Omitting the relay?

[krilli]

Hi,

I'm building an Amp4 that may see some ghettoblaster duty at 12V. The assembly docs say that the relay won't close at under 17V, so I'll have to jumper the relay I think.

If this is the relay:


____________
||
|____________|->ampoutputs,edgeofboard
||||
ABCD


... can you confirm my understanding?: If I jumper from from C to D, the output circuit is closed, I get sound at the outputs, and the amp works normally.

And -- Do I need to omit any relay driver transistors? I was planning on having them sit there on the board, to be able to drop the relay in later, if wanted.

ps. Here's relay datasheet: http://ecommas.tycoelectronics.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Data+Sheet%7FRT 2%7FFE1%7Fpdf%7FEnglish%7FENG_DS_RT2_FE1.pdf

[PedalPower]

I don't have the PCB to hand, but if B connects to nothing, then that is correct. Alternatively, check with a meter: there should be no resistance between B and either C or D with the relay open.

The relay is likely to remain closed if it is given more than 16V or so to make it close - but I guess that doesn't help you.

You can leave the transistors behind; they'll sit there doing very little.

Of course you could try to find the equivalent relay with a lower coil voltage, and use the capacitor technique I wrote about to make it work over the full range. Or you could make a charge pump circuit to generate a higher voltage for the relay; in fact you should be able to combine the two ideas to give the relay a pulse of about double the supply voltage to switch it on when it needs to close.

In case you haven't spotted it, check the assembly instructions about disabling the voltage sensing on the 2000 chip or it will be muted at 12V. This will then make driving the relay more complicated if you choose to follow the ideas I talk about above, because it'll try to switch on at a lower voltage. Hmmm... not so simple after all!

[krilli]

Thanks for the reply! And yes, for interested parties' future reference, I disabled the voltage sensing - thanks for the reminder!. IIRC I omitted R54 and R52 had a low value.

Can it be that B actually connects to ground? That way the relay doesn't present the chip with the harmful situation of driving the output filter only (as in running the amp with no load connected). B looks like it's ground.

[Scratchy]

krilli, you never cease to mystify me.
You are doing things the hard way for no apparent reason [?][?][?]

- building a regulated 5VDC PS to replace the built-in onboard supply?
- running an amp way under-voltage?

To what advantage?
Perhaps you could explain what benefits you hope to gain from these unorthodox building methods?

***It's so easy, everyone should be doing it***

[krilli]

quote:Originally posted by Scratchy

krilli, you never cease to mystify me.
You are doing things the hard way for no apparent reason [?][?][?]

That's what my boss always says

quote:Originally posted by Scratchy

- building a regulated 5VDC PS to replace the built-in onboard supply?
- running an amp way under-voltage?

The external-5VDC guy wasn't me! Promise. Wasn't it wadoka or someone? Cool project though

I'll be running this amp at 24V most of the time, for sure. I'm just taking the opportunity to at least let the amp play at 12V when needed. It will serve as a hi-fi camping-amp - 12V are pretty easy to scrounge up in the field ...

[PedalPower]

No, B (assuming that's the normally-closed contact) is not connected to anything. No harm will come to the amplifier if it has no load; shorting its outputs to ground, on the other hand, leaves only the overcurrent protection to save the high-side FETs. (Valve amplifiers with transformer outputs don't like their loads being removed.)

I haven't heard about this external supply thing. If I can be bothered, though, I'll disable the LM317 9V pre-regulator and use the 12V line I've got, which is being generated with a switch-mode regulator so more efficient.

[krilli]

quote:Originally posted by PedalPower

No, B (assuming that's the normally-closed contact) is not connected to anything.

You're absolutely right, of course. I had a proper look at the PCB it's clear as day now - it must have been too much solder fumes the other day.

[krilli]

Confirmed - jumper from C to D and the amp is very happy at 12V. By god these things sound good.

[Scratchy]

quote:Originally posted by krilli

The external-5VDC guy wasn't me! Promise. Wasn't it wadoka or someone? Cool project though

I'll be running this amp at 24V most of the time, for sure. I'm just taking the opportunity to at least let the amp play at 12V when needed. It will serve as a hi-fi camping-amp - 12V are pretty easy to scrounge up in the field ...

My bad about the 5V supply [B)]
As for the CAMP AMP (great idea), why not go AMP9?
It will operate on both 12 & 24V.

Some camp amp ideas:
Hollow out some firewood and mount some speakers on the end.
Mount the speakers in a small plastic insulated cooler.
Mount the amp in a mess kit.
http://www.surplusandadventure.com/s...um-301750.html




***It's so easy, everyone should be doing it***

[krilli]

THAT MESS KIT IS PERFECT, thank you for that sir! French military, too Amazing

Re. Amp4 / Amp9, I considered it but don't remember now exactly why I took the Amp4 this time. Probably curiosity about how it sounded.