My Stiletto Ace mods

[JustPassingThrough]

It's a well trodden path. We all know the Stiletto series can be bright. I also found it needed 10% more gain and a thicker, more solid mid range as well as a little bit of attenuation at the high end as there's enough available with minimal effort. Here's what I did.

C3= 500pf to 2n2 (affects all channels)

This is the first treble peaker. The 2n2 cap adds some thickness to the lower mids. You find this in the Soldano SLO, it's an easy win for thicker tone.

C13 = 2n2 to 6n8 (affects CH2)

This is a coupling cap from v1a and is responsible for determining how much bass enters the next stage. 2n2 is very small. Marshall et al use a 22n, but this was too flubby. A 6n8 gets a good amount of low end at all ranges on the gain pot.

R25 = 39k to 27k (affects CH2)

More gain on Tite and Fluid drive. This is the cathode resistor off v2b. This is the fabled cold clipper circuit, more designed for wave shaping but it's an easy target for more gain (although the asymmetry of the gain is part of the design intention). Note it's in parallel with the 220k when fluid drive is selected (along with a 2u2 bypass cap on v3a) so be careful with the value. Too low and it's crazy and gets blatty. I wanted just a smidge more gain and liked the sound of the 27k. It definitely wakes it up. FYI, a 91k resistor soldered over r25 will result in 27.3k total.

R38 = 39k to 47k (affects CH2)

Slope resistor in the tone stack of channel 2. Makes the mids deeper, allows more upper mid content. This isn't a huge change (8k). Soldano use a 56k here. I went with Dual Rec values and the 47k was good to my ears.

Treble pot on CH2 = 330pf in parallel.

This knocks off some of the high end, making it bearable. Just solder a 330pf cap between the outer legs on this pot. Easy.

Maintenance carried out:

Replaced the 15uf tantalum cap that filters the fan PSU (parallel with R17). My fan was noisy and audible through the speaker. Tantalum caps fail. I switched it for a 22uf/50v electrolytic. I also changed the stock crappy fan for a Noctua A6x25, which is a far superior and far quieter fan.

Note.

These mods can be carried out 'topside', that is no need to pull the board. You can solder caps in parallel onto the legs of existing caps to up their values as capacitance is additive in parallel. This also means the mods are reversible by clipping out the added caps.

This doesn't apply to the slope resistor mod sorry, for that the resistor itself needs to be removed and replaced. Easily done from topside as theres solder pads on both sides, but FYI.

Dangers.

As always. Don't trifle here. Unplug your amp. Give it 20 minutes to discharge. Check the voltages of the big caps with your dmm and discharge them if you need to. Be careful. Above all be careful. Focus. You can do it, but this ain't the time for cavalier attitudes and sticking your fingers in places they shouldn't be.

Results.

The amp is thicker sounding, more aggressive, great on palm mutes, more authoritative with less spiky treble from 1 on the dial. It's basically a lot more balanced with a slight hint of Dual Rec about it and I'm enjoying it a lot more than I did last week.

 

[rarebitusa]

Assuming this is an Ace? Do you have any pics of the updated reworked areas?

Yea the PCB is fairly spacious for rework and I'd like to experiment a bit with it. Which of these mods made the biggest difference? My biggest complaint is that Crunch mode on Ch 1 is a bit too bright. Did you list the mods in order of impact with your goals.

Thanks for posting them!!

 

[JustPassingThrough]

1- yes, that's why the title says "stiletto Ace mods".

2- no, but they're clearly visible on the board.

3- hard to say, they all contribute to the whole. Modding amps is a balancing act as you affect everything up and down stream from the component. You need to have an objective in mind so you're not stumbling around. I knew what I wanted to achieve so that's where I focused my efforts.

4- you can remove the bright cap from CH1, but this would only matter at lower gain settings.

5- no, just in the order they appear in on my drawings hence the ascending part numbers.

6- you're welcome.

 

[rarebitusa]

Oh yea it did have a title Stiletto Ace Mods didn't it

Thanks for following up, just curious are you running the original Mesa v30 or something else?

 

[JustPassingThrough]

Oh yea it did have a title Stiletto Ace Mods didn't it

Thanks for following up, just curious are you running the original Mesa v30 or something else?

Yep, stock v30.

 

[rarebitusa]

You need to have an objective in mind so you're not stumbling around. I knew what I wanted to achieve so that's where I focused my efforts.

Very true... I've done my share of stumbling around.

FWIW... My initial goal was to tame the overall brightness and found the v30 was a major contributor. First went with a Scumback M-75 which removed that mid-range hump. Eventually moved the M-75 to a Recto 30 cab. The blend with a v30 was more to my liking. Always run a GEQ in the loop which provides more tonal shaping. The Depth mod provided much more low end.

So since my immediate goal is to deal with Ch 1 crunch mode brightness I am wondering if the treble pot cap will work on that chan like Ch 2? I like "Easy"

 

[JustPassingThrough]

Very true... I've done my share of stumbling around.

FWIW... My initial goal was to tame the overall brightness and found the v30 was a major contributor. First went with a Scumback M-75 which removed that mid-range hump. Eventually moved the M-75 to a Recto 30 cab. The blend with a v30 was more to my liking. Always run a GEQ in the loop which provides more tonal shaping. The Depth mod provided much more low end.

So since my immediate goal is to deal with Ch 1 crunch mode brightness I am wondering if the treble pot cap will work on that chan like Ch 2? I like "Easy"

Man, all that expense. These mods are about $5 and probably achieve a similar thing without much real effort. It's a really really nice and well balanced amp now. I've played it at gigs and rehearsal and it's not shown a weakness for what we do.

And yes, the cap in parallel will work on CH1 just as well, but be mindful of the other modes on that channel. You could always clip a bright cap out as well, but that's more prevalent when the gain is low.

Just try it, you only need a pair of crocodile clips to see if it works for you or not.

 

[rarebitusa]

Man, all that expense. These mods are about $5 and probably achieve a similar thing without much real effort. It's a really really nice and well balanced amp now. I've played it at gigs and rehearsal and it's not shown a weakness for what we do.

And yes, the cap in parallel will work on CH1 just as well, but be mindful of the other modes on that channel. You could always clip a bright cap out as well, but that's more prevalent when the gain is low.

Just try it, you only need a pair of crocodile clips to see if it works for you or not.

LOL... wish I was that pragmatic. TBH I do have a weakness for digging in the speaker rabbit hole so that kinda plays into it. Will definitely clip it in to try.

 

[rarebitusa]

You need to have an objective in mind so you're not stumbling around. I knew what I wanted to achieve so that's where I focused my efforts.

Ok, so I do have an objective in mind now maybe asking too much but will throw it out there. Its my 1st real dive down into the tube circuits and what the associated components values effect.

Ch 1, thicken up Crunch voicing and trim bass response on Tite Clean. Currently I find I have to cut back the Gain in Tite Clean to like 10-10:15 in order not to get a real flabby resonance on the low E. Anything over that requires more bass reduction. Switching to Crunch with those settings proves shrill and bright. The Gain up higher provides better bass response in Crunch. The current fix is to run a EQ Block on the input and trim the bass off in the patch that is run with Tite Clean. That way the gain can go up and Crunch mode is happier.

I believe V2A is the input stage with Tite Clean, Fluid Drive. C5 I'm assuming is analogous to C3, however there is the relay RL1/R that switches in R12. Not sure where the control of that comes from. Assume I could look at the CH 1 Gain stage could be tweaked. Anyway any input for a novice into these two stages would be welcomed.

 

[JustPassingThrough]

Well, c5 and C3 are treble peakers. Changing that cap will change the EQ that gets amplified from stage to stage.

Relay 3 also seems to bring in another bright cap for channel 1. It's normally a 120pf, but the relay brings in another 500pf at c9. That's gonna add a lot of treble. If that's the crunch mode relay you could snip the 500pf so it doesn't add that in.

That's if it does that, I presume it does based on what I hear.

 

[rarebitusa]

I believe V2A is the input stage with Tite Clean, Fluid Drive.

Correction is it Fat Clean, Fluid Drive, my bad.

If that's the crunch mode relay you could snip the 500pf so it doesn't add that in.

Yea that makes sense. Now if I have this correct, the relay schematics nomenclature does burn my limited brain cells, then RY-L3 is on with CH 2 FD and Ch 1 Crunch. I don't want to lose too much top end on the FD so probably best to play with some values in parallel. thanks

 

[JustPassingThrough]

Alrighty, figured I'd tie this off as I'd lived with the mods for a couple of months but wanted to refine things a bit more:

R83 is now a 7k5 and 50k trimpot in series for a bias control. Remove r83 and replace with a resistor and trimpot in series.

C13 is 10n/630v. Anything larger value than this and the amp loses gain and clarity. 10n adds a lot of bass back into things so the bass control in the tone stack is actually useful whereas before I'd leave it on 10 permanently.

Installed 220pf in parallel with r27. This knocks off high end.

On v1b cathode there is a 2k7/680n combo. I made this 1k8/1u as is it on Soldano SLO amps. More gain, more body as the cutoff is lowered.

Removed c9 and c7. These are the bright caps. Goodbye.

Removed the 330pf that I had on the treble cap, thanks to the cap over r27 this isn't needed.

Removed the resistor in parallel over r25 to return it to 39k. Reason being if you add the 1k8/1uf earlier you don't need to make any more gain here, there's plenty available.

C14 is a 2n2.

R38 is 47k.

This amp is glorious and, to my ears, way more usable.