49.5V-0-49.5V transformer taps. What to do with them?

[charlielaub]

I have a pair of beefy multi-tapped toroidal power transformers, probably 300W. These came as part of a plate amp from a pair of active loudspeakers. I bought then on Ebay for next to nothing. I have:
49.5V-24V-0-24V-49.5
taps to play with. I have bought a pair of LM3886 modules that I plan to put on to the +/- 24V leads to give me about 34VDC rails.

I almost found a perfect match for the other taps: there is an amp sold at ApexJr called the "Cerwin Vega full range" that needs to have its 220V transformer replaced with a 120V version. The amp needs 63VDC rails, but the 49.5V taps would be giving 65VDC. It's close, but I chatted with Neil Davis about it and he thought that pushing the output devices any more past 63V might invite disaster as it is on the edge of the SOA. I am still thinking about this, as it would be purrr-fect use of all the taps of the tranny in an active speaker. I should probably hook it up and measure the actual no-load voltage at the taps in case it is a little lower, and there will be some sag under load I assume...

I could also use two more LM3886 based amps that are each powered off of one of the 49.5 taps as a single supply amp. I could do this for two woofers (for instance) and power each one from one of the LM3886s. This would be the equivalent of AC +/-24.75V giving rails that were 0V and +/-70VDC. I would need some kind out output cap to kill the DC to the speaker. I see that there is a design for a single end power supply in the LM3886 datasheet so this is definitely a possibility...

But I thought I would throw this out to all of you to see if you had any other great ideas on what to do with the 49.5V taps. Your thoughts???

-Charlie

[wg_ski]

Re: 49.5V-0-49.5V transformer taps. What to do with them?

Two possiblilities for what was originally intended - either a high efficency class H amp, or high and low voltage for bi-amp use. Either one is likely with a powered speaker. No reason why you can't use just one set of windings - but you probably cant get full power running with just the 24-0-24.

[nick29498141]

Re: 49.5V-0-49.5V transformer taps. What to do with them?

With a voltage quadrupole-ing circuit you're looking at about 200V.. Could make for a nice tube preamp, maybe a couple of 5687s..

The above idea is better though.. Class H would be great with those rail voltages.

NK

[neildavis]

Re: 49.5V-0-49.5V transformer taps. What to do with them?

I have a pair of beefy multi-tapped toroidal power transformers, probably 300W. These came as part of a plate amp from a pair of active loudspeakers. I bought then on Ebay for next to nothing. I have:
49.5V-24V-0-24V-49.5
taps to play with. I have bought a pair of LM3886 modules that I plan to put on to the +/- 24V leads to give me about 34VDC rails.

...

But I thought I would throw this out to all of you to see if you had any other great ideas on what to do with the 49.5V taps. Your thoughts???

-Charlie

I would consider an amp based on the LME49810. It's a great driver chip that could make a true reference amp to go with those LM3886's. Connexelectronic makes a nice module with 3 pairs of output transistors:
http://connexelectronic.com/product_...bgfsk2s3d3f2f5 .
There is another version with a heatsink, and they sell power supply modules.

[AJ]

Re: 49.5V-0-49.5V transformer taps. What to do with them?

http://users.ece.gatech.edu/~mleach/lowtim/

As far as I know, the professor still sells PCB's for the Low TIM.

[dougjohnson]

Re: 49.5V-0-49.5V transformer taps. What to do with them?

Connexelectronic makes a nice module with 3 pairs of output transistors:
http://connexelectronic.com/product_...bgfsk2s3d3f2f5 .

They need to buy themselves a spelling checker. That description reads like spam from some non-English speaking country. -- Doug

[neildavis]

Re: 49.5V-0-49.5V transformer taps. What to do with them?

They need to buy themselves a spelling checker. That description reads like spam from some non-English speaking country. -- Doug

I like these instructions to modify the HLLY amp better:

http://www.hllyelectronics.com/download.php?action=download&filename=TAMP-90+improvement.doc

The guy from Connex posts on diyaudio.com and he seems legit and responsive. But I haven't tried the amp module or heard of any feedback on it, so it might be a risk. And I'd second the Leach amp boards--that is a good recommendation for a "reference" amplifier.

Also, there are probably some ICEpower or UCD modules that would work with those voltages. They will provide more power (more efficient Class D, to make better use of that transformer), but the audio quality may not be as good.

[AJ]

Re: 49.5V-0-49.5V transformer taps. What to do with them?

Also, there are probably some ICEpower or UCD modules that would work with those voltages. They will provide more power (more efficient Class D, to make better use of that transformer), but the audio quality may not be as good.

The UCD modules would work fine for the mid/low driver in a biamped setup. Minimal heatsinking would be needed too, probably just bolt it to an aluminum plate.

[datrumole]

recently got some bp7006s with the 'hum' issue everyone reports. rather than dumping additional money into fixing them with the cap mod/replacement in hopes they stay fixed or even paying the $200/ea for new modules. i was thinking of just taking the transformers out and building a linear power supply with them and adding an amp module to power them instead

i have put together a 3ch ICEPower ASP amplifier (500asp and 2x 500a hangers) but this was much more plug and play and didnt require me too deep into anything there. obviously buying a SMPS or even meanwell power supply is what i would do if i were buying a net-new amp, but i figured i already have the transformers, lets take it from there. so i have some general knowledge, just not a ton

just measured the 8" driver in the BP and it's 4ohm

regarding the transformer:
1) i am a complete noob here on building a linear power supply. i understand i have 49.5v and 24v rails. i have no idea what that means. do i have a SE 49.5v or a +/- 49.5v available to me?
2) ok, so i have these AC rails, i need to send them through a 'power supply' which i believe to be a rectifier and regulator in one to get them to DC?
3) how do i know what my final output voltage will be when i send them through this power supply? i'm looking at connex and it doesnt say how much AC voltage i need to bring to the table to get the output DC voltage

regarding amp module:
1) 2x L15D
2) i have a 250a module just sitting around, however finding these is challenging for a second, and just one doesnt look like it's 2ohm stable
3) 2x mx50
4) 1x 3e 3251
5) other suggestions?

[djg]

Keep one hand in your pocket.

[AEIOU]

6Volts is not lethal, wouldn't even conduct through dry unbroken skin. It isn't considered to be high voltage until about 48 or 50 Volts, if I remember correctly.

[datrumole]

Keep one hand in your pocket.

never understood this
come to an audio forum to learn
post question clearly above my CURRENT knowledge level
hope people who like to spread knowledge respond to help to get me to an understanding so i can answer these questions above, and procure the proper parts
get told to piss off with some pointless insult
thanks for furthering the discussion? i mean what was the point. either you dont know, and move on to something you can contribute to, or you do know and are too entitled to answer and feel the need to belittle folks who have taken an interest? whats the end game here, ha?

[datrumole]

i dont disagree, and just because i'm not familiar with linear power supplies, doesnt mean i dont understand that it's dangerous. as noted, i've assembled icepower asp modules before, so i have a decent understanding of the dangers

just asking for some guidance to learn more about them, to your point of learning from the bottom. now i'm not going to go as far down as to be a designer of these modules, but prebuilts are as low as i should need to go. just need the knowledge of what specifics i need to make it all work

[AEIOU]

Do an internet search for Audio Amplifier Power Supply Design. https://www.all-electronics.de/wp-co.../517ag1010.pdf

[djg]

That was a work habit of Tesla. To prevent a high voltage shock across his chest. Just offering advice. Not an insult. I still remember my Dad warning me about electricity. He shorted a wire across a 6 volt automobile battery. It smoked, the insulation sagged off, the wire turned orange and vaporized, in about a second. 6 volts. Be careful.

[datrumole]

did some research last night and was able to answer all of my above questions, for anyone who stumbles on this here is the crash course below

regarding the transformer:
1) i am a complete noob here on building a linear power supply. i understand i have 49.5v and 24v rails. i have no idea what that means. do i have a SE 49.5v or a +/- 49.5v available to me?
1A) the type of transformer i have is a toroidal center tapped transformer. this is indicative when you see 24-0-24 output style nomenclature. in my case, 49.5-24-0-24-49.5, which means i have a +/- 49.5 Vrms and a +/- 24 Vrms set of rails i can use
2) ok, so i have these AC rails, i need to send them through a 'power supply' which i believe to be a rectifier and regulator in one to get them to DC?
2A) yes, you need to send it through a full wave bridge rectifier (often called a linear power supply board). this takes the AC voltage and turns it into DC. this, with a lot of capacitors, are what give you the steady DC output voltage. if a full wave bridge rectifier is used with a standard transformer (24v-0) output you will get a single ended/supply DC voltage. with a center tapped transformer (24-0-24) once you pass it through a full wave bridge rectifier, you have the option to now provide a single supply or a split supply DC voltage. to be noted, this is not a regulated supply, it will have some DC ripple (voltage drops during capacitor discharge), determined by the amount of capacitance in your circuit
3) how do i know what my final output voltage will be when i send them through this power supply? i'm looking at connex and it doesnt say how much AC voltage i need to bring to the table to get the output DC voltage
3A) the voltage in the transformer is representative of Vrms, which is an average output. to find the peak output, multiple by the sqrt of 2, or 1.41. we will use the peak AC voltage to find our DC output. in our above 24v use case, we get 24v*1.41 = 33.8 Vp, so when converted to DC, we would get 33.8 DCV. the rectifier bridge on average has a 1.4v loss, so 32.4 DCV would be our approximate voltage output (will change once we have a load applied to it) but thats the voltage used to determine your supply voltage for the amplifier modules. the same calculation can the be applied to the 49.5 Vrms taps for ~68 VDC (i'm not sure why OP put 65 VDC from the 49.5 taps, perhaps i've done something wrong in my calculation)

other random info, there is no amp rating on the label of the transformer i have, and googling the model number didnt produce any results. all i have to go on is that it's a 300W amp from the spec sheet, so i can only assume 300VA rating. the 24v rails should be able to provide about (edited to12.5amps) (300VA/24V = 12.5A) and the 49.5 rails ~6A (i think the Vrms is used in this calc)

so it sounds like i have some serious power available to me here on these transformers. i follow up on some amp module recommendations elsewhere

[AEIOU]

did some research last night and was able to answer all of my above questions, for anyone who stumbles on this here is the crash course below

regarding the transformer:
1) i am a complete noob here on building a linear power supply. i understand i have 49.5v and 24v rails. i have no idea what that means. do i have a SE 49.5v or a +/- 49.5v available to me?
1A) the type of transformer i have is a toroidal center tapped transformer. this is indicative when you see 24-0-24 output style nomenclature. in my case, 49.5-24-0-24-49.5, which means i have a +/- 49.5 Vrms and a +/- 24 Vrms set of rails i can use
2) ok, so i have these AC rails, i need to send them through a 'power supply' which i believe to be a rectifier and regulator in one to get them to DC?
2A) yes, you need to send it through a full wave bridge rectifier (often called a linear power supply board). this takes the AC voltage and turns it into DC. this, with a lot of capacitors, are what give you the steady DC output voltage. if a full wave bridge rectifier is used with a standard transformer (24v-0) output you will get a single ended/supply DC voltage. with a center tapped transformer (24-0-24) once you pass it through a full wave bridge rectifier, you have the option to now provide a single supply or a split supply DC voltage. to be noted, this is not a regulated supply, it will have some DC ripple (voltage drops during capacitor discharge), determined by the amount of capacitance in your circuit
3) how do i know what my final output voltage will be when i send them through this power supply? i'm looking at connex and it doesnt say how much AC voltage i need to bring to the table to get the output DC voltage
3A) the voltage in the transformer is representative of Vrms, which is an average output. to find the peak output, multiple by the sqrt of 2, or 1.41. we will use the peak AC voltage to find our DC output. in our above 24v use case, we get 24v*1.41 = 33.8 Vp, so when converted to DC, we would get 33.8 DCV. the rectifier bridge on average has a 1.4v loss, so 32.4 DCV would be our approximate voltage output (will change once we have a load applied to it) but thats the voltage used to determine your supply voltage for the amplifier modules. the same calculation can the be applied to the 49.5 Vrms taps for ~68 VDC (i'm not sure why OP put 65 VDC from the 49.5 taps, perhaps i've done something wrong in my calculation)

other random info, there is no amp rating on the label of the transformer i have, and googling the model number didnt produce any results. all i have to go on is that it's a 300W amp from the spec sheet, so i can only assume 300VA rating. the 24v rails should be able to provide about 9amps (300VA/24V = 12.5A) and the 49.5 rails ~6A (i think the Vrms is used in this calc)

so it sounds like i have some serious power available to me here on these transformers. i follow up on some amp module recommendations elsewhere

Transformers are rated in VA, not Watts. If the VA is unknown, you can infer the Amperage by comparing the size of the transformer to a similar sized transformer of a known VA.

[datrumole]

Transformers are rated in VA, not Watts. If the VA is unknown, you can infer the Amperage by comparing the size of the transformer to a similar sized transformer of a known VA.

there is a fuse on the input, not sure if this tells us anything?

from the manual: 3.25-amp 250-volt slow-blow fuse for 110-volt version