AC power question (TR-9090)

[miminashi]

I've been sitting on a TR-9090 kit for over a decade, and I'd like to finally start assembling it.

For the power supply, there is the option of using an internal mains transformer (in my case, to go from 120VAC to 15VAC) or an external AC-AC adapter. Depending on what kind of case I end up with I might eventually use an internal transformer, but for now I plan on using an external adapter.

My question relates to this passage in the construction guide:

The standard method of connecting a mains adapter to the 9090 would be using a low voltage barrel-type connector, often referred to as ‘DC power’ connectors. They are available in a small number of sizes; 2.1 or 2.5mm internal pin diameter connectors would be ideal here. Your AC adapter may already have a suitable plug attached, so you will require a matching socket for that. The socket is then wired to pins 2 and 4 on connector J8. If your socket has a metal body mounted against a metal chassis, then it is essential that J8, pin 2 (0V) is connected to the outer shroud (outer contact) of the socket. Otherwise excessive hum or even damage could result.

This is the wiring diagram forJ8:

9090_ac_power_input.png (5.61 KiB) Viewed 101 times

My AC adapter has a two-prong plug and provides two outputs. Am I wrong in thinking that there is no 0V connection? Does it matter how the two outputs are connected to J8? AC power is a real mystery to me.

Thanks a billion.

[amonti]

I take it you've perused this 2016 thread:
viewtopic.php?f=17&t=118599

Williamcliffe wrote: Connect pins 2 & 4 on J8 to the barrel connector, but make sure the outer ring (or the pin connected to chassis ground) is connected to pin 2...

[miminashi]

Thanks for pointing out that post. I had seen it but I was still had some lingering doubts. But if I'm understanding correctly now, the two outputs from the adapter are different AC phases, and either one can be connected to 0V/chassis ground? Hehe, I suppose that's about the only way to interpret the build guide, but I wanted to be sure.

Thanks again.

[amonti]

The nomenclature seemed odd to me as well - I initially thought 0V referred to running a ground to the chassis to avoid hum (some AC/AC adapters pass through a ground on a separate pin), but the way williamcliffe built 3 units appears as you described, plus Gino's picture confirms that configuration (although there's no follow-up, I'd assume it worked as described).

[EATyourGUITAR]

I've been sitting on a TR-9090 kit for over a decade, and I'd like to finally start assembling it.

For the power supply, there is the option of using an internal mains transformer (in my case, to go from 120VAC to 15VAC) or an external AC-AC adapter. Depending on what kind of case I end up with I might eventually use an internal transformer, but for now I plan on using an external adapter.

I think you made a mistake. if you want +15v DC, 0v DC, -15v DC after the rectifier after the regulators then you need to start with 26VAC or 28VAC depending on cap size and how much heat you care about. that curly line ~15v means VAC. with the center tap that means 15v AC, 0v, 15v AC(phase 180). the total VAC is like 30 or 28. the bigger you go, the more heat you will have in the 15v DC regulators. MFOS says 25.6VAC for +/-15v DC. see 25.6*(square root of 2)= 36V peak to peak. read what he said about 18v peak dc for a 15v DC regulator. this assumes perfect huge caps before the regulators. which is exactly why I think 28VAC or 30 VAC would be better with smaller caps in a small case.

http://musicfromouterspace.com/analogsy ... LY2009.php

the build docs should have information on how to regulate +15v DC down to +5v DC with a 7805 regulators or something else that provides 5v DC. make sure you have air flow, heatsinks, cooling where needed. I don't know how much current your device uses.

[miminashi]

I'm not quite sure how the MFOS power supply factors in, I'm not looking to re-engineer the TR-9090 power section.

The TR-9090 build docs calls for 15VAC, and all of the DC conversion is handled (correctly, it would seem?) by the power section. Feel free to peruse the guide if you are curious: http://www.9090project.co.uk/download/9 ... 161102.pdf

[amonti]

Eatyourguitar is 100% right, but in the other thread, Altitude909 points out that you can run a 1/2 wave setup no problem - amongst the various talk of employing regulators (which is what I think started the thread). As you point out, all the components are already on board to support the 15VAC wall wart, so there wasn’t much of an advantage AFAIK.

[miminashi]

Ah, interesting. Thanks to you both for the info

[EATyourGUITAR]

I'm not quite sure how the MFOS power supply factors in, I'm not looking to re-engineer the TR-9090 power section.

The TR-9090 build docs calls for 15VAC, and all of the DC conversion is handled (correctly, it would seem?) by the power section. Feel free to peruse the guide if you are curious: http://www.9090project.co.uk/download/9 ... 161102.pdf

no I'm not trying to reengineer it either

Internal mains transformerIf you chose to use a mains transformer, then it should have a centre-tapped, or twin secondary. With the centre tap, or common, of the secondaryconnected to J8 pin 2, the secondary winding end wires are connected to J8 pins 1 and 4. In this configuration each side will draw approximately 200mA. For various reasons I suggest overrating by a factor of about 2, so a transformer of rating 15V – 0 –15V @ 500mA,or 15 – 0, 15 – 0 @ 15VA total should be used at minimum.

this specifically states that each tap is 15VAC. you have two taps on a center tap transformer. the directions state that you should only use a center tap type if you are using an internal transformer. 15VAC + 15VAC = 30VAC center tapped transformer with 15 VA (volt amps). this is derived from 500mA*30VAC (0.5A*30VAC).

this is the link to buy the correct part for 30VAC 15VA. this is the perfect size rated for 500mA per rail. you won't find a smaller transformer with metal chassis mount. this is it. hammond manufacturing and triad magnetics are the two popular brands you can find in the united states.

https://www.mouser.com/ProductDetail/Ha ... 0sjg%3D%3D

[miminashi]

Thanks, I'll keep that in mind if I opt for a mains transformer down the road.