Wiring of speaker output terminals

[Brinkman]

Quick question:

I am pretty naive when it comes to DIY, so I hope I'm not cluttering the space up with the following question:

I am wiring new speaker binding posts to the rear of my ST70, but due to the increased diameter of the new posts, I can only use a connection from one of the three provided taps from the output transformer (4, 8, or 16 ohm impedence) on each channel.

So when I select and wire one of these impedences, what should I do with the wires for the remaining two values, ground them to the chassis? Terminate them with wire nuts?

Best,
Brinkman

[TomMcNally]

Don't ground 'em ! Wire nuts on the unused terminals is
fine, but remember that the feedback gets tapped from the
16 ohm lead (yellow) so you need to leave that connected.
You might want to terminate the unused wire and 16 ohm
with feedback connection on a phenolic terminal strip.

[Slartibartfast]

Don't ground 'em ! Wire nuts on the unused terminals is
fine, but remember that the feedback gets tapped from the
16 ohm lead (yellow) so you need to leave that connected.
You might want to terminate the unused wire and 16 ohm
with feedback connection on a phenolic terminal strip.

Or he could tie the feedback to the tap he is going to be using for his speakers and reduce the feedback resistor by 1/2 for the 8 ohm tap or 3/4 for the 4 ohm tap. This is a common mod on ST 70 amps, but that may be more than he wants to get into though...

[Brinkman]

Don't ground 'em ! Wire nuts on the unused terminals is
fine, but remember that the feedback gets tapped from the
16 ohm lead (yellow) so you need to leave that connected.
You might want to terminate the unused wire and 16 ohm
with feedback connection on a phenolic terminal strip.

The wiring instructions when I built it specified the feedback wire come from the black lead ("C" on the chassis).

I think this won't be important, as the driver board upgrade has been modified so as to run without NFB. Unfortunately, the gentleman who instructed me on this procedure is too busy at the moment to assist me with the post-installation testing, so I'm not doing much in the meanwhile.

As for the question at hand, I have to choose between a 4- or 8-ohm impedance. My Klipsch Fortes are said to be 6 ohms nominal impedance. Which should I choose?

Thanks!
Brinkman

[Slartibartfast]

As for the question at hand, I have to choose between a 4- or 8-ohm impedance. My Klipsch Fortes are said to be 6 ohms nominal impedance. Which should I choose?

Thanks!
Brinkman

Well the Klipsch website shows the Forte and Forte II as 8 ohms impedance...

[Brinkman]

As for the question at hand, I have to choose between a 4- or 8-ohm impedance. My Klipsch Fortes are said to be 6 ohms nominal impedance. Which should I choose?

Thanks!
Brinkman

Well the Klipsch website shows the Forte and Forte II as 8 ohms impedance...

The imput terminal cup on each of my Fortes specifies 4-ohm nominal impedance. They each also specifiy a sensitivity of 96db 1W/1M. Here's a quote from another forum:

The Forte' specs can be confusing as some crossover cups and literature gave the wrong sensitivity of the speaker. It is actually 98dB 1w/1m for all the Forte's except the Forte' II which is 99dB 1w/1m. Earlier Forte's listed the impedance as four ohms which is closer to the truth than the eight ohm rating on later units. If I remember right the T1 was a cheaper version of the T2A that did not have multiple taps and would have been in later units and eventually replaced by the T10 like in the Forte II. There were no significant changes to the Forte' throughout its run as the woofer, mid, and tweeter stayed the same. It is common on earlier round crossover cup models to have the inductor break off the cup and dangle freely on the inside of the cabinet.

Consistent with all of this (I had a dangling inductor and a T2A transformer in my crossover circuit), I can deduce I have a pair of early production Fortes.

I can't recall where I got the 6-ohm figure I posted prior, but it may explain the varied use of the 4- and 8-ohm impedances. And if 6-ohm is true, which impedance would be best to use, 4 or 8?

Thanks!
Brinkman

[Slartibartfast]

As for the question at hand, I have to choose between a 4- or 8-ohm impedance. My Klipsch Fortes are said to be 6 ohms nominal impedance. Which should I choose?

Thanks!
Brinkman

Well the Klipsch website shows the Forte and Forte II as 8 ohms impedance...

The imput terminal cup on each of my Fortes specifies 4-ohm nominal impedance. They each also specifiy a sensitivity of 96db 1W/1M. Here's a quote from another forum:

The Forte' specs can be confusing as some crossover cups and literature gave the wrong sensitivity of the speaker. It is actually 98dB 1w/1m for all the Forte's except the Forte' II which is 99dB 1w/1m. Earlier Forte's listed the impedance as four ohms which is closer to the truth than the eight ohm rating on later units. If I remember right the T1 was a cheaper version of the T2A that did not have multiple taps and would have been in later units and eventually replaced by the T10 like in the Forte II. There were no significant changes to the Forte' throughout its run as the woofer, mid, and tweeter stayed the same. It is common on earlier round crossover cup models to have the inductor break off the cup and dangle freely on the inside of the cabinet.

Consistent with all of this (I had a dangling inductor and a T2A transformer in my crossover circuit), I can deduce I have a pair of early production Fortes.

I can't recall where I got the 6-ohm figure I posted prior, but it may explain the varied use of the 4- and 8-ohm impedances. And if 6-ohm is true, which impedance would be best to use, 4 or 8?

Thanks!
Brinkman

The part you quoted about sensitivity is in line with the Klipsch website. 98db for the earleir models and 99db for the Forte II.However, it looks like they got lazy and quoted the impedance for both the Forte and Forte II as 8 ohms. To answer you question, I would probably say 4 ohm, cosidering the impedance changes with freq. and can dip down as low as 2 ohms.

[Brinkman]

All right, 4-ohms it is.

I wish I understood the frequency/impedance relationship better, but I'm assuming a lower frequency will require a higher current to drive the load and in doing so will decrease the impedance? Is that what you mean by "dip down as low as 2 ohms"?

I'm probably way wrong. At any rate, I begin an engineering program next Fall, so I'll have these relationships figured out next year some time.

Thanks for the help.

[Slartibartfast]

All right, 4-ohms it is.

I wish I understood the frequency/impedance relationship better, but I'm assuming a lower frequency will require a higher current to drive the load and in doing so will decrease the impedance? Is that what you mean by "dip down as low as 2 ohms"?

I'm probably way wrong. At any rate, I begin an engineering program next Fall, so I'll have these relationships figured out next year some time.

Thanks for the help.

I wish I understood a lot of this stuff better. I have an AA degree in Electronics Eng. and I have forgotten a lot of this stuff. Doing computer support will do that to ya!

I am not sure which end of the freq. range that impedance can drop to such low values. I just remember reading it somewhere. THe low end makes sense though.

Just an FYI, my Bang & Olufsen S70 speakers list their impedance 4-8 ohms. They are connected to the 4 ohm tap on my ST 70. I can't wait to hook up the ST70 to my LaScala speakers.

Where did you get your Forte speakers?

[Brinkman]

Where did you get your Forte speakers?

I got them off the 'bay. And for too much money, considering the condition they arrived in (just over $500 after shipping). I have since seen them cheaper on Craiglist, so I should have waited.

I have since put another buck-fifty into a simultaneous crossover remounting/cap upgrade. This is why I'm going full-bore with the speaker binding post upgrades.

And as soon as I install the new driver board into my ST70, it'll be off the bench and making music. I'll never know what upgrades caused what, but I can't wait.

Best,
Brinkman

[Slartibartfast]

Where did you get your Forte speakers?

I got them off the 'bay. And for too much money, considering the condition they arrived in (just over $500 after shipping). I have since seen them cheaper on Craiglist, so I should have waited.

I have since put another buck-fifty into a simultaneous crossover remounting/cap upgrade. This is why I'm going full-bore with the speaker binding post upgrades.

And as soon as I install the new driver board into my ST70, it'll be off the bench and making music. I'll never know what upgrades caused what, but I can't wait.

Best,
Brinkman

You are going to hate me, but let me say up front, I have only found three deal like this in my life. I got my LaScalas from a church that had their sound system upgraded. All I had to do was replace the grill cloth on the wall opening and replace the voice coils in each of the tweeters.

My ST70 has a new driver board ( same as the original), and a pwr supplt capacitor upgrade from Curio and I am running solid state rectification. The amp is has more punch than with the vacuum tube rectifier.