Naxo Circuits

Last updated 23/5/2001.

The easiest way to get a Naxo is to pick up an old second hand unit. Unfortunately that is often easier said than done as they are relatively rare, and in demand. For those of you willing to do it yourself, then here are some circuits I reverse engineered. The High Frequency unit appears to be generic for all the speakers (SBL, Kan, Sara, Isobarik etc). I noticed however that an old Naxo 4 for use with Kans had a few different components (adjusting the crossover region a touch) compared with more modern SBL circuits, although the difference is small. In fact I have tried both with both speakers and I would say it isn't anything to loose too much sleep over. So take your pick. I include both for completeness.

High Frequency Circuit (high pass filter 3kHz crossover)
Click here for ps file. Click here for pdf file.

SBL Low Frequency Circuit (low pass filter 3kHz crossover)
Click here for ps file. Click here for pdf file.

Kan Low Frequency Circuit (low pass filter 3kHz crossover)
Click here for ps file. Click here for pdf file.

To set the relative low/high frequency output levels, the input signals are fed in through a potentiometer. I think older Naxos used 50k pots, although I would think 20k pots would be ok too. Note for the really keen, once you have found your favourite setting, making a potential divider with a couple of resistors sounds a lot better than using a pot. Note also, that if you do similar tweaks to Naxo boards as to the preamps, eg, individual regulators near each circuit, then the 27R resistor at the input of the power rail can be removed, in my opinion.

To set the relative bass/treble output, I would recommend having your pots 'full on' ie, so the gain is unity for both bass and treble boards. This ensures you start with balanced channels, and passes the signal through the least amount of carbon track (if you are using pots). And then decrease one of the boards as you find fit. You'll probably find that 'straight through' will be too bright, and so you'll probably want to pull down the treble a little. Once you have found your favourite levels, setting them with a scope is a good idea to get both channels balanced. I tended to find with Kans and SBLs, that having the treble board operating at about -1dB (ie, at the 90% level of the bass board) was about right for my room at the time. Some rooms might need reigning back more.

Some one is bound to be wanting a 3 way version. Unfortunately I don't have the component values to hand that were used for eg, the Isobarik, although I know some people have 'Spiced' the circuit to play around and pick their own knee points. The 3 way Naxo for Isobariks uses double the number of circuits. The treble unit is unchanged ie, high pass filter with its knee at around 3 KHz. The bass unit is the same but with the knee point moved way down, ie a low pass filter with its knee at around (I think) 150 Hz. The mid unit comprises 2 circuits running back to back; a low pass filter with its knee at around 3 kHz, running into a high pass filter with its knee at around 150 Hz. Thus you get the 150-3000 Hz band-pass filter.