The AI-1 Dreadnought Project Pt.2 - Upgrade to 1000VA Transformer

[DarqueKnight]

Introduction

I have considered upgrading the Dreadnought to a larger isolation transformer for some time. During discussions on this topic with forum member RickTfromAZ, he mentioned an Avel Lindberg transformer that was designed for audio applications. A-L promptly supplied a spec sheet for a 1000VA transformer, model number AV-047528. When I called to ask about the technical specifics of the low noise "Silent Technology" design, I was told that details pertaining to the noise performance of the AV-047528 were proprietary. The AV-047548 was specifically designed for audio applications for a contract client. It features an integral peripheral magnetic screen with a resin filled center. A-L just happened to have a few left over from the custom manufacturing run. A-L would not divulge the name of the contract client or the products the AV-047528 was used in. The spec sheet did not include inductance and direct current resistance (DCR) values for the windings. I was told that A-L could provide that information, but someone in engineering would have to dig it up, or retrieve a transformer from the warehouse and measure it. I was also advised that only two remained in stock. I decided to order both units and measure them myself. Price: $155 each + $44.27 shipping.


Figure 1. New 1000VA transformer on left. Former 800VA transformer on right.


Figure 2. Avel Lindberg AV-047528 1000VA transformers.


Figure 3. 1000VA transformer installed.

The Sound

The initial upper midrange grain and softening and slowing of bass that was heard with the previous Y236906 transformer was also heard with the new AV-047548. After 24 hours of play time, the midrange and most of the bass deficiencies were gone, but an annoying smearing of bass transients and articulation remained. Conditioning on the Audiodharma Cable Cooker for 11 hours removed the last of the bass deficiencies. An additional 10 hours of Cable Cooker conditioning provided no audible difference or improvement.

The new transformer provided more overall detail, bass weight and spatial enhancement. Sound stage width did not change, but on some recordings, images that were formerly in front of the speakers moved further to the outer side. The biggest spatial change was in depth, which took some getting used to. Some vocals and instrumental images in the center were repositioned 2-3 feet rearward of their previous position. The opposite effect was heard at the sides, where some images came forward 2-3 feet.The overall effect was that the sound stage took on a more pronounced crescent shape that was thicker in the middle and
longer at the peaks.

Specifications and Measurements

The specifications provided by Polk Audio for a toroidal transformer replacement for the original AI-1 Non-Common Ground Interface were:

"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. Turns ratio of 1:1.

The Dreadnought's previous transformer, the Avel Lindberg Y236906, was an 800VA unit. An old Russian proverb states: "trust, but verify". The parallel configuration DCR specifications provided by Avel Lindberg agreed with my measurements, but their values for parallel configuration winding inductance were way off from what I measured. Transformer winding inductance should be measured with the opposite side shorted (all leads connected together). I assume that whoever supplied the Y236906's inductance values did not account for the shorting requirement when they took measurements or when they calculated the values.

DCR measurements were taken with a Fluke 8050A digital multimeter. Inductance measurements were taken with an MCP BR2822 LCR meter. Noise spectrum (Fast Fourier Transform) measurements were taken with a Tektronix TDS 2012 digital oscilloscope. Room response measurements were taken with Dayton Audio's OmniMic system.

Table 1. Measured and OEM Specifications for Avel Lindberg Y236906 800VA Transformer


Table 2. Measured Specifications for Avel Lindberg AV-047548 1000VA Transformers

Figure 4. Room response with 800VA and 1000VA transformers.

The bass decay plots show how long it takes the sound to decay at each frequency. The ideal situation is flat response which means that some bass notes do not last much longer than others. Significant differences in decay times can cause a decrease in bass definition.


Figure 5. Bass decay with 800VA transformer.


Figure 6. Bass decay with 1000VA transformer.

The color coded lines in the harmonic distortion plots represent the following:

Black - frequency response.
Dark blue - sum of 2nd-5th harmonics.
Red - 2nd harmonic.
Purple - 3rd harmonic.
Green - 4th harmonic.
Light blue - 5th harmonic.

It is easier to see differences in the harmonic distortion plots if they are saved to your computer and viewed in succession.


Figure 7. Harmonic distortion with 800VA transformer.


Figure 8. Harmonic distortion with 1000VA transformer.

With the 1000VA transformer, there was a small decrease in energy at the room resonance peak of 41 Hz of about 1/2 dB (fig. 4). This correlated with the decrease in bass decay times in the 40-45 Hz range (fig. 6). The second harmonic, where most acoustic noise energy was concentrated, was lower overall with the new transformer (fig. 8). The reduction in the second harmonic was also seen in the FFT plots in figures 9-14.

After hearing Such Good Sound from the 1000VA transformer, I was thrilled that I had bought a second transformer to make a Dreadnought for my CRS+'s.

Noise Study

Test signals generated by the MCP BR2822 LCR meter at 100 Hz, 1 kHz and 10 kHz were applied to each transformer and the output signal noise spectrum (FFT) was analyzed on an oscilloscope. As shown in figures 9-14, the harmonic suppression capability of the AV-047548 is outstanding. The AV-047548 is out of stock and discontinued. An A-L sales representative said that making a few units would be cost prohibitive. A comparable alternative is the Plitron medical grade 1000VA isolation transformer with peripheral magnetic shielding (Plitron part # 6166-X0-00, 8.7 amps max current, $252).

It is easier to see differences in the FFT plots if they are saved to your computer and viewed in succession.


Figure 9. FFT plot of 100 Hz test signal through 800VA transformer.


Figure 10. FFT plot of 100 Hz test signal through 1000VA transformer.


Figure 11. FFT plot of 1 kHz test signal through 800VA transformer.


Figure 12. FFT plot of 1 kHz test signal through 1000VA transformer.


Figure 13. FFT plot of 10 kHz test signal through 800VA transformer.


Figure 14. FFT plot of 10 kHz test signal through 1000VA transformer.

[DarqueKnight]

The Second 1000VA Dreadnought

The second Dreadnought was evaluated with a pair extensively modified SDA CRS+'s set up in my home theater system. Even with the home theater's modest electronics, the sonic superiority of the Dreadnought over the strap/custom IC cable configuration and the original AI-1 was immediately evident.

The original AI-1 sounded veiled compared to the strap/custom IC cable. In fact, the loss of detail and clarity caused by the AI-1 was intolerable. The strap/custom IC cable configuration sounded great in every respect, but the Dreadnought took stereophonic attributes to a new level: more image weight, more clarity, more detail, more sound stage depth, more articulation and more tactile sensation.


Figure 15. The second 1000VA transformer was used in a Dreadnought for a pair of SDA CRS+'s.


Figure 16. I had about 1/4" of clearance in the front of this smaller 10" x 10" x 4" case. I would have just
drilled a new mounting hole further back if I had needed more space.


Figure 17. The obligatory Dynamat Xtreme to damp case ringing.


Figure 18. The obligatory Cardas CCGR-S binding posts...only because they look so good.


Figure 19. Completed second Dreadnought assembly with Monster Cable Z3 Reference speaker cables.


Figure 20. Enhanced stereophonic listening pleasure from the little black box.

Associated Equipment - Main Two Channel Audio System Listening Evaluation

Pass Labs X0.2 preamplifier
Pass Labs XP-25 phono preamplifier
Parasound Halo JC 1 monoblock power amplifiers (800 watts continuous into 4 ohms)
Cary Audio CD 306 Pro Version SACD player
Teres Audio No. 255 turntable with Ortofon MC Windfeld cartridge and Graham Phantom tonearm
AudioQuest Sky XLR interconnects
AudioQuest Everest speaker cables
Polk Audio SDA SRS 1.2TL loudspeakers (extensively modified, 4 ohms nominal impedance)
PS Audio P10 AC Regenerator

Associated Equipment - CRS+ Listening Evaluation

Sony TA-P9000ES preamplifier
Adcom GFA-5500 power amplifier, 350 watts continuous into 4 ohms
Pioneer Elite BDP-09FD Blu-ray, CD, DVD player
Monster Cable Z2 Reference speaker cables
Monster Cable Z200i interconnects
PS Audio P10 AC Regenerator
Polk Audio SDA CRS+ loudspeakers (extensively modified), 4 ohms nominal impedance.

References

1. The AI-1 Dreadnought Project Pt.1

2. Improved SDA Interconnect Cables

[Lasareath]

They Look like the transformers that are in the Musical Fidelity Titan power supply.

[thsmith]

Question is how to get more.

[RickTfromAZ]

DarqueKnight,

I just knew that you were up to something. You've been way too quiet. Did you ever pursue the Jantzen inductors for the HF crossover section?

[DarqueKnight]

I did.

Parts Express provided the following price information:

Jantzen 0.4 mH 22 AWG, Jantzen part number 1489, $2.86 each.
Jantzen 0.65 mH 26 AWG, Jantzen part number 1772, $2.33 each.

These are special order items and would take 8-12 weeks to receive.

I am still waiting on a reply regarding a custom 0.7 mH 25 AWG inductor.

[RickTfromAZ]

I've been holding off on doing the LF inductors in hopes I'd hear something from you about the HF inductor results.

In the mean time, I got bored and made me a really large impulse purchase...Yup

I got a pair of JC-1's, a JC-2 and a Cary 306 Pro. Incredible.

Being single is so cool.

[headrott]

So I guess in this case, there wasn't too much wire to degrade the sound using the A-L 1KVA transformer?

Greg

[DarqueKnight]

In the mean time, I got bored and made me a really large impulse purchase...Yup I got a pair of JC-1's, a JC-2 and a Cary 306 Pro. Incredible.

Congrats on the excellent equipment investment!

So I guess in this case, there wasn't too much wire to degrade the sound using the A-L 1KVA transformer?

Yeah, that bullet was effectively dodged.

[headrott]

Raife, you suggested the Plitron 1KVA transformer as a substitute transformer for the A-L ttansformer. Did you get the specs sheet for the Plitron? Or, did you suggest it because it is shielded, 1KVA transformer and the closest to the A-L transformer based soley on those two aspects? I ask because ther is still the TCM 1KVA transformer as well.

Greg

[DarqueKnight]

Both.

I did get the spec sheet from Plitron. It is attached below. As is typical, the spec sheet does not include figures for coil DCR and inductance. I am waiting for Plitron to respond to my inquiry on those.

I don't know anything about the TCM transformers other than what I read on their website. The Plitron transformer is very similar in design to the one I am currently using, particulatly with regard to low noise performance. That is why I felt comfortable in recommending its consideration.

[Toolfan66]

Nice write up Ray.. I did email Avel and you did in fact get the last two

[DarqueKnight]

Did you ever pursue the Jantzen inductors for the HF crossover section?

I did.

Parts Express provided the following price information:

Jantzen 0.4 mH 22 AWG, Jantzen part number 1489, $2.86 each.
Jantzen 0.65 mH 26 AWG, Jantzen part number 1772, $2.33 each.

These are special order items and would take 8-12 weeks to receive.

I am still waiting on a reply regarding a custom 0.7 mH 25 AWG inductor.

Bev Ruggiero at Parts Express emailed me yesterday and informed that Jantzen will not custom make a 0.7 mH 25 AWG inductor.

Looking through Jantzen's current coil catalog, I didn't find a single inductor that used 25 AWG wire. I found an abundance of inductors with 24 AWG or 26 AWG wire.

I am going to order the 0.65 mH 26 AWG coils and see what happens. I will only be risking $4.66 and a few dollars in shipping. The 0.65 mH coil DCR matches the original part, but the inductance is 7% less. However, this is still within the 10% tolerance of the orignal part. Jantzen's 0.4 mH 22 AWG coils are an exact match for the original parts, so I don't expect any problems with those.

[thsmith]

Knowing what you know now about the 2 transformers and the fact Avel is out of this transformer, which transformer would you recommend that is close to this one?

Thank you for all you do for us!

[DarqueKnight]

Knowing what you know now about the 2 transformers and the fact Avel is out of this transformer, which transformer would you recommend that is close to this one?

A comparable alternative is the Plitron medical grade 1000VA isolation transformer with peripheral magnetic shielding (Plitron part # 6166-X0-00, 8.7 amps max current, $252).

I did get the spec sheet from Plitron. It is attached below. As is typical, the spec sheet does not include figures for coil DCR and inductance. I am waiting for Plitron to respond to my inquiry on those.

I don't know anything about the TCM transformers other than what I read on their website. The Plitron transformer is very similar in design to the one I am currently using, particulatly with regard to low noise performance. That is why I felt comfortable in recommending its consideration.

....

[thsmith]

Thanks

[thsmith]

One more question, since these have peripheral magnetic shielding I should be ok putting the transformer in a wooden box without any additional shielding?

[DarqueKnight]

I don't know.

I did listening and signal quality measurements with the old transformer comparing it inside and outside of its aluminum case. I did not do the same with the current transformer.

[RickTfromAZ]

Bev Ruggiero at Parts Express emailed me yesterday and informed that Jantzen will not custom make a 0.7 mH 25 AWG inductor.

Looking through Jantzen's current coil catalog, I didn't find a single inductor that used 25 AWG wire. I found an abundance of inductors with 24 AWG or 26 AWG wire.

I am going to order the 0.65 mH 26 AWG coils and see what happens. I will only be risking $4.66 and a few dollars in shipping. The 0.65 mH coil DCR matches the original part, but the inductance is 7% less. However, this is still within the 10% tolerance of the orignal part. Jantzen's 0.4 mH 22 AWG coils are an exact match for the original parts, so I don't expect any problems with those.

That's also the same conclusion that I came to regarding the 0.7 mH replacement. The 0.65 was the closest spec-wise.

What I was really curious about was which one of the 0.4 mH coils you were going to choose; the 21 AWG (#1364) or the 22 AWG (#1489), since they both have the same DCR.

What I also found a little surprising is that even though these two inductors are only one wire gauge size apart, the 1364 is quite a bit larger and almost 50% heavier than the 1489. Guess it took quite a bit more 21 AWG wire to reach the same resistance.

[Toolfan66]

Ray,

Can't we use Part # 1855 0.7 mH 20 AWG (0.57 omh)?

[DarqueKnight]

It is important to keep the DCR the same as the original part. The original 0.7 mH inductor DCR is 1.66 ohms. The part you listed has way too low DCR.

[Toolfan66]

It is important to keep the DCR the same as the original part. The original 0.7 mH inductor DCR is 1.66 ohms. The part you listed has way too low DCR.

Yep I got my notes wrong, and I thought I was on to something..

[headrott]

Any reply from Plitron about the 1KVA transformer you suggested as a substitute Ray? Although, I am not sure there is a better substitute available regardless of the reply on the coil DCR and inductance of the transformer, but I'd still like to know what they are if you recieved a reply Ray. I assume they have not replied or you would have posted their reply, but thought I would ask. Thanks Ray.

Greg

[Toolfan66]

I received an email from Melanie from Avel that they did find one more of the AV-047548

And yes I called to have it shipped to me..

[brgman]

I received an email from Melanie from Avel that they did find one more of the AV-047548

And yes I called to have it shipped to me..

And you're giving to your buddy brgman right?

[DarqueKnight]

Any reply from Plitron about the 1KVA transformer you suggested as a substitute?

I sent the email on 2/21/12. No reply yet.

I received an email from Melanie from Avel that they did find one more of the AV-047548

Congrats. They probably have a few more unaccounted for in the warehouse and test lab.

[thsmith]

Ray, in the PDF for the PLITRON there appears to be an extra wire (number 2 and 5), would us just tape those off and not use them?

[Toolfan66]

Congrats. They probably have a few more unaccounted for in the warehouse and test lab.

Thanks!! I think I got lucky on this one, I have another case running through the shop as I don't want to take my other one apart to install the new one plus this will make it easy to do an A/B test between the two..

I emailed Jantzen about the inductors and asked if they would make some if I ordered 10-20 of them through Parts Express, not sure if they will respond but it doesn't hurt to try I guess..

[FTGV]

in the PDF for the PLITRON there appears to be an extra wire (number 2 and 5), would us just tape those off and not use them?

Not used as they are extra taps on the primary for wiring the transformer for use in countries with 100 volt service such as Japan.

On another note that particular transformer looks like an excellent candidate for use in a DIY balanced power conditioner.

[Toolfan66]

We had a job in the shop thar required Pre-Anodized Aluminum, there was enough drop for me to cut another case for the Dreadnought to house the new Avel Transformer that should be here Friday. I picked up the case from paint on my way home, and the plater delivered the face plate yesterday that I had black anodized.

Tonight I put the Cardas binding post's in as well as the brass spikes. The Dynamat I ordered should be here tomorrow that I will install. I am really looking forward to A/B testing the two units this weekend, of course my testing will be nothing like Ray's but looking forward to it nonetheless.

Ray are the wires the same as the other Avel, and do they go in the same place as the other transformer? If not can you post where you soldered the wires?