[TimS]

I have a Perpetual Technologies P-3A DAC (9VAC@1.8 amps) powered by a cheap wall-wart and I thought that this low voltage AC component would benefit from some form of power conditioning.
Would it be worthwhile to use the Felicia design and use a different transformer (T2 from the Felicia schematic) with a primary output of 4.5V(?)/9V to achieve my desired 9 VAC output?  Or is this overkill and should I simply put some capacitors across the output of my existing transformer?

cheers

Tim

[Occam]

Tim,

I can't think of a convenient way for a Felicia to produce 9vac at its output. One could get a small 50va isolation transformer -
http://www.newark.com/jsp/search/productdetail.jsp?sku=18M9252
and use it as the input transformer and use you existing wallwart as the output transformer, adding X2 caps 'betwixt and between' across the line. As to how much capacitance, you'd have to experiment. This seems like a lot of trouble for unknown results. If there were easily available 9vac transformer of top quality available for reasonable cost, I'd suggest replacing the transformer with a Flatpack/Flatstack semi-toroidal transformer. These are wonderful transformers that provide excellent isolation as well as minimal leakage inductance. Sadly, they can be had with 8vac or 10vac outputs, but not 9vac. While I might personally try a 10vac configured transformer, assuming the ps/regulators internal to you P3 have sufficient heatsinking to dissipate the extra voltage -
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=190171108081&ssPageName=STRK:MEWA:VRI
I can't suggest that you potentially jeopardize your own component......

Abandoning a transformer based solution, I'd go with a Felix type conditioner

While I typically suggest a CMC rated for above 15amps as I build my Felixs into a powercord, and you don't know what someone else is going to plug it into, the fact that your wallwart is going to be drawing very little current affords you an opportunity to throw a whole bunch of inductance at it, substantially increasing the filter efficacy.
30 mh 2.3A JWMiller 8109 CMCs are available inexpensively, $5.70, from Newark -
http://www.newark.com/jsp/Passives/Inductors,+Chokes+&+Coils/BOURNS/+JW+MILLER/8109-RC/displayProduct.jsp?sku=63K4076&_requestid=44356
This offers substantially more filtering than the 17amp 2.4mh Miller 8120 CMC I use on general purpose filters.

You also have an alternative way of implementing this Felix. Rather than filtering the incoming 120vac, you could filter the wallwarts output of 9vac. The 2.3amp rating is below the nominal 1.8amp max rating of the wall wart, and it allows you to muck about with 9vac which is far safer than 120vac. The increased loading of the filter minimizes the potential for the filter exhibiting unwanted high 'Q' peaks for a given amount of parallel capacitance. You could simply build this Felix into a small plastic enclosure whose input connector mates with the output connector of the wallwart ps, and the output would simply be a 'pigtail' terminated with the same output plug as the wallwart. Additionally, your filter isn't dealing with 120vac anymore and the requirement to use, at minimum, X2 rated caps. For starters, a Jantzen 400vdc CrossCap .47uf paralleled with a .1uf on both sides of the CMC would work very well. -
http://www.partsexpress.com/mfg/jantzen/jantzen.cfm?CFID=1317523&CFTOKEN=62613455#capacitors
or any other polypropylene cap, > 100vdc rating, bespoke or industrial, that strikes your fancy.

FWIW,
Paul

[kyrill]

Tim,

I can't think of a convenient way for a Felicia to produce 9vac at its output. One could get a small 50va isolation transformer -
http://www.newark.com/jsp/search/productdetail.jsp?sku=18M9252
and use it as the input transformer and use you existing wallwart as the output transformer, adding X2 caps 'betwixt and between' across the line. As to how much capacitance, you'd have to experiment. This seems like a lot of trouble for unknown results. If there were easily available 9vac transformer of top quality available for reasonable cost, I'd suggest replacing the transformer with a Flatpack/Flatstack semi-toroidal transformer. These are wonderful transformers that provide excellent isolation as well as minimal leakage inductance. Sadly, they can be had with 8vac or 10vac outputs, but not 9vac. While I might personally try a 10vac configured transformer, assuming the ps/regulators internal to you P3 have sufficient heatsinking to dissipate the extra voltage -
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=190171108081&ssPageName=STRK:MEWA:VRI
I can't suggest that you potentially jeopardize your own component......

Abandoning a transformer based solution, I'd go with a Felix type conditioner

While I typically suggest a CMC rated for above 15amps as I build my Felixs into a powercord, and you don't know what someone else is going to plug it into, the fact that your wallwart is going to be drawing very little current affords you an opportunity to throw a whole bunch of inductance at it, substantially increasing the filter efficacy.
30 mh 2.3A JWMiller 8109 CMCs are available inexpensively, $5.70, from Newark -
http://www.newark.com/jsp/Passives/Inductors,+Chokes+&+Coils/BOURNS/+JW+MILLER/8109-RC/displayProduct.jsp?sku=63K4076&_requestid=44356
This offers substantially more filtering than the 17amp 2.4mh Miller 8120 CMC I use on general purpose filters.

You also have an alternative way of implementing this Felix. Rather than filtering the incoming 120vac, you could filter the wallwarts output of 9vac. The 2.3amp rating is below the nominal 1.8amp max rating of the wall wart, and it allows you to muck about with 9vac which is far safer than 120vac. The increased loading of the filter minimizes the potential for the filter exhibiting unwanted high 'Q' peaks for a given amount of parallel capacitance. You could simply build this Felix into a small plastic enclosure whose input connector mates with the output connector of the wallwart ps, and the output would simply be a 'pigtail' terminated with the same output plug as the wallwart. Additionally, your filter isn't dealing with 120vac anymore and the requirement to use, at minimum, X2 rated caps. For starters, a Jantzen 400vdc CrossCap .47uf paralleled with a .1uf on both sides of the CMC would work very well. -
http://www.partsexpress.com/mfg/jantzen/jantzen.cfm?CFID=1317523&CFTOKEN=62613455#capacitors
or any other polypropylene cap, > 100vdc rating, bespoke or industrial, that strikes your fancy.

FWIW,
Paul

Very very interesting it may persuade me to accept the standard or a better but still not that expensive SWPS for the SB3. So a felix before and after the SWPS, worth trying

thx Paul and "consultants" 

[tanchiro58]

Hi Paul,

I can see you and Gary used mostly 400-440V X2 parallel caps for the Felix and/or Felicia projects. Is that necessary to use those high value voltage in the Felix? How about 250-275V X2 parallel caps (to fit in a small space) would that be safely accepted? Thanks in advance.

Tan

[JoshK]

Hi Paul,

I can see you and Gary used mostly 400-440V X2 parallel caps for the Felix and/or Felicia projects. Is that necessary to use those high value voltage in the Felix? How about 250-275V X2 parallel caps (to fit in a small space) would that be safely accepted? Thanks in advance.

Tan

250V is fine for the low voltage side, even more than fine.  However, that doesn't give a lot of leeway on the 120V side.  You have to design for transient voltages that may exceed the line voltage by a substantial amount.  I am not sure what the rule of thumb is, but quite often one uses 400-600V rated caps for 120vac and 800-1200v for 240Vac.

[Occam]

Tan,

For ac cross the line use, if you're going to stick with caps approved for that use, in 120 or 240vac countries, you can use X2, X1, Y2 or Y1 rated caps. I've been using X2, and have experimented a bit with Y2 caps, but my experience hasn't been extensive enough to offer any subjective or objective opinions. You might want to ask your question directly of Gary on his 'Felix meets the Squeezebox' thread.

X type caps are 'guaranteed' (by an ETL from their testing procedures) to have a failure mode to either fail completely open taking the cap out of the circuit, or completely short which should trip either the fuse or the mains breaker.

Similarly, Y type caps are 'guaranteed' to fail open. For real Y capacitor applications, from either neutral or hot to safety ground, one is restricted to Y caps.

The '1' suffix indicates the voltage rating is higher, typically 440vac, than of a '2' suffix cap, typically a minimum of 275vac.

If one is applying a Felix type conditioner to lower voltage output (say <48vdc or ac) from a wall wart type supply, the range of caps applicable expands tremendously. This is because the supply is outputting a voltage that is far less dangerous and these supplies, leastwise the SB wallwart, their output is certified as isolated from the ac mains supply.

I'd use caps that are minimally rated for 50% higher than the AC or DC voltage, as applicable. This is a typical bypass application and therefore, from a technical perspective, I'd look for low inductance caps, such as stacked film caps like those from Epcos or Panasonic. Then again, we're not in a danger zone so you can use whatever audiophile type caps you've a mind to.

As filtering the output of these supplies is a lower impedance situation that filtering the AC input, you can feasibly eliminate the caps before the CMC, and if that output is DC, use electrolytics.

FWIW,
Paul