Squier 15 upgrade?

[squier15]

Hi All:

I have a 1988 MIK Squier 15 (not a Champ), and I have opened it up in my very first attempt at amp repair/modification.

I am addressing 2 issues. The first one I think I can handle. The second one is over my head:

1. It has a wonderful Vox-esque clean tone but not enough headroom for strummed chords, even with the preamp set to "1", so I am gong to install a Bourns 500K trimpot inplace of R1 and adjust to taste.

2. I wonder, while I have this thing disassembled, if there is anything a newbie like me can do to improve the distortion on this thing.

It ALWAYS amazes me that there are so many great solid state distortion PEDALS but so few nicely distorting solid state AMPS. My favorite solid state distortion is from my 1968 Vox Nova, which generates its distortion by accident... it was never designed to distort, as it was built for horn players who wanted to compete with guitarists. This little guy thinks it's a plexi Marshall! But I digress... back to the Squier 15.

ANYWAY, can any of you guys give me any pointers?

thanks,
Tim

[joecool85]

I'd need to see the schematic to even begin to help.  btw, my Dean Markley K-20X has great built in overdrive.

[squier15]

Thanks for answering. Here's the schematic.
http://natcade.tripod.com/schems/Fender/squier15.gif

[joecool85]

Thanks for answering. Here's the schematic.
http://natcade.tripod.com/schems/Fender/squier15.gif

I didn't have much time to look at this, but you can't hot link with tripod.

[squier15]

Sorry if you had difficulty with the link, and thanks for posting the schematic for all to see. It's the only source I found online.
I'd be grateful for any words o'wisdom you or your pals could share. (I did not inherit my dad's godlike engineering skills ;-)
~Tim

[teemuk]

What characteristics in distortion you wish to improve? IMO, "Improving" is a very vague and subjective term. Giving you any tweaking ideas without knowing what you want is extremely difficult. Realize this: This circuit can be modified in many ways but it does not contain an "ordinary" clipper circuit (similar to DS-1 and its countless variants) and it will not lend itself to typical modifications. Essentially, your amp is what it is and changing it to another amp (that you prefer more) may mean a nearly complete rebuild. Maybe you should just sell it and buy an amplifier you like more...?

Some characteristics of this circuit you may wish to know are:

- The first gain stage has a bandwidth limiting property: It is basically a gain dependant band pass filter. When gain is increased the bandwidth decreases and this can make the distortion sound nicer since you decrease the amount of "farting" bass and "screeching" high frequencies. Unfortunately a circuit like this may also make the amp sound "boxy", "lifeless" and "thin". If you have issues with this characteristic you can decrease the limiting effect on bass frequencies by increasing value of C5 or on treble frequencies by decreasing value of R3. Right values are naturally a matter of experimenting.

- The tone control circuit is not an ordinary "fender style" passive circuit either: The initial response with all controls at "5" is boosting the middle, thus you are not getting the typical "scooped middle" response that most guitar amplifiers have. Middle scooping is possible with this circuit (either by setting mid to zero or by increasing treble and bass) but in practice this amp requires another mentality for tweaking those tone control pots: Forget possible combinations you learned from other amps and just use your ears. This is not a bad circuit, just different. Due to possibility to boost mids it is in fact more versatile than the tone control circuit you find from most guitar amps. You can tweak the circuit to get alternative frequency responses but I don't think it really is necessary or worth the effort. Just learn another mentality for setting it up and see if it helps. This circuit does not behave similarly than the tone control circuit of most amplifiers and this fact explains a lot.

- Thirdly, there is not much tone shaping after the very basic clipping section. Typically clipping circuits achieve a "mellower" tone by introducing a low-pass filter after the clipping stage. This removes harsh and annoying high frequencies from the signal content. This amplifier does not have this kind of filter (unless you count in the filtering effect of the speaker). This would be "easy" to compensate by adding a capacitor "shunt" in parallel with R17 or R18 but another inherent (and major) problem shows its face: Clean and overdrive do not have separate channels (I prefer term signal paths) so this would suck up some "sparkle" from your clean tones. Basically, any mod you do to enhance distortion will affect the clean tone as well. Another very important issue to realize: Many amplifiers introduce the tone controls after the clipping section. This has a drastic effect on tone of overdriven signals.

You can naturally tweak this amp but you can't change its inherent characteristics - at least not very easily. If you think you can change few components and make it sound like Marshall you are likely wrong.

[squier15]

Well, this site erases typing when it times you out, so here I am retyping my response. (ARRRGH!!!!)

First off, thanks for your thorough answer. No, I am not looking to make this thing into a Marshall. My Vox does a good Marshall impersonation, but I am not expecting such things from the Squier.

Making the distortion less ratty was my second priority anyway, behind the main goal of increasing the pitiful headroom, so I am not too disappointed to hear that modding the distortion is impractical. I have good boxes if I want dirt. ;-)

I will go with the amp's strength -- a nice, musical, midrange-heavy clean tone. To do this, I will replace the woefully low-valued R1 with a 500K Bournes trimpot and adjust it until the amp passes what I consider a reasonable test: it should remain clean with a strummed Les Paul, as long as Preamp 1 is set low (3 or under).

To reiterate, as it stands now, it sounds sweet but only with single-note lines, double-stops, and gently brushed chords. Anything more and it starts to splat, even with the preamp on 1! (A Jensen ceramic speaker was a good cheap upgrade but did not solve the inappropriate clipping threshold.)

I remember GUitar Player mag testing a similar amp (the transistor version of the Champ) and complaining that the input needed more "padding."

My tech thinks my plan will work, and he thinks it's easy enough to be a good newbie project for me.

I'll let you know how it works!

Thanks for your help.

Yours in Sound,
Tim
www.myspace.com/timmungenast

[squier15]

Howdy!

SUCCESS... mostly.

Well, the trimpot's legs were not far enough apart to replace that resistor, but I used a 100K metal-film resistor instead, and it worked great. Way more rich, clean headroom.

Just for fun, I kludged a connection into my closed-back 1x12, plugged in my "frankentele," and the sound was HUGE. And loud. First preamp on 2, Second preamp on 0, Master on 2. Sounded good when I ran test leads to the amp's 8" Jensen as well.

Now all I wanna do is use the headphone-out jack as a speaker out, for those times when I need to hear the Squier's clean goodness through a separate cab.

My tech did a reversible mod to my solid state Vox Nova whereby I could plug into a TRS jack that would defeat the internal speaker and send the speaker juice to an external cab. I tried to copy what he did EXACTLY, hooking up just the right wires with the same lugs on an identical TRS jack, and all I get is either stone silence or ugly oscillation like when an 8-track tape is changing channels. Bypassing the whole mess with test leads restores the great tone.

Can any of you please help me? I really think I can do this, and if I have my tech do it, well, let''s just say he's way busy re-tubing Marshalls. It could be a helluva wait. (LOL)

~Tim

[teemuk]

Sounds like you are experimenting on a dangerous territory: If you accidentally short the output you can likely kiss the power amp goodbye. I suggest you stop modifying the amp until you have a clear idea of what you are doing.

Copying a circuit is a whole different thing than knowing what the circuit you are copying is actually doing. Both methods can lead to a successful result but the chance for that is a lot better in the latter case. Anyway, the bottom line is that the particular mod should be extremely easy to do. Assuming you really followed the original mod exactly (instead of misdeliberately doing something completely different) all I can think of what went wrong was either...

a) What you refer to as "right wires" were wrong
b) The "identical" TRS jack was not identical (i.e. Switchcraft lists 37 different switching jack configurations)


Are you trying to replace the existing headphone jack with an external speaker out jack or are you adding another jack for the external speaker? I would suggest the later configuration as it is a lot more reversible and easy to do. ...And on top of that you still have the headphone out left for "silent" practicing.

See:

http://www.rru.com/~meo/Guitar/Amps/Kalamazoo/Mods/speaker.html#ejack

Your amp does not have an output transformer but it nevertheless has two wires running to the speaker from the amp. Clip them and put this circuit in between. The important thing is to ensure that the jack is indeed the right type. (Remember: At least 37 different alternatives exist). You can mount the jack on a piece of bent metal and mount the whole thing to the cabinet wall with a pair of wood screws. Very reversible.

As an extra, that external panel can house more than just a single jack so you can use two (or more) jacks for switched series/parallel wirings et cetera. i.e. One jack disconnects the internal speaker, another jack wires the external speaker cab in series with the internal speaker. Possibilites are nearly endless. These additions are very easy to do as well once you get familiar with different switching configurations those TRS jacks can include.

[squier15]

Thanks for your intelligent advice.
I see now that I was using the wrong jack... my TRS jack was not a "switching* TRS jack, and it has one less lug than the one my tech used on the Vox Nova. GAWD, I FEEL LIKE SUCH AN IDIOT!  At least I did not toast my power amp.

Another big difference between the Vox Nova and the Squier 15 is that, while both are solid state, the Nova has an output transformer... it thinks it's a tube amp.

Anyway, I will not do anything until I am sure I know what the hell I am doing.

...or I will just have a pro deal with it. (LOL) This is a very good-sounding amp, and I do not want to ruin it.

I'll let you know what happens.

Cheers,
Tim

[joecool85]

I put 2 x 1/4" jacks on the back of my K-20X.  One goes to the amp and the other to the internal speaker.  Works great.  If I want to use the internal speaker, I just use a 12" patch cable and hook that up, if I want to run a cab, I unhook that and plug in a cab.  Most of the time I'm not using the internal 8" speaker, but rather my 10" Dean Markley cab, as it sounds much better and is louder as well.

[squier15]

Man, that is the "K.I.S.S. principle" in action!
Hat's off, tone brother.
~Tim

[joecool85]

Man, that is the "K.I.S.S. principle" in action!
Hat's off, tone brother.
~Tim

I'm all about simplicity.

[squier15]

So I wussed out and had a pro do the work. Tom at Aztech Electronics installed an even beefier R1 (220K this time, as 100K still was not enough input attenuation) and did my strange bidding, namely to turn the headphone-out jack into speaker out.

Well, the amp is cleaner and overall better sounding, but even with an upgraded speaker (an Italian ceramic Jensen via Roticon), it still sounds kinda splatty when pushed hard. I guess it's really hard to make an 8-incher in such a tiny cab feel open and free. (Well, duh!)

However, when I plug this thing into my 1x12 and play my frankentele through it, it's a joy.

I may try this thing again without the back panel, just for yucks. In the meantime, I know it will act as a very capable spare head via the speaker-out jack if my Orange Tiny Terror ever flames out.

Peace,
Tim

[squier15]

So, while I steel myself for the ass-ache of replacing my 220K R1 with a beefier resistor, two questions arise:

1. would I be better off just mounting a guitar potentiometer in the chassis, setting it to where the amp stops clipping without provocation, and then letting it be, OR is a pot somehow going to kill the highs like a half-open volume pot does on a guitar?

2. Seeing as the other Retocon/Jensen I own (in the Vox) blew up on me, I want to start looking for a replacement *before* this one in the Squier blows up, too. One one hand,I don't wanna throw too much money at this amp (even though it has potential), but I do want something better than the ceramic Retocon/Jensen that's in there now... something durable, efficient, and toneful (nice balance, maybe some "chime" as a bonus, although I find chime is in my fingers).

I do like this little amp even though its great tone only shows up when I play single-note stuff on a low-output guitar.

If you cats could offer me any more advice on how I can help it to "be all it can be," that would just rock my world.

Peace,
Tim