Sparkle Control for Blues Junior III (and others)

With the Series III, introduced in September, 2010, Fender implemented a “sparkle mod,” which means that they removed a voicing capacitor, C9 on the cream board, which limited the amp’s high-frequency brightness. The Series III is definitely brighter than previous BJrs, but it can also be harsh and strident, even irritating. The Sparkle Control makes the amount of sparkle reduction adjustable from zero (stock Series III) to the same as the series II, to even darker, like the old green board (1995-2000) Blues Juniors. When you pull up on the knob, it defeats the control and gives you the stock BJr III amount of sparkle.

Click for larger image.

The Sparkle Control operates much like a tweed-era tone control, rolling off harsh highs gently, across a spectrum that covers the treble control and steadily declining through part of the high midrange. Instead of the usual tone control location in the preamp, the Sparkle Control is positioned just before the output stage, so it “seasons” the tone regardless of your bass, mids, and treble settings.

Why not just turn down the treble control? The treble control actually has  a “balance” function built into it. When you turn up the treble, it reduces the input from the bass and mids controls, and vice versa. When you turn down the treble, it increases the bass and mids, which is why your amp will distort more easily if you back off on the treble. With the Sparkle Control, the ratio stays the same, but the highs are tamed.

You can make a Series III sound like a series II, a Series II (2001-2010 cream board) sound like a Series III, and either of them sound like the old 1995-2000 green board. It will also brighten the green board, giving it a high-end sheen that you didn’t know was there.

It works well with the presence control and gives you a wide variety of additional tones and inflections.

In this picture, the small knob on the left is the presence control. The one between the Middle and Master is the new Sparkle Control.

I’ll have recordings up shortly.

 

41 Comments

  1. aes87 says:

    Hey Bill- Thanks for posting so much info here- not only can I mod my amp, but I (as an EE) gain some understanding as to what I’m doing. Question on this one-

    If I would like to add this mod for a pre-series 3 green board BJ, would I get there by pulling the C9 voicing cap? While I like the stock high end pretty well, I’ve played on a series 3 and occasionally would enjoy making my older edition sound as hot.

    Thanks!
    ~aes

  2. yan says:

    Hi Bill,

    I can see this amp has both presence and sparkle mods.
    I don’t know how to mod my amp. I want to cut high frequencies harshness.

    apart from the schematic difference between these two mods that I am able to figure out would you say that presence mod is better for Jazz players and de-sparkle mod (on series “II”) is better for Blues or Rock players that use more preamp gain and FAT switch on.

    can’t wait for de-sparkle recordings 🙂

    • bill says:

      I think the presence control is probably best for jazz tone on a series II Blues Junior. But the basic mods will do much more for your tone, to round it out and give it fullness.

  3. eddie_bowers says:

    I just ordered this mod. I already have the presence control.
    I know you said they work well together, but i’m curious about what to expect.
    My assumption is that the sparkle control will impact higher frequencies than the presence control so you could increase the highs with this control and pull back the high mids with the presence control if desired.
    Is this correct?

    I find that most of the character in a guitars tone is in this high mids to high area, so I’m hoping for finer control.

    • bill says:

      The sparkle control does start at the highest frequencies, but it’s a classic tweed tone control. It rolls off highs at a -3dB per octave slope until you get to about open E, below which its action can’t be heard. The presence control affects highs too, but it’s more about the attack of the notes, not the frequency. The presence control can both exaggerate or soften the attack, the leading edge of the note.

  4. Billatl says:

    The mod was definitely worth doing on my series II 30Watt Blues Junior with C-Rex & Ruby tank. It’s really my wife’s amp, and she heard the difference even better than I did. I lost hearing the highs years ago. She intends to make good use of it.

  5. SamZ says:

    Hi Bill – With this mod on the Series II cream board, will pulling out the knob make it sound like a stock series II or a series III amp? in other words, does this mod require removing the C9 capacitor on the series II cream board?

  6. SamZ says:

    Thanks Bill – I just ordered this sparkle control and a few other mods. Can you tell approximately what position the knob should be at to be at the stock Series II? I got this mod so I can darken my amp in certain situations. Using the bridge pickup, I find it too ice picky, and I roll off the tone control on my guitar to compensate. The fact that I can get it as bright as a Series III makes me a little nervous, but I just have to make sure not to go there 🙂

  7. ernieg says:

    Just wanted to share this. I did the sparkle mod by removing the C9. But after a lot of reading on your posts I realized the twin stack mod might help. I didn’t like it that bright so I put a 750 back on instead of the 1500. Put a legend GB128 (per your blues tone suggestion), did the twin stack mod and WOW. HOLY *^#$#*%. The amp sounds ridiculous GOOD. I see the reason for the sparkle control you have created. To have access to dial that sparkle would be way cool but i really like the static setting. Man I am in love with this setting. I have a 69 silver face twin reverb and this BJ now sounds so its baby brother. The 750pF allowed for the sparkle to still come through but seems much more tame. the twin stack mod brought out more bass as I bring the volume up which I love. Looking forward to getting my mod kits to get the full BillM Mod experience. Thanks Bill. 🙂

  8. thed0ct0r says:

    Hi Bill.

    I spoke to my local music store’s repair shop and they guessed correctly where I got my info from. He knew your site well. Popular guy, Bill! Anyway, after a lengthy discussion the technician asked me if I really wanted to have a hole drilled through the chassis and add a knob or do I simply want to eliminate the Sparkle Mod feature altogether? This idea actually appealed to me the most. So as your intro says, “…they removed a voicing capacitor, C9 on the cream board”. Would it be too much trouble to ask what the voicing capacitor is rated at and…this is going to sound so stupid….does C9 on the cream board literally mean C9 ON THE CREAM COLORED BOARD? (I hope someone got a laugh out of that.) Thanks!

    • bill says:

      Yes, it literally means that. If you remove C9 and replace C10 with a jumper, your older cream board Blues Junior will sound like a Series III. If it’s too bright, however, you can always install the sparkle control.

      You can see C9 on the schematic that came with your amp (or at Fender.com): 1500pF, 1KV.

      • thed0ct0r says:

        Sorry. I’m confused. Didn’t Fender introduce the Sparkle Mod on the Series III 2010 to make the amp sound brighter by removing C10 with a jumper and removing C9 entirely? That’s the amp I own. I want to restore the warmer tone by undoing this. The “Series III Blues Junior: What’s Different?” page explains the changes.

        I think we got our wires crossed somewhere(?) Sorry if I’m being a nuisance.

        Brian

        • bill says:

          That wasn’t clear from your post.

          Sure, just put a 1500pF 1KV cap into the C9 holes. Don’t replace the C10 cap. It makes tone thinner, not stronger.

  9. thed0ct0r says:

    Yeah…I have a problem with confusing people. Sorry about that. Thanks Bill!

  10. yan says:

    Hey Bill,

    I want to experiment something and need your advice.
    did you ever tried removing the 100pF cap bypassing the volume pot in the 1st preamp stage to get less treble ?

    • bill says:

      The purpose of the treble bleed cap is to prevent the amp from sounding muddy when the volume control is at low levels. The effect decreases as you open the control more and more. If the amp is too bright, I would look elsewhere. I do have one customer, a pedal steel player with a heavily modified amp, where we made it switchable. The pedal steel sometimes needs dark, low-gain settings and it works well for that.

      • yan says:

        Bill I was asking this because I have built a 5F2a with roughly the same V1a stage that the 1st BJr stage (not the 10k series but the classic 68k) and was surprised to get solid bass tones (even huge) with the Bjr stock speaker and same strat bridge pickup…

        I know I cannot directly compare EL84 PP and SE 6v6 – two different worlds – and I’m talking only preamp.

        but I was thinking, we have 3 stages in the BJr, maybe I can boost the low end or cut the high end/upper midrange somewhere (I already have the tone stack mods).

  11. KtownRock says:

    Bill,

    Would the Sparkle Control work the same (tone-wise) on a Made in the USA but cream board (circa 2002)? Also, your kits and mods come with instructions? Sorry for the stupid question, thanks!

  12. Parksidedrive says:

    Hi Bill

    I just started working through some of the mods I bought from you.

    I don’t quite understand the instructions for the Sparkle Mod on the Green Board…. It says “solder to the orange wire at the bottom of C9.” Does that mean the cap at C9 should be removed, or just add the wire to the bottom of C9 along with the cap?

    Also the r56 replacement resistor needed for reverb mod didn’t make it. I received the 471k cap with the jumper attached.
    We have a pretty decent shop in town, what’s the proper resistor to replace R56.

    Thanks Bill

  13. smallcraftwarning says:

    I have a very early green board BJ’s and not sure if it makes sense to add the Sparkle mod or not. Seems like this mod is designed to remove harshness from the newer models. How can this mod darken the later models, yet brighten the green board models? BTW this site is just amazing and I am looking forward to having my amp modded!

    • bill says:

      The sparkle control goes both brighter and darker than the voicing in the green board, or any Blues Junior. But the presence control would probably give you all the zing you want from the green board. It’s pretty easy to add the sparkle control in the future if you want additional high-high frequency brightness.

  14. rychus says:

    I want to start by saying the mods were an awesome improvement. Thanks for the great tone.

    I seemed to have stripped the set-screw socket on the sparkle knob. It no longer tightens down. Is there a source for replacement? I want it to match the presence knob so I am looking for the exact one. Can you supply this knob as a spare?

    Thanks.

  15. Julian_Australia says:

    Hi Bill, I just did the sparkle mod, it’s great. However, I would like to have less brightness than what this control allows for. This is mainly because I am using a G12H speaker. I am considering replacing the cap of the sparkle control with another cap. Any recommendations? The cap you gave me reads “DMT630V-CD332K”.

    • bill says:

      The cap on the sparkle control is .003uF or 3000pF. It’s twice the size of the old voicing cap in the green board and series II cream board Blues Juniors, so you can go from nothing (stock BJr III) to greater than green/old cream board. It’s a broad, 3dB per octave roll-off, and it ceases to be effective at about the same point the treble control is at its halfway point. Making it larger would, in fact, make the whole amp darker, but would also kill pick attack and string articulation. I recommend turning down the treble, perhaps in conjunction with your guitar tone control.

  16. rduval says:

    Hey Bill, can something like this be used on the new ’68 Princeton Reverb; I love it but it’s a little dark, even on Treble 10, especially with Humbuckers.

  17. vseager says:

    Hi Bill,

    I’ve just bought a Blues Jr III with the Canniabis Rex speaker. Despite most popular opinion being that this speaker is warmer than the stock (I have nothing to compare it to), I actually find the ice pick effect on the highs so bad at even low volumes that I worry about my ears when playing my strat with single coils.

    I’ve been looking at your sparkle control and presence control but can’t decide which one would be best. As I get the impression they both affect the higher frequencies. I understand they both work in different ways electronically, but could you expand on the differences between them in sound characteristics they produce?

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