Yet another stack switch

[max_lwedge]

While I like the Skyliner Tone Stack, it is just too thick for my taste on some things. I tried the 10n/22n/47n switch on the mid-cap, but it didn’t quite do what I wanted. Here is what I ended up with, the ‘trick’ being the split slope resistor. I’ve been playing about a month with it, happy so far. FWIW, the test mule is a non-HRM 6V6 amp.

With the switch off, it is just a Skyliner, minus the 1n across the Bass pot. Engage the BM cut, and the stack morphs into something more like a BM stack. The 10n/250k Skyline mid cut is still engaged. They are additive, but the 3db point is different. The BM cut is usually dominant, and of course the BM returns through the bass pot tail, whereas the Skyliner is just a cut to ground. I’m not a spice guy, but I’m guessing this smears the mid-cut trough you normally see on the tone stack plots. My mind thought about making the bass tail resistor a 2nd mid control trimmer for the BM cut, but my ears haven’t asked for it yet, so it remains a resistor. You can’t make the tail too big, or you lose the bass pot’s lower range.

If anybody tries this, I’d like to hear how it goes.

[Guitarman18]

Max,

That looks like a great idea, I'll have to give it a go sometime. Thanks for posting.

Cheers,

Paul.

[wjdunham]

Curious what kind of guitar you typically play, single coils or humbuckers? I see you have a slightly different configuration for the treble/mid boost, .001 in series with 390pf vs. .002/330pf. About the same without the mid boost, but less mids when you hit the boost switch? I have tried a switchable .01, .02, .047 mid cap on two different amps, the difference is very slight, if audible at all with a 150K slope resistor.

What I really want is a mid control pot that does something useful. It seems like everyone winds up with switchable settings to get the mids right (myself included). If I'm using a particular guitar or speaker or whatever where I'm not happy (usually with the mids) it seems like there isn't a combination of knobs that really changes things much for the better. When I show friends my "cool" homemade Dumble amp, their first comment is, "sounds great, but there's only one sound, and the tone controls don't do very much...". Really that's their second comment, first is usually "you made that, am I going to get electrocuted?

Anyway, back the the topic at hand, I have some time this week, I'll give it a try and report back.
Bill

[Structo]

I agree, my mid and bass control don't really function that well to my ears.

I don't mean they don't do anything but, it just seems as if I turn them both up it just makes the bottom more muddy.

When I turn a bass knob on an amp, I want it to boost or take away the actual bass frequencies.
Does changing the slope resistors help with that?

They seem very interactive which is probably a characteristic of this type of tone stack.
I have another amp here that has that the tone stack works well on so I know it's possible to have one that works well.
But it is a modified Baxendale or James type stack with a 47K slope resistor and has a mid pot as well.

Maybe it's just a quirk of this type amp (ODS).

[max_lwedge]

What I play the most is a so-what 90s LP with Fralin unbuckers. Coil tap for SC is wired and is useful, but played mostly as HB. Also use a reissue 57 Strat and an early 70s Tele with Lollar special PUs. That covers a lot of ground. The Strat has been by far the hardest to get a good OD sound with.

On the mid-boost, the .002 was just too much for me and makes the treble knob pretty ineffective, I liked the .001 better. The 390 pf instead of 330 pf is a Kentucky windage adjustment for the .001 substitution. On this particular amp, what is left off the drawing, (already too busy) is a 47k below the Skyliner mid pot that I switch in and out with the mid-boost, so I’m coming at mid boost from both sides. I set the mid control moderately low, and then the mid boost has something left to say.

I am with you on the knobs' range. IMHO, the FMV tone stack and variations are to filter design what grilled burgers are to fine cuisine; primitive and inflexible, but work great for their one trick. The mid pot design is a little bit of a hack and everything affects everything else. The tough thing is, so many people have spent so much time making FMV work right with a guitar, and if you do something different, you are on your own.

Here’s something I noticed with the Duncan TSC and the HRM stack. If the OD is too fizzy, the natural thing to do is to turn the treble trimmer down. Surprise, if the mid trimmer is turned up, the treble is capable of boost but hardly any cut. It’s just not intuitive to turn down the mids to make the treble capable of cut. As an internal adjustment that’s ok, but most players wouldn’t think of that.

[llemtt]

Hi max

can you post a picture of HRM settings with Duncan TSC achieving treble cut?

thanks

[max_lwedge]

These are done with Marshall, impedance adjusted for no CF. There are 3 shots with treble at 0, one with treble at 10, mid at 0. With treble 0, mid at 10, cut goes from 5 db at 80 hz (~E2) to about 11 db at 200-300 hz (~A3) on, with a hump in the bass. The dimed mid has relegated the treble to boost only.

With mid reduced to 3, the treble cut goes from 5 db at 80 hz (~E2) to 20 db at 1100 hz (~D6), which is pretty significant. With mid reduced to 0 and treble still at 0, the cut looks to be falling at the nominal 6 db per octave from 80 hz on, now that is treble cut. With mid still on 0 but treble back up to 10, there is a big scoop at about 600 hz, but the treble begins climbing back and recovers pretty much by 2000 hz.

So that was my aha moment when I saw that the mid control largely determines whether the treble is a full range control or a boost only.

[Structo]

On your drawing you have a 47K slope but on the TSC you have a 33K.
Is that something you changed to in your amp?

[max_lwedge]

The drawing is of my main stack between V1a and V1B, and it does have the 47k as shown. I haven't experimented with the tap point, my initial go was more of a mimic of the BM stack. I thought about reversing the 100k and 47k and using a 22n or 47n bass cap, more like a Wreck. I felt that might not be enough of a difference to warrant the switch, but you never know until you try & listen. The fact that I haven't fiddled with it in a month is good sign.

My rant on the HRM stack was unrelated to the drawing. The request for HRM curves showing treble cut I took to mean the post drive trimmers, so the TSC shows 33k, which I think is normal there. I think I saw posts much much earlier in the forum about different slope resistors in the HRM stack, but nothing lately.

My own guess as to why HAD did the HRM was to lower the bass through going the OD to get rid of the mud at higher drive levels and then use the post stack to adjust the bass level back up and dial in the effect of the snubbers, all without soldering different parts in and out.

[llemtt]

many thanks for the pictures

I've been playing around with TSC long long ago before I went into Spice things, but I see it's still a very useful tool.

What I see match my memories: there's no way with the HRM stack to have some real treble cut, I mean an almost flat response till 3-4khz and then a cut, it works more as a "bass boost".

But there are some alternative designs to HRM... the "treble bleed" control is one of them.

bye
teo

[Guitarman18]

max_lwedge,

Where did you place your switch, on the back panel? Did this cause any lead dress issues that you needed to deal with.

It seems to me that it would also be a suitable method to switch between Skyline/Classic tone stacks in some way, which I would like to implement on my new build.

Cheers,

Paul.

[max_lwedge]

For testing, I placed the switch on a push pull pot for the bass, all I could find was a A1M, the taper is a little off, but no great difference. It could have been the volume as well, so A1M would be right. The test mule board wasn't originally done as a D-style and has become a Frankenstein, so actual isn't real helpful - I desperately need to redo it. I don't think you would have trouble putting a switch on back panel, but haven't tried it.

I have hand sketched the pull-on switch diagram and two partial board layouts, board layouts not tried, so YMMV. There is a hack of the standard D-Lite preamp layout showing extra cap and tapped slope resistor added to the existing board. Not pretty, but saves existing boards. The second is how it could be done with a new board layout, slightly tweaked.

[Guitarman18]

Thanks Max,

I'll give it a go and report back.

Cheers,

Paul.