Pro Audio, Amps and Marketing

Fender Blackface Princeton Reverb AA1164
Fender’s Princeton amps, some with reverb and some without, have always been my favorites for studio recording. They are low wattage amps that can get gnarly distortion when pushed, but also can get some of the smoothest and fattest clean tones I’ve heard up to about 7 on the volume knob. If you’ve ever had difficulty taming a bright guitar, well I’ve never met a Princeton Reverb that couldn’t do the job.

The first Fender Princeton Reverb amplifier (minus the reverb) I ever bought was a mid 60′s Blackface model. It had a smooth tremolo, but this effect was nothing that would be considered “bold”. These Princeton amps used a different type of circuit to achieve volume modulation compared to the other, larger amps of the day. Instead of using an optocoupler as used in the Vibrolux, Tremolux, and Vibroverb amps, the Princeton Reverb amps used tube biasing for tremolo, or “vibrato” as Fender called it.

Princeton Reverb DIY Build
I had wanted to build one of these Fender amps from scratch with the best components, so I finally found some time to get to the project. The chassis came from Thailand from an ebay user who makes very accurate reproductions of certain Fender parts – the Vibrolux, Princeton Reverb, Bassman, and others. Unlike the Mojotone chassis, these ones are more historically accurate and look very much like the original Fender chassis, especially when evaluating the chassis mounting through holes. I have a Vibroverb chassis made by Mojotone and it’s fine, but it’s different in some ways from the originals. The Mojo chassis appear to be cheaper to make and that seems to be reflected in their lower price. However, these are small details and won’t affect the sound, so don’t get too caught up on them. Both chassis are good options – use the one that makes you happy. Here’s a post on a much rawer DIY Fender Princeton amp build if you are more interested in the Tweed Fender amps.

Electronic Components
I had Heyboer make some custom power and output transformers for the Princeton Reverb. They did a great job – Heyboer transformers are some of the best I’ve heard. I ended up using a combination of Mojo Dijon capacitors, the Jupiter Vintage Tone caps, or ceramic caps for the small value coupling capacitors. The small electrolytic capacitors were Sprague ATOMs and the capacitor can was made by CB Engineering. The resistors were high quality carbon composite types.

Princeton Reverb Mods
I made a few small mods or changes to the circuit (several from this good Fender mod site) that I wanted to incorporate into the build. The pots are simply located between preamp tube sockets to minimize the appearance of the amp being totally modded and because these aren’t things I see myself fooling with every session. If I do need to change the settings, it’s within easy reach but it won’t disturb the stock functionality or look of the amp. These changes included an adjustable bias circuit, a switchable mid control, and a switchable, adjustable negative feedback loop. You can see these knobs in the picture between the 1st and 2nd preamp tubes and the 3rd and 4th – the switches are slightly behind the tubes.

The bias circuit is explained in that previous link, but it’s pretty simple. That 22K resistor in the bias supply is the fixed bias resistor. You want to take that out and use a pot to vary the resistance from some minimum level (not zero ohms) to some amount higher than stock.

Like many smaller Fender amps, the Princeton Reverb was made without a mid control and instead used a 6.8K resistor across the bass control. I added a SPST switch to switch this stock resistor in or out of the circuit. I added a pot that acted like a mid control and when the stock resistor was switched out, this pot would be switched in. Simply take a lead from where the 6.8K resistor gets soldered to the back of the pot and run it to the center pole of the switch. Then wire one side with a 6.8K resistor to ground and the other side to a 10K linear pot with a 3.3K resistor to ground. This gives you the ability to have a lower value than stock and a higher value too, just like a mid control. I can see where this would be useful for a recording studio – the ability to make fairly minor tweaks to the sound at the source is important. At the same time, too many controls and options can be a negative thing. Better to keep this switch out of the way and not think too much about tweaking it forever. If it sounds good, it is good.

The other small mod was to incorporate an option to vary the amount of negative feedback. On one side of the switch, you’ve got the stock Princeton Reverb resistor. On the other, you have a pot to vary the feedback. The setup is similar to the mid control except you want to be able to select no feedback via the pot. I tend to like switches that let you immediately get back to the stock circuit. It’s a “hard” point of comparison to know exactly what the stock circuit sounds like and whether you like a certain option better. Often, I find that my preferred tweaks are quite close to what Leo Fender designed in the first place.

Princeton Reverb Cabinet and Speaker
I’m going to build a custom cabinet for this amp that will use a 12″ Weber Alnico Blue Dog 30 watt speaker. I love the sound of these and highly recommend Weber’s speakers. Weber makes a wide range of speakers and every single one I’ve used, whether ceramic or Alnico, sounded great and lasted a very long time (I have never had one fail yet and I’ve also never been able to kill a speaker by abuse, either).

For more musician-focused information on great, small Fender amps, check out the link. As always, Antique Electronic Supply, Triode Electronics, and Mojotone are good guitar amp shops where I do most of my shopping. Nebraska Surplus Sales is also a great place to find obscure and well-built military components, but I rarely get to order from them. Triode and Mojotone have always been excellent in the customer service department. I had a small issue with a Antique Electronics shipping policy recently that they resolved satisfactorily. Even though the issue came up in the first place, I’d rather know that they will fix things in the end. All three shops (Antique, Triode, and Mojotone) are reputable – I suggest that you support them when repairing or build amps of your own.

New Princeton Reverb Cabinet
A few months later after I completed the chassis, I finally finished the cab. It looks pretty sweet:

A custom Fender Princeton Reverb cabinet