Help please to join 2 pre-amp channels into one

[hamfist]

Fdesalvo, sounds like a very cool build and ....Yup, definately relays are the way to go.

I've finally now succesfully got enough DC from my centre-tapped AC heater supply to power relays (I have actually only needed one DPDT relay to switch inputs and outputs of my two pre-amps to switch channels).
The circuit I've used, which works, is the voltage tripler one originally thought of by Steve Conner, adapted by Vaughan (shown below).

I've used slightly different cap values to those shown, but I don't think they are critical.
I'm getting 11.5V DC, ready to power a 5V positive voltage regulator (LM7805), putting out a steady 5V to power the relay when the latching footswitch allows the current to ground.
I'm at the stage where I've tested the relay switching, using the footswitch, with a 5V DC Wall wart, and it all works great. I've also got the right input voltage for the regulator. I'm expecting the correct regulators to arrive in the mail tommorow. I was actually struggling with the wrong regulators for a while.
When the correct regulators arrive, it should be a simple job to solder it in and I'm expecting it to all work like a dream (truly hoping !).

If I can get this thing working then anyone can, I'm sure. I'm generally quite a doofus, although am learning fast.
When it's all up and running to my satisfaction I'll post pics, and try to draw schematics of what I've done for others like yourself to base their own circuits on.
I can't tell you how gutted I was when the postman did not deliver the regulators today. I'll be snatching them out of his hands tommorow !

[fdesalvo]

Sweet!

[HTH]

I can't tell you how gutted I was when the postman did not deliver the regulators today. I'll be snatching them out of his hands tommorow !

who did you order from?

'Rapid' live up to their name and are VERY fast - I ordered a box of 16/0.2 wire yesterday evening and have it here this moring before 12pm (free delivery too).

It's a pity they don't stock the caps and resistors I use otherwise I'd use them for everything.

[hamfist]

who did you order from?

'Rapid' live up to their name and are VERY fast - I ordered a box of 16/0.2 wire yesterday evening and have it here this moring before 12pm (free delivery too).

It's a pity they don't stock the caps and resistors I use otherwise I'd use them for everything.

Are we talking "Rapidonline" here ? they always seem to have a minimum delivery charge of £5 when I use them. I wasn't going to put up with that for 76p's worth of parts.

[hamfist]

THe correct voltage regulators arrived in the mail today. Soldered straight in (I had the circuit all ready to accept it).

INput voltage of 11.5V, output voltage was pretty much bang on 5V.

Channel switching is superb using this circuit. Quiet, smooth, no pops at all.

I ended up using the circuit below,
My cap values were :-
C101 - 1500uF
C102 - 1500uF
C103 - 2200uF
C104 - 10uF

All diodes were IN4004.

My only other alteration was that I permanently grounded caps C103 and C104. In the circuit shown those caps are only grounded when the switch is closed. I have them grounded (and therefore charged) at all times.
I also have not used an LED.

[HTH]

hey Hammy,

what relays did you use? - got a link and part# ???

[hamfist]

hey Hammy,

what relays did you use? - got a link and part# ???

I got a couple of them from ebay (I think).

Manufactured by "Ry", part number RS-5. They are pretty standard 5V (1A at 125VAC, 2A at 24VDC) DPDT PCB relays.
I just superglued and siliconed the relay upside down onto the chassis to secure it, exposing the relay's pins, and soldered directly to the pins on the relay.
The pins are relatively fragile, so I secured all the heavier (ie. shielded) leads pretty close to the relay.
Despite my inexperience, I found it to be a piece of cake !

[hamfist]

OK, here's a schematic of the exact circuit I ended up using. it works a treat !

[HTH]

The pins are relatively fragile, so I secured all the heavier (ie. shielded) leads pretty close to the relay.

You could mount the relay to some vero/perfboard then solder the wires to the board - more secure connection if the relay pins are a bit flimsy.

You've inspired me with this thread - I've dug out some 12v relays I've had lying around for ages and am gonna have them setup to channel switch and maybe switch in an extra gain stage for a boost.

[hamfist]

You could mount the relay to some vero/perfboard then solder the wires to the board - more secure connection if the relay pins are a bit flimsy.

You've inspired me with this thread - I've dug out some 12v relays I've had lying around for ages and am gonna have them setup to channel switch and maybe switch in an extra gain stage for a boost.

I couple of guys suggested a similar board-type assembly (in this thread - http://music-electronics-forum.com/s...ad.php?t=10694).

I'm pretty happy, in the end, with the way I've done it (although it's not pretty !!). All the heavier leads are now secured very firmly, very close to the relay. So there's pretty much no chance of damage to the joints or relay pins through fatigue.

I'm glad you feel inspired. I'm certainly thinking of some way I can make use of a relay in my other amp !

Even though you have 12V relays already, it might be an idea to consider lower voltage ones, as powering the 12V ones could prove to be slightly more problematic.
5 or 6V ones seem to work really well, and are easily powered from the heater filament supply.

One think I'd like to know is how to work out if a PT can cope with extra current from it's LT secondary.
With the build I've just done, the PT was designed to power heaters for ten pre-amp tubes, whereas I was only using 6. So I was very confident that the PT had enough "spare" to power my relay.

However, my other amp is running the full complement of tubes it was designed for. Any ideas about how to work out if it's safe to take a bit more current from the heater filament supply ?