Need some help

0 Members and 1 Guest are viewing this topic. Read 2371 times.

Tubes 4 Ever

  • Full Member
  • Posts: 429
Need some help
« on: 29 Jan 2008, 04:32 pm »
Hope I am in the correct circle. I need some info for a novice DIY guy, that be me. Can a simpleton like, me, install a volume pot on an amplifier. I have been considering buying a passive unit but hate to add another box and add the multiple connections in the path. So if someone could let me know how and where I thought I would give it go. If you think a average joe could do it. Thanks gang.  :thumb:

Folsom

Re: Need some help
« Reply #1 on: 29 Jan 2008, 06:01 pm »
Well first off is there room? I am sure it would not be very hard at all if there is room.

Tubes 4 Ever

  • Full Member
  • Posts: 429
Re: Need some help
« Reply #2 on: 29 Jan 2008, 06:20 pm »
plenty of space

Folsom

Re: Need some help
« Reply #3 on: 29 Jan 2008, 06:35 pm »
Okay well the things you have to do...

You have to run wires from the RCA's to the volume pot/stepped. Then from there you just run some to the place the RCA's originally connected too.

Can you take pictures inside of the amplifier?

You will have to drill a hole and then make a notch or another small hole. What type of pot are you going to use? The Alps Blue velvet are simple and have no need for a resistor added to make a fake logarithmic function.

What type of RCA's are on it, are they ones mounted to PCB or do they have wires soldered to them? It might be worth replacing them if they are soldered to the PCB. It will make the job easier.

If you want to get real fancy you can even mount the pot in back near everything to reduce signal wire running, but that is definitely more complicated, even though you can buy kits for it.

Tubes 4 Ever

  • Full Member
  • Posts: 429
Re: Need some help
« Reply #4 on: 29 Jan 2008, 09:25 pm »
No problem on the drilling and such. It has RCA's connected via wiring. It sounds pretty straight forward. Any recomendations on pots

Folsom

Re: Need some help
« Reply #5 on: 30 Jan 2008, 04:43 am »
What kind of amplifier?

http://www.partsconnexion.com/catalog/controlsswitches.html

Click on the Pots button below.

The 10k and 100k Alps Blue Velvet are very nice for the money. Now it depends on what one you want. I find the 10k is best for amplifiers with 20wRMS+ and not extremely efficient speakers. I would go for the 100k if I had very efficient, SET type stuff.

Do you need wiring diagrams? I will tell you not it DOES not work by just connecting the positive from RCA's, and then the positives to the boards. You have to have a common, drain, as well, or it will not work. I can draw a schematic up if you need one. The basic idea is you are letting it ground out to the common, back to the source, but the more you turn the knob the more you are letting pass through the amplifier to go back to the common, to the source, but through the amplifier, which causes amplification on that signal, and then is ran through the speakers.

If your stuff has lead free solder in it you need to get some stuff to deal with that, or add solder to everything you work on. Do not make mistakes I did (even if it is on simpler stuff). Also standard RCA's are by far the suck in my opinion for getting really good non-cold solder joints, I prefer Cardas because the plastic inside never melts, however you have to attach the ground with the RCA separate from the chassis or you will never get anything but a cold solder joint (their spot for ground is frankly too large, it needs a loop or something).

What type of soldering iron do you have? Do not use a solder gun. If there is any silver coating you will need silver solder. If you have to run the signal lines to the front consider some wiring like MIC cable or something that has a little bit of shielding on it, if it passes by much stuff (close too) (even Coaxial will work).

I like to use rubber dinosaurs and things for volume knobs :) The expensive ones they sell on any website are nice but they cost a fortune. Plus if you do use an animal you can name them. "Give Teddy a turn"

2wo

Re: Need some help
« Reply #6 on: 30 Jan 2008, 04:49 am »
Judging by your moniker 8), it's a tube amp. get a 100K pot...John

Tubes 4 Ever

  • Full Member
  • Posts: 429
Re: Need some help
« Reply #7 on: 30 Jan 2008, 10:44 am »
 aa you bet

2wo

Re: Need some help
« Reply #8 on: 30 Jan 2008, 05:54 pm »
What Amp are you using?

When you order your pot, order a few small 1meg resistors as well. metal film would be fine or if you have a favorite get them. They wont have to pass any real current so 1/4 or 1/8 will be fine...John

Tubes 4 Ever

  • Full Member
  • Posts: 429
Re: Need some help
« Reply #9 on: 30 Jan 2008, 07:27 pm »
Music Reference EM7. Roger would probably do it but I am a tight wad and want to save some bucks.

2wo

Re: Need some help
« Reply #10 on: 31 Jan 2008, 02:55 am »
OK, 6EM7 right?  I haven’t seen the schematic but I can take a good guess.

There will be a resistor, either on the RCA jack or the tube pin #4 to ground. Looking at the bottom of the socket, start from the gap and count clockwise. This resistor will probably be in the 100K to 470k  range and is the grid resistor . Clip it or replace it with one of the 1meg resistors. The pot will replace this resistor. The 1 meg resistor is only there in case the pot goes bad and is sort of a belt and spenders approach. With a low power amp you can leave it out.

Now mount your pot, looking from the back the wire that goes to the center of the RCA jack now goes to the center term of the pot. The left term goes to the center or the RCA.
The right term goes to ground, the outer part of the RCA jack. Good luck…John