Rich sound and bass is excellent. I love it. So many years still listening to it.

No weakness and I can't found a single fault with it.

It appears that there have been no reviews or comments on the Audio Innovations Series 500 for many years now so I thought I'd add this.

I have owned a Series 500 for over 15 years now. Before that a series 400. Over the time I have owned the amplifier it has been mainly trouble free. I have had a few issues with the low quality selector switches and volume pot but these were replaced with high quality alternatives.

Recently my 500 has undergone some pretty major upgrades. All internal capacitors have been replaced using NOS Blackgate or Mundorf alternatives. Much of the internal wiring swapped out along with the removal of the balance pot and unused inputs such as tape etc.
Valves are NOS Mullard & Telefunken.

Running in this configuration my amplifier is truly stunning and will outclass anything you care to stand it alongside within it price range. They can be purchased secondhand these days for around £500 in the UK. I suppose realistically I've maybe spent another £700.00 on the service upgrades in addition to the NOS valves. I consider this absolute value for money.

The 500 series was always a good amplifier as standard but was held back by poor quality volume pots, switch gear and valves. Modernising the internal components overcomes the ageing effect and lifts it's performance level to way beyond anything it ever achieved when originally manufactured.

Transparent, musical and very untiring to listen to. Very critical of source components but will sound louder than 25W (without the glare) with well matched speakers.

Needs TLC, but will always reward your efforts to keep it in tip top condition.

Beautiful, glare free, detailed treble, detailed mid range and tight, accurate, tuneful bass. The performance of this amp does diminish with age and it should be serviced at least every 5 years - although that mostly entails revalving, which you can do yourself. I haven't heard a better sounding amp in this price range. The Sugden A28 comes close. Input switches and volume/balance pots are not of the highest quality and when the time comes for an extensive service it is a good idea to replace them. I don't know much about valves, but I'm told by Boarder Patrol that the standard ones can be improved on considerably. The amp has been in daily use since 1988 and has broken down once. Fixed and serviced promptly by the makers - now sadly defunct. In the process of upgrading other components over the years, I have listened to may amps, some much more expensive and have never wanted to part with my 500. It may not have any big strengths but it does everything well and has a knack of just disappering, leaving only the music. In its 15th year (with two services in the interim), the addition of a higher quality front end (Naim CD5 with Hi Cap) has exposed slight raggedness in the top end, some lack of bass control and a sligh L/R imbalance. As I write this, it's at Boarder Patrol being refurbished to 1996 spec, having the volume pot changed, and they'de talked me into an external power supply. In a week's time I will likely be set for another 15 years. Although rated at 25W, this amp has balls. And it looks beautiful. Highly recommended if in good working order. Don't be put off by the way some valve amps sound. This one is a belter.

Similar Products Used:

None.

sounds great.

noisy pots and phone plug are loose.

this is my first valve amp and i think i hit it lucky,i have a pair of kef 105s purchased of another friend for £200 and used a pair of quad transistor mono blocks sounded good but then purchased the ai 500 could not belive the differance in sound,extended bass and a stereo image and transparence like i had never heard,betterd when a invested in some qed silver speaker cable.love it!!! intrested in any mods?

Similar Products Used:

none

i am very happy with the sound that it produces.they have put in other condensators(blackgates)this is a very good improvement to the 500 model.and it looks great

the buzz from the transformators but a couple of rings will do the trick.

every one likes a different sound

Similar Products Used:

a couple of transistor amps.

Just a followup to my review below. I have since added a Borderpatrol power, changed the coupling caps to auricaps, and the cathode electrolytics to Blackgates. The sound is truly remarkable. I've compared it to amps in the $3-$5000 range with outstanding results. Before the changes this amps weaknesses were its mushy bass and its inability to remain articulate during complex passages. No longer. Now the bass is tight and textured, imaging is holographic, and the amp is infinitely more musical. My recommendation for somebody who doesn't have the cash to pay for the Borderpatrol(amazing!) is to change the cathode electrolytics to Blackgates. It's cheap, and in my case it provided the next biggest improvement.

Similar Products Used:

Rogue Audio Tempest, Rogue Audio M120's, Manley Stingray, Audiomat Solfege, Conrad Johnson (yuck! can't remember the model), Krell & Levinson (too hi-fi and artificial sounding)

with a few modifications this amp strikes a perfect balance of detail retrieval and musicality.

cheap pots and switches, difficult to work on

In stock form this amp does suffer from soggy bass and mediocre dynamics as the reviewer mentioned below. However with a few modifications the difference in performance is like night and day. Tweaks I suggest are: ---> change all linestage and phonostage tubes to quality NOS - I use Telefunken and Siemens ---> change output tubes to Svetlana or JJ Tesla el34 - I use Svetlana ---> use an aftermarket power cord - I use the asylum cord at diycable.com ---> replace the cheap pots and switches - I use a DACT CT2 attenuator and I will soon be replacing the balance pot and switches as well ---> use some kind of isolation device - I built a diy seismic sink and it looks almost exactly like the Brighstar product. The sound I have achieved with these modifications is very gratifying. A midrange like butter with crisp and extended highs. A broad and transparent soundstage with excellent imaging. The bass does''nt have the slam of of solid state but for jazz and acoustic this amp really sings. Also, in a couple of weeks I''ll be fitting a Border Patrol power supply which is supposed to ameliorate the bass issues while simultaneously improving dynamics and tonality. Can''t wait - It appears I''ll be the first in the US to take the Border Patrol leap. Yikes! An attractive and musically coherent second hand purchase. Definitely five stars.

with a few modifications this amp strikes a perfect balance of detail retrieval and musicality.

cheap pots and switches, difficult to work on

In stock form this amp does suffer from soggy bass and mediocre dynamics as the reviewer mentioned below. However with a few modifications the difference in performance is like night and day. Tweaks I suggest are: ---> change all linestage and phonostage tubes to quality NOS - I use Telefunken and Siemens ---> change output tubes to Svetlana or JJ Tesla el34 - I use Svetlana ---> use an aftermarket power cord - I use the asylum cord at diycable.com ---> replace the cheap pots and switches - I use a DACT CT2 attenuator and I will soon be replacing the balance pot and switches as well ---> use some kind of isolation device - I built a diy seismic sink and it looks almost exactly like the Brighstar product. The sound I have achieved with these modifications is very gratifying. A midrange like butter with crisp and extended highs. The bass does''nt have the slam of of solid state but for jazz and acoustic this amp sings. Also, in a couple of weeks I''ll be adding a Border Patrol power supply which is supposed to ameliorate the bass issues while simultaneously improving dynamics and tonality. Can''t wait - It appears I''ll be the first in the US to purchase the border patrol supply. Yikes! An attractive and musically coherent second hand purchase, five stars.

With certain components and internal wiring upgraded this old thing is too good to sell on

A real pig to work on

Patience is necessary for rewarding results and a good place to buy the components that make the difference is border patrol.

With proper components and internal wiring upgraded it gives excellent sound

I’ve owned the AI 500 for ten years. I bought it first-hand in 1989. The amp is very good stock standard: its mains and output transformers, as well as some crucial passive components are of very good quality. Manufacturers managed to achieve a competitive price saving money above all on the quality of the tubes, on the input rotary switches and on the carbon pots used for volume and balance controls, more suited to cheap consumer goods than to high-quality audio equipment.
After a few months from purchase I experienced the same kind of problem reported by audio enthusiast Tungsak in his review dated 11/13/97. The trouble he reported with fire was probably caused by the general poor quality of the valves the amp was equipped with - the EL 34s in particular, whose plate tended to overheat with the consequent burning of both the plate itself and the cathode resistor. Replacing both the original EL34s with selected matching pairs from Golden Dragon (as in my case), and of course the original cathode resistors with good quality ones (Resista), has eliminated the problem (I haven’t experienced it for more than five years since then).

Indeed, the amp benefits greatly from tweaking. Given the poor quality of the valves - in my amp, for example, phase splitting was obtained through a couple of PCC88s (cheap TV tubes) instead of the far better and more expensive 6922s - a complete revalving of the amp is a “must”. Besides, I’ve tried different tweaks, which can be summarized into two main options: a “basic” and an “extreme” one.
BASIC (costing about US $ 70 in passive components):
1. Replace the EL 34 cathode resistors with Resista type and remove the poor electrolytic capacitors connected in
parallel to these resistors, whose function is to partially decouple them and, consequently, to “soften” clipping at high volume levels. The tweak will help reduce sound grain. Clipping will be sharper, but you won’t face the problem at
all with sensitive speakers. If you don’t want to remove these capacitors, replace them with high grade audio types such as Elna Cerafine or Nichicon Muse.
2. Remove the two input 0.22mF/400V ERO MKT 1813 capacitors. Their only function is to protect the circuit from possible residual AC (EU requirements?): signal will be cleaner.
3. The two generic 100mF/50V cathode electrolytic capacitors in the drive stage should be replaced with Elna Cerafine or Nichicon Muse types. You should extend the tweak to the phono stage, if you use it often.
4. Decoupling capacitors: the generic 33mF/350V capacitors decoupling the drive and final stages should be replaced with compact radial or snap-in 105°C low ESR types.
5. Input selectors: they are quite poor and should be replaced with better types (silver contacts), ensuring great precision for long periods;
6. Volume control: the original potentiometer is of poor quality: a standard ALPS will guarantee a long life with no “scratches”.
EXTREME (add further US $ 120):
7. Power supply: replace the generic bridge rectifiers with IR Hexfred HFA08TA60C (anode voltage) and Schottky
SB 340 soft recovery diodes (driving and phono stage filaments);
8. Coupling capacitors: the AI 500 is equipped with very good ERO MKT 1813 capacitors, among the best sounding in the polyester series. Yet, their replacement with Jensen paper in oil capacitors (aluminium foil)
will allow a significant improvement in detail, depth and imaging. The considerable dimensions of paper in oil capacitors make replacement complicated, as it implies a new design in the printed circuit of the stage.
9. Replace Beyschlag metal film anodic resistors with 2W matching pairs Allen Bradley carbon film resistors.
Tweak 8 is quite demanding, since it implies a new design in the printed circuit of the final and drive stages which, in turn, will allow the use of the AB resistors, bigger than the Beyschlag. Yet, in combination with the other tweaks, it will allow a great improvement in the general performance of the amp. The sound I have obtained is really gratifying. It is larger in the three dimensions, closer to that of monotriode amplifiers: power seems to go far beyond the 25 Watts declared, probably because of the illusion created by a sound which seems to be “big” without being massively loud. Mids are revealing, high frequencies airy and silky, drums acquire in depth and realism. That slight haze, especially in the upper mid and in the higher frequencies, which prevented me from listening with full precision before the tweak, seems to have disappeared: imaging is solid and close to real, vocals lifelike and involving, impact and dynamics surprising for a valve amplifier. With about 200 US $ added to the amp price and a bit of my spare time I have managed to obtain an amp whose sound can rival with that of amps costing the triple. Give it a try, bearing in mind that tweaking tube amps requires care: anode tension is almost 400V in the AI 500, so do not proceed in any case if it is the first time you use a solder!