Deathtube 667's Altec Mini Vott system

DIY 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. The 414-4B runs full range with no crossovers out to 3kHz and begins rolling off. There is a moderate amount of pink fiberglass insulation inside the box to control the backwave from the 12" driver.

An Altec 811B sectoral horn with 808-8B compression driver crosses over 1st order @ 6.5KHz with a single oil cap as per Joe Roberts . The compression driver diaphragms are OEM Altec aluminum replacement units (part# 34627 8 ohm) .

A Crites 3636 autoformer provides a -6dB pad to level match the 414-8B to the 811B horn.

Finally, a Mirage BPS 150 bipolar subwoofer fills in the last few octaves from 70Hz down.

The resulting system is fine sounding and adaptable to most music genres.

IMO, get the biggest best Altec system within budget and space considerations.

DT 667

crossover

Inspired by Joe Roberts

DT667 uses a 1st order crossover inspired by Joe Roberts, a well known person in the audiophile community who has posted on AA forums in the past.

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.

Bob Crites Speakers

Website link here

Speaker Wire and Connectors

Military Grade Wires

DT667 uses a single run for each polarity +/- of "military grade" 12AWG silver coated copper stranded wire between a SE tube amp and main speaker driver (Altec 414-8B alnico). Part # M22759-11/12.

Note : MLP design team members typically use 3 parallel runs of the "military grade" wire for each polarity +/- to optimize "transfer efficiency" into their Altec speakers. They do this because they are running their Altec systems with only one low power SE tube amplifier.

Since DT667 is using a subwoofer to help on the low bass Hz's, the extra parallel runs of speaker wire for each polarity +/- are not an absolute necessity.

The wires are terminated into RCA brand banana plugs. These use screws that secure the wires to the barrel of the plug. The ends of the plugs are filled with Kester 60/40 rosin core solder to permanently secure the connection. These are NOT sold as solder banana plugs. There is a trick to filling the barrel with solder so it does not destroy the compression fitting at the end of the plug. Proceed at your own risk!

The speaker boxes are fitted with cups on the back panel with 5-way binding post similar to what is offered by Nakamichi and many other EBAY vendors. There are two sets of binding posts on the back of the speaker box to connect the amp and horn crossover circuit.

A single run of the same type of wire in 16AWG is used for wiring the horn compression driver crossover. Wire termination in the crossover are soldered ring terminals and push-on connectors commonly found at a home improvement store.

DT667 7/11/2021

Speaker Wire Experiments

Speaker Wire For Altec 414-8B

DT667 listened to the mil spec 12AWG wire with soldered on RCA brand banana plugs for a few weeks. Subjectively, DT667 was not totally satisfied with the soldered on RCA brand banana plugs . Too much solder was needed to secure the wire inside the banana plugs and imparted some harsh aspects to the presentation, so the mil spec 12AWG was removed. Or perhaps there was a break-in period for this sort of wire termination but DT667 was not patient enough to wait around to find out.

DT667 purchased some Legrand On-Q banana plugs (part # 366827-V5) and installed them on Original Monster Cable 12AWG with Duraflex insulation as main speaker cable for Altec 414-8B. The Monster Cable is basic oxygen-free stranded copper cable, not tinned or cheap CCA (copper covered aluminum). This is a good sounding combination of wire and banana plugs.

DT667 has ordered some KnuKonceptz Kord Speaker Wire - 10AWG 462 strand OFC PVC jacket off of EBAY to create some DIY speaker cables along with the Legrand On-Q banana plugs for comparison to the Monster Cable 12AWG wire.

DT667 also installed DIY PASS Camp Amp SE solid state stereo amp with linear power supply to drive his Altec speaker system. Great sounding 5W solid state amplifier.

The SE DC tube breadboard amp - reimagining the current state on breadboard.

DT667 7/25/2021

deathtube 667