Help with preamp build

[The Dude]

So, as I go back to my Tubes4hifi sp6 or VTA Sp6 with ph6 phono stage. As I wait for Roy to get back from vaca, I can't help to think how I can make this pre turn out right.

My first question what is a good volume potentiometer, I don't care for anything that clicks such as a 24 step attenuator, unless they don't actually click.

Second since my McIntosh has left and right gain controls I want to eliminate the balance pot, I don't know if I need to replace it with a resistor. But could use some help doing so.

Since it looks like its best to have the power switch separate from the volume pot. I would like to incorporate a led to let me know if the unit is on(since this will be in my Bozak cab and won't be able to see the tubes). I don't know if one of those rockers with the built in led is best.

Last for now, I will have a tape input and the tape out. So a sub question, do I need the monitor switch, and what does this do I have never used these features. But will be wanting to use my tape deck. Plus these two items are on my Dynaco PAT-4 pre amp so that is what I am basing it off of.

My goal for looks is the just 2 knobs(selector switch, and volume knob), with the power switch and tape switch if needed in the middle. Then of coarse the VTA SP6 logo on top.

[Guest David H]

For the volume pot, I would use an ALPS Blue.

No need to add a balance pot, or resistors, just use the volume pot.

Are you going to record on your tape? if not no need for tape out, however if you intend to record the tape out connects to the input of the volume pot I believe. It has been many years since I assembled one of these.

For the power switch I like to use a rotating switch so it matches the selector and volume, keeps the faceplate clean. You can always add a power led.

You may also consider adding a .001 600v cap across the power switch to minimise power on/off thump.

Dave

[The Dude]

Dave, thanks for your input

Is this what your are talking about for the ALPS Blue, I like how it comes with the circuit card for easy of hook up. I just hate ordering from China, may wait and see if Roy has any. I thought I have seen some of builds in the past with them, could be wrong.

http://www.ebay.com/itm/1pc-ALPS-potentiometer-100KAX2-and-1pc-gold-plated-potentiometer-PCB-/200857093712?pt=US_Amplifier_Parts_Components&hash=item2ec4040650

I don't plan on recording anything to tape just listening to tapes, I just noticed that all of Roys pres have the source/tape switch. But if I can eliminate it I will as I don't think I will need it.

I at first was looking for rotating volume/power switch but from what I have read that they aren't great to use. But maybe just a power switch as I to like the look a lot better. Do you have one you recommend. I will take your advice on the .001 600v cap across the power switch as I hate the on/off thump.

I have this crazy idea of making a glass face plate, kind of based off of my McIntosh power amp. Looks like I will need to make a light diffuser out of plexi glass. I just need to figure what kind of lights and how many. I have a buddy who can make me a vinyl decal I can put on the back of the glass then paint with a gloss back and peel off the decal so the light can shine through. I don't know how this will turn out but I am going to give it a try since I have some of the resources.

[Guest David H]

I lile the glass face plate idea, and that volume pot should do fine. I like the circuit board as well.

I have not had any issues ordering from China, in fact the custoemr service I have received from China is top notch. however I prefer to order from the U.S as well.

Dave

[The Dude]

I have only one crappy product from china which I never needed. Bit I just hate the wait, but I think one company gave a 7-15 day wait which isnt to bad. If I sell some tubes this week, I will get started on the glass face asap and will take pictures as well. I have the chassis built now, just waiting on the rest of parts.

[ZombieWoof]

You can use real glass & have the holes sand blasted out & then have a light sand blast across tyhe back side of the whole panel & that would defuse the glass quite nicely , most glass shops can cut holes & frost the glass as well . plexi can hold a slight electrical charge IIRC

[The Dude]

You can use real glass & have the holes sand blasted out & then have a light sand blast across tyhe back side of the whole panel & that would defuse the glass quite nicely , most glass shops can cut holes & frost the glass as well . plexi can hold a slight electrical charge IIRC

I am trying to take in this idea, not through it out, but more or less understand. As I am all ways looking for options.

But from little searching I have done, is based on the McIntosh MC2505. Which from what I can tell they use a stencil of some sort for the lettering, then paint the black. Then they use a piece of plexi about 3/32ns with white paint were the lettering is on the glass it self, in between the glass and the lights to difuse the light properly through out the lettering. I know I would have to drill out the hole for the selector, volume, and on and off switch. But have seen some videos on youtube where they just use a diamond bit and and water. I don't know if the Mc's are tempered but if they are I would think it would have to be done after the drilling before the painting.

Oh wait I just read your post several times and are you saying instead of using plexi glass for the difuser use real glass with the method you speak of. Dammit I am slow at times. If that is the case disregard my last paragraph.

[ZombieWoof]

yeah real glass , a good glass shop can do writing in frost & the darken as well,

they use this in Lawyer offices on the glass doors

they cut the holes as well for the handles on doors too

[The Dude]

Does anyone know if the diffuser and faceplate are sandwiched together or is there a gap between the two. I can't find any good pick on line but it does look like the lights are flush with the chassis or maybe protrude out a bit, I have a couple of ideas to mount them but looks like it will be trial and error.

[The Dude]

Here's the start of the chassis work, its nothing great. I had a old battery charger at work I hacked up with the plasma cutter. I just have the rca jacks in.

[The Dude]

another before I add the ground wire.

[The Dude]

Its alive, and it testing stage. I have taken some pics, I am not where I want to be with the face plate but it has came a long ways. I still need to figure out how to wire in some leds, and find a rotary power switch I like, and some metal trim. But as long as everything goes fine tonight I will be rolling the phono section tubes I have, since the ones I am using are cheepos. I was getting a hum in the left channel, pulled the output board and re-soldereda some iffy joints and so far so good, I have a slight buzzing sound from both speakers that seems to get louder when turning up the volume pot, but not loud enough when music is playing, just when the source is off and volume is turned way up. I will look at that down the road, unless anyone has any ideas now, but I think its having some power wires close by, I will once I get everything cleaned up and cables/power wires ran properly. But for now back to Randy Rhoads tribute.