...because it's what's on the inside that counts.

[Robin]

ARC's Multi-Channel ~ Deep Inside...

The ARC Multi-chnnel inside looks like a computer with pull-out bays and everything...

 

[Dreamer]

OK. And now for something completely different...

The guts to my "Ghetto Passive Preamp"...

ALPS 100k stereo pot, ALPS 2-pole 6-throw selector switch, 6-9's stranded 22ga copper wire, soldered with jewelers-grade Silver Solder. RCA jacks, knobs and project box from RatShack. Front panel and side panels are wood. Front panel label is a laser printout, that is glued and laminated.

Don't laugh until you've heard it...

--Richard

 

[Robin]

Their is Nothing There?

OK. And now for something completely different...

The guts to my "Ghetto Passive Preamp"...

ALPS 100k stereo pot, ALPS 2-pole 6-throw selector switch, 6-9's stranded 22ga copper wire, soldered with jewelers-grade Silver Solder. RCA jacks, knobs and project box from RatShack. Front panel and side panels are wood. Front panel label is a laser printout, that is glued and laminated.

Don't laugh until you've heard it...

--Richard

Richard,

Their is nothing there...? It's just two knobs to wire and some RCA jacks... How does it control the volume? Their is not resistors or magnets or anything... Is this a joke passive... Your kidding right? OK I get it "Ghetto Passive Preamp"..., you really had me going their for a minute... Very funny.

 

[ralflar]

He's not kidding. You can see 3 line inputs into the source selector, into the stereo pot, into the single line out. Simple. Minimum parts. Beautiful. I bet it does sound good, too. Richard has another related thread going.

 

[Dreamer]

Their is nothing there...? It's just two knobs to wire and some RCA jacks... How does it control the volume?

The knob (on the right) that has a whole bunch of wires going to it is the "source selector". It is a 2-pole, 6-position switch (the last 3 positions are not used--it only has inputs for 3 sources). The knob (on the left) that has fewer wired going to it is a 100k stereo potentiometer, which is essentially a variable resister. This one controls the volume. For some reason, it works backwards though. I turn it counter-clockwise to make the volume louder. I don't know if I just wired it wrong, or if it's actually made to turn counterclockwise. If I remember correctly, I wired it according to the schematic on the pack it came in. I think I tried wiring it backwards too, but it would't work that way.

The next one I build (I'm already researching parts sources) will probably have a "ladder attenuator", which is the sort of volume control you are talking about--basically a 72-position switch with resisters soldered across all the poles. And I'm going to build it in an antirely metal cabinet, and jacket all the wiring with sheilding of some sort (probably tinned braid, jacketed in braided PET tubing). I'd also like to use all-silver wiring throughout, with PET or some other non-teflon insulator. And of course, use good-quality gold-plated RCAs...

Their is not resistors or magnets or anything... Is this a joke passive... Your kidding right? OK I get it "Ghetto Passive Preamp"..., you really had me going their for a minute... Very funny.

No, this is not a joke. Just hard-core, bare-bones DIY. You don't need relays or ICs, or complicated ladder attenuators or any sort of high-tech hooha in your pre to get good sound from line-level components like CD players, or reel-to-reel tape decks. In fact, there are some folks in the high-end world who believe that the closer you get to a straight wire from source to speaker, the better it will sound. Of course, for running a turntable through such a system, you do need a seperate Phono Preamplifier, but that is a WHOLE other thread.

Look at the insides of some of the ultra-high-end low-watt tube gear that is used with horn drivers. Some of those hyper-expensive 300b tube amps are dead-simple. Sure they sound great with the right speaker, but believe me, there is not anywhere close to 5-figures worth of parts and labor in those amps or pre's. You're paying for the finish, really. Some of Cary's amps are based on 80-year-old amp circuits, and are ultra simple, the only parts being a transformer, a few tubes, and a handful of caps and resisters. I'm not saying they are not worth the money (if what you want is a low-power ultra-stable amp that sounds as beautiful as it looks) but if you have the skills and tools to do the cosmetic work on a DIY amp, biulding a low-watt tube amp is pretty rudimentary tech, especially if you have a few good manuals on amp design and if you're handy with a soldering iron and wire strippers, you can build a pretty great-sounding amp for a few hundred dollars. Now, the chome-plated, piano-laquered chassis and weirdly-shaped tube cages and gold-plated transformer covers will cost you either a LOT of time in the workshop or a pretty penny to have them fabricated at a shop, but I've seen some tube amps built on overturned aluminum cake pans that sounded AMAZING. Sure they looked like something the Professor would biuld on Gilligans Island, but let's be honest--the chrome and mirror-finish laquer doesn't make it sound better. Would you rather have a perfectly-running, but scraggling-painted vintage Porche 911t for peanuts, or a new-off-the floor Lexus at retail? You'd be surprised how many people would choose the Lexus, just because it has a paint job you can do your makeup in...

And a passive pre is even easier than "old-school purist" tube amps, because it is JUST a selector switch and a volume control, which in it's purest form, is nothing more than a variable resistor.

KISS.

Of course, this is coming from a guy (me) who owns Martin Logans, and drives them with Carver amps, and is writing this post on an Apple MacBook Pro 17" laptop running OS X, perhaps three of the most controversially high-tech brands in the world, so take it for what it's worth...

--Richard

 

[MotorToad]

This one controls the volume. For some reason, it works backwards though. I turn it counter-clockwise to make the volume louder. I don't know if I just wired it wrong, or if it's actually made to turn counterclockwise. If I remember correctly, I wired it according to the schematic on the pack it came in. I think I tried wiring it backwards too, but it would't work that way.

Almost universally, a variable pot will look like this:

..... A >---/\/\/\/\/\/\/\/\/\/\---< B
.......................... |
.......................... ^ C

I can't get this thing to use a series of spaces, so please ignore the periods.
A-B will always be 100K Ohms, but A-C is inverse of B-C. If you're using A-C and it's backwards, just go with B-C and vice versa. School was a long time ago so I can't recall the standard terminology. If others use your system, this could result in some accidental full-volume use!

Would you rather have a perfectly-running, but scraggling-painted vintage Porsche 911t for peanuts, or a new-off-the floor Lexus at retail? You'd be surprised how many people would choose the Lexus, just because it has a paint job you can do your makeup in...

I can see that you're one that understands! My senior design project was a microprocessor-driven additional injector controller that worked closed-loop with a wide-band oxygen sensor, and had an additional feature that it replaced the stock narrow-band oxygen sensor with a variable signal from the wide-band that I could manipulate to change the air:fuel ratio to improve fuel economy, and even map air:fuel over RPM. The idiots that shared my lab got a higher grade on their grade-school tinker toy project (an infrared sensor that turned on an LED!) because it was in a nicer box.

 

[Robin]

Amazingly Simple Desgined Engineering...

The knob (on the right) that has a whole bunch of wires going to it is the "source selector". It is a 2-pole, 6-position switch (the last 3 positions are not used--it only has inputs for 3 sources). The knob (on the left) that has fewer wired going to it is a 100k stereo potentiometer, which is essentially a variable resister. This one controls the volume. For some reason, it works backwards though. I turn it counter-clockwise to make the volume louder. I don't know if I just wired it wrong, or if it's actually made to turn counterclockwise. If I remember correctly, I wired it according to the schematic on the pack it came in. I think I tried wiring it backwards too, but it would't work that way.

The next one I build (I'm already researching parts sources) will probably have a "ladder attenuator", which is the sort of volume control you are talking about--basically a 72-position switch with resisters soldered across all the poles. And I'm going to build it in an antirely metal cabinet, and jacket all the wiring with sheilding of some sort (probably tinned braid, jacketed in braided PET tubing). I'd also like to use all-silver wiring throughout, with PET or some other non-teflon insulator. And of course, use good-quality gold-plated RCAs...

No, this is not a joke. Just hard-core, bare-bones DIY. You don't need relays or ICs, or complicated ladder attenuators or any sort of high-tech hooha in your pre to get good sound from line-level components like CD players, or reel-to-reel tape decks. In fact, there are some folks in the high-end world who believe that the closer you get to a straight wire from source to speaker, the better it will sound. Of course, for running a turntable through such a system, you do need a seperate Phono Preamplifier, but that is a WHOLE other thread.

Look at the insides of some of the ultra-high-end low-watt tube gear that is used with horn drivers. Some of those hyper-expensive 300b tube amps are dead-simple. Sure they sound great with the right speaker, but believe me, there is not anywhere close to 5-figures worth of parts and labor in those amps or pre's. You're paying for the finish, really. Some of Cary's amps are based on 80-year-old amp circuits, and are ultra simple, the only parts being a transformer, a few tubes, and a handful of caps and resisters. I'm not saying they are not worth the money (if what you want is a low-power ultra-stable amp that sounds as beautiful as it looks) but if you have the skills and tools to do the cosmetic work on a DIY amp, biulding a low-watt tube amp is pretty rudimentary tech, especially if you have a few good manuals on amp design and if you're handy with a soldering iron and wire strippers, you can build a pretty great-sounding amp for a few hundred dollars. Now, the chome-plated, piano-laquered chassis and weirdly-shaped tube cages and gold-plated transformer covers will cost you either a LOT of time in the workshop or a pretty penny to have them fabricated at a shop, but I've seen some tube amps built on overturned aluminum cake pans that sounded AMAZING. Sure they looked like something the Professor would biuld on Gilligans Island, but let's be honest--the chrome and mirror-finish laquer doesn't make it sound better. Would you rather have a perfectly-running, but scraggling-painted vintage Porche 911t for peanuts, or a new-off-the floor Lexus at retail? You'd be surprised how many people would choose the Lexus, just because it has a paint job you can do your makeup in...

And a passive pre is even easier than "old-school purist" tube amps, because it is JUST a selector switch and a volume control, which in it's purest form, is nothing more than a variable resistor.

KISS.

Of course, this is coming from a guy (me) who owns Martin Logans, and drives them with Carver amps, and is writing this post on an Apple MacBook Pro 17" laptop running OS X, perhaps three of the most controversially high-tech brands in the world, so take it for what it's worth...

--Richard

Richard,

Thank you for explaining this to me. I do apologize for thinking you passive preamp was a joke amp. I just looked, to my very un-tained eye, like your preamp was missing parts, which as you explained is just not the case. I am curious, what does your DIY preamp really sound like when playing music through it?

I'd like to ask a few more silly questions, If I may... Why would you use all silver wiring for you next preamp? Wouldn't the silver give more emphysis for the high's tones and less for the bass sounds? Also why non-teflon insulation? I thought teflon was supposed to be a good insulator?

Naturally, I am the kinda person who would have choosen the Lexus for the piant job and the ease to do make-up...

 

[Sambob2]

OK. And now for something completely different...

The guts to my "Ghetto Passive Preamp"...

ALPS 100k stereo pot, ALPS 2-pole 6-throw selector switch, 6-9's stranded 22ga copper wire, soldered with jewelers-grade Silver Solder. RCA jacks, knobs and project box from RatShack. Front panel and side panels are wood. Front panel label is a laser printout, that is glued and laminated.

Don't laugh until you've heard it...

--Richard

You're right, we don't see much of this anymore. At least not in the mainstream of things. It's more the bling bling shiny chrome plated stuff that grabs attention.

Richard,
Thanks for posting this minimalist approach to passive pre-amplifiers (really it's just an attenuator and switching device with no amplification) and reminding me that there is more than IC's, caps and transistors. I wonder how this sort of circuitry affects impedance or do they?

Sam

 

[Dreamer]

I am curious, what does your DIY preamp really sound like when playing music through it?

Sounds pretty good! Erik (a local DC-Area ML guy) was over to my place last Saturday, and we did a VERY unscientific A/B/A with the DIY an my CArver C-4000t that was VERY revealing as to how both of them sounded. You can read his post about this on my "System" page:

http://www.martinloganowners.com/~tdacquis/forum/showthread.php?t=3412&highlight=158

I'd like to ask a few more silly questions, If I may... Why would you use all silver wiring for you next preamp? Wouldn't the silver give more emphysis for the high's tones and less for the bass sounds? Also why non-teflon insulation? I thought teflon was supposed to be a good insulator?

Again, in Erik's he discussed the effect of silver cables. I think that in some people's systems, silver cables sound as you decribe (harsh highs, restricted bass). But in my system, //i prefer the sound (or lack of sonic signature) that silver interconnects have.

And now that you mention it, I probably WILL use teflon insulation, for just the reason you say.

Silver wire, to my ears, sounds good with the components I have. And since I plan on moving up to Sunfire amps, I'm thinking silver wires will sound just as good,because to my ears, Sunfires have a similar sonic signature to Carvers. Maybe it won't sound as good--I'll just have to try them.

As for the passive attentuator Im planning to build, I figure tha since most manufacturers make such a big deal about using silver solder, and since I like the sound of silver ICs in my system, why not just wire the thing with silver throughout?...

Naturally, I am the kinda person who would have choosen the Lexus for the piant job and the ease to do make-up...

I have seem some pretty ghetto-looking DIY gear over the years. I've seen ams that used overturned 9x9 aluminum cake pans for their chassis, but you know what, chrome and stripes don't make it go faster (as they say in the hot-rod world)...

When I get all the parts together and build this new unit, I'll be sure to document the whole process with pics, and post it here!

--Richard

 

[Peter Hogan]

For some reason, it works backwards though. I turn it counter-clockwise to make the volume louder. I don't know if I just wired it wrong, or if it's actually made to turn counterclockwise.

Almost universally, a variable pot will look like this:

..... A >---/\/\/\/\/\/\/\/\/\/\---< B
.......................... |
.......................... ^ C

Hi,
To reverse the direction of the potentiometer, you want to swap the wires at points "A" and "B",.... "C" remains wired the same.

Peter

 

[Rich]

As for the passive attentuator Im planning to build, I figure tha since most manufacturers make such a big deal about using silver solder, and since I like the sound of silver ICs in my system, why not just wire the thing with silver throughout?...

Then again, you could always wire it with cut up Nordost Valhalla wire and wrap non-conductive paper around all the wires.

Just joking, of course. I think making your own passive pre is a great DIY project that allows you to get neutral, uncolored sound from a really simple design that costs very little to make and provides the satisfaction that you can only get from knowing that you built it yourself. Thanks for sharing, Richard.

 

[Robin]

Interesting...

When I get all the parts together and build this new unit, I'll be sure to document the whole process with pics, and post it here!

--Richard

Richard,

:cheers:Thanks again, I will look forward to following your progress on your next passive preamp endever.

You do excellent DIY electrical projects...