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Hand made in the USA and sold customer direct with a lifetime warranty!
Available in 100 ~ 120 volts  220 ~ 240 volts.

The Z-ROCK is a single-tube EQ designed to restore the bass and missing
tone from many hi-fi systems, be it the result of speakers that are too small, bad room acoustics or even just bad recordings.

It's similar (but superior) to the "loudness button" on vintage audio gear from the 1970's.

rear view showing input and output jacks, EQ Curve switch and fused power cord connector

Basically, you just insert a Z-ROCK tube stage between the source and preamp or between the source and amplifier if you don't use a preamp. 

There are three things you can adjust:

1) Output Level - a variable volume (gain) control goes from 0 to MAX.
2) EQ Curve - you may select between two equalization curves.
3) You can activate a bypass switch to disable the Z-ROCK.

Below is a graph of the most commonly chosen EQ curve.

The graph above shows the Z-Rock frequency balance between 20 Hz and 20 kHz. The bypass level (dotted line) represents flat response and is in theory what you get when not using a Z-Rock. As you can see, the blue line is adding bass between 20~60Hz in a very linear manner followed by rolling it off from 60~260Hz.

The reality is that your speakers and room will roll this low bass off leaving you with a leaner, dryer, less rich sound. Below is the typical low bass performance found in many listening rooms. 

When you combine typical low bass performance like that shown in the room above with a Z-Rock you end up with a much flatter bass response in the bottom octave where many systems lack. A Z-Rock restores this missing information and makes your music sound full and rich at lower volumes. Rock music gains a nice "hit" that you normally don't get unless you're at a concert or club, and does so without having to be turned up loud.


This long overdue product was designed to make listening to classic rock on streaming internet radio a less hateful experience on high end systems that have no means to adjust frequency balance.  And it fixed that big time, but to our delight it is also usable in higher fidelity settings.

Remember when classic rock was recorded... speakers were generally large and had no shortage of bass. Receivers had a loudness button that in concert with the bass and treble controls made listening to these recordings more enjoyable. Also, music was analog which in general contains more density. Fast forward to today where audiophiles are trying to listen to classic rock mp3's streamed over the net on systems that have no tone controls or loudness contour and you can see the problem.

The most commonly seen fix for this
has been to add a sub-woofer and turn it up a bit. Sadly the sub-woofer often does as much damage as it does good, resulting in a sound that is smeared. 

Even a perfectly executed sub-woofer will do nothing for enriching the tone of the midrange which is also essential to balancing an increase in bass. The truth is, you need help all the way out to around 1 KHz.  A sub-woofer usually stops at 100 Hz.

shown with 12AU7 tube removed

Unlike a loudness button which peaks the response at around 100 Hz, the Z-Rock creates a low frequency shelf which has flat response from 20 Hz ~ 60 Hz followed by a controlled roll off where things flatten out in the midrange. In addition there is a subtle roll off above 10 kHz to remove edginess. The result of this is an incredibly rich, full sound with big increases in midrange tone.  It animates the music rather well.


One of the reasons bass and treble controls and graphic equalizers died off with the rise of hi-end audio is because they were often done in such a way that they created changes in the phase angle resulting in a subtle but noticeable smearing of the sound. To ensure these side effects don't find their way into the Z-Rock, we use a simple passive filter and a single-ended triode to restore the gain lost from the filter.

shown with bottom cover removed

There is no negative feedback in this design and only a single tube with no circuit boards so transparency is extremely high. Most users who showed concern about it having negative effects on imaging and sound stage size reported that instead of getting worse, those things actually got better.


A Z-Rock is appropreate virtually any time you wish there was more bass and more hit and better tone with less glare. This makes it possible to listen at lower volumes since the bass is not lost when the volume is turned down. It is also possible to listen louder in untreated rooms that are bright to begin with. 


When you add a Z-Rock to the shopping cart there are a couple options that we can explain here:

Voltage - Select the proper voltage for your country

Volume Control - There is an option to replace this with a 20 position stepped attenuator. Since this level control is usually near full during operation the added transparency of a stepped attenuator becomes harder to hear.

Signal Capacitors - The Z-Rock is built stock with audiophile grade film caps that are suitable in almost every situation. You may however have your Z-Rock built with our Cryo-Treated Beeswax film and foil caps which are the same as what we use in our amplifiers.


This amplifier is hand built in the USA by DECWARE / High Fidelity Engineering C0. It comes with a lifetime warranty to the original owner. If you purchase one second hand and ever have questions or technical problems we WILL be happy to check it out for you and service it if needed for a very reasonable rate.

We also have a support forum with many people who's experiences you may benefit from.


You may read reviews on our products here.

front view showing level control, bypass switch, 12AU7 tube


Weight   7 lbs. ea.
Dimensions   2.5" H x 6" W x 11.0" D
Circuit type   Single ended Class A Triode
Gain   Adjustable 0 dB to 16dB Gain.
Input voltage   5 volts max
Output Impedance
<1000 ohms
Input Impedance
47 K Ohms
Noise / Hum   -80dBV / -62dBV
Response   10 Hz ~ 90 kHz
Feedback   ZERO negative feedback used
Rectification   UN4007
Signal tube   12AU7 
Biasing   Self-Biasing
Resistors   precision WW/MF by DALE, VISHAY
Signal Cap   Polyurethane Film Caps or Beeswax Film/Foil Caps
AC cord   Removable power cord
Consumption   13.5 watts at the outlet
Input jacks   RCA type 24K Gold
Output jacks   RCA type 24K Gold
Warranty   Lifetime to original owner


ZBOX - Flat response tube buffer stage that has no gain.

ZSTAGE - Flat response tube gain stage that has gain.

C l a s s  A  -  S i n g l e   E n d e d   T r i o d e  -  A l l   T u b e  E Q




View Cart or Check Out

Hand made in the USA and sold direct to the customer with a lifetime warranty!
Available in 100 ~ 120 volts  220 ~ 240 volts.

Customer Comment ~ Feb 2017

I will start with the effects on recordings that I "thought" already sounded as good as I would ever want them to.

The ZROCK made a very noticeable improvement in density throughout the frequency range everything sounded richer, fuller with more detail and with an unexpected increase in the sound-stage which surprised me. I am also now able to reduce the toe in of the speakers quite a bit since the density is so much better. I am really surprised by how much more information I am hearing now and how much wider and deeper the sound-stage seems to be. I was worried that it would be the opposite since I was adding another device into the signal path. Just a note I did have this built with the Beeswax caps as with my other gear.

I was also concerned that I would have too much bass, you know the non musical fill in type bass, not the case at all, everything is very balanced tight and full.

Now with things that were harder to listen to on a reveling system such as mine.
First there are two settings on this that give two distinctly different EQ signatures, one is very clear and dynamic and the other while increasing the lower end also rolls off the highs and should do an excellent job at allowing us to listen to some very poor recordings making them listenable again, thank you for this.

So far everything I have listened to has sounded excellent with the more dynamic setting.

With the increase in the lower register it really makes everything sound better in that it is fuller richer and deeper I also don't have the urge to turn it up to try and gain some density and impact anymore.

Before I would get up and turn it up and then get up and turn it down because it was just louder not better, and the real litmus test is my wife hasn't asked me to turn it down for two days meaning first, it isn't too loud anymore and second it sounds really good.

This is not just a low frequency boost on my system but a density boost all the way through.

I have to say this again because it is such a surprise to me, the part that floors me the most is how much more depth and width I seem to have now and it even seems clearer and more detailed probably because all of the information is better balanced now.