The AI-1 Dreadnought Project Pt.1

DarqueKnight

I'm not sure why you are getting what you are getting.

Are you using an Avel-Lindberg Y23 series isolation transformer?

Prior to purchasing my Y236906 isolation transformer, I verified with them that the turns ratio between primary and secondary windings was 1:1. I know that, by definition, an isolation transformer has an identical number of windings on the primary and secondary, but I also know that sometimes manufacturers do something crazy and I wanted to make sure. I try not to take things for granted.

The Y236906 has dual primary and dual secondary windings, so there are a total of four identical windings. Connecting the dual primaries in parallel and the dual secondary in parallel would still give a 1:1 winding ratio. Likewise, connecting the dual primaries in series and the dual secondaries in series would also give a 1:1 winding ratio.

According to the Y23 series winding chart below, which was taken from the Avel-Lindberg website, the "corrected" winding configuration you suggest has the primary windings in parallel and the secondary windings in series. This is not one of the three winding configurations specified by Avel-Lindberg. Furthermore, it would not be a 1:1 ratio.

Avel-Lindberg Y23 series transformer winding configurations. (Link)

Before anyone goes inside their AI-1's and starts snipping, they can just measure the AC output voltage at the left and right outputs. With music, the AC voltage from the left and right outputs of my Dreadnought was approximately 1 volt and the the AC voltage measured at the left and right speaker stereo inputs was approximately 2 volts.

Certainly, I think we would have heard lopsided SDA by now if our custom AI-1's were wired incorrectly. I have two SDA rigs. Using the same music and comparing the SDA effect between my original SRS's and my 1.2TL's with the Dreadnought produced no proportional differences.

dorokusai

Yeah, probably a good idea to hash out everything prior to posting new threads and suggesting the snipping of wires in an vintage Polk iinterface. I just soft deleted the other thread for now.

DarqueKnight

ben62670 wrote: »

The top picture clearly shows both primary and secondary coils parallel. It also is clearly marked 2:1

The first picture says "2xI", meaning the current capacity is doubled when both primary and secondary are in parallel. You also see a "V" under the "2xI" meaning that the voltage remains the same between primary and secondary when the windings are in parallel.

The second picture says "2xV", meaning the voltage capacity is doubled when both primary and secondary are in series. You also see an "I" under the "2xV" meaning that the current remains the same between primary and secondary when the windings are in series.

When I constructed the Dreadnought last year, I measured output voltages with a true RMS voltmeter and an oscilloscope. The readings from left and right outputs were essentially the same:

Oscilloscope measurements (notes dated 10/12/08) :

Left output: 333 mV.

Right output: 395 mV

Voltmeter measurements:

Left output: .4 V.

Right output: .4 V.

Even more than the above, a 2:1 lopsided SDA effect would be easily heard. I certainly don't hear this and I don't know of anyone else who has.

You may have a defective transformer. If I recall correctly, you have built custom AI-1's for a few of the forum members. Did any of them report a lopsided SDA effect? I'm sure you did listening evaluations prior to sending them out. Did you hear a lopsided SDA effect in your system?

ben62670

Never did a listening eval I have nanners, and no pin blade. Have you taken a measurement with an ohm meter, and also have you tried to put 120vac in one side? I tried to call, but had no answer. I preferred to do this over the phone. I doubt very seriously that it is defective as I tested it with 120vac and it was 60vac on the secondaries. I'll try calling again.
Take care.
Ben

DarqueKnight

Never, not even in the farthest reaches of my very expansive imagination, would I have thought to apply 120 VAC to a transformer intended to convey audio signals.

I will leave you with the following:

1. The left and right outputs of my Dreadnought measure essentially the same output voltage when playing test signals and music.

2. The voltage amplitude of the SDA signal is approximately 1/2 that of the stereo signal, this is as it should be. Therefore, my SDA's are operating within design perameters.

3. I do not hear a 2:1 disparity, or any disparity at all, in SDA strength between the left and right SDA SRS 1.2TL.

4. My Avel-Lindberg Y236906 isolation transformer has its primary windings connected in parallel and its secondary windings connected in parallel. According to the A-L's connection chart and according to what I was personally told by an A-L employee, parallel connections on both sides of the transformer results in a doubling of current capacity (2xI) and the input and output voltage remains the same from input to output.

5. How long do you think I would tolerate a distorted SDA effect? I can assure you the time could be measured in pico seconds.

MillerLiteScott

My symmetrical leaning brain tells me to stick with my current wiring configuration.

Scott

RichCanDo

Transformers and voltage:

Think of connecting the coils in series and parallel as below. (An isolation transformer will have the same number of turns in each coil.)

If the primary coil has 2x as many turns as the secondary, output on the secondary will be 1/2 of the input voltage.

If the secondary has 2x as many turns as the primary, the output voltage will be 2x the input voltage.

DarqueKnight is correct when saying when both coils are connected in parallel, or in series, makes no difference. You still have a 1:1 ratio. Voltage in, equals same voltage out.

You do not want to change the voltage. The reason there are 2 primary and 2 secondary coils is to be able to use different input voltages on the order of 110V and 220V. You would use primary and secondary coils in parallel for 110V input, coils in series for 220V input. (as this is an Isolation Transformer, it is not made to be used as a Step-Up or Step-Down transformer. ie "voltage changer")

I would connect the primary and secondary coils in parallel. The reason is, we are dealing with a very low voltage. Connecting the coils in parallel is like connecting 2 single wires in parallel, less resistance.

I have spent most of my life working as an electrician, so have installed many transformers.

RichCanDo

A few more notes on this isolation transformer.

The resistance measurements on each of the four individual coils should be the same. (Some special isolation transformers may have different readings on each of many coils, not this one. These are like several transformers in one package.)

If primary and secondary windings are both connected in series, resistance measurements should be the same for primary and secondary. - If both connected in parallel, again, same resistance both sides, but about 1/2 the resistance of a series connection.

If you input 120VAC and get 60VAC output, then the primary coils are in series, the secondary coils are in parallel, and you have the transformer wired as a step down transformer, which it is not designed to be! (If you input the 120VAC to secondary coil side, you will get 240VAC output.) Inductance is usually the same in all coils of an isolation transformer. The Inductance of individual coils is much more critical for stepping transformers, input and output windings usually have different inductance values.

Connecting the windings in parallel, about doubles the current handling capacity of the transformer. It also halves the resistance that you would read connected in series. (Aside from having 2 coils providing one output, in effect you are also increasing the size of the coil wire.)

If I remember correctly from another thread, the recommend minimum capacity was 5 amps and this Avel is 6.95? amps. When connected in parallel, this capacity should be about 13.9 amps. Plenty more than required, with less resistance when connected in parallel.

Voltage and Current are 2 different things!

F1nut

Certainly, I think we would have heard lopsided SDA by now if our custom AI-1's were wired incorrectly.

That was my first thought after I read Ben's post earlier today. I called Scott and asked him if his were out of balance. He said, no.

ben62670

They sent the wrong transformer!
Y236905 not Y236906.
I will shoot Doro a pm to delete "My wiring correction" post.
I knew that DK is a very smart man, and after rereading his results I knew something was up.
My apologies to all, and thanks DK for reposting your data.
Ben

michaeljhsda2

ben62670 wrote: »

They sent the wrong transformer!
Y236905 not Y236906.
I will shoot Doro a pm to delete "My wiring correction" post.
I knew that DK is a very smart man, and after rereading his results I knew something was up.
My apologies to all, and thanks DK for reposting your data.
Ben

Glad it was straightened out. I held off on making any changes.

ben62670

I'm glad michael. Again sorry about that.
Also thanks Doro for deleting my "fix".
Ben

dorokusai

Anything for you lover.

Schurkey

DarqueKnight wrote: »

A couple of years ago, Matthew Polk provided the following specifications for a toroidal transformer based AI-1:

"1. DC Resistance of primary and secondary should be less than 0.8 ohms and preferably less than 0.5 ohms. The lower the better.

2. Inductance of both primary and secondary should be at least 10mH. Ideal is around 14mH.

3. Current capacity to saturation should be 5 Amps minimum.

4. Of course the turns ratio is 1:1."

I sent those specs to transformer manufacturer Avel-Lindberg and they recommended the following two toroidal transformers:

Avel Part No: Y236856, 5.4" diameter, 2.6" high, 10.8 pounds weight.

Avel Part No. Y236906, 6.3" diameter, 2.2" high, 13.2 pounds weight.

I chose the Y236906 since it was the more robust of the two and its specifications exceeded the requirements. Listening evaluations confirmed that The Y236906 works exceptionally well.

Y236906 Specs:

DC Resistance: 0.275 ohms primary winding, 0.360 ohms secondary winding. The dual primary and secondary windings were wired in parallel as follows:

Inductance : 153.3 mH primary, 168.8 mH secondary.

Output Current Capacity: 6.95 Amps

Output Current Capacity To Saturation: 6.32 Amps.

I'm considering the size of the transformer in the OEM AI-1; and the transformers suggested in the Polk-authored DIY .pdf (Post 6) at

http://www.polkaudio.com/forums/showthread.php?t=55888

SPC Technology 81N5406, 2" x 3 !/4" x 1 3/4", $15.99 or;
Stancor 01F043, 2" x 3 V? x 1.8", $20.04 or,
Magnetek Triad 03F1017, $16.46

MP's items 2 and 3 (above, in blue) therefore strike me as odd.

The big toroidal you've chosen has more than ten times the "ideal" inductance. I don't know how that affects sound quality--perhaps it doesn't.

IF (big IF) there was a decimal error in item 3--current saturation of .5 amps rather than 5 amps--I think sourcing a transformer closer to the "ideal" inductance while still meeting the amperage requirement would be considerably cheaper.

How might we verify MPs recommendation for amps vs. saturation?

DarqueKnight

Schurkey wrote: »

How might we verify MPs recommendation for amps vs. saturation?

If you read earlier in this thread, you will find that I "verified" that everything was alright by comparing the Dreadnought to the stock AI-1. Polk's customer service can forward a message to MP for you.

Schurkey

I don't mean to suggest that your "Dreadnought" doesn't work better than the AI-1. I'm considering that fixing a decimal error could lead to a "mini-Dreadnought" that might work as well. (Or perhaps subject to the "80/20 rule": 80% of the performance of the full-scale Dreadnought for 20% of the price.)

Some Assumptions:
1. The transformers listed in the .pdf for a D-I-Y version of the AI-1 are similar in specs to what Polk used for the OEM AI-1. (Polk didn't DOWNGRADE the transformer specs for the homebuilt AI-1)

2. The AI-1 as sold by Polk or as specified as a DIY project was compromised to make the price more palatable.

SO: I plugged the suggested D-I-Y transformers into the Newark.com web site search box. The part numbers as listed in the .pdf document seem to have been discontinued; but those numbers cross over to currently-available replacements.

SPC Technology 81N5406 data sheet shows 1.3mA secondary output. http://www.spctechnology.com/prodinfo/specs/81n5406.PDF

It is no longer available. Crosses over to become Newark Part Number: 10M5581. Newark calls it an "exact substitute" but I can't find specs on secondary current.

Stancor 01F043 crosses over to Newark p/n 16M3806; Secondary Current Nominal:0.13A

Magnetek Triad 03F1017 crosses ("exact replacement") Newark Part Number: 78K8609; again Secondary Current Nominal:0.13A

From this, I conclude that the ORIGINAL AI-1 had a secondary current of .13 amps or very close. An upgrade to .5 amp capacity would result in almost FOUR TIMES the amperage capacity of the original AI-1!

I wonder how a .5 amp isolation transformer in the SDA signal path sounds compared to a 5 amp transformer?

IF (big IF) the .5 amp transformer is closer to the "ideal" 14uH inductance; and IF the inductance makes an audible difference; and IF there really isn't 5 amps going through the transformer--maybe the .5 amp transformer sounds BETTER than the 5-amp unit??? Less copper loss, less iron loss.

I don't know. I'm just trying to make sense of an 800 VA transformer in an application where the OEM transformer was 15 VA; and wondering if there's a more cost-efficient way that doesn't involve noticeable compromise...

DarqueKnight

Schurkey wrote: »

I don't mean to suggest that your "Dreadnought" doesn't work better than the AI-1.

I didn't take it that way. "Better" is relative to what you like.:)

Schurkey wrote: »

I'm considering that fixing a decimal error could lead to a "mini-Dreadnought" that might work as well. (Or perhaps subject to the "80/20 rule": 80% of the performance of the full-scale Dreadnought for 20% of the price.)

The big Avel-Lindberg transformers have been steadily increasing in price, plus some people just aren't interested in the extra performance offered by the Dreadnought. I'm sure a lot of people would be interested in your findings.

Matthew Polk is very good about responding to these types of inquires.

Schurkey

DarqueKnight wrote: »

The big Avel-Lindberg transformers have been steadily increasing in price, plus some people just aren't interested in the extra performance offered by the Dreadnought. I'm sure a lot of people would be interested in your findings.

I got a quote from A-L dated 24 February 10; the results are:

Avel-Lindberg Sales Rep wrote:

Type: Y236856 (dual 115V pri & sec)
1 pc: $92.81
Delivery: Stock

Type: Y236906 (dual 115V pri & sec)
1 pc: $117.48
Delivery: Stock

Shipping via USPS: $11.00
MasterCard and Visa accepted.

To order, please call 800-979-1022, x 1, or fax 860-354-8597.

I'm sure they'd want me to mention that prices are subject to change at any time...blah blah blah.

DarqueKnight wrote: »

Matthew Polk is very good about responding to these types of inquires.

The question has been posed via the customer service web-form. There's no way to direct it to MP; so I suppose it'll work it's way through channels for awhile. I'm hopeful. At least I have a cat here with me inside this box of uncertainty.

Now, to get quotes from Avel on a .5 amp transformer...

You have an AI-1 Dreadnought.

I'm perhaps going to have an AI-1 Doughnut.

DarqueKnight

Schurkey wrote: »

The question has been posed via the customer service web-form. There's no way to direct it to MP; so I suppose it'll work it's way through channels for awhile.

I would always send these types of questions directly to Ken Swauger, who was Polk's customer service manager. Ken was very knowlegable about SDA's and if he couldn't answer a question directly, he knew who to route it to.

You still have access to Ken since he is now a moderator on our forum. Send him a PM and he will get you taken care of promptly.

Schurkey

I'll give it a few days to percolate. I'd hate to send the same question to multiple people, and then have each of them separately trying to get Matthew Himself involved.

If I don't hear anything in a few days...I'll involve Ken.

Avel-Lindberg's smaller isolation transformers are $30 (.7 amps 80VA p/n Y236358) and $35 (.96 amps, 100VA, p/n Y236407) I forgot to ask about shipping; but the Big Dog is $11 via USPS; I bet these smaller ones are either the same or perhaps $9. Melanie Roman at A-L is in the process of finding out the inductance specs.

hearingimpared

Schurkey wrote: »

I'll give it a few days to percolate. I'd hate to send the same question to multiple people, and then have each of them separately trying to get Matthew Himself involved.

If I don't hear anything in a few days...I'll involve Ken.

Avel-Lindberg's smaller isolation transformers are $30 (.7 amps 80VA p/n Y236358) and $35 (.96 amps, 100VA, p/n Y236407) I forgot to ask about shipping; but the Big Dog is $11 via USPS; I bet these smaller ones are either the same or perhaps $9. Melanie Roman at A-L is in the process of finding out the inductance specs.

Ken's the man. Don't worry about the "multiple people" thing. He on right now as a matter of fact so now would be a good opportunity to contact him.

Schurkey

hearingimpared wrote: »

Ken's the man. Don't worry about the "multiple people" thing. He on right now as a matter of fact so now would be a good opportunity to contact him.

Done.

[Deleted User]

I've sent him a message and will let everyone know what he responds.

[Deleted User]

Here's the response:
Ken -

Yes, I did mean 5 amps. The transformer will have to handle nearly the entire amplifier output for any signal that is primarily in one channel or the other. The impedance of the sda drivers in series is around 6.5 ohms. So, a 5 amp rating will deliver up to about 160 watts to the sda drivers before saturation. The inductance determines the frequency at which the transformer will shunt low frequencies to ground allowing the sda driver to produce the same low frequency signal as the strereo driver in that cabinet. 14mh puts that point well below 100 Hz. That means that the sda signal will be preserved at full strength down to 100 Hz which is important for best imaging. Higher DC resistance just attenuates the sda signal and the bass. I think the transformer in the SRT system had a DCR of 0.3 ohms, 14mh inductance and saturation current around 7.5 amps.

-msp

Schurkey

Schurkey wrote: »

2. The AI-1 as sold by Polk or as specified as a DIY project was compromised to make the price more palatable.

Well, at least I got THAT much right.





Hmmmm. I guess I'm screwed; and the cat with me in Schrodinger's box is definitely dead.

I wonder if 14mH inductance is "ideal"--because it's sounding like "more is better"; and if there's enough the SDA signal is able to go below 20 hz. I suppose if the SDA signal goes lower than ~100 hz, it gets produced by the passive radiator and screws up the imaging and perhaps the bass response.

So aside from ordering a SRT transformer, where do we get one that meets both the amperage and the inductance specs??? (How much is the SRT transformer; and are there any in stock???)

And I wanted to SAVE money.

[Emily Litella Voice]Never Mind![/Emily Litella Voice]

Schurkey

Schurkey wrote: »

(How much is the SRT transformer; and are there any in stock???)

Just got off the 'phone with Polk Customer Service; no transformers available. Entire electronics package available; about $700.

Hawkeye

DK, where did you get the box?

Gordon

DarqueKnight

The anodized aluminum enclosure came from Par Metal (www.par-metal.com).

Hawkeye

Thanks for the link DK.

Gordon

Toolfan66

Thanks for this write up Ray,

I know this thread is old but I am going to be ordering parts Monday and this is a huge help, and will be a very fun project. of course I will be building my own aluminum case for this project, the only thing I'm not sure of using is speaker wire, I will give it some thought this weekend.

There was a time this thread was gibberish to me, HEHE.

"Again Ray" thanks for all you share and do. This has been very helpful.