What to build with 2x22V 160VA tranny and Heatsink

[transducer]

I've got a Plitron 160VA 2x22V secondary transformer lying around, plus ONE heatsink measuring 10" wide by 4.75" high with fin depth of 1 5/8" on a 5/16" thick base, 22 fins total. I'd like to try a small 2 channel class A amp, is there anything I can do with these two parts that is worth it? My new speakers will be pretty efficient, around 90dB 4ohm load. This is just for fun, and to get a taste of a Pass style amp, I don't want to spend a lot of money on it though. Maybe a Mini-A? I lost track of what was happening with that one.

Thanks,
RonS

 

[AudioFreak]

The rails will be too high for a Class A Power Amp given a 4 ohm load and the VA rating of the transformer. Your really limitted to a class AB power amp of about 40W/channel into an 8ohm load, a line level circuit (perhaps a preamp) or a (possibly Class A) headphone amp.

 

[Variac]

I was gonna say a gainclone, but noticed we are in the Pass area,
http://home.attbi.com/~greggbaker/invertedLM3875.gif
Edit- I think it is too small for your chips, but it might sqeak by for a 25w/ ch
Wot's Planet 10 say?, ask him

 

[transducer]

Audiofreak, So the VA rating is too low for a class A amp using these rail voltages? (by the way, I estimate around 29VDC) This tranny actually came out of a preamp that I had done years ago, based on Corey Greenbergs buffered preamp.

Variac, I had thought of a gainclone, I actually have 7 LM3886's lying around, had also thought of a paralleled bridged configuration for 200W but the tranny is too small. Would this tranny be fine for a pair of gainclones using the 3886? I guess my overall power would be lower than full potential.

RonS

 

[Peter Daniel]

If your transformer has option for 110/220V you could connect primaries in series and effectively reduce secondary voltage in half. Mini A would be tempting then. Too bad Grey's not around.

 

[transducer]

Unfortunately there is only one set of primaries for 117VAC

RonS

 

[AudioFreak]

Loaded voltage will be about +/-25V i suspect which leaves +/-20V swing assuming you use LM3886's. Now, the transformer is good for about 4.5Amps rms output which equates to 50W max rms per channel into 4ohms or about 40W rms average into 4ohms assuming a normal stereo musical signal. This drops to 20W rms per channel into 4ohms if the input signal is mono.

 

[Nelson Pass]

How about a nice pair of Zen channels? You should be
able to put two 10 watt originals on that sink, or better
yet, a pair of 10 watt channels with the Zen Variations 2
circuit and a little value adjustment.

One secondary per channel, isolated as with the Zen Lite.

 

[AudioFreak]

Now that is a good idea!!!

 

[transducer]

Hi Nelson,

Wow, an answer from the man himself, and to my first ever question on this forum!

I'm interested in the Zen variation 2, but I cringe at the thought of that big ol cap on the output My source is single ended, so I can't do anything there. Any other thoughts?

Cheers,
RonS

 

[transducer]

Dear Moderator

I specifically posted this to the Pass Forum because I am interested in a Pass type amplifier, whether it be a Zen or Aleph or Mini-A. The post would get better exposure in the Pass Forum as originally placed.

Thanks,
RonS

 

[Nelson Pass]

I don't cringe at the thought of a big ol cap at all.

First, they aren't nearly as bad as the transformers that
tube amp lovers have to put up with.

Second, we enclose it in the feedback loop, so that its
effects are reduced by the feedback factor.

Third, you can always use the best caps you can find
in parallel, big ones and small ones.

Fourth, you can bridge two Zens and DC couple the speaker
anyway.

Fifth, only battery driven amps can claim no capacitors
in the signal path

 

[planet10]

I was gonna say a gainclone, but noticed we are in the Pass area,
http://home.attbi.com/~greggbaker/invertedLM3875.gif
Edit- I think it is too small for your chips, but it might sqeak by for a 25w/ ch
Wot's Planet 10 say?, ask him

The rails are a bit high for 25W, and for a top notch gainclone 2 trafos this size would be specified, but it will work just fine... there are lots of guys out there using less.

If you did a choke input for a Class A amp that would bring the DC rails in under 20V, might make it more useful.

dave

 

[planet10]

Would this tranny be fine for a pair of gainclones using the 3886? I guess my overall power would be lower than full potential.

Full Potential for 4 ohm speakers uses 25V rails w about 25W into 8 ohms.

dave

 

[transducer]

Nelson

Okay, I see that the large caps are in the feedback loop. I cringe at an electrolytic in the signal path, but what the hay, lets try it

or better
yet, a pair of 10 watt channels with the Zen Variations 2
circuit and a little value adjustment.

Can you give me some direction with this? As I mentioned, the tranny is a 160VA with two secondaries of 22 volts each, only single primary at 117V. I'd like to do 2 channels on the single heatsink. I saw how to do the power supply on the Zen Lite, no problem there.

Thanks!

RonS

 

[hifiZen]

You can lower the rails and stretch the VA rating of that trannie by using a choke-input power supply... might still be good for a little DC coupled class-A action after all!

 

[AKSA]

Tranducer,

You could build a Class AB amp of up to 60W, but for best imaging you do need two of those 22-0-22Vac transformers. I sell a kitset amp of 55W which is powered from 36V rails; your 22V trafo would give you 31V rails which would be fine for an AKSA.

Of course, you need to make a choice between Class A and Class AB; there are severe thermal issues with Class A, and while Nelson's designs sound very good, there are also good Class AB amps around, including the gainclone. However, I tend to avoid chip amps because there is little flexibility of design.......

Cheers,

Hugh

www.aksaonline.com