Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Solid State => Topic started by: twelveax7 on February 12, 2014, 10:01:38 am

Title: Relay switching POP minimizing question
Post by: twelveax7 on February 12, 2014, 10:01:38 am

I have two separate tube channels i need to select between. They both share the first stage. Clean has 3 stages and Drive has 4 stages. The plan is to use two DPDT relays (Omron) to switch the input to both channels after the first shared stage. At the same time i'd like to switch the preamp output's master volumes directed towards the PI.  Has anyone tried this ? 

The output from MV's in my opinion should come from the MV into a resistor to the relay. Then the relay would be referenced to ground. When 'off' the relay would be shunting that MV to ground turning off that preamp channel. When switched the relay would open and release ground letting signal continue to PI. Other side of relay would be opposite at this time. Swapping between channels to be shunted to ground without popping is the goal. The idea of this was taken from TUT book but very vague when applied to an actual relay. I need to know resistor sizes to be used AND if i need to incorporate a capacitor also for stopping DC without affecting the output signal other than lowering the output signal a small amount which is not a problem.

I've read many accounts of using relays and other forms of switching but NO one seems to give enough info and specifics. Just trying not to waste time.
Channel pop cannot happen.  Any precise info on this is GREATLY appreciated.
Thanks.

Title: Re: Relay switching POP minimizing question
Post by: mat janssen on February 12, 2014, 10:18:41 am

I have done that many times. No problem at all. Put a diode over the relais coil, that dampes the high voltage jump.
The input and the output of the contacts must all have the same dc level. No capacitors must be charged or discharged during switching.
The best way is that all capacitors who are switched have no charge. If needed I can make a schematic diagram to explain.

Title: Re: Relay switching POP minimizing question
Post by: twelveax7 on February 12, 2014, 11:30:14 am

So taking the output as an example. Would this work?

MV ---> 330K ---> relay pin --->  (resistor ?) ---> PI ---> cap
                                             what value ? 

_______________________________________________________________________
 Relay  pin one is positive so looking at the relay boards for sale on here i get this:     
 Diode  with cathode on positive side of relay going to neg. side ?       

Title: Re: Relay switching POP minimizing question
Post by: mat janssen on February 12, 2014, 12:00:16 pm

Here is an example