Hello all. I was given a toroidal transformer (VTX-146-160-224) that has 24v secondaries. I thought I would use it to build a gainclone. I purchased a couple of the cheap XY boards and made modifications suggested on this forum. I'm also using one of these:
https://www.amazon.ca/gp/product/B0828FCC5L/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
My rail voltage after the rectifier board is about 39v. I'd like to bring the voltage down a bit and was wondering if I could use a premade step down converter like this:
https://www.amazon.ca/gp/product/B07X8XPXP7/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
If so, would I place these after the rectifier board or would I need to drop the voltage before the filter capacitors? Sorry, this is all new to me so please excuse my ignorance.
Would it be better to use an LM317 regulator (with a power transformer) to reduce the voltage?
Thanks so much!
Allen
https://www.amazon.ca/gp/product/B0828FCC5L/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
My rail voltage after the rectifier board is about 39v. I'd like to bring the voltage down a bit and was wondering if I could use a premade step down converter like this:
https://www.amazon.ca/gp/product/B07X8XPXP7/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
If so, would I place these after the rectifier board or would I need to drop the voltage before the filter capacitors? Sorry, this is all new to me so please excuse my ignorance.
Would it be better to use an LM317 regulator (with a power transformer) to reduce the voltage?
Thanks so much!
Allen
Your nominal 24+24VAC transformer is fine for your LM3886 giving nominal +/-34VDC, perfect for 8 ohm loads.
You measure slightly higher (+/-39V) only because your supply is unloaded, it will drop to normal under use.
And even if 1 or 2 V high (again, under load), yu are within the acceptable range.
Don´t overcomplicate your life adding those switchers, and IF still worried, better replace your 24+24VAC transformer by a 22+22VAC one.
Go to the root of the problem,do not apply bandaid over bandaid, but worst case , you are still in a "safe" zone.
Or add a primary bucking transformer to reduce Mains a bit.
You measure slightly higher (+/-39V) only because your supply is unloaded, it will drop to normal under use.
And even if 1 or 2 V high (again, under load), yu are within the acceptable range.
Don´t overcomplicate your life adding those switchers, and IF still worried, better replace your 24+24VAC transformer by a 22+22VAC one.
Go to the root of the problem,do not apply bandaid over bandaid, but worst case , you are still in a "safe" zone.
Or add a primary bucking transformer to reduce Mains a bit.
Not that much if we remember transformers are customarily overwound 5%, the capacitor bank is huge, and we are not sure what actual wall voltage is.
Every little bit adds up.
Of course the elephant in the room is that the supply was unloaded.
Then any line spike will charge capacitors to peak and stay there.
Agree it would be worrying if voltage stayed that high with amp working.
Every little bit adds up.
Of course the elephant in the room is that the supply was unloaded.
Then any line spike will charge capacitors to peak and stay there.
Agree it would be worrying if voltage stayed that high with amp working.
Thanks for the help everyone. I appreciate it. My mains voltage runs a bit high at 120.6v. The 24v rails coming from the transformer actually read 28.5v. After the rectifier board, I'm getting 39.2v DC unloaded. I'm likely going to use 8ohm speakers but I was hoping to have the flexibility to run both 4 and 8ohm. I was a little worried the 39.2v would be a bit risky so I thought it might be wise to drop the voltage a bit.
Just checked transformer datasheet.
For starters, it has nominal 115VAC primaries, that alone justifies 5% higher secondaries given your 120.6VAC mains.
Add "unwritten rule" about typically overwinding secondaries by 5%, you already start with very easy to explain 10% high secondaries.
If you really want to test that supply but not risk chipamp, you can load each rail with a Pi*8 ohm resistor, so 25 ohm 50-60W each.
Or to save money for a short test use 25 ohm 20W ones but drop them into a bucket of water first, not kidding.
Rail voltages will be the same as when driving the amp just to clipping.
For starters, it has nominal 115VAC primaries, that alone justifies 5% higher secondaries given your 120.6VAC mains.
Add "unwritten rule" about typically overwinding secondaries by 5%, you already start with very easy to explain 10% high secondaries.
If you really want to test that supply but not risk chipamp, you can load each rail with a Pi*8 ohm resistor, so 25 ohm 50-60W each.
Or to save money for a short test use 25 ohm 20W ones but drop them into a bucket of water first, not kidding.
Rail voltages will be the same as when driving the amp just to clipping.
You could always add 3-4 power diodes in series with the V+ and V- supply leads. That'll drop the voltage by 2-3 V.
Tom
Tom
I think that's what I'll do. I have about 10 1N5401s I salvaged. Would those be ok and do I place them before the rectifier board and filter capacitors? Thank you so much!
1N5401 only handle 3 A. Given that diodes are usually rated for average current and that I'm assuming your amp will be reproducing music, you're probably OK with the 1N5401, but I think I'd err on the high side and use a 10+ A rated diode. You could connect a bridge rectifier to form two diodes in series. A handful of KBPC250x wouldn't set you back much and could easily be fitted in the bottom of the chassis.
Tom
Tom