Channel switching options ??

[Minion]

Hi , Im working on a 2 channel guitar amp build and am trying to figure out a good way to do the channel switching .....

I first considered using some sort of fet switching but Ive heard it can alter the sound so now I"m thinking relays ......

First question .....

Are relays suitable for audio channel switching ??

If so will it cause any poping noise when switching ??
If so is there a way to minimize it ??

I was going to use one of the Power amp power rails to power the relays and was wondering if it will cause noise though the power supply when engaging the relays ??

Thanx

[J M Fahey]

I first considered using some sort of fet switching but Ive heard it can alter the sound so now I"m thinking relays ......

We are talking guitar signals here, so a 0.5% distortion which will drive a Hi Fi nut dead won't affect you.

Are relays suitable for audio channel switching ??

Yes.

If so will it cause any poping noise when switching ??
If so is there a way to minimize it ??

Yes. Look at a Peavey or similar schematic to see how it's done but basically you put a backwards diode across the relay coil and choose carefully where you pull power from and where do you ground it.

I was going to use one of the Power amp power rails to power the relays and was wondering if it will cause noise though the power supply when engaging the relays ??

You will get 12 , 5, and 24V coils easily.
Personally I use 12V ones from an unregulated +15 to 18V which feeds the preamp, or 24V from the amp rails, in both cases adding a resistor in series to the adapt the relay to the rails I have, *and* add an extra electrolytic capacitor from the relay "hot" coil end to ground, to further separate it from the main rail.
My popping is almost inaudible.
The beauty of relays is that for prototype work you just glue them to the chassis or a free part of the PCB, "dead bug" style, meaning with the legs up, and add short pices of wire as needed.
It sure simplifies initial design, specially if it's an experiment.
Very important: it can also easily be re-routed, grounded somewhere else, etc., to test for lowest hum and popping.
If later on you will build a lot, design the proper PCB.

[Minion]

Hi < Thanx .... I was going to do a PCB for the Realy as I do PCB"s for allmost everything even with LED"s which I am also going to add to show which channel is being used....... I have (2x)24v AC(34vDC) available and two 6-8v AC rails that I"m not useing and a 320v DC rail that I"m useing for the tubes in the preamp and a 12v AC rail that I"m useing for the heaters but it is useless for anything other than heaters as it is elevated to 30v and not referanced to 0v .....

Maybe I"ll use the 6-8v AC rail and use 5v relays because they aren"t being used and they have 0.5a and 2a current capabilities ......

If is a 2 channel tube preamp with tone controlls and solidstate buffer on the output of the preamps and into a stereo TDA7293 poweramp  and an effects loop for my 15 band EQ .......

Thanx

[J M Fahey]

If is a 2 channel tube preamp with tone controlls and solidstate buffer on the output of the preamps and into a stereo TDA7293 poweramp  and an effects loop for my 15 band EQ .......

You can't go very wrong with a "Phatt" type amp 

[phatt]

If is a 2 channel tube preamp with tone controlls and solidstate buffer on the output of the preamps and into a stereo TDA7293 poweramp  and an effects loop for my 15 band EQ .......

You can't go very wrong with a "Phatt" type amp 

LOL,,,thanks, Mr Fahey you are so kind.
Yes I also thought it seemed a lot like some of my circuits but I do try not to bragg too much.

@Minion,
          I'll soon be posting my updated floor preamp circuit that might give you some ideas to work with. :tu:
Phil.

[Minion]

@Minion,
          I'll soon be posting my updated floor preamp circuit that might give you some ideas to work with.
Phil.

I look forward to it ..... I"ll eventually get around to posting a Zip file of PCB and Layout/Schematic for the Tube preamp , I don"t want to post the PCB images because it is from a PCB I bought on-line that I converted to a single sided version and changed some Values in .... I don"t know what the protocal is for basterdized versions of someone elses design ......

Thanx guys ....

[phatt]

@Minion,
          I'll soon be posting my updated floor preamp circuit that might give you some ideas to work with.
Phil.

I look forward to it ..... I"ll eventually get around to posting a Zip file of PCB and Layout/Schematic for the Tube preamp , I don"t want to post the PCB images because it is from a PCB I bought on-line that I converted to a single sided version and changed some Values in .... I don"t know what the protocal is for basterdized versions of someone elses design ......

Thanx guys ....

I doubt that would be a problem as you have changed it and redesigned it.
The issue is not so much circuits as most are prior knowledge anyway,,hard to claim copyright on diode clipping circuits and like stuff, LOL
BUT directly copying *Brandname stuff* and even worse using their brandname to make profit,,, ouch then you are in deep water.
Oh yes I have posted my circuit under hybrids;
http://www.ssguitar.com/index.php?topic=2226.0
Phil.

[Minion]

Well guys , I finnished designing and building my Relay board , after a coulpe false starts (I screwed up the PCB so I had to cut a couple traces and run jumpers) I got it working perfectly .... It makes no noise switching and the proper LED lights to indicate the channel selected ......

I got the PCB down to about 2.15in x 2.15in , but even then i had a hard time finding a place in the Chassis to mount it and ended up mounting it above the power amp ......

The Chassis is only 6in high , 6in deep and 16in long and it has 2 preamps (4 tubes) , the High voltage Power supply (200uF at 400V) the high Voltage transformer , a 10H choke , a 1A 12v Transformer for the heaters , a stereo TDA7293 with speaker protection and a 400Va Transformer , the Relay switching circuit and the solid state buffer .....
Needless to say it is a very cramped chassis , I also used aluminum plate to seperate the power transformers from the audio preamps to offer some protection from the EM from the transformers ...... I just have to hook up the Power amp now .....

I do have one problem though , Channel 1 sounds great and its totally noise and hum free , But Channel 2 which also sounds great , has quite a bit of hum , both channels are identical accept the one that hums has 22uF of local supply filtering and the one that hums has 22uF ...... Could this be causing it to hum ?? or be why the good channel doesn"t hum ??


Thanx

[J M Fahey]

Rather than filtering, I think you have a grounding problem.

[joecool85]

Minion, I'd love to see pics of the inside of this beast.  Please share!

[Minion]

I just realized I mis-spoke in my post .... Channel 1 has 47uF local filtering and channel 2 has 22uF ..... Both channels have the exact same grounding scheme but I suppose it could be just wires laying in the wrong place , I"ll work on that ....

I"ll post pics once it is done , or at least mostly done .....


Cheers

[joecool85]

I just realized I mis-spoke in my post .... Channel 1 has 47uF local filtering and channel 2 has 22uF ..... Both channels have the exact same grounding scheme but I suppose it could be just wires laying in the wrong place , I"ll work on that ....

I"ll post pics once it is done , or at least mostly done .....


Cheers

Doesn't hurt to add more filtering.  I'd start by swapping in a 47uF cap for the 22uF on channel 2.  I don't think it's your issue, but it will rule that out and it's a cheap fix if it is the issue.