Sweetwater Tweed Princeton Reverb Review



I picked up this amp from Sweetwater a few weeks ago. It's offically entitled "Fender '65 Princeton Reverb 15-watt 1x12" Tube Combo Amp - Lacquered Tweed" and can be viewed on the Sweetwater site:

See amp at Sweetwater

OK, so this is just another variation on a circuit board based resissue Princeton Reverb right? Well as you can see in the internal pics below, it IS a circuit board based amp for both the main circuits and the controls. What I really love about the amp to start with is the tolex finish coupled with the vintage-style brown and gold grille cloth. It is absolutely gorgeous! The matching brown faceplate is a nice touch and shows great attention to detail! The cabinet build is solid and there are no flaws or workmanship errors in the one I received. The other big deal about this amp is the fact that it comes with a 12" speaker and not not just any speaker but the well regarded Eminence Cannabis Rex Patriot Series 12" 50-Watt 8 ohm speaker. See it and the great reviews it gets here:

See speaker at Sweetwater

While I like this speaker a lot I should mention that quite a few people have opted to replace it with the Eminence Hempdog 12 - 12" 150W speaker, NOT CHEAP!:

See Hemp Dog speaker at Sweetwater

Another nice speaker choice suggested by a few users is the Jensen P12Q which has a street price of $154. It will break in a bit faster than a hemp speaker and has more of a vintage sound with an Alnico magnet and perhaps a bit more flabby bass and more highs. It can be viewed many places including:

See speaker on Jensen web site and See speaker on Amazon.com

This amp comes with a decent reverb tank, a Ruby Tubes model RRVL2AB1C1BV4 (pictured below). I have been replacing most of my stock amp reverb tanks with Mod brand tanks. To my ears, the Mod tanks sound lusher, have less discrete echos and are less tinny than most other brands on the market today. This tank and the Mod replacement have LONG decay times. I use reverb stomp boxes with my setups because I like the hall reverbs a lot more than I do the spring reverbs. However for all the sound files in this review I used the stock Ruby tank. The recommended Mod reverb tank for these amps is the 4AB3C1B.

See Mod reverb tank

Weirdly enough this amp does not come with a schematic! The amp chassis is however just a '65 Princeton Reverb Reissue as shown here:

Amp schematic




A full song recording with real pedal steel, lead guitar, bass, rhythm guitar, EZDrummer drums, and RealBand (BIAB) piano and fiddle. All pedal steel and guitar parts are played through the Princeton amp and mic'd with a Shure SM57.
Click here to listen to Think I'll Just Stay Here And Drink


Review Summary

This amp is pretty quiet in terms of hum and white noise. The tubes that come with it are pictured below and do a nice job. I have the 6V6's biased at 21 mA and tried varying the bias from 19 to 23 MA with very little change in sound to my ears. I did break the speaker in a bit by running full range music through it at pretty high volume for 51 hours. More hours of use and aging are probably needed for the hemp surround to loosen up a bit more but my patience ended at 51 hours! Overall I think this is a great amp for my standard guitars and decent enough to use for a practice amp for pedal steel guitar. Not having to swap out the stock speaker and baffle for larger ones makes this amp a great Princeton and close enough to a Deluxe Reverb that I could use it for a long time as is. I'm not really concerned about the lack of a turret board and it will be many years before I'd have to worry about servicing anything on the PC board. Besides, the tube sockets are all chassis mounted and flexibly wired over to the PC board. This reduces the risk of PC board mechanical breakage and heat damage. I've included a song (see above) recorded with this amp and a bunch of individual sound samples below as well a some basic bench tests. My vintage Princeton reverb has smoother sounding reverb than this amp but I'd have to swap the new Mod tank into this amp to see if this would still hold true (only a $21 item). The vintage Princeton with its flabby old speaker has a bit warmer tone but who maybe the reissue Princeton will get there with time. For $650 to $1000 I'd say the vintage Princeton is a better amp but this new amp is no slacker in the sound department and it's the sharpest looking amp in my studio now. I don't use a lot of amp vibrato but it sounds great on this amp, deep and not choppy.

For comparison here are the relative weights of some popular amps:

Fender 65 Princeton Reverb 34 pounds
Fender 68 Custom Deluxe Reverb 40.2 pounds
Fender Steel King with casters 64.4 pounds
Peavey Nashville 400 57.0 pounds
Allen Encore 43.7 pounds





Sound Samples



Here's some sound samples. All pedal steel samples use the Lehle volume pedal with 12' of George L's cable between the amp and volume pedal to roll the highs off a bit, Fender Princeton amp with a Shure SM-57 mic, onto a Zoom R24 recorder then ported to Reaper to convert them to mp3 files at 320 kbps. The samples are very raw and close to what I hear sitting next to the amp. The guitar samples omit the Lehle volume pedal. My initial amp settings (subject to change):
  • Volume = 6
  • Treble = 5
  • Bass = 5
  • Reverb = 3 - 5


Selection
Recording Method
 		Comments
Shure SM57
 Pedal Steel - E9th - Sample 1
Shure SM57
 Pedal Steel - E9th - Sample 2
Shure SM57
 Ibanez ArtStar AS-153 Sample 3
Shure SM57
 Reverb/ Vibrato Demo - Sample 4
Shure SM57
 Epiphone Les Paul with Gibson Pickups - Sample 5
Shure SM57
 Fender Player Tele - Sample 6
Shure SM57
 Tube Screamer - Sample 7



Bench Testing and Accessories

I used the Weber amp cradle while initially powering up and bench testing the amp. LIne voltage was 122 VAC rms. Input voltage at input 1 was 0.4 volts peak-peak. For a dummy load I used the Weber TRU-LOAD DUMMY LOAD with a mod to switch out the unit's internal speaker motor allowing for a more resistive load. This keeps the load voltage and current in phase eliminating power factor considerations which simplifies power calculations.

  • Weber TRU-LOAD DUMMY LOAD

    Here's a schematic I traced out showing the added switch (click on picture for full size pdf file):

    Note that you can save some money by just buying discrete resistor loads. Also its possible to use only three 200 watt resistor to creat 2,4,8 and 16 ohm loads at 400 watts each! This is pretty cool and you can click on the picture below to see my implementation of it using simple ohm's law calculations.

    For bench testing I used an audio signal generator, 200 MHZ digital scope, variac set at 122 VAC with the dummy load set at 8 ohms. A tube amp will deliver maximum power to it's load when the load matches the amp's internal impedance. A lower or higher load will result in a lower power output to the load but can result in useful damping transient and tone changes in actual use. Note that a 3 db increase in audio level only yields a slight increase in audible volume but requires twice the power! Similarly a 6 db increase requires 4 times the power and a 10 db increase requires 10 times the power but will sound twice as loud. Nevertheless, amps are heavily marketed based on wattage and it's hard to convince buyers that whether an amp is 10 or 20 watts or even 40 watts really doesn't much matter in terms of sound levels. Going from 40 to 300 watts for example is a useful power change if you need higher sound levels.


    For my setup I used a sub $100 audio generator and it's pretty amazing. You can see the waveform purity immediately below and pictures of the setup far below. The scope has a somewhat useful FFT (Fast Fourier Transform) function that shows a frequency domain representation of the signal. What is REALLY cool about the scope is that it calculates the RMS value of the waveform allowing for accurate output power calculations of various waveforms. A square wave will have a lot higher power output than a sine wave at the same frequency. Thus, as the amp starts to get pushed out of it's linear region , you can get more watts of RMS power out of it.

    The first picture below shows the amp delivering a fairly clean 13.1 watts with a 400 mV peak to peak input signal at 1 khz. Most passive pickups that I've seen put out between 90 and 400 mV. The 6V6 plate voltages are at 406 volts and the tubes are biased at 21 mA. The plate voltage is at 446 VDC with no signal input so some serious power supply sag occurs at higher volume levels resulting in really cool sounding compression.

    The next picture shows the amp delivering 15.3 watts when pushed into output clipping.






    There are quite a few pictures below. Click on them to see them full size or at least sized to a browser window. Click on the picture again if needed to zoom in even more!







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