Analog SA I think you misunderstand me
What I'm suggesting is to regulate the output of batteries with high quality audio regulators like Jung's.
That way you get the advantages of low noise and low output impedance without the variable sonics batteries are claimed to suffer from. It also gets rid of the RFI from the mains and rectification process that can affect mains powered PSUs. That way you get the best of both worlds.
Correct me if I'm wrong but I don't think anyone has tried this approach before.
Gopher
What I'm suggesting is to regulate the output of batteries with high quality audio regulators like Jung's.
That way you get the advantages of low noise and low output impedance without the variable sonics batteries are claimed to suffer from. It also gets rid of the RFI from the mains and rectification process that can affect mains powered PSUs. That way you get the best of both worlds.
Correct me if I'm wrong but I don't think anyone has tried this approach before.
Gopher
I'm not sure that's right.richie00boy said:
A regulator can have an output impedance that is lower than it's source impedance. That's the active bit of the regulator coming to the fore.
But there is a condition to allow this to happen. The time period of the current draw must not be excessive.
Well we have already said that batteries in general have a poor high frequency impedance and an exemplary very low frequency impedance. It seems that this characteristic may just be what suits the regulator. The reg passes through the battery low frequency impedance and at higher frequencies the active reg lowers the output impedance to normal active regulator output impedance.
The gap in between may be the problem, but maybe that where capacitance and active are designed to fill that gap.
Gopher
I think your suggestion has merit at least in theory. That is, assuming that the regulator does not have a strong sonic flavour of its own. I really don't know.
For many years i've shunned regulators in preference of nice unregulated supplies. All regulators seemed to impose a dynamic and spacial "strangulation" on the sound. Now i'm kinda used to the regulator sound; i'm very likely brainwashed by the regulator virtues and may really prefer the precise but overdamped sound most nfb regulators bring.
I have always had a preference for tubes and a really striking effect of using batteries is that most annoying solid state artifacts seem to disappear. How would a regulator affect this? No idea.
I think your suggestion has merit at least in theory. That is, assuming that the regulator does not have a strong sonic flavour of its own. I really don't know.
For many years i've shunned regulators in preference of nice unregulated supplies. All regulators seemed to impose a dynamic and spacial "strangulation" on the sound. Now i'm kinda used to the regulator sound; i'm very likely brainwashed by the regulator virtues and may really prefer the precise but overdamped sound most nfb regulators bring.
I have always had a preference for tubes and a really striking effect of using batteries is that most annoying solid state artifacts seem to disappear. How would a regulator affect this? No idea.
I have used a home built, battery powered preamp for years (hence DCPreamp) with flawless performance. I’ve recently built an improved version with equally flawless performance (attached picture).
It’s true, batteries, specifically the SLAs I use, have an extremely low impedance at DC, but it rises with frequency. So, I run them through a substantial C-R-C filter made up of large electrolytics, plus mono-ceramics, plus tantalums, both across the batteries’ terminals and from the +/- rails. This presents an extremely low supply impedance across the entire audio band plus well into the RF region. I do not use any secondary regulation, and even though the battery voltage eventually drops, it’s so slow as to have zero effects on the preamp circuitry.
When experimenting with battery power, I compared filtered batteries with several three-terminal regulators and with several variations of discrete “super regulators” and always found the batteries far superior in noise, impedance, dynamic response, complexity, repeatability, and cost. It was a no-brainer to use batteries and the necessary decoupling. There also no internally generated noise and no chance of ground loops.
My final design is two 12V, 1.2Ah Gel batteries series-connected for a +/- 12V supply. They are then decoupled with a multitude (probably excessively) of caps including 2 x 12,000uF, 16V electrolytic caps (see my avatar pic for the PCB).
For recharging, I use a power indicating LED with a 20V Zener in series to indicate the batteries are approaching +/- 11V. The charger itself is a 24VDC Gel battery charger rated for 3A peak and 100mA continuous charge. It quickly and nicely tops off the batteries. Because of the low power demands of the op-amp and preamp circuitry, it will run for months without a charge (depending on use), but the Gel batteries are excellent “shelf-sitters” and give years of performance following these cycles.
I highly recommend trying the battery power supply. As long as you avoid shorts or reverse connections, they are easy to implement and forgiving of layout and load.
Enjoy!
It’s true, batteries, specifically the SLAs I use, have an extremely low impedance at DC, but it rises with frequency. So, I run them through a substantial C-R-C filter made up of large electrolytics, plus mono-ceramics, plus tantalums, both across the batteries’ terminals and from the +/- rails. This presents an extremely low supply impedance across the entire audio band plus well into the RF region. I do not use any secondary regulation, and even though the battery voltage eventually drops, it’s so slow as to have zero effects on the preamp circuitry.
When experimenting with battery power, I compared filtered batteries with several three-terminal regulators and with several variations of discrete “super regulators” and always found the batteries far superior in noise, impedance, dynamic response, complexity, repeatability, and cost. It was a no-brainer to use batteries and the necessary decoupling. There also no internally generated noise and no chance of ground loops.
My final design is two 12V, 1.2Ah Gel batteries series-connected for a +/- 12V supply. They are then decoupled with a multitude (probably excessively) of caps including 2 x 12,000uF, 16V electrolytic caps (see my avatar pic for the PCB).
For recharging, I use a power indicating LED with a 20V Zener in series to indicate the batteries are approaching +/- 11V. The charger itself is a 24VDC Gel battery charger rated for 3A peak and 100mA continuous charge. It quickly and nicely tops off the batteries. Because of the low power demands of the op-amp and preamp circuitry, it will run for months without a charge (depending on use), but the Gel batteries are excellent “shelf-sitters” and give years of performance following these cycles.
I highly recommend trying the battery power supply. As long as you avoid shorts or reverse connections, they are easy to implement and forgiving of layout and load.
Enjoy!
Attachments
phn said:
I’d like to see more specifics about the test setup for those graphs. Seeing the 50Hz spike tells me there’s grounding issues or a high-impedance letting in radiated noise somewhere. Then, there’s no notation of the battery capacity or state-of-charge.
Anyway, I’m not surprised at all with the upper-frequency noise and that’s precisely why I add lots of decoupling and aim for a broad-spectrum, low impedance source. I use an LM4562 op-amp in my design and idle current is only 10mA, so with the graph normalized with C-R-C filtering, it’s more likely that I’m sitting closer to the dark blue graph - perhaps -120dB or so. But, maybe not.
I lack the test equipment to perform the tests presented in the website, but my good ol’ Hitachi analog scope is pretty darn quiet referenced to ground (about 0.1mV at max sensitivity and focus dialed-in) . So I use that as my reference when testing regulators and three-terminal devices and discretes have never been below 5mV despite my best decoupling tricks. The 12V SLAs when fully decoupled look to be (we’re talking about a 1.5mm trace-thickness) somewhere between 0.5 and 1mV. The output of the LM-4562, preamp at maximum sensitivity and inputs open, is around 1.5mV (pk-to-pk) and not a hint of 60Hz noise. Not too bad if I dare say so.
For reference, a friend’s ADCOM GFP-555 preamp measured in the same test conditions above, measured around 10mV of output noise and another friend’s “super-duper tweeko-to-the-max” tube preamp measured about 25mV. Both friends preamps sound very good, but mine is definitely cleaner and more open. Some good double-blind testing would be nice, but we just keep to our own likes and remain social.
I believe the Dartzeel preamp uses a regulated battery powersupply.http://www.6moons.com/audioreviews/dartzeel2/preamp_4.html
Q: Let's discuss the batteries. A few designers have tried them with success but it is certainly not in the mainstream. The trend in high end preamp seems to be separate components with massive power supplies, high filtration and regulation with tons of current capabilities. Why battery power?
A: The problem with external power supplies is that you still have the umbilical connecting wire so the impedance in the preamp is higher. You need to add regulation inside it to lower the impedance of the power supply. No matter how much you filter the power supply, you still have residual noise. With batteries, you don't have any noise because there is no magnetic field.
Q: I am not an engineer but I have heard that batteries while low in noise, suffer from their own impedance problems.
A: That is true when you use a battery to power the circuit directly. Manufacturers sometimes think, "Okay, we use batteries so we don't need to regulate because there is no hum or alternating current." But it doesn't work like this. We have a twelve volt battery regulated at ten volts. The regulators lower the voltage because when a battery is full it outputs thirteen volts and declines as it discharges to about eleven volts. This is not good for the circuit if the voltage is not constant. Also the impedance of the battery is lowered so everything is happy.
Q: Let's discuss the batteries. A few designers have tried them with success but it is certainly not in the mainstream. The trend in high end preamp seems to be separate components with massive power supplies, high filtration and regulation with tons of current capabilities. Why battery power?
A: The problem with external power supplies is that you still have the umbilical connecting wire so the impedance in the preamp is higher. You need to add regulation inside it to lower the impedance of the power supply. No matter how much you filter the power supply, you still have residual noise. With batteries, you don't have any noise because there is no magnetic field.
Q: I am not an engineer but I have heard that batteries while low in noise, suffer from their own impedance problems.
A: That is true when you use a battery to power the circuit directly. Manufacturers sometimes think, "Okay, we use batteries so we don't need to regulate because there is no hum or alternating current." But it doesn't work like this. We have a twelve volt battery regulated at ten volts. The regulators lower the voltage because when a battery is full it outputs thirteen volts and declines as it discharges to about eleven volts. This is not good for the circuit if the voltage is not constant. Also the impedance of the battery is lowered so everything is happy.
RAYSIMMONS said:
No you don't. A relatively small amount of capacitance inside the chassis would take care of the umbilical issue. Or you can simply put all your reservoir capacitance in the preamp chassis.
I don't see why it would be bad for the circuit if the voltage declined a few volts over a relatively long period of time.
That can be done with capacitance.
se
gni said:
FWIW, attached are the schematics for my preamp. Nothing spectacular, just simple adherence to time-proven, quality designs right off data-sheets. AC coupled, HF bypass, quality components, and solid construction. Of course the main difference being the battery supply, which I’ve already described.
For component selection, I used a Goldpoint stepped attenuator and input selector as they seemed to be the best quality for the money and have proven to be rock solid and silent. They are also the most expensive part of the entire project. The PCB was designed using ExpressPCB software and is one of their 3-for-$51 standard size boards (2.5” x 3.8”, double-sided, through-hole plated). I used Teflon wire for signals because I had some and it’s very good quality, but used 20AWG for all power and ground connections. The gold RCA connectors are from Parts Express and are nothing special – just solid, secure fitting parts. One unique item is the “telephone pole” wiring for routing the signal wires from the rear of the chassis to the input selector. I simply took small pieces of black Teflon block, cut/shaped/drilled it and mounted them on stand-offs. It seemed better than bundling the wires in hopes of minimizing crosstalk and gives a good planned/organized look to the interior. The project box is a cast aluminum part measuring 10.8 x 6.9 x 2.5 and runs $27 at MPJA.
I wish I could provide a comprehensive list of specifications, but I lack the test equipment for that. What I can say is that noise is exceptionally low, frequency response is -0.1dB from 20 to 20K, crosstalk is negligible, and it does just what I want a preamp to do; select inputs, high Z-in, low Z-out, provide adjustable gain, not add noise or coloration, and look nice. Of course, offering all that plus the sense of DIY-satisfaction is a great mix.
Attachments
Hello,
I´m going to build a mic preamp, it´s a nice design based on the Green pre. It can be supplied to +/-20v even it would work ok with less voltage. Anyway, four 9V batteries could do the job.
The issue is that I want the mic preamp to be portable, so have the option of the batteries, or DC-DC converter.
As DCpreamp told, batteries would be less noisy than any DC-DC converter, so that´s the way I´ll go, probably.
My doubts here are about the implementation for the battery setup. Only caps? or a linear regulator?
If understood ok, DCpreamp only use caps, isn´t?
Whell, I thought about use Li-ion batteries, that comes with built-in pcb protection inside, see http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2644
or this other new type that are safer, and non explode: http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3071
NiMH, have similar price, and suffer of much higher self-discharge, so those Li-ion seems nicer for a low consumption mic pre.
I would like to now, any information of the Li-ion "noise" if it has, and the Z, aswell if the PCB that comes with the first model, maybe can have an influencia on the noise or Z, since it´s an IC.
The second type, is a new Li type, that has no IC, but it´s more stable and safer, so have advandage of the low selfdischarge, without the problem of the Li-ion ones..
I would like to know your opinions, and any help of what caps would I need to implement the DC PSU.
Thanks a lot, nice thread.
I´m going to build a mic preamp, it´s a nice design based on the Green pre. It can be supplied to +/-20v even it would work ok with less voltage. Anyway, four 9V batteries could do the job.
The issue is that I want the mic preamp to be portable, so have the option of the batteries, or DC-DC converter.
As DCpreamp told, batteries would be less noisy than any DC-DC converter, so that´s the way I´ll go, probably.
My doubts here are about the implementation for the battery setup. Only caps? or a linear regulator?
If understood ok, DCpreamp only use caps, isn´t?
Whell, I thought about use Li-ion batteries, that comes with built-in pcb protection inside, see http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2644
or this other new type that are safer, and non explode: http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3071
NiMH, have similar price, and suffer of much higher self-discharge, so those Li-ion seems nicer for a low consumption mic pre.
I would like to now, any information of the Li-ion "noise" if it has, and the Z, aswell if the PCB that comes with the first model, maybe can have an influencia on the noise or Z, since it´s an IC.
The second type, is a new Li type, that has no IC, but it´s more stable and safer, so have advandage of the low selfdischarge, without the problem of the Li-ion ones..
I would like to know your opinions, and any help of what caps would I need to implement the DC PSU.
Thanks a lot, nice thread.
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