FM-DP1 "Deluxe Plexi 1" Preamp

FM-RDP5A3 "Retro Deluxe Plexi 5A3" Preamp

FM-DP2S "Deluxe Plexi 2" Stereo Preamp

FM-800Z "Rocker 800" Stereo Preamp

HB-1 "Hot Box Preamp"
HB-1 "Hot Box Preamp"




Open Chassis



Rack Mount 

 Hot Box 1 Preamp

Model No. HB-1

"Hot Box" Clean & Boost Overdrive Vintage Tube Tones From Your Amp..

Open Chassis................$395.00  

25% Off Sale Price $295.00


Retro Cage Mini Head..Add $100.00  $75.00
2U Rack Mount.............
Add $195.00  $150.00



This is the latest version of the custom FRENZEL  HB1 Hot Box Tube Preamp.  This  preamp  provides so many tones and overdrive that it will drive you crazy trying to choose the one you want. Perhaps a more detailed description would help.  I am sure all  you guitar guys know about the vintage Matchless Hot Box,and what a great tube effects pedal it was, so I won't go into a history of it...but I will tell you a little about the original Hot Box circuitry. The original  Hot Box  used two 12AX7's. They were wired so that, in the clean mode, you had one stage of gain, with a Gain control. The clean stage had a bright cap and some other audio filtering that made the tones  sparkle. For the boost stage you had three stages of gain, with circuitry very similar to the vintage Marshall preamps. The boost channel had Gain and Master level controls. The three stages of gain drove a cathode follower which fed a two band tone stack. All in all a really ace combination....but  despite it's excellence, it had a few problems and we have endeavored to correct them by listening to  suggestions made by our "rock on" guitar buds.    

The first change was to replace two band tone stack in the Boost channel with a   3 band type tone stack similar to the one was used on the JTM 45.This stack  allows you to create a much wider range of fantastic overdrive tones. We also changed the CLEAN/BOOST channel switching circuit to use a sealed ultra low noise relay to eliminate switching noises and loud pops. Another problem with the original Hot Box was that they all had a lot of 60 cycle hum. We have corrected this by using DC on the filaments. In the CLEAN amp section  we installed a BRIGHT pull switch on the Clean Gain control. These two changes give you a much larger range of tones. Also, a second pushbutton was added to the footswitch to allow you to completely bypass the Hot Box. This gives the player three options.....Bypass, Clean, and Boost. Regarding the footswitch, we have added LED's so that you know which mode you are in. 

Additional features include a standard IEC plug-in 3 prong ground power cord and all point-to-point handwiring. The controls are Input, Clean Gain with Bright Switch,  Boost Gain with Boost Switch, Boost Bass, Boost Mid, Boost Treble, Boost Master, Power LED, and Power On/Off. The rear panel has a 1/4" footswitch jack,  1/4" Output jack, Output Level control, and power line fuse.  The tube line up is 2 -12AX7's. 

If you have never played through a Hot Box... you are in for a real treat. If you have, you are still in for a trip, because of the new features that have been added.  It makes any tube amp sound better......and for you guys with solid state amps who are craving that vintage tube sound, you can insert it in front of your solid state amp and get that classic Hot Box  preamp tube overdrive distortion tones.

The preamp is built on a small 10" x 6" x 2" chassis. It is constructed with all  top of the line parts....Neutrik heavy duty jacks, JJ 12AX7's, Micalex premium tube sockets, polypropylene caps, metal film resistors... etc.  It comes with a two button Marshall style footswitch.  A retro cage enclosure and rack mount chassis are available as upgrades.

Standard Features

Input Jacks isolated from chassis to eliminate eddy currents and hum.

DC on filaments to eliminate 60 hz hum.

Star ground system to eliminate induced current chassis noise.

Hot Box Clean and Boost Channels or Bypass selected by dual botton footpedal switch.

Classic 3-BAND TONE STACK for extended flexibility in shaping your tone.

Bright Pull-Switch on Gain

MASTER level control on Booost channel so you can  overdrive the preamp without overdriving the output tube.

Preamp tubes are JJ 12AX7's known for low noise and linearity. You may also use 12AT7's or 12AU7's for different tones and less preamp overdrive.

Classic Knobs and Toggle Power Switch

Standard IEC plug-in three prong grounded power cord. 

Rock solid point-to-point hand wiring using only the best of parts...low noise tubular polypropylenes caps, metal film resistors, Micalex sockets, Neutrik  jacks...etc.

Sweet vintage clean to classic overdrive tones with three different types of  distortion depending on whether you are overdriving the preamp, output... or both! 

Weight - 8 lbs. 

Choice of Cabinets: 2U Rack Mount (19"W x 12"D x 3.5"H)   Retro Mini-Head  (10"W x 6"D x 7.5"H) or Open Chassis

Tubes:  2 - 12AX7 preamp


         CLEAN GAIN
         CLEAN TONE

         PILOT LIGHT


        LINE OUT 


- Input Impedance:  1 megohm
- Input Level:  Instrument Level (100 millivolts RMS)
- Output Impedance:  10K ohm
- Output Level:  Line Level (1.5 volts RMS) 


Upgrade Options

These options allow you to  customize your amp to meet your special individual requirements.

1. 100 - 240 VOLT  POWER TRANSFORMER - for operation outside the USA. Please specify line voltage. Add $40.00 

2. ONE WATT POWER AMP - Add a power amp using a 12AT7 as a Class A output stage which will deliver F and M crystal clear cleans or great overdrive tones at 1 watt of power into an 8 ohm speaker. This allows you to use the HB-1 as a low power practice amp as well as a preamp. With this option a speaker jack is added to the rear panel. Add $90.00


Hi Jim, Your HB-1 preamp is awesome! It can be sweet and clean or warm with gobs of gain! Thanks so much Frenzel family. Doug F. ( New York)  

Hi, I received the Hot Box HB1 preamp, but I'm not sure if I like it. Because I absolutely Love it . 
BTW I appreciate the status emails, its been very personal. Thank you, and Kudos.  Rick C. (Kansas)
"I will never be able to play without this preamp in my life, its the best thing that had happened to me since I played guitar for the first time, nothing comes close to the quality of what you have built... it sounds like heaven. Nothing else to say." Thank you Jim, you are building a legacy.  Cesar L. (Guatemala)
"the unit works beautifully and sounds terrific. I only started playing with the different settings - and then played with it splitting the signal between the Blues Junior amp with the HB1 and the piezo output to a Crate acoustic amp. Amazing to have the warm overtones accompanied by the clean acoustic sounds." Thank you very much! Scott B. (Maryland)

Hello Frenzel Amps - I love my HB-1 and have had a great experience as your customer. I purchased HB-1/RACKMOUNT serial 2315070 on 9/28/2015. I use the clean channel as an always-on preamp with my TC Electronics G-system (in the insert loop) and going into a Quilter Power Block head (set to line level input). It adds depth and sparkle and is the foundation of my sound. I use the G-System to switch the HB-1 to overdrive  for leads and a creamy distortion. Great product and superb value!  Mike F. (California)

For more reviews please check our Customers Reviews page.