Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Solid State => Topic started by: kagliostro on March 13, 2011, 12:06:11 pm

Title: LDR use instead of relays and/or pot in Tube amps - need infos
Post by: kagliostro on March 13, 2011, 12:06:11 pm: I'm interested to discover LDR possibilities of use in a tube guitar amp

In this page I've read the author used an Home Made optic substitute for relays

Quote
http://home.arcor.de/guido.boehne/Boogie%20new.htm

the page is in german but you can translate with google translator

The channel switching is no longer as in the first version with relay, but with optical switches. These switches consist of a LDR (Light Dependent Resistor) of type A1060 and a super bright yellow LED, which are wrapped in black shrink tubing. The LDR has a resistance in total darkness of> 20MOhm. If it is illuminated by a light source with a wavelength of about 600nm, decreases its resistance decreases to about 400 ohms. This process happens smoothly without jumps in a few split seconds, thus preventing an unwanted Umschaltknacken.

I've find this LDR

http://it.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0596141

can it be used that way ?

Also in Merlin's book there is a description to use an LDR and a led in some position of the amp, instead of conventional potentiometers, because with an LDR you don't get scratch noise

Do you know other available use of LDR in guitar tube amps ?

which models are easy to be find to build Homemade Units (LDR + Led)

there are commercial products for this purpose (optic unit builds) ?

Thanks

Kagliostro
Title: Re: LDR use instead of relays and/or pot in Tube amps - need infos
Post by: sluckey on March 13, 2011, 12:19:27 pm: You may get a euphoric feeling from rolling your own but there are lot's of readily available opto devices. The vactec VTL5C1 (http://www.hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=Lamps&ORDER_ID=!ORDERID!) opto switch is used in a lot in guitar amps...
(http://www.hoffmanamps.com/MyStore/catalog/images/IMG_2317_small.jpg)

EDIT... Here's one I rolled a few years ago using RadioShack parts.
Title: Re: LDR use instead of relays and/or pot in Tube amps - need infos
Post by: tubeswell on March 13, 2011, 12:53:36 pm: Quote from: kagliostro on March 13, 2011, 12:06:11 pm
there are commercial products for this purpose (optic unit builds) ?

The SLO100 uses optocouplers (instead of relays) for channel switching. (Is that what you were asking?)
Title: Re: LDR use instead of relays and/or pot in Tube amps - need infos
Post by: Fresh_Start on March 13, 2011, 06:28:01 pm: If you want to learn more, there were several long discussions on the subject of LDRs for switching purposes on the AX84 forum a few months ago.

Chip
Title: Re: LDR use instead of relays and/or pot in Tube amps - need infos
Post by: kagliostro on March 14, 2011, 03:48:28 pm: Many Many Thanks Sluckey - Tubeswell - Fresh_Start

for the given info

Kagliostro
Title: Re: LDR use instead of relays and/or pot in Tube amps - need infos
Post by: jerrydyer on March 15, 2011, 11:06:26 am: I love em. I use them in mine I also had a guy build me a board like the one on the Mojotone site. I can put togther a cheap kit if you want to play around with them. the vactrols arent cheap though. It takes to to make one SPST switch.