I am building an stereo amplifier using two separate mono boards. Each board accepts a max voltage of +/-55VDC. I would like to provide +/-50VDC to each board. My problem is that I am using a 40-0-40VAC toroidal transformer that, after it has passed through a rectifier board, produces +/-58.5VDC. I’m hoping there is a way to reduce this down to +/-50V while maintaining a viable ground scheme for the input voltage to each amp board.
The rectifier board has 6 output terminals: 2 – positive, 2 – negative, and 2 ground. Each amp board has a positive, negative and a single ground input for the voltage, which is perfect. I have a couple of buck regulators that nicely reduce the voltage, and I would hope to use one to power the B+ and one to power the B- rail for both boards. That raises some questions:
Many thanks,
Jonathan
The rectifier board has 6 output terminals: 2 – positive, 2 – negative, and 2 ground. Each amp board has a positive, negative and a single ground input for the voltage, which is perfect. I have a couple of buck regulators that nicely reduce the voltage, and I would hope to use one to power the B+ and one to power the B- rail for both boards. That raises some questions:
- Can I use 2 buck converters total: 1 BC to power 2 amp modules (i.e. send the +50V out to 2 different B+ rails)?
- Do I need 4 buck converters: 2 BCs for each board. Each rail getting its own dedicated BC.
- Either way, how would I handle the ground connections from each of the BCs to the amp board? Since there is only one ground input on each amp board, I’m doubting that it is okay to connect the two separate grounds from the 2 BCs to the one GND terminal. In effect, by using the buck converters I no longer have a 50-0-50V sources but rather two 50V sources.
Many thanks,
Jonathan
I don't think the extra 3.5V will matter at all. Once the PSU is under load the voltage will drop anyway.
A hybrid bleeder could be the solution: a ~8V2 5W zener in series with a resistor sufficiently low to draw enough current when the amp is idle.
Some power will be wasted during idling conditions, but as soon as the amp becomes active, it will reduce to almost nothing. Simple, cheap and effective
Some power will be wasted during idling conditions, but as soon as the amp becomes active, it will reduce to almost nothing. Simple, cheap and effective
Use two capacitor multipliers, voltage drop 4 a 5V. You get cleaner power supply.
How much current/power has the supply to deliver?
How much current/power has the supply to deliver?
Based on Binjo's and Rayma's responses, with the 40-0-40VAC 500W toroidal installed, I cranked up my Variac until I hit 120VAC (matching the wall voltage) and they were, of course, right -- the current draw from the amp boards dropped the voltage to 55V. The board pulls 420mA on the positive rail w/o an input signal. With a 1V sine wave input the channel pulls 1.16 amps and the voltage drops to 51.3V. Connected to 8 ohm speakers the amp seems to sound really good driven by the higher power (although I can't swear that it is much different than the 40V supply). With sine waves everything gets really hot: transistor at 78C, resistors even hotter, but hooked up to 8 ohm speakers playing music the transistors run nice and cool. Some of the 1/2W and 5W resistors get up to almost 90C after about 30 minutes of such regular listening (not sine waves). So, aside from my main question about limiting voltage, I would appreciate feedback about whether I would be pushing things too far using the 40-0-40VAC transformer without modifications.
Elvee, if I were to implement the 8V2 5W Zener+resistor, would I connect these to each of the B+ and B- rails (i.e. 2 sets for each board)? Any ballpark suggestion for where to start with the resistor values and resistor wattage rating? How much heat dissipation would be expected through each resistor assuming a 5V drop from the supply voltage (i.e. 55V to 50)V? When I ran the comparison (above) between a 55V vs 50V supply, the transistor temp went from 78C to 73C.
Many Thanks,
Jonathan
Elvee, if I were to implement the 8V2 5W Zener+resistor, would I connect these to each of the B+ and B- rails (i.e. 2 sets for each board)? Any ballpark suggestion for where to start with the resistor values and resistor wattage rating? How much heat dissipation would be expected through each resistor assuming a 5V drop from the supply voltage (i.e. 55V to 50)V? When I ran the comparison (above) between a 55V vs 50V supply, the transistor temp went from 78C to 73C.
Many Thanks,
Jonathan
Would it be that hard to hand-wind a couple of coils and connecting them out of phase to each 40 of the "40-0-40" to "buck it back down" to a voltage closer to the value you're looking for? Possible to put such a winding in "buck" on the "0" center tap, so you'd only have to wind one? That's harder to comprehend, sitting here amidst an occular migrane...
Yes, but since the quiescent current of the amp is already sufficient to act as a bleeder, it is now irrelevant
So you now run the device with absolute maximum voltage of +/- 55V at +/- 55V ?
Please consider what the factor time will do. Then consider finding out why the absolute maximum is +/- 55V. Are it the electrolytic caps voltage ratings? Are the amp boards being damaged by overvoltage causing overcurrent? What can possibly happen? Most important: are the amplifier boards equipped with loudspeaker protection? If not find out what is more expensive. A new woofer or a toroid.
1. All this when you can have certainty that stuff stays OK with a 2 x 35V transformer.
2. All this when you already have a 2 x 30V transformer that causes no penalty at all besides theoretical lower output power that you will never need anyway 😉
3. Ask yourself what you will gain by running stuff at absolute maximum ratings and higher temperature of semis when you have the solution at hand.
Please consider what the factor time will do. Then consider finding out why the absolute maximum is +/- 55V. Are it the electrolytic caps voltage ratings? Are the amp boards being damaged by overvoltage causing overcurrent? What can possibly happen? Most important: are the amplifier boards equipped with loudspeaker protection? If not find out what is more expensive. A new woofer or a toroid.
1. All this when you can have certainty that stuff stays OK with a 2 x 35V transformer.
2. All this when you already have a 2 x 30V transformer that causes no penalty at all besides theoretical lower output power that you will never need anyway 😉
3. Ask yourself what you will gain by running stuff at absolute maximum ratings and higher temperature of semis when you have the solution at hand.
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Jean-paul, I have been asking myself the same thing for the last several weeks. I was really curious to find out if I would hear a difference if I ran the system at the higher voltage. It definitely sounds really good at the maximum voltage, but as there is no difference in the quiescent current and since I have been listening at reasonable levels with 89dB speakers, it is questionable whether there is an apparent sonic difference between the two transformers. Seeing the resistors getting so hot definitely gives me pause. So, as you say, the most sensible thing is probably to use the smaller transformer and save the big one for a future project. Not surprisingly, some say that this Dartzeel NHB-108 (clone) board sounds better when powered at higher voltages, but unless I am convinced that there's a noticeable difference in the sound of the amp I'll probably soon revert to the lower voltage. Thanks for the sensible advice.
BTW, I have a soft-start board that limits in-rush current as well as a speaker protection board with delayed relays and dc sensing.
Thanks for everyone's input!!!
BTW, I have a soft-start board that limits in-rush current as well as a speaker protection board with delayed relays and dc sensing.
Thanks for everyone's input!!!
Smaller transformer!? Please speak in details and be specific when stuff is pretty specific. The 2 x 30V should not be small with regards to power rating. Its voltage is lower but that is not smaller. It is not a 2 x 30V 100 VA versus a 2 x 40V 500VA is it?
Please mention VA rating of both transformers.
The amplifier may sound better/best on maximum allowable voltage but it would be a pity if it sounds good for a short time. Repairing amplifiers is also annoying compared to building them.
Please mention VA rating of both transformers.
The amplifier may sound better/best on maximum allowable voltage but it would be a pity if it sounds good for a short time. Repairing amplifiers is also annoying compared to building them.
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So I guess taking advantage of torroidal construction to much more easily wind additional buck/boost coils - for a few volts outside of ideal - is an idea so far out there... How hard can it be?
A fellow at my first employ - a product safety guy - told me he made a connector current capacity testing device out of on old Variac coil, winding his own secondary using large guage wire. Said he could put all the Amps he wanted through that connector scheme, to verify a manufacturers claim.
A fellow at my first employ - a product safety guy - told me he made a connector current capacity testing device out of on old Variac coil, winding his own secondary using large guage wire. Said he could put all the Amps he wanted through that connector scheme, to verify a manufacturers claim.
Not hard but DIYing a toroid may not be beneficial for its properties and isolation values. I would do only so when potting them in slow curing epoxy.
BTW I see what you mean, just looked up what a 500VA toroid costs and these have become expensive. This hobby can not survive with the current prices of parts.
If it is for instance a 2 x 30V 300VA OP has I would know what to do. Too bad those that want specific answers rarely give specific information that is really needed for useful advice.
BTW I see what you mean, just looked up what a 500VA toroid costs and these have become expensive. This hobby can not survive with the current prices of parts.
If it is for instance a 2 x 30V 300VA OP has I would know what to do. Too bad those that want specific answers rarely give specific information that is really needed for useful advice.
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Didnt mean to imply DIYing the whole thing, only adding to an existing construction to "adjust" its state more toward a desired specific voltage value. People do bust apart and reassemble an ordinary transformer to accommodate extra windings; I just think the torroidal construction would be far easier to do such with.
Good guess. it is indeed a 30-0-30V 300VA toroidal which is, in fact, smaller than the 40-0-40VA 500W toroidal. Your thoughts then?
Sorry to be one of "those" vague posters. I always try to supply the necessary information.
Thank you,
Jonathan
It is a 150W amplifier, right? Then 300VA seems OK (not knowing the exact type of amplifier as it is a clone). It’s what you have so not much choice there 😉 Or do you have only 1 300VA transformer for 2 channels?
Then you could just sell both toroids and buy the exact right one. Probably a 2 x 35V 500VA type. Look it up in the specs of that clone of a device and you’ll know (we don’t). Doing stuff right has its merits. Or make it more complicated with buck converters, use the one with too high voltage etc.
Then you could just sell both toroids and buy the exact right one. Probably a 2 x 35V 500VA type. Look it up in the specs of that clone of a device and you’ll know (we don’t). Doing stuff right has its merits. Or make it more complicated with buck converters, use the one with too high voltage etc.
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Yep, only 1 300VA transformer for the 2 channels. I've seen the board rated as a 100W amplifier but some claim to get 140W.
Honestly, given my listening habits, 55W is likely more than I even need. So, the 30-0-30V 300VA toroid might be a good way to go. That's kind of what I'm trying to determine. The speakers (Spendor S100) that I'm most likely to use with the amp perform really well with a 20W per channel class AB tube amp. Even my 12W mono block class A amps (Nelson Pass Amp Camp Amps) sound great with sufficient preamp gain.
So, I'm not overly invested in running the amp at its maximum rating which is why I wanted to explore viable options to take advantage of the 40-0-40 500VA transformer while running the boards at a lower voltage. You seem to be suggesting that the proper way to solve the problem is to select the correct transformer and forget about the other options. That makes good sense and I appreciate that advice. I'm inclined to go with the 30-0-30V, but before I can decide that I need to know more about the pros and cons of running an transistor-based amp at a higher voltage.
Acknowledging that heat is the enemy of longevity, is there any value (sonically) in running a Class AB amp at a higher temperature (i.e. at higher voltage)? My understanding is that Nelson Pass suggests that running transistors hot offers sonic advantages. Or is that only relevant only to Class A amps? Similarly, if one never uses the headroom afforded by a higher wattage amp does the extra power matter at all?
Jonathan
Aswell as extra secondaey windings on an Xformer can be used to add voltage it can be used to reduce it if the extra winding is connected 180 degrees out of phase.
Simply done by reversing the wire that is used to connect the two (*2) wires in series and measure voltage.
It can be Vsec+ Vextra or Vsec-Vextra.
One disadvantage is that one or two extra windings usually looks like sh*t as they are not covered by insulating foil.
Transformer VA rating ia derared proportionally to output voltage.
In this case it is safe to assume it is linear.
Tranaformer rating is based on power loss, ie I^2 R losses.
Simply done by reversing the wire that is used to connect the two (*2) wires in series and measure voltage.
It can be Vsec+ Vextra or Vsec-Vextra.
One disadvantage is that one or two extra windings usually looks like sh*t as they are not covered by insulating foil.
Transformer VA rating ia derared proportionally to output voltage.
In this case it is safe to assume it is linear.
Tranaformer rating is based on power loss, ie I^2 R losses.