Looking for Bright options...

[Bob M.]

Hi,

I've got a SF Princeton Reverb, slightly modded but very much still a SF PR. It's got a 12" speaker in the cab. The amp was too bright for me with my Ricky 12 (on a recent gig) so I benched it and took out the 43pf bright cap I had added across the volume pot, ala a Deluxe Reverb. Now the amp is dull and lifeless. I have to run the treble control higher but that's the wrong frequency. It's too much in the middle of the treble range. I need more 'air' in my sound. Besides trying a 39pf, 36pf or a 33pf bright cap, what can I do to put more of the very top end back into my amp? I find that putting in a presence control has not always worked for me in the past for these airy frequencies but maybe I'm just using the wrong cap in the presence circuit. Any suggestions would be most appreciated.

Thanks in adv.,

Bob M.

[pdf64]

Speakers have a massive impact on this type of thing; suggest that you try some different ones with the amp.
Pete

[Enzo]

Eggs-ackley.

Speakers by far have the most impact on your sound. Plug the amp into as many different ones as you can to explore this aspect of your amp.

[Bob M.]

Yes, both of you are completely right. I do have access to many different 12" speakers here. There is a Weber 12" Alnico in the amp now and I've learned by these A/B comparisons that I really prefer ceramic speakers, generally speaking. Of course, this is dependent on the amp in question. However, my experience tells me that the lack of bright issue might need some help on the component level as well. I'll try a few things: I've seen some bright circuits that are more involved than just a simple small cap across the volume control. Also, I'll try some presence applications, experimenting with the cap value. Enzo, I usually use a .1uf for presence applications. Should I use a smaller cap to affect higher frequencies?

Thanks for the replies,

Bob M.

[olddawg]

You didn't mention the kind of music you are playing. If you are fairly clean I would recommend finding an old 12" JPL like they had as an option to Twin Reverbs back in the day.

[Pedro Vecino]

I need more 'air' in my sound.
Bob M.

One possible solution is to reduce the treble capacitor value. Until 180pf or even 150pf. Require raising the treble setting slightly

[Steve Conner]

Try the same 43pF bright cap you had before but with a resistor in series. Use a 1M trim pot wired as a variable resistor and twiddle to taste.

[Dave H]

..I usually use a .1uf for presence applications. Should I use a smaller cap to affect higher frequencies?

Thanks for the replies,

Bob M.

I think you would need a larger cap than .1u in the PR. A .1u cap is used in amps with a 5k Presence pot. The PR has a 47 ohm in place of the 5k pot. To get the same frequency response as 5k and .1u with 47 ohms you would need something like a 10u cap.

[Pedro Vecino]

It is a good system to adjust the brightness, but there remains the final volume dependence. It can be very misleading.
The proposal to lower the treble capacitor value does not have identical effect but is practically independent of the volume. Fender uses it in some amps.

[pdf64]

Pedro, those responses are different to my findings.
It looks like you're using TSC - which tone stack type have you got selected, what component values, control settings?
The treble cap value should alter the turnover frequency rather than the overall level of the treble 'shelf' above the turnover frequency.
Pete

[Mark Hammer]

Q: Does the 10pf cap in parallel with the 3M3 resistor need to be there? I'm wondering if its removal would allow the stock tonestack to do its thing without being quite as objectionable with the existing speaker.

That's not a strong recommendation, merely a query for consideration.

[Pedro Vecino]

Itīs a typical Fender tonestack with the middle adjusted to 6K8 and reducing treble capacitor value (250>180>150).
Each reduction step involves raising the treble control a unit to maintain the middle ratio approximate.
250pf - Treble 5 (starting point)
180Pf - Treble 6
150pf - Treble 7

In my opinion is interesting to try for this purpose.
Regards

[Bob M.]

Hi,

Thanks for all of your replies. Always good food for thought to hear what others have to say.

First off, I'm not a fan of JBL speakers for electric guitar. I play a wide variety of musics and I find that if you have a great sounding amp, it works for almost everything. The amp in question already has a treble tone stack cap reduction abilities (as well as boost) but it's not quite the same thing. I will try introducing some resistance along with the bright cap in a traditional wiring setup and see if that gets me closer. Mark, removing the 10pf across the 3.3meg will dull up the amp even more. I have increased this cap in the past for other mods when I wanted to allow more (and lower) frequencies to pass. I guess I could try a 5pf here. I think the treble tone stack cap, the bright cap and the presence circuit/cap all do slightly different things in the treble frequencies. In the past, I've been a fan of smaller bright caps across the volume control but for reasons unknown, this amp is not responding as expected. However, it's been a long held contention of mine that no two amps sound (exactly) the same. I will keep experimenting...

Bob M.

[NorCalTuna]

Hey Bob, resurrecting an old thread, but here's some ideas. Try a LARGER and different construction bright cap, leave everything else the same. That will put a little more wood to the sparkle, while the pot still holds back the bass and most of the mids. I've built a few princetons and put a 6 way rotary switch on one that could select different bright caps. I think my winner was a 68pf paper or poly something I got at salvage. It sounded awesome, but they all sounded different (though many same value). I know science doesn't essentially agree with that statement, but the 20-30 people who played this amp all noticed.