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Deathtube 667's Altec Mini Vott system
Altec 2-Way Horn System
DT667's primary audio system uses Altec 414-8B 12" Alnico magnet drivers in 2.7 cu. ft. internal enclosures tuned to about 40Hz.
Altec 811B horns with Altec 808-8A Alnico magnet compression drivers sit on top the cabinets mounted on wooden baffles.
Altec N809-8A crossover networks and Altec 30923 compression driver circuits are employed for frequency dividing and midrange frequency attenuation.
DT667 11/16/2022
ALTEC NETWORKS and COMPENSATION CIRCUITS
Altec N809-8A front view
Altec N809-8A front view
Altec N809-8A front view
DT667 has recently installed a 800Hz 2nd order crossover network in the Altec Mini VOTT system- the N809-8A.
The circuit is essentially a 2nd order Butterworth at 800Hz with a horn attenuation circuit.
Altec N809-8A top view
Altec N809-8A front view
Altec N809-8A front view
N809-8A parts are:
JB JFX Premium 18uF 400V capacitors.
Russian K40-Y .01uF 600V bypass capacitors.
Jantzen 2.2mH 18AWG air core inductors.
The horn attenuation parts are:
8 ohm 15 watt L-PADS.
Altec 30923 front view
Altec N809-8A front view
Altec 30923 front view
The Altec 30923 is a "compression driver compensation circuit" that attenuates midrange frequencies for a more linear acoustic frequency response.
This version of the 30923 circuit uses an 8 ohm L-PAD with series resistor for variable attenuation.
The use of the 30923 circuit in combination with the N809-8A crossover network will allow Altec Theatre products to be used effectively in domestic listening environments.
Altec 30923 top view
Altec N809-8A + 30923 2X
Altec 30923 front view
30923 parts are:
Arcotronics 6uf 400V 5% MKP capacitors.
3.9 ohm 10W 5% non-inductive power resistors.
8 ohm 15W L-PADS.
Dale 2 ohm 5W 1% power resistors.
Altec N809-8A + 30923
Altec N809-8A + 30923 2X
Altec N809-8A + 30923 2X
The N809-8A crossover network and 30923 compensation circuit connected together as a complete unit.
The modular nature of this design will make experimenting with different crossover frequencies easier.
It is a good reason to keep the crossovers outside of the cabinets.
Altec N809-8A + 30923 2X
Altec N809-8A + 30923 2X
Altec N809-8A + 30923 2X
Left and right channel crossover and compensation circuits wired together.
The four boxes are stacked on a small wooden table between the speakers.
Subjectively, the sound is a bit different from the Joe Roberts inspired 1st order high pass horn and full range woofer configuration DT667 had been listening to for several years.
Hearing the 811B horn operating over its full range from 800Hz up and the 414-8B functioning as a proper mid-woofer has been enlightening.
DT667's SE 7C5 "LOW DCR" stereo breadboard amp is currently powering the Altec horn system to great effect.
DT667 11/18/2022
1st order crossover
Inspired by Joe Roberts
In the past, DT667 has used a 1st order crossover inspired by Joe Roberts, a well-known person in the audiophile community who has posted on various audio forums on the internet.
In complexity, it is one step beyond a simple cap and L-Pad arrangement but not that difficult to execute. The most difficult part is determining the value of the crossover cap.
Use the formula to determine crossover cap uF value:
1 / 6.28 x reflected Z for dB attenuation x desired crossover frequency
DT667 7/11/2021
High Frequency Horn Attenuation
Crites 3636 Autoformer
I have been using a Bob Crites 3636 autoformer in my Altec horn system since December 2018.
The autoformer would replace a typical L-PAD to provide level matching between the horn and midrange or low frequency drivers in a multi-way speaker system.
The chart above provides values for reflected Z if the crossover cap is placed before the autoformer.
The impedance can also be changed by paralleling a resistor across the autoformer input terminals.
Or move the crossover cap between the autoformer and horn driver and the crossover point will not change with varying attenuation levels.