All DECWARE products are made in the USA

Purist Tube EQ for Bass and Tone Restoration

Wholesale price includes Lifetime Warranty

Made in USA

Insert the ZROCK2 anywhere in the signal path.

There are three things you can adjust:

1) EQ Level - fully variable from flat to boosted.
2) EQ Curve -  two available equalization curves.
3) Bypass -  a true bypass switch to disable the ZROCK2.

Below is a graph of the less-aggressive of the two available EQ curves.

The graph above shows the
ZROCK2 EQ turned all the way up. The lower dotted line is what you get when the ZROCK2 is bypassed.

This means the knob on the front of the unit can adjust  your music from flat all the way to the bass heavy, treble rolled curve shown above or anywhere in between. 

As you can see, the blue line creates a linear shelf of bass between 20 ~ 60 Hz followed by a gradual slope out to 260 Hz where it flattens out through the midrange and then gently rolls the treble. 

Remember this EQ is infinitely adjustable so if you want less bass and more highs simply adjust the EQ knob a bit.

More info with graphs can be found in our support forum at the following post.


This long overdue product was originally 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. Happily it is also usable in high fidelity settings and with any type of music.

It can be used to fix bass shy recordings, fix bass shy speakers or fix overly bright listening rooms or any combination of the three.

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 the frequency balanced of 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.

ZROCK2 shown with its 12AU7 tube removed

Unlike a loudness button which peaks the response at around 100 Hz, the ZROCK2 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.


The reality is that many speaker/room combinations will roll off the lower bass leaving you with a leaner, drier, 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 ZROCK2 you end up with a much flatter bass response in the bottom octave where many systems lack.

A ZROCK2 restores this missing information and makes your music sound full and rich at lower volumes. Using a ZROCK2 gives 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.


ZROCK2 has two built in EQ curves that have been crafted to accomplish the goal on two basic types of systems. Both are fully adjustable letting you "dial-in" just how much EQ you want.

The EQ switch is located on the rear.  When the switch is UP it is using EQ-A and when the switch is DOWN it is using EQ-B.

EQ-A is designed for systems that characteristically sound lean.  That is to say the speaker/room combination yields results similar to the graph above where bass is diminished.

EQ-B is designed for systems that have perfectly good bass when it's in the recording, but you want to listen to classic rock where many of the recordings lack bass at low volumes.  EQ-B makes it possible to dial in a nice dry perfectly articulate hit without becoming too heavy. 

Both of these equalization curves have been designed so that the "perfect sound" is obtained at about the 3/4 position on the dial.  This way EQ-A can still be used to not only fix your room speaker issue, but still add bass when needed to lean recordings.  EQ-B, while characteristically drier is also a steeper EQ slope capable of more bass boost, and more high frequency cut when turned up all the way.

BYPASS SWITCH makes setting the EQ completely painless.  This is because it lets you hear exactly what effect the EQ is having as you adjust it.  It does this by letting you compare your equalized setting to the non-equalized (flat) setting as many times as you want while you're adjusting the knob. You hear exactly what effect it your adjustments are having.


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
ZROCK2, we use a simple passive filter and a single-ended triode to restore the gain lost from the filter.

ZROCK2 shown with bottom cover removed

There is no negative-feedback in this design and only a single tube with no circuit boards keeping the transparency extremely high.

Most users who showed concern about a
ZROCK2 having negative effects on imaging and sound stage size reported that instead of getting worse those things actually got better.


ZROCK2 is appropriate 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.


ZROCK2 is not designed as a preamplifier, it is assumed that you will have either a preamp or amplifier with a volume control to actually adjust the volume in your system.

The way the
ZROCK2s variable EQ knob was deigned is this:
From 0 to 1/2 way, the control acts as a regular volume control with no EQ.

At the 1/2 way point, the output level and the sound exactly match the way the
ZROCK2 sounds when it is bypassed.

From this 1/2 way point to 3/4, the sound will get louder and the EQ slope grows proportionately.

From 3/4 to full the EQ slope continues to grow and high frequency attenuation starts to becomes apparent.

OPTIONS / Available in the shopping cart.

Rear view

Voltage - Select the proper voltage for your country

Signal Capacitors - Select from standard film caps to hi-end copper foil Miflex caps.

Knobs - You may choose from the following knobs.

Left to right is Ebony, Gold, Black Chicken Head, Cream Chicken Head, Rosewood.

RCA Jacks - Choose between Gold or Silver RCA jacks, both are precision made in the USA.

Note:choose the metal that matches your cables.

Left to Right are Silver and Gold RCA jacks.


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.


Weight   7 lbs. ea.
Dimensions   2.5" H x 6" W x 11.0" D
Circuit type   Single ended Class A Triode
Input voltage   0 ~ 15 volts max
Input Impedance
47 K Ohms
Will Drive

Preamps or amps with 10Kohms to 500Kohms inputs.
Noise / Hum   -80dB / -62dB
Response   5 Hz ~ 90 kHz
Feedback   ZERO negative feedback used
Rectification   UN4007
Signal tube   12AU7 / 5963
Biasing   Self-Biasing
Resistors   precision WW/MF by DALE, VISHAY
Signal Cap   Film or Copper Foil
AC cord   Removable power cord
Consumption   13.5 watts at the outlet
Warranty   Lifetime to original owner


Dec 2016 ~ July 2017 original model ZROCK

July 2017  ~ ZROCK2 with the fully adjustable EQ.

Aug 2019 - Anniversary Mods were made available in the shopping cart.


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

ZSTAGE - Flat response tube gain stage that has gain.

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


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

Wholesale price includes Lifetime Warranty

Made in USA

Customer Comment

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

The Z-ROCK 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.


You can read more customer comments here.