ZERO, Autoformers, Impedance Multiplying, Transformer cables

[Guest " "]

DeanG

Agree on the technical implications

Thats why I am going to focus on user perceptions rather than measurement metrics.

There are clearly some scenarios that these devices would be an automatic shoe-in for.

And sure, a system that has reached a certain level of modification maturity (high-end xovers, amps with flexible output stages, bi-amp or tri-amp) may not be a prime candidate for impedance multiplying devices.

Putting an iron or air core autoformer on an SS amp is not something that fits my normal thinking frame work. But with all the claims and validations out there for these devices, wanted to give it some of my attention. The speaker wires with the autoformer in the middle of them is the most non-traditional thing I ever saw done to speaker wires in this decade. Atlas and a few others did mount autoformers and tranny's to speaker baskets in years past.

[Rocketman4274]

McIntosh has been using autoformers in most of ther amps for forty years or more.

[Guest " "]

Rocketman4274

yes they have.

This is still being looked into, so far, there's something to this.

[DizRotus]

This is a very interesting and educational thread. Especially to someone who is contemplating a DIY OTL to drive DIY Khorn derivatives with DIY versions of ALK Universals. The nominal impedance of Khorn or La Scala might present a problem to an OTL.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

The measured impedance on the La Scalas I just worked on was 3.7 Ohm. My sons Heresies show 7.6 ohm. Are those impedances correct? As I recall, my old Speakerlab Skhorns were the optional 8 ohm versions (standard was 4 ohm) but I ran two pair in parallel to produce a 4 ohm load. I never actually measured the impedance.

While I had the DMM out, I measured the impedance of my Radio Shack 40-1197 single drivers in Fostex FE-103 designed rear horn enclosures. They measure 7.6 ohm without the notch filter (10 ohm resistor in parallel with 2.2 uF) and 17.6 ohm with the notch filter. The filter, obviously, lowers the efficiency, but tightens the bass and smoothes the midrange.

Its slightly OT, but Id welcome a tutorial on why notch filters, including the famous, or infamous P-Trap) work.

[Guest " "]

Yes OTL amps as well as SS amps can run optimal if you can give them an optimal load. And putting two pairs of LaScala's, Cornwalls, K-horns, Hersye's on a 2 channel amp is trouble for most amps.

Those readings are at DC or 0 herts. Depending on the taps used on the t2a autoformer for the sqwaker, the middle frequecies will have a significanly higher reading. Tap 4 doubles the sqwakers impedance, tap 3 rasies the sqwakers impedance by a factor of 4, etc.

See the below links on info about both imepdance matching speakers to amps and about OTL assumptions reguarding speaker loads.

http://www.tnt-audio.com/accessories/zero_autoformer_e.html

http://www.responseaudio.com/zeros_white_paper.htm

The radio shack solution of putting a resitor in parallel with the speakers is often refered to as a dampening resitor since it improves the dampening factor of the amp, and as a result, the bass sounds more controlled. The capcitor in parallel is just there to make the drivers less bright. This approach is pretty messy.

Links for autoformers.

http://www.edcorusa.com/transformers/em/em_auto.htm

The Zero has the same operating principal when it comes to impedance matching at about one fourth the cost.

I am using a pair of atlas sound af140's to imcrease the load on my amp. The amp sounds better if I increase my LaScala's impedance by a factor of 1.5, to an average of 9 ohms. It sounds better with the autoformer reguardless of the crossover I use (al-4, es400+es5800, AL-3, AL, AA, etc).

http://www.atlassound.com/products/partNumber.cfm?pn=AF140

[DizRotus]

Here are the direct links to the sites referred to above.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

http://www.tnt-audio.com/accessories/zero_autoformer_e.html

http://www.responseaudio.com/zeros_white_paper.htm

http://www.edcorusa.com/transformers/em/em_auto.htm

[BEC]

This is a very interesting and educational thread.  Especially to someone who is contemplating a DIY OTL to drive DIY Khorn derivatives with DIY versions of ALK Universals.  The nominal impedance of Khorn or La Scala might present a problem to an OTL.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

The measured impedance on the La Scalas I just worked on was 3.7 Ohm.  My sons Heresies show 7.6 ohm.  Are those impedances correct?  As I recall, my old Speakerlab Skhorns were the optional 8 ohm versions (standard was 4 ohm) but I ran two pair in parallel to produce a 4 ohm load.  I never actually measured the impedance.

 

While I had the DMM out, I measured the impedance of my Radio Shack 40-1197 single drivers in Fostex FE-103 designed rear horn enclosures.  They measure 7.6 ohm without the notch filter (10 ohm resistor in parallel with 2.2 uF) and 17.6 ohm with the notch filter.  The filter, obviously, lowers the efficiency, but tightens the bass and smoothes the midrange.

 

Its slightly OT, but Id welcome a tutorial on why notch filters, including the famous, or infamous P-Trap) work.

Sounds like you are just measuring the DCR not impedance. On the Lascala, for instance, measuring at the input terminals of the crossover, you are simply just measuring the resistance of the woofer voice coil plus the DCR of the woofer inductor.

To measure impedance, you would input AC (audio) and measure impedance at different frequencies.

Bob Crites

[tigerwoodKhorns]

I have a set...homemade boxes and use them with my magnepaner smga (4ohm) and a Nakamichi SR-2A amp.....also rebuilt the xo's which was pretty simple (maybe dean remembers those big 50uF auricaps).....Paul is a good guy to talk about your set up....liberal return policy if I remember....settled on the 3x taps (12ohms).....email me if you want more info -Al

Al,

I though that those speakers looked familiar. I have a pair of SMG Maggies that I rarely use. I'd like to use them in a workout rom but don't feel liek putting much money into them.

Can you email me to discuss? (I don't want to hijack a thread)

nevadamail@hotmail.com

Thanks,

Chris

[Guest " "]

Here is another autoformer find. This one has a power rating of 100 watts and a bandwidth of 35hz - 19khz. It has quite a few more taps than the atlas af140.

I am still using the atlas af140 to increase the impedance of my LaScala's from 6 ohms to 9 ohms.

AutoformerWEB_SHEET.pdf

[Guest " "]

finally found a toridal autoformer

Frequency Response:

+/- 0.5 dB (20 Hz to 20kHz).

Insertion (Core) Loss:

0.41 dB max

this one is sold by crown. price is 60 - 90 bucks.

this is the second best spec's so far. the first best cost 215 each.

crown autoformer 135086.pdf

[Guest " "]

Another toy for Mikey.

[djk]

A good part for a good price.

I have several of those (but they have amplifiers attached to them too).

[Guest " "]

I received the two Mac Autoformers yesterday. They each weight 21 pounds. Rated at 300 watts. frequency response is 10hz - 100khz.

I tested them and was surprised to find all the leads/taps worked. Was expecting at least one of the leads between 5/6/7/8 to be open or all of them shorted. Why would someone remove functional autoformers from a Mac amp?

So I reconstructed the terminal strip and have the transformers connected to my garage amp. Basically using these autoformers in the same manner the "Zero-Autoformer" product is being marketed. Nothing smoked. By changing the tap settings I can change the load the amp sees.

So it turns out that impedance multiplication is not new, and certainly not a discovery of the "Zero-Autoformer" folks. Mac Amps have had autoformers (even on their SS amps) for decades. Atlas has a product that has been around just as long. Crown even sells a toridal autoformer.

Next goal is to actually construct an 8 tap toridal autoformer.

[Guest " "]

So now that I spent a few days playing around with the Mac Autoformer, the 5x setting seems to sound the best. 5x brings my 6 ohm LaScala's to about 30 ohms. The connections look something like this.

I did some tone burst test while measuring the voltages across all the taps and confirmed the 5X multiplication factor.