I'd buy a kit/pcb, but id also be interested to see and learn from the schematic!
30% off all Honey Amp kits, check it out at https://store.ssguitar.com !
This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.
Show posts MenuQuote from: Loudthud on April 18, 2018, 12:15:48 AMQuote from: HamSandwich on April 16, 2018, 06:40:06 PM
Hmm I don't quite get this one. The transformer is in the AC wall mount adapter, which is a 2 prong device. It's a class II power supply, so rather than have an earth connection for safety, it has double or reinforced insulation between the mains and the secondary. This is going to be an issue?
Without some kind of ground, there will be a leakage current on the secondary. Inside the transformer there is capacitance between primary and secondary. You can't shield it because there is nothing to connect the shield to. The capacitive coupling will most often be towards one end of the primary. If you can reverse the phase of the primary, one phase will give lower leakage current. A safety ground just gives something to short the leakage current to. Without the safety ground, you will have hum and may feel a little tingle when you touch your guitar and something that is grounded like a microphone.
I don't know what country you are in. For USA or Canada you can get wall transformers up to 50VA with a ground from MG Electronics (Google them). I've also seen switchers up to 48V with a ground and universal input 100VAC to 250VAC without a switch.
Quote from: Loudthud on April 16, 2018, 02:11:48 AM
The power supply you linked does not have enough filter capacitance to deliver 1 Amp. Those 100uF caps just past the diodes need to be increased to 1000uF or 2200uF. The 15VAC 2.5A wall-wart transformer will be enough if you limit the load to 8 Ohms or higher. These type transformers may run a little warm and they usually have some kind of internal fuse or circuit breaker. When they die, you have to buy another one.
Quote from: Loudthud on April 16, 2018, 02:11:48 AM
Special Note: The transformer you use should have a safety ground on the Mains side or the amp will have a Hum that you won't be able to get rid of. Connect the safety ground to your circuit ground at the power supply.
Quote from: Loudthud on April 16, 2018, 02:11:48 AM
Technically, the power supply is a Voltage Doubler. While some people here might poo-poo the Voltage Doubler, they actually work pretty well. What won't work is running the LM1875 from the +/- 15V regulated outputs. The power amp chip needs to run right from the filter caps. Call those points the +/- 20V outputs. The regulator chips won't be able to maintain 15V on the outputs. It's better to just run the preamp from unregulated power. Just use a decoupling network of something like 470 Ohms 1W and 470uF cap on each rail and that should be enough. Checkout some of the Marshall Lead 12 schematics, that's how they do it.