Altec 612 speaker question

[johnny_fever]

I'm so excited to finally have found a pair of 612's in great condition. The driver's look incredibal. My question is about the crossover. It claimes to operate from 8 to 16 ohms. Will picking 8 or 16 ohm offer any benefit sound or power wise? I'm gonna give them a nice long demo tonight when I get home. I will take more pics later. Thanks JF

 

[twiiii]

For most SS amps thats of no consequence. For tube amps and Mac amps with Autoformers preceding the 7000 class amps you may find a difference. 16 ohms gives you more voltage to the speaker but less current and if the impedances get below 12 ohms that maybe an issue for a particular amp. I would start with the 8 ohm tap. Listen for a day or so to get accustomed to the sound and then switch to 16, you'll either be surprised and really like the change or there will be very little difference in which case you stay with 8 ohms. Each amp will react in a different way. Now if you said a MC275 I would say 8 ohms, A 2105/2100, 8 ohms, and Marantz model 9 16 ohms. Ive been there and done it at the Hi FI shop and at the Radio Station. Dyna kit Model III 16 ohms. My MC 60's I liked 16 ohms, but a 275 at 8 ohms was truer to the original performance. But the best sound comes from SS amps Like DC 300'a, Mcintosh 7100 and 7200, and MC 502, that are direct coupled. Be careful I would imagine the crossover caps are compromised due to age, and should be replaced before applying much more than 2 watts of music to the speakers.

 

[elitopus]

Hey those look nice!

I would recommend building the Markwart crossovers for those. I love the way my 604’s sound with those crossovers.

 

[johnny_fever]

Thanks guys. I'm running a Sansui AU-111 tube amp (45 wpc) Can't wait to get home and play with them.

 

[johnny_fever]

What makes the amp work harder 8 or 16 ohms? Thanks Rick

 

[bowtie427ss]

What makes the amp work harder 8 or 16 ohms? Thanks Rick

The "work" is the same in a transformer coupled amp. The amp always sees the same load, the load the OPT primaries present.

The real question if your OPT's have multiple secondary taps is "which taps offer the best fidelity and frequency range for a given speaker load?"

 

[johnny_fever]

Thanks Bowtie427ss. Maybe I need to make more time to demo these speakers correctly. So far I have not heard any difference on 8 or 16ohms. Adjusting the control knob seems to make no difference in sound either. I am going to try a different pair of 16 ohm crossovers for grins.

 

[johnny_fever]

Should the control knobs make a noticeable diff ?

 

[bowtie427ss]

assuming they have an L-pad, you should be able to adjust the HF output from clearly too much to turned completely off, or any point inbetween.

If the knob is a 5 or 6 position rotary switch with different levels of fixed attenuation you should still distinctly hear a difference between extremes.

 

[johnny_fever]

Thanks BT427ss. These are loaded with N-1500A Crossovers. I tried to clean the pots best I could. I noticed the big resister attached to the pot had heated up al most to the point of unsoldering itself (1 crossover) Not sure why setting makes no diff. Rick

 

[johnny_fever]

Merry Christmas.
Cleaned the pots again and they are now working fine. What would cause the resister on the pot to heat up that bad?

 

[bowtie427ss]

While it's possible for other fault conditions to be the cause, generally significant clockwise rotation of the big knob was involved at some point.

Also, consider that most types of resistors, including the resistive elements in an L-pad will get quite warm under normal operation that approaches their working load limits.

 

[gdmoore28]

While it's possible for other fault conditions to be the cause, generally significant clockwise rotation of the big knob was involved at some point.

Also, consider that most types of resistors, including the resistive elements in an L-pad will get quite warm under normal operation that approaches their working load limits.

Could the burned resistor be an indication that the speaker may have been used at one time with a malfunctioning amplifier? Too much voltage?

GeeDeeEmm

 

[bowtie427ss]

Certainly, GDM. Don't overlook malfunctioning operators as well.

Consider this scenario, for whatever reason the L-pads have been dialed way back leaving the speaker system bass heavy. Current operator of the system cranks up the treble knob to compensate. A while later the radio DJ plays the current system operator's favorite tune, and the system gets cranked up. Now you have the amplifier producing an excess of HF power that is mostly being dumped into a shunt resistor somewhere, in this case one of the resistive elements of the L-pad.

As we all know from audio basics 101, amplifier power going into a speaker system that isn't producing acoustic energy is producing heat.

 

[johnny_fever]

Thanks guys. That now makes total sense BT. only one XO had the heated connection . Here is a picture of the good one. It' a good size resistor. The speakers sound pretty good now. I will be starting a speaker placement post soon. Thanks again. Rick