Pics of my HRM Funk Build

[odourboy]

Yes - it's a 100k trimmer. Isn't the pre-OD network R supposed to total ~230K? (ignoring the 470/47p)

You are correct (200K + 22K trimmer + 4.7K tail = 226.7K ~230K). Not sure why Scott would suggest otherwise.

Your build looks very nice indeed, congratulations.

Gil

Spoke to Scott. He was just trying to verify that I did indeed use a 100K trimmer (rather than the typical 22K, in which case i would have had a error)

[ayan]

Yes - it's a 100k trimmer. Isn't the pre-OD network R supposed to total ~230K? (ignoring the 470/47p)

You are correct (200K + 22K trimmer + 4.7K tail = 226.7K ~230K). Not sure why Scott would suggest otherwise.

Your build looks very nice indeed, congratulations.

Gil

Spoke to Scott. He was just trying to verify that I did indeed use a 100K trimmer (rather than the typical 22K, in which case i would have had a error)

Blame it on "NJ English" then. Since Scott mentioned the 120K resistor last an said it "should be a 100K one" I thought he was talking about the 120K resistor, and not the trimmer.

Gil

[dogears]

LOL! Sorry guys!

[Aharon]

Nice job!!.
Listen,I see that everybody is going with a regulated relay power supply now,was the old way using a resistor causing trouble?.
I'm also using the Omron G5V-2-H1-DC5 relays and I was going to use a resistor(56R) like before......
Should I make another PS board for the relays and use a regulator?.
Does anybody have the layout for the new PCB?.
Thanks a lot guys....basically my D'Lite is stuck right there now.
Aharon

A regulator just makes sense here, since it maintains a steady voltage under varying load current. Perfect for this application, and cheap and easy to implement.

Thanks for the answer......
Does anybody have a schematic of the new PS?
Thanks again for the help.
Aharon

[odourboy]

When you say the new PS - are you referring specifically to the relay supply?

This thread here in the files has a schematic that I used as the basis for mine:

http://ampgarage.com/forum/viewtopic.php?t=3344

[Aharon]

Thanks a million Odourboy....I think I can make a PS from that (yes,I was refering to the relay power supply).
I'm going to abuse your generosity by asking one more question,I'm using the same Omron 5V relays,just two of them,OD and PAB........what voltage regulator did you use,5V or higher?
Thanks
Aharon

[tele_player]

That relay PS is better than some I've seen, but it could be improved. Using a 12V transformer and 12V regulator, it doesn't have much margin for variation in line voltage (brownout), and 12V isn't really the correct voltage to use with 12V relays with an LED in series, though it will work.

A more correct design would maintain regulated DC voltage when input voltage drops 10-15%, and the regulated voltage would be chosen taking the voltage drop of a series LED into account.

An 8V regulator, and 5V low-current relays makes more sense to me.

Fortunately, it appears the relays are pretty tolerant.

[heisthl]

I've had really good luck not using a regulator for 12V relays, just bridge rectify the 12vac and stick a 1000uf cap on the output. This lets you run several relays with LED indicators and you don't have to worry about going below the 7812's input requirements. I've never had a problem with noise using this arrangement and I haven't had to isolate the grounding.

[tele_player]

I was just talking about correct design. Lots of 'not quite correct' stuff works, too.

[odourboy]

Let me point out that I believe that by putting a 12VAC transformer output through a full wave bridge rectifier results in about 17V DC (1.4X). Lots of margin for a 12V regulator.

Another trick I've seen though I've never tried it is to offset the regulator's reference voltage to accommodate the diode drop by putting a similar diode under the common. So if there's say, a 1.5V drop across the diode, then the 5 V regulator would put out 6.5. If I have this right, there's the issue of making sure you don't use the chassis as your heatsink 'cuz you'd need to keep the tab isolated.

[ayan]

That relay PS is better than some I've seen, but it could be improved. Using a 12V transformer and 12V regulator, it doesn't have much margin for variation in line voltage (brownout), and 12V isn't really the correct voltage to use with 12V relays with an LED in series, though it will work.

A more correct design would maintain regulated DC voltage when input voltage drops 10-15%, and the regulated voltage would be chosen taking the voltage drop of a series LED into account.

An 8V regulator, and 5V low-current relays makes more sense to me.

Fortunately, it appears the relays are pretty tolerant.

I disagree because:

1. Rectified 12 VAC gives you about 17 VDC. Your AC can safely go down by about 25% before your rectified DC approaches the point where the volatge regulator will start to frown.

2. The LEDs are NOT in series with the relays. They are in parallel with them, being fed by 1K dropping resistors each.

Cheers,

Gil

[odourboy]

2. The LEDs are NOT in series with the relays. They are in parallel with them, being fed by 1K dropping resistors each.

In fairness, the schematic I referred him to has the diodes configured in series.

[tele_player]

That relay PS is better than some I've seen, but it could be improved. Using a 12V transformer and 12V regulator, it doesn't have much margin for variation in line voltage (brownout), and 12V isn't really the correct voltage to use with 12V relays with an LED in series, though it will work.

A more correct design would maintain regulated DC voltage when input voltage drops 10-15%, and the regulated voltage would be chosen taking the voltage drop of a series LED into account.

An 8V regulator, and 5V low-current relays makes more sense to me.

Fortunately, it appears the relays are pretty tolerant.

I disagree because:

1. Rectified 12 VAC gives you about 17 VDC. Your AC can safely go down by about 25% before your rectified DC approaches the point where the volatge regulator will start to frown.

2. The LEDs are NOT in series with the relays. They are in parallel with them, being fed by 1K dropping resistors each.

Cheers,

Gil

You're ignoring the voltage drops in two diodes. The filtered DC output of a bridge rectifier is approximately the peak input voltage, minus about 1.4.
So, 12 x 1.414 = 16.97. Minus 1.4 = 15.57.

The dropout voltage for LM7812 is 2V (per the Fairchild datasheet). So, anything under about 11vac, an 8% drop, will cause regulation to fail.

Some schematics I've seen use series LEDs, some parallel. Yes, in this case, the circuit would be more tolerant of brownout using parallel LEDs.

[ayan]

[quote="tele_playerYou're ignoring the voltage drops in two diodes. The filtered DC output of a bridge rectifier is approximately the peak input voltage, minus about 1.4.
So, 12 x 1.414 = 16.97. Minus 1.4 = 15.57.

The dropout voltage for LM7812 is 2V (per the Fairchild datasheet). So, anything under about 11vac, an 8% drop, will cause regulation to fail.

Some schematics I've seen use series LEDs, some parallel. Yes, in this case, the circuit would be more tolerant of brownout using parallel LEDs.[/quote]

Right you are on the voltage drops, crow for me for dinner. Now, you can feed 12VDC to a voltage regulator and you will get out... 12 VDC under relay load. You may want to try this!

LEDs in series with the relay are a no no, unless one is tapping off the filament supply and needs to knock down the rectified voltage a few volts to use with a 6 V relay.

Cheers,

Gil

[tele_player]

You might get 12V out of a 12V regulator with 12V in, you might not. It's certainly not guaranteed under varying load, that's what the dropout voltage is about.

Only thing I can see that's a no no about a series LED is if it fails open, that would incapacitate the relay. I think they're pretty sturdy, though.

OK, enough about this