Years ago I bought a Hiraga PrePre from 404 Not Found
I've used it before and was able to zero the offset. However, this time I am using a battery bank (to charge phones) and the voltage is 5.18VDC. When powered up I cant get the offset lower than about 20mv. Would this fry my coils of my Denon DL103 cartridge?
Any tips how to get a lower mv? Do I need to install a different pot or could I do it a different way? I have also noticed that the offset voltage goes up when I remove the battery bank. Is this normal? (voltage might go up to several volts)
I've used it before and was able to zero the offset. However, this time I am using a battery bank (to charge phones) and the voltage is 5.18VDC. When powered up I cant get the offset lower than about 20mv. Would this fry my coils of my Denon DL103 cartridge?
Any tips how to get a lower mv? Do I need to install a different pot or could I do it a different way? I have also noticed that the offset voltage goes up when I remove the battery bank. Is this normal? (voltage might go up to several volts)
20mv will not cause any issues. What's the DC resistance of this cartridge... 40 ohms ish ?
20mv would allow 0.0005A or 0.5 milliamps which would be a power dissipation of just 0.00001W or 0.01 milliwatts into 40 ohms.
Perhaps if the supply voltage is now different the offset control is now out of range somehow. Can't guess on that without seeing a circuit diagram.
Your link doesn't seem to work for me:
20mv would allow 0.0005A or 0.5 milliamps which would be a power dissipation of just 0.00001W or 0.01 milliwatts into 40 ohms.
Perhaps if the supply voltage is now different the offset control is now out of range somehow. Can't guess on that without seeing a circuit diagram.
Your link doesn't seem to work for me:
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Thanks for your fast reply. I just noticed that I have made a mistake in my wiring as I need +5V, -5V and ground. I just connected +5V and ground. Will see if I have an other USB cable I can sacrifice to my 'project' 😉. I am using an Anker power bank with 2 USB out ports and am curious how it sounds. If all else fails I have a spare Reflektor-D I could perhaps use.
I will let you know if when I have it up and running.
I will let you know if when I have it up and running.
Hmmm... Still a problem. The Anker power bank has 2 usb ports. Perhaps a bit simple I thought I could use the ports to get +5V, -5V and ground. I got 2 USB cables and connected the cables as follows:
cable 1 red is 5V+, black ground connected to red 5V of cable 2
cable 2 black is -5V, red is connected to ground of cable 1 which are both connected to ground
However, when I use both USB cables I don't get the right voltages. When I connect 1 USB cable to the power bank (while the other is still connected to the PCB PrePre), I get 5.18V and -4.80V. +V stays stable and -V decreases gradually.
Is it possible to use a power bank as a supply to begin with or have I wired something incorrect?
cable 1 red is 5V+, black ground connected to red 5V of cable 2
cable 2 black is -5V, red is connected to ground of cable 1 which are both connected to ground
However, when I use both USB cables I don't get the right voltages. When I connect 1 USB cable to the power bank (while the other is still connected to the PCB PrePre), I get 5.18V and -4.80V. +V stays stable and -V decreases gradually.
Is it possible to use a power bank as a supply to begin with or have I wired something incorrect?
I used a second power bank and get roughly +5Van -5V. Offset however fluctuates, however when I press the button to check if the battery is full the offset is stable. Will try an other power bank to see if I can get it stable.
Hard to say without seeing the set up or having it drawn out but I would say with pretty much 100% certainty that you need two power banks to generate a -/+5 volt supply.
One power bank no matter how many USB ports it has will just have those posts connected to the same cells in the bank. In other words you can not generate a -/+ rail from one bank.
The DC offset may fluctuate in response to small rail variations (pressing a batt check button may load the supply and cause a drop) but that is a design issue with the preamp. Ideally there should be no change in DC conditions provided the supplied voltage is within the design spec limits.
One power bank no matter how many USB ports it has will just have those posts connected to the same cells in the bank. In other words you can not generate a -/+ rail from one bank.
The DC offset may fluctuate in response to small rail variations (pressing a batt check button may load the supply and cause a drop) but that is a design issue with the preamp. Ideally there should be no change in DC conditions provided the supplied voltage is within the design spec limits.
Hello,
It is probably noisy because usually the things that are connected to this kind of power supply dont care to much about noise.
Maybe it does not like the supercap that is mounted on the board.
I used this pre pre named Autographe 30 years ago with BIG batteries. I remember reading that Jean Hiraga told us to use a big power supply so i did.
If i would build it again i would try it with the little shunt supply circuit from Guido Tent. You can mount them right on the circuit.
Greetings, Eduard
It is probably noisy because usually the things that are connected to this kind of power supply dont care to much about noise.
Maybe it does not like the supercap that is mounted on the board.
I used this pre pre named Autographe 30 years ago with BIG batteries. I remember reading that Jean Hiraga told us to use a big power supply so i did.
If i would build it again i would try it with the little shunt supply circuit from Guido Tent. You can mount them right on the circuit.
Greetings, Eduard
Thanks. You look to have it wired correctly but I would say that such a circuit is never going to have much DC precision with regard to the operating point of the circuit, at least not without tightly regulated rails.
I powered it with batteries and DC offset is stable and spot on. Will try BIB to see if I can further improve it. It's been lying in a drawer for years so now is the time to do something with it. 🙂
OK.