SDA Dreadnought Isolation Transformer Output Voltage Balance
DarqueKnight
Posts: 6,765
One question that comes up about the Dreadnought 1:1 toroidal isolation transformer is, since we are using the transformers in an application with bi-directional signals, will the SDA signal be imbalanced. The answer is no. Although there is a small difference in output between the primary to secondary and secondary to primary directions, the difference is inaudible, on the order of fractions of a dB.
This subject was first discussed in posts 62-71 of this thread...
The-AI-1-Dreadnought-Project-Pt.1
...and again in posts 167-174 of this thread...
The-AI-1-Dreadnought-Project-Pt.2-Upgrade-to-1000VA-Transformer
and most recently in posts 11-18 of this thread:
Dreadnought-Assembly-Questions
When I measured the left and right stereo and dimensional outputs of the Y236906 800VA transformer in 2008, there was a few percent difference in the outputs of each direction, but it certainly could not be considered as an "imbalance".
In terms of dB, the differences in voltage amplitudes between channels are:
60 Hz
0.12 dB stereo, 0.26 dB dimensional.
1000 Hz
0.38 dB stereo, 0.39 dB dimensional.
With all of the things going on in a stereo sound field, most people would not (or cannot) notice a difference of 0.1 dB to 0.4 dB difference in sound level between channels.
Consider that any isolation transformer, even the one used with the original AI-1, will have a small difference in output when comparing primary to secondary direction and secondary to primary direction. This is unavoidable since a 1:1 isolation transformer must include a small step up function to account for transformer losses. It is unavoidable that a signal going in the secondary to primary direction will see a small step down function. However, the output differences between directions should be (and are) inaudible and should be (and are) within the range you would expect from differences in amp channels and differences in loudspeaker drivers and crossover components. The difference between the outputs of each direction will also vary with frequency. Table 2 shows the output voltage differences according to direction among the original AI-1, 800VA Dreadnought, and 1000VA Dreadnought. The SDA circuit operates from 1600 Hz down.
Figure 1. Left to right: original Polk AI-1 Non-Common Ground Interface, 800VA AI-1 Dreadnought, 1000VA AI-1 Dreadnought.
This subject was first discussed in posts 62-71 of this thread...
The-AI-1-Dreadnought-Project-Pt.1
...and again in posts 167-174 of this thread...
The-AI-1-Dreadnought-Project-Pt.2-Upgrade-to-1000VA-Transformer
and most recently in posts 11-18 of this thread:
Dreadnought-Assembly-Questions
When I measured the left and right stereo and dimensional outputs of the Y236906 800VA transformer in 2008, there was a few percent difference in the outputs of each direction, but it certainly could not be considered as an "imbalance".
Table 1
In terms of dB, the differences in voltage amplitudes between channels are:
60 Hz
0.12 dB stereo, 0.26 dB dimensional.
1000 Hz
0.38 dB stereo, 0.39 dB dimensional.
With all of the things going on in a stereo sound field, most people would not (or cannot) notice a difference of 0.1 dB to 0.4 dB difference in sound level between channels.
Consider that any isolation transformer, even the one used with the original AI-1, will have a small difference in output when comparing primary to secondary direction and secondary to primary direction. This is unavoidable since a 1:1 isolation transformer must include a small step up function to account for transformer losses. It is unavoidable that a signal going in the secondary to primary direction will see a small step down function. However, the output differences between directions should be (and are) inaudible and should be (and are) within the range you would expect from differences in amp channels and differences in loudspeaker drivers and crossover components. The difference between the outputs of each direction will also vary with frequency. Table 2 shows the output voltage differences according to direction among the original AI-1, 800VA Dreadnought, and 1000VA Dreadnought. The SDA circuit operates from 1600 Hz down.
Table 2
Figure 1. Left to right: original Polk AI-1 Non-Common Ground Interface, 800VA AI-1 Dreadnought, 1000VA AI-1 Dreadnought.
Proud and loyal citizen of the Digital Domain and Solid State Country!
Post edited by DarqueKnight on
Comments
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Thank you, DK, for spending the time 'n' effort to address this.
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Thanks DKHome Theater/2 Channel:
Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer
dhsspeakerservice.com/ -
i have a stupid question, is this device the same type of isolation transformer that would have been used on 120 volts line, like that used for some electronics repair? the reason i ask is i own 3 isolation transformers that are kinda used as door stops at 20 amps, they are a pull from a perfusion system so it's overkill in it's ratingsThere is no cure....
Luxman M117, SDA SRS 2.3, rear monitor 10, back rear bose 4.2, valodyne sub and 2 Onkyo m-504 amps Onkyo TX-NR709
8mm, 7.62x39mm -
These are audio quality transformers, not really sure that what you have is.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
what i have is a medical grade isolation transformer for 115 in and 115 out, 1:1 ratio, what i don't know is it's impedance or it's inductance or DCR, i can measure some of it after i dig one out.There is no cure....
Luxman M117, SDA SRS 2.3, rear monitor 10, back rear bose 4.2, valodyne sub and 2 Onkyo m-504 amps Onkyo TX-NR709
8mm, 7.62x39mm -
I think i found the numbers i need in another thread. What has my curiosity are the similarities to equipment i own.There is no cure....
Luxman M117, SDA SRS 2.3, rear monitor 10, back rear bose 4.2, valodyne sub and 2 Onkyo m-504 amps Onkyo TX-NR709
8mm, 7.62x39mm -
The Dreadnought links were there in 2014 but now gone in 2016 I think i damaged my 3.1TL's w/ my 150 watt Kenwood L1000M a dual balanced mono amp (have not yet checked w/ multi meter but think it's not a common ground amp) or my (much weaker Adcom 555ll) mistakenly running it bridged. Bought the 3.1's from the Good Guys who (like me) had no Idea what we had (SDA) so from what I am reading on the forum the dreadnought may be the answer. Rekindled my love for music listening recently when visiting a friend who had a pair of 2.3TL's fresh off of a full box & X-over overhaul (haunting). So instead of going thru my 3.1's I found a pair of non TL 2.3's (3 hr round trip) for $600.00 w/ the 2000's already changed out for the 194's. Do not want to go backwards w/ my 2 Yamaha M-80's (supposedly even more power than the Adcom (B.S.)). So now that i thought the only thing i have yet to order is my new custom made granite caps do i have to build a (or 2) dreadnought(s)?
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You need one Dreadnought per pair of speakers. Even if your amp is common ground, a Dreadnought will improve the sonic performance of your SDAs.
Here are the links:
http://forum.polkaudio.com/discussion/74472/the-ai-1-dreadnought-project-pt-1/p1
http://forum.polkaudio.com/discussion/129829/the-ai-1-dreadnought-project-pt-2-upgrade-to-1000va-transformer/p1
http://forum.polkaudio.com/discussion/73304/ai-1-dreadnought-preliminary-results
http://forum.polkaudio.com/discussion/160494/dreadnought-assembly-questionsProud and loyal citizen of the Digital Domain and Solid State Country!
