Transcendent Sound       Vacuum Tube OTL Audio Amp Kits

The Slider

A True Innovation In Tube Technology

Variable Gain Preamp with Phono Stage

Zero Feedback Design

Complete Kit Without Tubes Only $549

Variable gain?  What's this all about?

There are many misconceptions about how volume controls and attenuators work.  They do not function like an accelerator pedal in a car.  An active preamp always runs flat out.  The volume control reduces the loudness of the signal by reducing the signal going into the preamp.  When a volume control or attenuator is set to about the 9 o:clock position, around 95% of the signal is burned off.  Then it is boosted back up to where you started, or a bit more.

Now, you paid for that signal.  All of the front end equipment in your system developed a high quality signal for your amps.  Then, you end up throwing most of it away and boost it back up again. By throwing away the pristine signal, noise and distortion must be added back in to achieve the desired level.  This makes no sense but is how preamps have always worked.

Then there is the problem of too much gain or not enough.  Many sources, like DACs, provide so much signal that an active preamp must have the volume turned way down, throwing away good signal.  Phono preamps may not provide enough signal requiring more boost.  Sometimes there isn't enough signal left to really rock out.  The Slider allows the gain to be adjusted so that most of the signal is always utilized.  Ideally, the gain can be set so the volume control is at the 2 or 3 o:clock position, which preserves much of the original signal and still allows for more gain if required.  Another benefit is that volume controls track much closer when turned up.  It's at the low end where channel imbalances become noticeable.  

The Slider provides a variable gain from -3dB to +20  db.  This is a great enough range to overcome the limitations of conventional preamps.  It is possible to run the preamp with the volume control at max and adjust the signal down with the gain control, if conditions allow.

How did we accomplish this?  The Slider is based around the magnificent 6386 tube (new production).  This tube was originally used in compressors.  By varying the electrical paramaters the tube operates within, the gain of the tube can be adjusted.  The sound of the 6386 is very luxurious, somewhere between a 12Au7 and a 300B.  No wonder those old compressors from the 1960's are still in great demand.

Zero Feedback Design

The Slider incorporates a 100% zero feedback design for both the variable gain line stage and the phono stage.  Feedback is necessary in power amps and in the Masterpiece because they must drive low impedance transducers.  The Slider is intended to drive high impedance loads only, so feedback is not required.  By eliminating all feedback, the sound has much more breath.  It is more dynamic.  Digital sounds much closer to vinyl.  The air  of the original signal comes through.  It's a much more open and spacious sound.  This is quite noticeable when compared to any feedback preamp.

Since there is no feedback, the bandwidth is flat out to 500 kHz with no ringing or overshoot.

The phono section is based on the venerable 12AX7 and has the classic 12AX7 sound.  Since there are so many types, makes and varieties of 12AX7 available, different tubes can be sampled to get the most desired sound possible.  When properly utilized, the 12AX7 is incredibly quiet.

Tube Rectifier Powered

That big tube in the center is an EZ81 rectifier tube.  It provides DC current directly to the tube circuits.  It adds another layer of smoothness to the sound making it sound even more luxurious.  Another benefit is the rectifier tube provides a soft start that gently ramps up the voltage to the tubes.  This helps them to last longer.

Dead Quiet

Both sections of The Slider are incredibly quiet, virtually dead quiet, even the phono stage.  About the only way to generate any noise would be with both the gain and volume turned all the way up. By that time, your ears would be pounding from the volume.  There is very little increase in noise when the phono stage is engaged. Please Note:  It is important to buy the 6386 from a dealer who tests for noise.  This is critical for best perfomance.

All In One

By combining the phono and line stages in one unit, ground loops between the two are eliminated.  A separate phono preamp is not required.  Space is saved.  Much cost is saved.  A set of interconnects are eliminated as well as another power cord.  

The Best All Around Preamp

The circuity, perfomance, and function of The Slider is the result of decades of experience in tube design.  Transcendent Sound always moves forward, striving to push the envelope of high end audio, and at prices that most people can afford.

This is the A weighted noise spectra of the line stage with both the gain and volume controls at the 2 o:clock position.  The largest component is a 40 microvolt RMS spike at 180 Hz.  The rest are below 20 microvolts.  This sums to a net of 75 microvolts RMS which corresponds to a S/N ratio of 82 dB, A weighted, referenced to 1V RMS output.

This is the noise when switched to the phono input with both controls at the 2 o:clock position.   Notice there isn't much difference.  We see a slight baseline hump of treble noise.  This sums to a net of 115 microvolts RMS which corresponds to a S/N ratio of 79 dB A weighted, referenced to a 1 V RMS output.

This is the phono noise with the volume at 2 o:clock and the gain control maxed out, a realistic worst case senario.  We can finally see an increase in noise.  This sums to a net of 460 microvolts RMS which corresponds to a S/N ratio of 67 dB, A weighted, referenced to a 1 volt RMS output.  That is still lower than the surface noise of a typical vinyl record.  For most applications, the noise of the above figure of 79 dB will be what is experienced.

The net maximum gain of the preamp through the phono and line stages is 57 dB.  That is quite a lot which is why operating with the gain control at max would be a rare occurence.  A more realistic gain setting would be a 2 o:clock or less,  yielding a S/N ratio close to 80 dB, A weighted.

This is the THD with a 1 volt peak to peak input signal and the volume and gain controls at the 2 o:clock position, a typical setting.  Abut half of the distortion spike at 1 kHz is residual from the signal generator.  This measures about 0.2%.

As with any zero feedback circuit, distortion increases with signal amplitude.  Increasing the gain to the 3 o:clock positon raises the distortion just under 0.5% and at maximum. under 1%.  Under typical operation, the gain control will rarely exceed the 2 o:clock setting.

This is the distortion of the phono input with both controls at the 2 o:clock position with 5 mV RMS input.  It measures just under 0.3%.  Max out the gain control and the distortion rises to 1%, which is still quite good.


Tube Compliment:

1-12ax7A

1- 12AU7A

1-  EZ81  

1- 6386 LGP

1- ECC99

Distortion: See above, from 0.2 to 1% depending on setting and input.

Bandwidth: -2 dB at 30 Hz and then flat to 500 kHz.

Noise:  See above.  Line stage typically 82 dBA and phono typically 79 dBA.

Output Impedance:  300 ohms from 500 Hz and above rising to 1500 ohms at 50 Hz.

Inputs:  DAC, Phono and two spare.

Controls: Volume, Balance and Gain.

Power: 120V or 230V, 50 to 60 Hz., 35 watts.

Footprint:  14 by 10 inches.

Weight: 10 pounds