retro-thermionic

Two Stage Tube Phono Preamp

2011-12-20T13:43:00.000-08:00

Tubecad, in a tutorial article, described a number of tube phono preamps. This is one of the simpler Tubecad designs and uses two 12AX7s in a two stage, passive RIAA equalisation, configuration. Golden Dragon tubes and quality tube rings are used here. The preamp employs a 24VAC wall wart which is step up to 260V and then well filtered. The HT filter is in two stages using a C-R-C-R-C network. The heater voltage is also rectified and filtered. There is a MM/MC switch to switch between 47K and 100 ohm loading. Gain is high.

All construction is on veroboard (strip board) and silver soldered. The four coupling capacitors are the Russian paper-in-oil (PIO) and the RIAA equalisation circuit uses Sprague “orange drops”. The enclosures are Hammond anodized Al cases. A separate power supply and substantial filtering helps keep noise out of the sensitive preamp cct. The sound is bright and very liquid. The preamp appears to work extremely well with pop, rock and jazz and most classical music.

"Paris" - 6EM7 Dual Mono 2W Integrated amp.

2011-11-02T14:28:00.000-07:00

In this construction, "Paris", is a dual mono build. The preamp tube at the front of the amp is the only shared tube. Each channel has its own power transformer, 5Y3 rectifier tube, choke and 6EM7 tube. The transformers are rubber mounted, sockets are ceramic and an Alps Blue Velvet pot attenuates the output from the preamp section. A power filter and Edcor 15W OPTs in the bas. A black chrome 4oz brass knob adds to the look and feel of the amp. The colour is called Sungold but some may say yellow. Paris contains two signal caps sets which can be switched between.

Two selectable inputs grace the back plate. This is a true integrated amp with a 4S Universal preamp section. Any 12A?? tube can be used for the preamp allowing the user to customise the "tone" of the amp. Sprague poly caps are used in the signal path. Power output is about 2W. Only sensitive speakers should be used. It has the besty mid-range detail I have ever heard in any amp.

Universal - 4S preamp MKIV

2011-09-12T05:11:00.000-07:00

This is the forth of these Super Simple Single Stage (4S) valve preamps. This was not designed by me but for me and has come after building three others and posting results on the diyaudioprojects forum. The others (see earlier posts) were specifically designed for the 12AU7 dual troide. This breaks away from that theme and will work with any of 12Axx available. This includes: 12AX7, 12AU7, 12AT7 and 12AY7.

Once more there is only one cct. brd. (this time strip board or veraboard) and holds both the PS and the amp itself. Expensive Solen caps were used in The Black but in this build MKP caps were used and less expensive parst and construction all round. With the right tube in place its sound is very close to The Black.

Housed in a Hammond Al case and quite sleek looking it is powered by the same 24VAC wall wart power pack the others are. It is quiet and has extensive gain. After some listening and comparing its performance across a number of different valves the Universal delivers a detailed sound with solid bass and airy mids and highs. The best valve tested with it so far is the 12AU7 Golden Dragon. Very easy to listen to all day!

The Black - 4S preamp MKIII

2011-07-23T02:36:00.000-07:00

This is the third of the 4S preamps I have built. It has been dubbed "The Black". This one carries quite a few schematic changes. No feed back from the plate to the grid with only an un-bypassed cathode resistor to act as feed back. Solen 680nf output caps, additional snubbing on the cct. brd. and different value blocking, load and cathode resistors.

A new Golden Dragon 12AU7 appears to work the best in this preamp which has good bass and a very balanced mid and high frequency repsonse. Detail and clarity abound. The gain with this build is very high, not something I have had with the previous builds. This is the best build so far.

Single Stage Tube Preamp MKII

2011-06-25T23:03:00.000-07:00

Shown here is the second build of the simple but good sounding preamp. In this version (MKII) two values were changed in the cuircuit which has caused a sharp drop in distortion (0.2%) and better performance from the whole preamp. Internally the build is neater and tighter. With even shorter signal path than in the previous build. The finish is beaten copper.

Again single brd. construction prevailed with no PCB. All component-2-component wiring using silver solder and wire wrap wire to connect to the pot and RCAs. An Alps Blue Velvet pot is used on the output with a solid brass black chrome knob. Any 12AU7 can be rolled to the provide different timbres and tone. The cast Al case is damped with tar/Al heavy foil and thick silicon feet fit-off this fine preamp.

Single Stage Tube preamp

2011-06-17T08:12:00.000-07:00

This simple single stage preamp requires only a single 12AU7, a 24V wall wart and the balance of a good stereo system. The construction consists of a single board with PS at one end and a tube at the other, but how it sounds beguiles its simplicity. The tube is a 12AU7, blue velvet attenuator with 4oz solid brass knob on the output and all component-2-component wiring. No PCB to dull the sound and silver solder used throughout. Frequency repsonse is from 10hz to 130Khz (-3db points).

A small amount of negative feed back is used in a local sense. The way this is applied contributes to the excellent sonic signature. The detail, warmth and deep sound stage exceed most of the preamps I have ever built both in the tube and SS camps. This one was commissioned and will be employed in an elaborate theatre system to add warmth and detail to the centre channel. But in a 2 channel system this absurdly rudimentary preamp really shines. And now one for me.

The Silver Dragon rises

2011-05-21T23:48:00.001-07:00

The finished Shiraz-Silver Dragon I built for a member of the Melbourne Audio club sounds as good as it look. It is what you would expect from an amp made from very expensive parts. It has taken almost nine months to gather the parts and assemble the amp. The final finishing touch came in the form of a Golden Dragon 5U4G rectifier tube. A great touch with the tube supporting a large dragon on the front.

Feature components of this amp are: TJ Full Music 300BSE limited addition tubes, 50 Year Treasure 6SN7, Mundorf M-Tube poly filter caps, ceramic sockets, silver hookup wire in the audio path, Audio Note Silver and Mylar inter-stage capacitors, 2mm Al plate, 30W Hammond OPTs, 200mA 10H Hammond choke, regulated DC to the heaters and over-size speaker binding posts.

This amp has extended, deep and very controlled bass, rich fully fleshed mids and bright crisp highs. The sound stage is very well defined but is not etched. The amp appears tonally balance across the sound spectrum. It does everything right and nothing wrong. It would be the first amp I have made I would never want to see go. Ironically it must.

Shiraz-Silver Dragon 300B

2011-03-28T04:18:00.000-07:00

Above is the most expensive amp I have ever made. This is only the amp section. The PS is separate. The parts alone came to AU$3.5K

The amp has been designed from the ground up by an American Electronics engineer. The components were selected by the future owner of the amp and the task of acquiring those components and assembling the amps fell to me. The power transformer was wound to our specifications locally in southern Victoria and the base made from Mirbeu timber.

The paint on the top and bottom plates is "Woodlands Grey" epoxy enamel and has been selected to compliment and contrast against the black OPTs. Gold coloured brass cones support the amp on thick brass pads and add to the look and performance of the amp as a whole. The chrome enhancements on the top plate are really just for show but may also add weight to the top plate and dampened resonances.

6AS7 SET amplifier

2010-07-20T06:25:00.000-07:00

This very special, one of a kind, SET is based on the 6AS7 twin power triode. A two stage amplifier with a 12AX7 driver. Only two valves in the audio circuit and valve rectification. The rectifier valve is a rare JAN CBXL-5R4GY (brown base). The power valve is an English United Electric and driver valve, 12AX7 Australian made AWA.

Valve rectification and a reactor filtered power supply ensure true musicality. Combine this with an internal power filer, vibration isolated power tranni and OPTs. This makes a very quiet and dynamic amplifier.

There is no input capacitor. The critical inter-stage capacitor, joining the driver stage and power stage, is a large and expensive Jensen, pure copper, paper and oil type. Silver wire is use to bring the audio to the driver stage and component-2-component wiring is used throughout. No PCBs exist in this amp!

After much listening I am convinced this is the best amp I have ever built. Not only based on its detailed mid-range and extended highs but its deep and weighty bass. The volume of bass I was not expecting. The sound stage is deep and wide both behind and in front of the speakers. Sibilance is natural and sustain and reverb. extremely well rendered.

A lovely Mirbeu timber base (custom built especially for this amplifier) holds something very different. A blue top plate carries exquisite but bulky componentry. Though only a few watts, with the right speakers this simple amp will delight and surprise you. With a frequency range from 12hZ to 50,000hZ it is easy to understand why this amp sounds so good. And why the bass feels extended and full. I true audiophile SET amp.

6SN7 remote driver stage for the Be Bamp

2010-07-06T16:07:00.001-07:00

The 6SN7 driver stage has enriched the musical performance of the Be Bamp. The bass weight is excellent, mid-range texture is extended and sound stage depth dimensional . Treble is controlled, detailed and mellow. Cymbals are naturally rendered and sibilance well controlled.

This remote driver stage is an improvement over the 6N1p stage (see other blog entries). Some may prefer the original driver stage to this with its brighter top end and crisp mid-range. The natural musical qualities of SE UL tubes amps is evident with the combination of this 6SN7 driver stage and the KT120 based Be Bamp.

For more technical information about the 6SN7 remote driver stage and Be Bamp see entries below.

6SN7 remote driver stage for the Be Bamp

2010-07-06T06:01:00.000-07:00

Having the flexibility to change driver stages allows many different types of valves to use with the Be Bamp KT120 power section. The original 6N1P drivers stage can easily be unplugged and other suitable drivers stages plugged in. The power amp does not have to be turned off but the amp is placed in stand-by.

This stage is based on the 6SN7 twin triode valve. It is an extremely popular valve used by audio craftsman. The valve sits atop and a small metal enclosure. The base is sprayed with an epoxy enamel paint and the finish is hammered copper. Once again Russian military paper, foil and oil inter-stage and low ESR capacitors are used.

There is no hook-up wire or PCBs. used and once more component-2-component wiring is employed. The driver stage is compact and attractive and brings a whole new sound scape to the Be Bamp.

Be Bamp with KT120 Tung-Sol tubes

2010-06-29T01:07:00.000-07:00

The KT88 Be Bamp is an excellent sounding amp and if taken no further would satisfy most audiophiles. But the Be Bamp with KT120 valves, replacing the KT88s, just takes excellence to a new level.

In previous iterations of the Be Bamp improvements were made to bass response and over all musical weight. Now with the replacement of the KT88s with the over-size KT120s so much more of the music is presented to the listener. Mid range and bass have lifted and the treble has received extra air.

Now bass is extended and controlled, mids are crisper, brighter and better defined and treble just a hint airier. Power has increased in the amp and though efficient speakers and still required to obtain voluminous listening levels, greater musical weight is heard right across the audio spectrum.

Classical, Opera, Jazz and other genera are brought into the listening area with greater presence than previously felt. Emotion from each track, weather CD of vinyl, is embraced with greater immediacy. Detail is better etched into the sound stage and the sound stage deeper than before. Simply a better audio amplifier from retro-thermionic.

Remote driver stage for Bread Board amplifier

2010-05-18T16:41:00.001-07:00

To increase the volume level of the Bread Board amp (Be Bamp), else where on this bLog, a driver stage was built. This is the original cct. used in the Merlot amps with some components upgraded. The is no volume control or input cap and pure silver wire used in the signal path.

The Be Bamp can deliver full volume to the point of clipping. Well short of clipping a high volume level can be obtained with large 91db sensitive 3-way tower speakers. The over-all sound of the system, which also combines a two stage valve preamp, is extremely musical. The sound is very transparent with good bass extension and weight, broad well imaged sound stage and natural tones of voice and instruments.

With the driver stage being remote other driver stages can be matched to the power stage and share the power supply. This provides another level of experimentation and flexibility with the over-all system.

Remote driver stage for Bread Board amplifier

2010-05-18T16:26:00.000-07:00

Because the Bread Board amplifier (Be Bamp) performed so well, though at low volumes, a driver stage was built for it. This stage is remote from the rest of the amplifier and is joined to the amp by interconnects. A multi-pin, high grade, plug and socket connect the 400V HT+ and the 6.3V filament voltage to the driver stage. This single stage front-end has been constructed in a Twinings Tea Box to match the two stage valve preamp else where on this bLog. Having the driver stage remote allows the trial of different driver stages while sharing the power stage and the and a common power supply.

The same drive stage as in the Merlot amp was used. This employs a 6N1P Russian tube. Parts of the original schematic were upgraded and Russian military paper, foil and oil caps were used for inter-stage connection. There is no volume pot or input capacitor. Low ESR grade caps were used where possible and pure silver wire used in the signal path. Construction is all component-2-component with no PCB or any other cct. brd. The timber Tea box is bitumanised Al foil lined.

KT88 Bread Board amp with no driver stage.

2010-05-03T00:13:00.000-07:00

This is the first bread board amp (said Be Bamp) under the retro-thermionic brand so it had to be a different to other BB amps and stand out. Also it was designed to be used with a high gain preamp because, in this model, there is no driver stage. It has been tested with the retro-thermionic Tea Box two stage valve preamplifier. Also all wiring is hidden under the board to give a clean neat look. To further enhance the look the two open OPTs are housed in a metal enclosure. The enclosure doubles as a mounting point for speaker and input terminals, all gold of course.

The driver stage has been removed to reduce the number of stages the music has to travel though before appearing at the speakers. This has resulted in an increase in transparency and detail. In future releases of the Be Bamp a version with the driver stage will be produced.

Though the wiring is hidden there is plenty of components above board. Also the high voltage (400V) rectifier is exposed so electrocution is possible both here and from other components. For a twist the HT standby switch, which must not by operated under one minute of warm-up time, is covered with a red rocket launcher cover. The board is Australian Pine and has been treated with Australian beeswax.

Main components are Hammond (over specified) power transformer and 10H Hammond, high current, choke. Edcor open OPTs are used. The Be Bamp will work with a number of different valves; 6V6GT, and EL34s being just two. A matched pair of JJ Blue Glass KT88s are shown in the image. The amp will produce about 5W if driven fully.

The retro-thermionic Fostex Back Loaded horns were used to evaluate the Be Bamp. Voice and all acoustic instruments display a very dimensional sound with voice sounding crisp and earthy with very controlled sibilance. The amp is absolutely hum, buzz and hiss free and is the quietest amp I have ever built. With a result of the deepest black back ground well know tracks sound new again and display extended fine grain detail.

On request retro-thermionic will provide this amp as a kit with rectifier module and power valve module assembled and tested. Ever part will be provided for the DIYer to assemble.

KT88 Bread Board amp with no driver stage.

2010-05-02T23:53:00.001-07:00

The bread board amp (Be BAmp) is just as attractive from the rear as from the front. The enclosure which houses the OPTs is also used to mount the speaker binding posts and input RCAs which are all gold plated and the RCAs are insulated. The fuse and mains switch are also visible from the rear. Only the power transformer is connected to the mains earth.

Merlot

2009-12-05T03:05:00.000-08:00

Merlot-entry level valve audio.

The build criteria for the Merlot valve amplifier was to construct a simple and excellent sounding valve amplifier from inexpensive parts. But this amplifier had to set an example of what can be expected from any valve amplifier.

Merlot's goal was to demonstrate to those listening to their first valve amplifier that, in a number of areas of quality audio, valve amplifiers can challenge, at a musical level, not only solid state amplifiers but inexpensive commercial designs. The design is single end (SE) and ultra linear (UL) with diode rectification.

Merlot uses two common valves: the 6N1P and KT88. The output valve can be replaced by a number of other valves: EL34, 5881, 6550, 6L6, 6V6 etc. I encourage "tube rolling". Feel free to replace the two output valves. Very different timbres and tonal balances can be obtained by tube rolling. This amplifier supports that practice.

If Merlot looks like this amplifier was hand built completely from scratch that is because it is. From the very solid Mirbeu timber base to hand assembled modules. There are no printed cct. brds. or commercially prepared modules Incorporated in construction. There is no additional wire used in the hand made modules, on component wires joined to other components. This is a technique I have used extensively here called component-2-component wiring. Fewer solder joints and less "hook-up" wire than point-to-point wiring. Individual modules are available.

retro-thermionic attempts to bring back some of the look and sound of early valve amplifiers. The use of heavy timbers, metal, large transformers and protruding valves is purposely done to produce a retro look and to reproduce music as it was meant to sound. Like music.

The sound of the Merlot is excellent mid-range tones, clean clear highs extending to 46khz and a balanced bass down to 35hz. Merlot's greatest strengths lay in its mid-range. Human voice and acoustic instruments are rended with great transparency, natural tone, real depth and immediacy. Output is 6.5W RMS per channel so efficient speakers are required.

This amplifier can be ordered and built with minor modifications should you require. Other models include: Cabernet and Shiraz which use more expensive parts but still the same retro look, more refind and detailed sound. These amplifiers will feature on this page.

Merlot - rear panel

2009-11-30T22:44:00.000-08:00

The rear of the Merlot amplifier carries all connections. These include: two switchable RCA inputs, speaker binding posts which will take spades, banana plugs or captured wire, power cord outlet, fuse and on/off switch. The Merlot can be configured for 11oV. A standby switch is atop the the amplifier. This allows you to switch off the high tension but leave the heaters on for immediate listening, during short breaks. This saves power and stops cathode stripping by applying the HT after the tubes have warmed.

Merlot with JJ KT88 Blue Glass

2009-11-29T21:42:00.000-08:00

A number of different power valves can be fitted to the Merlot. It is one of the great strengths of an open valve amplifier, that different tubes can be "rolled" for different tonal balances. In this instance a matched pair of JJ KT88 Blue Glass have been fitted. This has increased the low end weight and brought the mid-range forward slightly. Apart from the different tonality the Blue Glassed JJs look stunning. Many other valves and speciality tubes can be rolled into the one basic power amp. Have a favourite power tube which has the same pin outs and specs as a common KT88? Then roll it into a Merlot. Plug and play-your way!

Merlot - Black Top and Black Sable EL34

2009-11-28T07:07:00.000-08:00

This is the first of the Merlot range I constructed. In this build all switches, controls and connections are on the top plate. The paint used is an epoxy enamul and forms a tough and textured finish. Modular design was developed in this first "proof of concept" build. Once again component-2-component construction was used in forming the modules.

This amplifier diplays all the mid-range fine grain clarity of the second build (above). A number of different valves can replace the EL34s used in this amplifier. Matched Black Sable EL34s are installed in the amplifier above.

Merlot - Black Top EL34

2009-11-27T02:59:00.000-08:00

With the Merlot - Black Top build the valve sockets were recessed into the top plate.Therefore valves with large basses e.g. KT88 could not be installed. This issue has been corrected with the second build and now all bases sizes can be accommodated. Fortunately the amplifier sounded excellent with the EL34 Back Sables. This amplifier has also delivered excellent music with 6V6 Black Glass (original Australian made valves).

Merlot - Diode Rectification Module

2009-11-25T03:07:00.000-08:00

As with all retro-thermionic amplifier sections each part is modularised but no module contains any wire other than the component wire. The Diode Rectification Module is a full wave rectifier employing the centre tap of the large power transformer. A large 10H choke is also used as part of the rectifying and power smoothing network. When a large choke is used to reduce hum and noise in the amplifier smaller filtering capacitors can be used. Smaller power capacitors produce a better detailed mid-range this is one of the better traits of a SE UL design.

Wiring between modules is of the free style method. Copper hook-up wire runs the shortest and safest path to the next module. Internal wiring is loosely banded together for safety and to ensure minimum cross talk. By using the shortest wiring path, total signal path length is kept to a minimum.

I can provide these rectifier modules, or any other of the retro-thermionic modules, for the individual who would like to assemble their own valve amp. E-mail me for a quote.

Twinings Tea Box Preamp with Remote PS

2009-11-24T23:50:00.000-08:00

The Twinings Tea Box preamp is very much retro-thermionic. Always the mix of timber, metal and valves presents, not only a strong retro feel and unique images but very much a desire to get back to listening to good music the way it was meant to be. Controlled resonance qualities in natural materials can add a certain earthiness or natural tone often amiss in modern, commercial audio equipment. One of retro-thermionic's goals is to construct audio components in a novel and organic way, most often using timber, Bakelite or metal in audio component construction.

The inexpensive Twinings Tea Box provides a natural looking enclosure in which to construct a preamplifier using high-end and carefully chosen components. To further add to the lofty concept of the build a remote, valve rectified, power supply was added. In the image you can see not only was valve rectification and enclosed choke filtering used but a rare Australian made 5Y3 rectifier valve was also employed.

The chassis, on which the remote power supply is constructed, is die-cast Al. Hammond enclosed power transformer and 10H choke sits atop. Other electronics are housed beneath the solid chassis, which, like the preamp itself, reside on solid brass cones. Connection between preamp and associated power supply is via a high voltaqge short cord and XLR plug.

The Jensen copper, paper and oil capacitors and associated components (including the enclosures) make this a unique sounding andlooking preamplifier. Either coupled with a solid state power amplifier or a valve power amplifier this original almost conceptional preamplifier offers an exceptionally unique insight into electronics and audio reproduction equipment not seen in commercial units. And for the engineers amounsgt us the distortion figures fall below 0.05%. The musical rating figures: 99+. Listen and be convinced.

Twinings/Jensen Tea Box Preamp

2009-11-23T03:45:00.000-08:00

Jensen copper, paper and oil capacitors from Denmark, large and all as they are, fill the small timber Twinings Tea box preamplifier. Two preamp component-2-component modules are joined to the input and output gold RCA connections via pure silver wire. The wire is prepared by covering pure silver wire with heat shrink. French Solen capacitors form part of the feed back network. Both capacitors have pure silver leads. Expensive components to produce a very natural sounding, high detail valve preamplifier.

The timber enclosure is lined with bituminous Al foil. Alps attenuator is topped off with a heavy 4oz solid brass knob. An external valve rectified power supply delivers a very quiet 260 volts to the Tea Box components. Golden Dragon 12AX7 valves are installed but any similar valve can take its place. A truly unique preamplifier and part of the retro-thermionic range.

Twinings Tea Box Preamp PS and 5Y3

2009-11-22T03:06:00.000-08:00

Fortunately I have been able to acquire a number of Australian made rectifier tubes. This one being a 5Y3. When purchased today a much difererent looking tube. The 5Y3 and 5U4G(s) I now own are all in excellent working conditon. Most looking at 50 years of age with many years of service behind them.

If any single component is going to make an impact on the overall sound eminating from your speakers, it is your preamp. Many hard core audiophiles "roll" (change) thier rectifier valves to change the tonal balance and voicing of their system. This may engender a more natural and sonic balance.

Well aged Australian made valves and exceptional sounding Danish capacitors, in a light timber box, with a remote valve rectified power supply. Not only good sounding but who else has one. retro-thermionic.

Twinings Tea Box Preamp rear view

2009-11-21T02:18:00.000-08:00

As with the Merlot power amplifier the Tea Box preamplifier can have switchable inputs. The power from the remote power supply is delivered by a fix cord which terminals on a metal XLR plug. The power supply has a XLR socket to connect the two sections: preamplifier and remote power supply.

Twinings Tea Box Preamp

2009-11-09T02:37:00.000-08:00

Twinings Tea Box preamps are genuinely made from Twinings Tea boxes. Four fine and lightly scented teas come with the well presented box. Though the box timber is light weight and velvet lined, the adding of bituminous Al foil to the inside increases box weight and provides a RFI and EMI shielding.

No screws scar the the timber box top by the use of internal adhesive "stand offs" to mount the component boards. The two circuit boards are component-2-component wired. In a preamplifier, keeping the signal path as short as possible is essential. Only clean DC power enters the preamplifier section. With a remote power supply and valve rectification a very quite and detailed sound reproduction can be ensured. Not to mention the addition of a very cool looking timber preamplifier.

Fostex FE206E back loaded horn

2009-11-06T23:54:00.000-08:00

Retro-thermionic not only produces valve amplifiers and preamplifiers but also some finished speakers. Currently retro-thermionic is having constructed the back loaded enclosures to accommodate the Fostex FE206E drivers. After evaluating the the Fostex driver in a simpler two chamber enclosure, retro-thermionic, decided to have the more complex labyrinth style enclosures made. A CNC cutting machine was employed to make the most efficient cuts from the expensive and heavy 21mm multiply timber. Some panels are double layers of 21mm multiply. Panel bracing is extensively carried-out to control box colouration.

Sandbags can be layed in the bottom of the horn to tailor the bass to the listening room. Sandbagging can also be performed in the driver chamber to alter the level of other low frequencies. With efficiencies of the drivers reaching 96db the retro-thermionic amplifiers can produce high sound levels easily.

Fostex FE206E back loaded horn

2009-11-05T22:36:00.000-08:00

At this point the enclosures have not been stained. It is easy to see the excessive bracing which goes into these speakers. A large amount of internal dampening is used and the cabinets are held together with stainless steel screws, doweling and glue. Large clamps were used when two panels were attached to ensure a rigid and tight fit of all panels. These speakers will be stained a dark teak.

Sound stage is pin-point. Stage depth is is very evident. Bass weight can be tuned by placing the speakers closure or further from the wall. Placement is critical.