FAQs about GLOW ipod compatible stereo tube amplifier with USB and DAC
integrated valve amplifier with USB and DAC






Click HERE for our Speaker Compatibility Guide


Click HERE for FAQs on the

2009-2010 GLOW Amp (Series II)


Click HERE for FAQs on the

2011/12 GLOW Amp One (Series III).


Click HERE for FAQs on the

GLOW Amp One Version 1.3 (latest model).




My GLOW Amp won't turn on. Does it need servicing?


Check and make sure the AC cord is firmly attached to the rear of the amplifier. If that is not the problem, more than likely you need to replace the fuse. All GLOW amplifiers are equipped with a fuse to protect against power surges and damage to the unit. We also provide you with a spare fuse, so replacing the fuse is a pretty simple process. 

The fuse is in a compartment located on the back of the amp, at the base of the AC receptacle, where you plug in the AC cable. First, remove the AC cable. Locate the fuse compartment, and with a flat head screwdriver, gently slide the fuse holder out from the base of the AC receptacle. Inside the fuse tray you will find two fuses. One is the operating fuse, the other is a spare. Replace the operating fuse with the spare, slide the tray back in place, firmly re-attach the AC cord, and power the unit up. Don't forget to acquire replacement fuses and keep them handy!



How can I tell which version of the GLOW Amp One I have?

Over the years we have retained the classic look and acclaimed sound of the original Amp One. This can  make it difficult to determine which model you have, as we have made internal refinements and improvements each time we go into production:

The original 07-08 GLOW Amp One (Series I) has a magnetically attached tube cage; only one switch on the R side for on/off; it can use any EL84/6BQ5 tube; it has "007" in the serial number.

The 09-10 GLOW Amp One (Sereis II) has two switches on the R side, power on/off and light ring on/off; it has a screw down tube cage; it can only use Russian or Chinese EL84 power tubes; it has a strengthened headphone jack assembly, it has "008" in the serial number.


The 11-12 GLOW Amp One (Series III) has a stronger, all steel tube cage and is both a screw down and magnetically attached type; it has 2 switches on the R side; it can use any EL84 tube. It has am improved internal DAC with a custom gain stage, it has "011" in the serial number.


The 2013-14-15 rendition of the Amp One (Series IV, designated Version 1.3) has a number of significant refinements. It utilizes an external DAC allowing for better digital to analog performance. It has 2 RCA inputs instead of one and a side mounted input source selector switch. It has a hi/lo impedance switch for headphones to allow for use of a wider range of headphone types. It has "ver. 1.3" printed on the end plate, and it has "012" in the serial number.  


Why is the GLOW sound so detailed and full? 

We have eliminated unnecessary “bells and whistles” to minimize the amount of circuitry impacting the signal. The signal has to travel through fewer stages, and requires less negative feedback, than with the typical transistor amplifier (the Amp One has only two gain stages, many transistor amps have 9 or 10 or more gain stages, and must use lots of negative feedback to control distortion).  The result is a pure, realistic sound…. the sound of the music…. with the detail, resolution and dynamics for which good tube amplifiers are famous.  If you want to hear what others are saying about the GLOW sound, take a moment to peruse the testimonials in the "GLOW Community" section.


Vacuum tubes and full range drivers? 

We are passionate about good sound.  It is regrettable that, while the digital age has brought so much wonderful technology to our fingertips, the sound quality of computers, MP3s and many home theater systems is nothing close to high fidelity. By taking a step back and a hard look at some of the fundamental assumptions in the audio industry, we have concluded that much of what is marketed to the consumer works against the goal of achieving true high fidelity sound.


How does the GLOW amplifier make digital music files sound so good?

With use of the optional GLOW DAC 1.3, the GLOW tube amplifiers provide plug and play USB connectivity. And, it is very easy to hook a portable device such as an iPhone or iPad directly to a GLOW amplifier, or wirelessly with bluetooth. When the GLOW amplifier plays a digital source, even a compressed source, something amazing happens... the harsh, flat digitized sound comes to life!  No, the tube amp cannot "repair" the compressed digital file. The fact is, much of the original musical content may have been lost as a result of the compression process. But, the tube amplifier does bring out the best of what is left, imparting air and depth and space that otherwise may not be reproduced by a transistor amplifier. You have never heard computer files or even an iPod or smart phone sound as good as when it is played through a GLOW system! 





Will my Amp One "clip" if the output is too high, and will it damage my speakers?

Tube amplifiers behave differently than transistor amplifiers when driven to capacity.  A transistor amplifier if driven too hard will "clip", meaning it will essentially cut off the top of the signal, sending a square wave to the speakers.  This can be disastrous; in addition to sounding terrible, it can damage or "blow" your tweeters.  But when a tube amplifier is driven to capacity, it simply "runs out of gas".  The "soft clip" of a tube amplifier prevents damage to the tweeters and avoids the harsh sound characteristic of a transistor amplifier being over driven.  Some transistor amplifiers, such as those made by NAD and Proton, incorporate a "soft clip" circuit in an attempt to replicate the manner in which tube amplifiers behave when overdriven.  Because nothing sounds worse than a transistor based receiver being overdriven.



Why do you recommend that users not use some types of EL84 power tubes

with one of the earlier versions of the Amp One?


All GLOW Audio Amp One and Amp Two units are compatible with any EL84, 6P14, or 6BQ5 power tube combination, EXCEPT for the 2009/2010 GLOW Amp One (Series II).

We strongly recommend that you do NOT use power tubes manufactured in Europe in the 09/10 GLOW Amp One.  The 09/10 Amp One is specifically designed around the Russian and Chinese EL84 power tubes, and features the Beijing variant of the EL84 designated the 6P14. 

European EL84s differ in design from their Chinese and Russian counterparts in one important respectOn all European manufactured EL84s, pins 1 and 2 are connected together inside the tube envelope. Chinese, Russian, and American EL84s do not internally link the pins 1 and 2.  Therefore, when a European manufactured EL84 is plugged into the 09/10 GLOW amp, the additional connection within the tube envelope in the European design is likely to cause premature failure of the tube. 

It is highly recommended for this reason that you NOT use European tubes in the 09/10 Amp One, as you will likely permanently damage your tube and possibly the amplifier. 

All Russian (except the Russian made N709 Genalex "Gold Lion" EL84) and all Chinese and American manufactured EL84 tubes are compatible with the 09/10 Amp One. For all other versions of the Amp One, you can use any make or style of EL84,6P14, or 6BQ5 power tube.

We strongly recommend that you verify that pins 1 and 2 are NOT connected in the tube envelope before trying out tubes in your 09/10 amp. We are aware that some sellers have been known (mistakenly or otherwise) to mislabel tubes as being from one source when they are actually something else.  




Why doesn’t the GLOW Amplifier have equalizers or tone controls?

The lack of “equalizers”, electronic “sound processors”, “bass boosters” and conventional bass and treble tone controls certainly gives our products an uncluttered and artful appearance. But there are two very good technical reasons for eliminating these signal altering devices: 1) Tube amps don’t need them like transistor amplifiers do, and 2) they make the sound worse, not better. Let us explain.

First, at low to moderate volume levels, a tube amplifier retains the tonal balance much better than its transistor counterparts, making it unnecessary to constantly adjust the tone controls or to play music at higher volume levels than otherwise desired.
Second, signal processing circuits color the sound and can mask subtle details of the performance. Most listeners aren't aware of how much music can be dampened and hollowed out by all the unnecessary circuits and processing, until all the "enhancements" have been stripped away. You shouldn’t pay for additional circuitry that makes music LESS realistic. Sound processing gimmickry might be fun when watching a Hollywood action movie, but it can make your favorite musical performance sound fake and unnatural. 

As for “surround sound”, it is our belief that stereophonic sound is the best way to create a natural sounding center stage effect for recreating a musical performance, simply because it does not need complex sound decoding circuitry that more often than not only serves to muddle the sound. 





How can the little GLOW Amp One sound more natural than transistor amplifiers that have 100 or more watts per channel?   


Transistor watts are cheap. You can buy a 100 watt receiver for a few hundred bucks at most any electronics outlet. But Big Name audio power ratings are NOT a reliable way to determine how an amplifier will perform.


A useful analogy is to compare a complex musical signal to a winding mountain road. Which would be better suited for such a road.... a small, well balanced sports car, or a monster truck? Sure, the big truck's massive engine can produce more torque and more horsepower, but does all that power allow it to navigate the mountain road with the same ability as the little sports car?

Power rating tests do not reflect real world conditions because they are conducted with a stable, non-musical signal, usually from a white noise generator, with the amp fed a constant 8 ohm load.  This is not music. Unlike a white noise signal, music provides a much more complex signal for an amplifier to recreate, presenting a varying, and not a constant, load.  In short, the wattage ratings of the typical Big Name amplifier tell you nothing about how the amplifier really sounds when it provides gain to a musical signal. While a transistor amplifier may test better, a well designed tube amplifier will inevitably SOUND better.


We like to think of our diminutive amplifier as the audio version of a sports car, well suited to faithfully reproduce even the most demanding musical passages.







Does the Amp One have enough power for my needs? 

With the typical transistor amplifier, there is a tendency to play music at much higher volume levels than otherwise necessary, to compensate for the inherently “thin” transistor sound. Turned down to moderate levels, many Big Name transistor amplifiers sound about as fulfilling as a clock radio. You either have to turn the volume back up or juggle the tone and loudness controls to make it sound better.  But relatively low power, single ended tube amplifiers are famous for providing breathtaking detail and a full, rich sound even at moderate volume levels, so that many users find it unnecessary to play music at high sound levels. When matched with efficient speakers, the GLOW Amp One will fill a small to medium sized listening environment with surprisingly full, tonally balanced, and extremely detailed high-fidelity sound. 

Our amplifiers are a perfect match for our GLOW loudspeakers, but will work well with many other home audio and studio monitor speakers. If you choose to use your own speakers with our Amp One, we recommend using speakers with a sensitivity rating of at least 90 dB SPL (“sound pressure level”) or higher. Your owner's manual will usually tell you your speaker's SPL rating; sometimes the information is even on the back of your speaker, and often you can get it from the manufacturer's website. 
Another factor to consider is the speaker's impedance curve.  Tube amplifiers like a resistive load. What that means is, when the impedance of a speaker is high, it is an easier load for the amp to drive.  The Nominal Impedance rating of a speaker, which may be all the manufacturer provides, is unfortunately not a very helpful measure. For instance, a speaker with a "nominal" rating of 8 ohms impedance may actually drop to less than 2 ohms along the output range. Thus, a speaker rated at 4 ohms nominal might actually be easier to drive than a speaker rated at 8 ohms nominal, because the 8 ohm speaker might have dips along the curve that render it a difficult speaker load.  If you can obtain the speaker impedance curve either from the manufacturer or from a reviewer, you can better determine its suitability.  A curve that does not dip substantially below 3-4 ohms along the output curve is better suited than a speaker that has a complex load that dips below 2-3 ohms.

Our amplifier works best with sensitive (efficient) speakers that don't present tricky impedance loads.  Click here for additional information on what speakers to use, or email us with your questions and we'll get back to you.



I find myself listening to my GLOW Amp all day, what makes it sound so smooth and mellow?


Another often noted advantage of the sound of a good tube amplifier is the minimizing of “listening fatigue”. The fast transient “attack” that is characteristic of transistor amplifiers may sound impressive at first, but with extended listening can produce fatigue.  Many analysts have attributed this to “transistor hash”, the tendency of transistor amplifiers to produce higher amounts of odd order harmonic distortion, and the tendency to emphasize sharp transients.  Because we have eliminated the transistor hash, you can listen to your GLOW Amp One for many hours at a time without the slightest listening fatigue.




How long can I expect my GLOW tube amplifier to last? 


GLOW tube amplifiers are built to last. Typically, Big Name audio components are mass produced.  Made primarily of plastic and displaying a generic “black box bristling with buttons” look, such components are often obtrusive in size and difficult to set up and operate. And it is often not long before you start noticing switching distortions induced by the very controls and switches that are ostensibly supposed to "improve" the sound and for which you paid good money.  Our elegant looking alternative is built within a sturdy steel chassis, not plastic. It is engineered to provide a long life, and is simple to set up and to operate.








How often will I need to replace the tubes, and where do I get them?

The tubes provided with GLOW amplifiers are quite rugged and will typically last for years. The type of tubes used are abundant and can be ordered from GLOW AUDIO, or from any of a number of web based tube suppliers. If your local music store sells guitar amplifiers, it will likely carry these tubes.

And, while a faulty transistor in a typical transistor amplifier is not easy to replace and would require a service technician to fix (often at a cost exceeding the value of the amplifier), the tubes in a GLOW amplifier are inexpensive and easy to replace yourself. If you can change a light bulb, you can change a tube!




GLOW amplifiers are assembled in China.  Does this make GLOW products any less reliable?

The simple answer is NO.  The fact is, most Big Name audio companies manufacture some or all of their products in China. Most laptops are now assembled in China, as are many of the most innovative products available to us today, such as smart phones, high definition televisions and other devices.  

We are fortunate to have retained some of the very best tube audio engineers in China.  We maintain a presence in China, to assure consistent quality.  

Each and every GLOW amplifier is tested at the factory to verify that it meets our specifications.  Each and every GLOW amplifier is then TESTED AGAIN by an independent testing firm retained by GLOW to make double sure our standards are met.  Prior to every shipment, we receive and review the full quality inspection reports that detail how every single unit performs.  No unit is shipped if it does not meet our specifications. We want you to be as confident as we are that the product you receive is of the very finest quality.



If you are interested in learning more on the subject of why TUBES generally sound better than TRANSISTORS, you can find a wealth of information on the web, including the following article:
Tubes Versus Transistors: Is There An Audible Difference?

By: Russell O. Hamm;  Journal of The Audio Engineering Society Presented at the 43rd Convention of The Audio Engineering Society, New York


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