Coffee Table for Stereo Gear and THAT

[iamnothim]

The next project is a follow-on to the speaker build.  I put some of the following info in a post on that thread.

As I posted in the speaker thread I will build a coffee table with a rear shelf for the ugly components that don’t need to be seen or accessed.  I am also building a Neurochrome "THAT" Preamp “THAT”.  It was designed by Tom Christensen,  the engineer that designed the DG300B amp I built.

A preamp boosts the input volume of source components like CD players and DACs.  A preamp for a phonograph is a totally unique beast.  That will be built down the road.

The preamp is small and simple.  There will be two 3” x 3” boards, one is the preamp the other is for differential/balanced/XLR inputs.  Like the round three pin connector used on microphones.  There is also a transformer for 120VAC and a power circuit.  I don’t want two volume controls, so I will orphan the volume pot on the amp and use it in the preamp.  I’m fine with that because the way the front knob on the amp connects to the pot is with a flexible shaft.  The tactile feel is very poor.

Right now the plan is to stack the boards in a wood cube on a plinth.  I will attempt to inlay dark wood for the volume graduation marks into the top.  That will be a first.  My fallback is to cut plugs for "dots". (I know someone will say use dominos, so Ill say it first) [smile]

I will use quarter sawn white oak for the table.
It will definitely be contemporary / mid century.  All hard angles and just ease the edges, not chamfered.  I have decided on planks without a border for the top.  Below is an illustration of the top.  A hidden 4" equipment shelf sandwiched between a 5/4 (or thinner)  hardwood top and bottom.  Probably 4" wide planks.  The legs will be steel “hoops.  I and found a guy, 10 min away, that makes them.  Perfect for the weight and minimalistic in style.  I could experiment with a patina.

The components have been ordered and I’ll pick out the stock very soon..  I will put up a few posts on building the electronics.  It’s a great complimentary hobby to woodworking.  I know very little about electronics.  I’m pretty much a solder monkey.  If you haven’t soldered, or have a hard time with it, watch the three part comprehensive soldering tutorial by Dave Jones of the “EEVblog” on Youtube.  After watching it, you will be able to solder ANY component, even tiny surface mount components and processors.  I had never done this before building the amp and with very little practice I can solder components the size of half a grain of rice.  It’s pretty cool.  Pictured is my very first attempt.  Not pretty but it worked.



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Someday I will finish the "Blue Pine Garage" [big grin]

 

[tjbnwi]

Hey---go get a job, youre making the rest of us look really bad by getting your projects completed in less than 1-5 years  [laughing]

Tom

 

[iamnothim]

I finished the preamp board.  Pretty easy.  However, there wasn't an etched board for the power supply.  Hence I'm going to make it on perf board.  I've never done this before.  Should be interesting.  I have circuit board layout software that would allow me to "etch" my own board, but I don't want to go there.

Below is a proto board layout of the power supply.  I'm not real strong at this either because I have spacial recognition issues.  I think it's correct.  I'll be sure to triple check when the last parts arrive.

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[iamnothim]

[member=8409]Tom R[/member]

I'm replying to your post here, because I've closed out the speaker thread  They'e done and they still sound great.  As the cones break in the sound is, I believe, getting better.  It's very difficult to describe and compare sound.  It's also hard to remember what something used to sound like.  IMO they've always sounded good with nothing I really wanted to "improve".

So it's on to this project.  The table and the Preamp.
Preamp(s) before the table.

I have expanded the scope of the preamp with two separate builds.  The first is the differential input / output preamp for my DAC.
This is the "THAT Driver Module and the "THAT Receiver Module".  These are built.

The second is a Balanced Phono Preamp designed by Douglas Self, Signal Transfer Co. UK.  I am waiting on the boards.  Mr. Self is a very accomplished audio design engineer with several books published on the topic.  I have high expectations for it.  Since it handles both MC (moving coil) and MM (moving magnet) cartridges I have to asked Santa for a turntable and a MC cartridge. [attachimg=3]

Once the board is built it's on to the sawdust stage and build the enclosure for both preamps.  It will have a two position selector switch and two volume controls.  The design is different, but complimentary to the 300B amp.

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[Cheese]

Asked Santa for a turntable and a MC cartridge.

Just curious what turntable and cartridge you asked Santa for?

 

[Holmz]

Asked Santa for a turntable and a MC cartridge.

Just curious what turntable and cartridge you asked Santa for?

My daughter asked for one.
In the olden days they used to ask me to put a "big CD" on  [huh]

There was a Swiss or Austrian job that was ~4-700 I think but I cannot find it.
Wondering what the good value is these days... A used Linn or Sota?

 

[bertv]

>>There was a Swiss or Austrian job that was ~4-700 I think but I cannot find it.

Thorens, maybe?

 

[iamnothim]

Just curious what turntable and cartridge you asked Santa for?

I've selected the Rega model RP3.   I think it's a good value and it's right at my pain threshold.  I've narrowed the cartridges down to the DynaVector model DV 10x5 and the Ortofon Quintet Red.  I'm leaning towards the Ortofon because it's a Lo output MC (0.5mV) versus the Dynavector which is a Hi output MC (2.5mV).

Together they equal a Kapex.

I have negligible understanding of the ramification of cartridge specifications.  It is my understanding that MC's are a bit more crisp and defined than MM's and that High Output MC's are designed to work with a MM phono preamp.  Since there is a "bunch" more circuitry (expense) in the MC section of the phono preamp I'm building I feel I should use it.  Just dumb logic.

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[iamnothim]

I’ve come up with an A/C Mains design that I think is pretty spiffy.

The preamp power supply is in a separate aluminum (al-lou-mini-um for UK readers) housing.  I want this box buried without a power switch that I have to feel for.  Since the 300B amp has a filtered entry module and beefy DPDT switch I am going to buss that feed to the preamp.  One switch turns on both.

To do this I will use color coded Neutrik PowerCon sockets and plugs.  One set for mains between the amp and the preamp power supply and another set for low voltage between the power supply and the preamp.  All plugs are twist lock.

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[Wuffles]

Dumb down the image please. I'll help you.

Just put the words "some wires" over it in big Comic Sans letters and my brain can rest.

Cheers.

 

[iamnothim]

Dumb down the image please. I'll help you.

Just put the words "some wires" over it in big Comic Sans letters and my brain can rest.

Cheers.

Heck, I said it's made from "Al-Lou-Mini-Yum"
I build this stuff on faith and a lot of pictures.  The amp was the first thing I built and I only have a vague idea how it works.
I'm a solder monkey.  The instructions tell me what parts to buy, then it's "bend da leads. put leads in da hole. add dab of solder"
(repeat)  "plug in wall.  look for smoke"

BWT Neutrik makes Rock Concert Grade 50A PowerCons

 

[iamnothim]

I went to the University of YouTube.

 

[Wuffles]

Dumb down the image please. I'll help you.

Just put the words "some wires" over it in big Comic Sans letters and my brain can rest.

Cheers.

Heck, I said it's made from "Al-Lou-Mini-Yum"

That's some sweet tastin' metric wording right there.

 

[iamnothim]

Dumb down the image please. I'll help you.

Just put the words "some wires" over it in big Comic Sans letters and my brain can rest.

Cheers.

Heck, I said it's made from "Al-Lou-Mini-Yum"

That's some sweet tastin' metric wording right there.

On Top Gear binge.

 

[Magpal]

I’ve come up with an A/C Mains design that I think is pretty spiffy.

The preamp power supply is in a separate aluminum (al-lou-mini-um for UK readers) housing.  I want this box buried without a power switch that I have to feel for.  Since the 300B amp has a filtered entry module and beefy DPDT switch I am going to buss that feed to the preamp.  One switch turns on both.

To do this I will use color coded Neutrik PowerCon sockets and plugs.  One set for mains between the amp and the preamp power supply and another set for low voltage between the power supply and the preamp.  All plugs are twist lock.

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Nice to see some electronics on the FOG! Looks like a nice project.

Is the picture showing the 300B amp? Are you using the 3-pin XLR for your input signal and are these signals differential (they usually are)? It seems like you have used two separate shielded wires for the differential input signal. This may cause noise problems due to the lack of magnetic noise suppression. Shielding (braided sleeve like you have used) is used for suppression of noise caused by electric fields whereas twisting is used for suppressing noise caused by magnetic fields. Since you have a pretty big transformer that radiates a lot of magnetic fields you should consider using twisted cables to reduce noise from the transformer (and mains input). You can usually get cables that has both twisted wires and a shield, so you could consider this if you experience noise problems.

As a rule of thumb you should always try to separate the high voltage and low voltage parts, so it might be a good idea to move the powercon connectors to the right (close to the power inlet). This will induce less noise to the more sensitive audio input.

If you are interested in learning about the theory you should consider the books from Douglas Self. They are really good, but they may require some basic knowledge on the topic.

 

[iamnothim]

[member=48770]Magpal[/member]
Yes the photo is of the 300B amp.  The jacks are RCA inputs.  At this very moment I have pulled the Alps volume POT and the RCA’s.  I am replacing them with XLR inputs.  The amp driver board, partial shown, is differential capable.  At one time I had XLR ports and a quad stepped attenuator for volume.

I do not have any noise.  There’s not much I can do with the leads from the power transformer.  The PCB in the back is the power board.  There is adequate separation.

The stack of small boards in the middle are voltage regulators (6.3v and 5v) for the valves.  The trans on the left is a high voltage choke.  That bad boy gets rid of any noise.  All the transformers (except power) were wound by Jack Elliano at Electra-print.

The new input lines will be Cardas 26a. silver in a teflon jacket surrounded by braided.  They’ll be home run from the jacks to the driver board.  That’s good advice for the mains switch to powerCon run.  I’ll see if I can put braid on it.  It will be affixed to the top panel so it's away from the output connections.  The Neurochrome THAT boards give me balanced inputs and outputs.  The volume pot will go between the two.

I have the Douglas Self book “Self on Audio”  I don’t understand much.  The RIAA phono preamp and PSU are designed and sold by Douglas Self’s company “Signal Transfer Co.”