively large cap you can leave the depth control active, say 100-120hz and below. And it is a good move because, with liveliness comes boominess on the bass department. It was pointed out to me and it is true, depth is pretty much matching the amp to what the cab can handle somewhat (and the amp). SLO can handle it but you have to lower bass etc...think the recto power amp which is different...much worse in the bass department you have to almost dial bass out.
Another thing to consider between the mid, treble interaction...treble control is like a mixer. 50%/50% at 12 o'clock for example and then it tilts the sound to what it is adjusted by its cap to as it is wound up or it tilts the sound towards whatever you do with the bass/mid controls. BUT what you do with the mid control, doesn't mean it doesn't have treble frequencies in fact it does have normal treble content with the mid maxed out. So you are not maxing the mids, you allow for the sound not to be trimmed and that includes treble and then you mix what you want with the treble control like the final mixer of the network. In essence, you are not really doing something that far magical with the mid dimed and treble at zero, but it's a combination that sometimes work.
This is applicable to the rectifier and JCM 800 hint hint why oh why? Oh because they are the same there lol.
I am interested to the op that has the new slo, does it have the switch to take the loop out? I think they made the amp with the "loop buffer 12ax7" moved after the master volume. I wonder if you understand a difference with the loop out and what it is.
