another new guy warning

[fishboat]

First post..never built an amp in my life, so be gentle..

I'm leaning toward building a Stereomour for an application similar to Ed's here:

http://www.bottlehead.com/smf/index.php/topic,1814.0.html

Ed has the GR Research  V1 speakers.  I have the Super V kit yet to build (sensitivity of 97dB at 8 ohms).  12 inch coax OB.  Each speaker has two subs driven by a 370 watt servo amp per channel, so the Stereomour would only be for the coax on top.

Additional Super V info is here:

http://www.bottlehead.com/smf/index.php?topic=2607.0

No doubt I may come up with some pretty dumb questions, but I'm a woodworker dabbling in building speakers and an amp, rather than an electronics guy dabbling in woodworking.

Has anyone built a Stereomour with the power & input/output jacks going out the back of the amp rather than out the top?

I also may follow Ed's build with eliminating the volume pot & selector switch as I have a remote-control passive pre (Jolida JD50A) that can handle those duties. 

EDIT:  Thought I'd toss in my room diagram(it has an 8 foot ceiling..just removed for viewing).  Its a balcony over a great room.  No wall behind my head, only a 7:12 pitch ceiling about 10 feet back.  The tall triangles in each corner are superchunk bass traps (18" each side, 64" tall).  The QRD diffuser in the center between the traps may be either 4' or up to 8' wide.  I won't know until  I get things up and running.

 

[randy@matrixq.com]

Welcome Fishboat.  I'm sure you will find the forum helpful and encouraging.  I love the 3D model of the room, what software did you use for that?

I've never built an amp with the inputs/outputs moved to the back but I own a few that were done that way.  There are a couple of approaches:
1.  Rout the inside back until you have a thin wooden panel on the back.  then drill for the jacks there.  This gives the most aesthetically pleasing (if you like wood) but requires a careful routing job.
2.  Rout out a rectangle and mount a metal panel on the back where you set the jacks.  This can still look really good and may have some benefits for grounding (not sure).

Something to consider is what to do with the holes left on top.  You might make some nice wood plugs or find some other use for them.  Otherwise, you could go all out and make a whole new plate with only what you will use.

As for ditching the stereomour's attenuator, there may be an advantage to keeping it.  If you put a stepped attenuator there, you can crank it and it would be just like it wasn't there.  Otherwise, you could have the option to adjust the volume on the preamp and the stereomour in a way that optimizes the signal/noise ratio of both units.  Just a thought, it will give you more flexibility in the future.  Especially, it you're like me, and move stuff around all the time.  I have a stereo in the garage, the listening room, bedroom, living room...  I'm always trying things in different places.

Good luck, and keep us updated.  We love build pictures.

 

[ssssly]

I have seen it done a couple of times.

The primary down side is that every time you want to remove the top plate to do something you will have to disconnect the RCAs. That or make the wires going to the RCAs long enough to remove the top plate drastically increasing the signal path.

 

[Grainger49]

IIRC they use a solid shielded twisted pair for the signals.  The shielding is grounded at one end only.  So if you decide to put the inputs on the back you could use a stranded shielded pair, maybe microphone wire. 

Stranded wire is much more robust when being moved, solid not so much.  However, the stranded is harder to terminate.  Strands can get loose and short from one terminal to another.  Just be careful and it will work well.

 

[fishboat]

Thanks guys for your thoughts.  I hadn't thought about the 'popping the top' aspect for adjustments or maintenance..good point. 

Building some sort of back plate should be fairly straight forward.  I have some very hard/dense wood that would mill well to thin panel.  An aluminum plate could be inset in a wood panel if grounding (?) is needed.  I have some heavy copper flashing that could be used also.  Buff it up to a shine and coat it with some lacquer..ooh

The holes in the top could be covered with a wooden trim piece of some sort.  Any time I mess up something I'm making I view it as a "design opportunity".  I'll draw up a model of the amp base to give me a chance to work out something that looks nice. 

porcup..another good point about the attenuator.  I'm on the fence with it in or out.  Taking it out does limit flexibility..have to think about that some more.

You're a math teacher..very cool.  I crunch numbers and build (math-based) models for a living. The room model was done in Trimble (until recently Google) Sketchup.  It's a free 3-D drawing program...VERY COOL. 

http://www.sketchup.com/

I use it for everything I build (woodworking) and it's a great help.  It's fairly easy to learn.  There's a ton of instructional videos available..all free...and a huge user community.  A good series of videos are done by Joe Zeh (Chiefwoodworker)

http://www.srww.com/blog/

This is a construction  model of the speakers:

This one is now obsolete, but you can see the guts..

 

[rockdrummer]

Hey fishboat.  I am planning the same setup as you as far as amp and speakers are concerned.  I have Super V tops and the Stereomour.  I watched your super v thread over on the GR forum. 

I haven't begun building mostly becuase my workspace in my garage is the best place to work and it's bleepin' cold here in MN still and my garage isn't heated. 

I can't give advice about whether to put inputs on the back or use or omit volume control, etc.  But the most common advice I have heard so far is build it stock first and go from there.  I have caps to eventually put in the stereomour to act as a high pass filter.  But that is as far as my eventual upgrades/tweaks plans are so far.

I'm going to check out that design program because drawing ideas for side wing designs isn't working.  Looks like my 4 year old son could do as well

I haven't even begun building yet and I've already had great help from this forum.  You will have an abundance of help at every step of the way.

GO TUBES!
ben

 

[RPMac]

This is something I did to help with the only flaw I've found with my early BH amps...too small top plates.

I cut a miter "picture frame" out of 1 1/4" x 2" brick door molding. The inside dimensions are about 3/8" narrower than the 6" x 10" top plates. I cut a narrow groove the thickness of the top plate 3/16" down from the top of the frame and about 3/16" deep. The front and two sides are glued together so that the top plate slides into the grooves of the frame. The back frame piece, which is also grooved, is screwed on to the two side frames. This framed top plate sits(and screwed) on a "standard" base I made out of 1x4 scrapes that fits the outside dimensions of the frame. It's not pretty!

When I need to work on the amp, I unscrew the base, unscrew the back frame, and slide the top plate out.

As a woodworker, I assume you will build your own bases. A variation on this would be to attach the back base/frame to the top plate. To work on the amp, you would unscrew the back base, slide the top plate and attached back out together from the grooved base. A metal plate could be mounted to the inside of the back-base and mechanically/electrically attached to the top plate. Route/drill holes in the wood back-base to access the metal plate for mounting whatever. Electrically, would be the same as mounting to the top plate.

Hope I was clear enough so someone besides me could understand.

 

[4krow]

Being a woodworker myself, I look forward to your designs. I would also enjoy seeing work that you have already done.  As far as the RCA jacks mounted on the back, I have made a cutout in the back of the box and then placed a brass plate in the hole space, with the RCA jacks mounted to the brass plate. I will post a photo later.

 

[Paul Joppa]

You can - in theory, I don't recall anyone actually doing this! - cut off the back 2.00 inches of the chassis, which has the connectors, and put it wherever you want (suitably adjusting the wire lengths of course). You can do the same with the front 2.00 inches, though the controls are then not centered so you should check for fit. This possibility is not an accident, by the way....  :^)

(You can't just bend it over, there's no room for the parts then, and the aluminum is pretty thick.)

 

[fishboat]

Rockdrummer..

It seems there will be a few GR-BH setups around.  It's too bad the SV is now gone, we could start a movement(beyond the movements started by others).  I haven't started the SV build either, beyond working up the model.  I'll be using MDF and I don't want to fill my shop with MDF dust.  When the weather gets better (I'm in WI) I'll do most all of the initial cuts and shaping outside..good reason to spend some spring days outside.

I picked up an SV sketchup  model from Steve in Australia.  It was drawn by some audio place downunder.  The drawing was a bit iffy in spots so I basically redrew it from scratch using the old one for dimensions..and I borrowed the sides, though I've made changes since then.  If you want the model I can send you a copy.  It is possible to print out 1:1 templates from SU onto Arch type E paper..that's my plan. 

I may well build the amp stock in most respects, but the back plate is still an attraction.  If you do a search here for "Danny" you'll get two hits..one of them has lots of tweaking info in it. 

RP..The slide in plate isn't a bad idea, particularly with the back attached.  I hope to get some time this weekend to draw up a few things and see where it takes me.  I have some ideas on the overall look, but they are fragments so far. 

4k..please do post a pic of your back plate..I'd like to see it.

Paul..hadn't though of that yet, but cutting off the back 2 inches does address lots of mounting issues. I have a carbide blade on one of my bandsaws..it would make short/clean work of slicing the plate. .hmmm

Lots of good ideas guys..thx.  Not sure where I'll end up, but I tend to dump lots of ideas into a pot and see what comes out.

 

[4krow]

Ok, so this not a BH product, but this is what I do to add inputs to the rear of a chassis.

 

[matthewmckay]

Hmm...  Greg, I am noticing a theme here. You must smoke a lot of cigars.

I hope you are building some sort of colossal "all cigar box" system..

 

[4krow]

LOL Practice makes perfect. I even saw ceegar box speeekers. Probably not the best performance. At least I don't used sardine cans.

 

[saildoctor]

As for ditching the stereomour's attenuator, there may be an advantage to keeping it.  If you put a stepped attenuator there, you can crank it and it would be just like it wasn't there.  Otherwise, you could have the option to adjust the volume on the preamp and the stereomour in a way that optimizes the signal/noise ratio of both units.

  +1

With 97db speakers you may find that your preamp has a hair trigger with the Stereomour turned up to full blast or rigged with just an input to ground resistor.  That was the case for me with my FPIII and Paramounts and my previous speakers.  I had to pad down the preamp's input some and put a L-pad on the inputs going into the amps.  Doing so also allowed me to try different settings and see what got the noise level down the most. (I could hear a small amount coming from the speakers even from a dozen feet away.)  It was a PITA taking everything apart several times and soldering different resistors, but worth it in the end.  You could leave the pot that comes stock in for now and find the level that works best with your setup, then measure the resistance on either side of the input and solder in some resistors close to the same ratio.  You'd need to make sure they added up to a minimum value so the pre isn't working too hard.

I've been thinking of drilling some holes and installing something like this:

http://www.siteswithstyle.com/voltsecond/12_posistion_shunt/12_position_pure_shunt.html

That way I no matter what source I'm using I can set my pre to 'medium blast' and dial in the amp to get me in the ballpark. 

 

[fishboat]

Kerry,

Can't argue with your & other's logic..I'll build it with the attenuator in.  It seems to offer more options with it in than out.

thx..

 

[fishboat]

Does anyone know how warm the top plate of the Stereomour gets with normal use? 

Room temp?, 90 degrees?, slightly warm..?

 

[rlyach]

I just measured my Stereomour after playing it for a while at almost full volume. The hottest part of the plate was about 96 degrees F. The power transformer reached 105 degrees F. I am not sure what you need the number for but the coefficient of expansion for aluminum is 12.3 micro inches / inch / degree F. So a 12 inch plate would expand by .016 inches from zero degrees. Just a guess that this is what you are after. BTW, the ambient temperature in my room was 78 degrees F and if you start there the expansion is only .004 inches.

 

[Grainger49]

Bottlehead plates and transformers run hot.  So do the tubes, the glass.  Paul Joppa, who designs the transformers, knows what heat will be seen during operation and it is taken into account.  That is to say a hot transformer/plate/tube glass is normal.

 

[fishboat]

Thx guys..exactly the info I was looking for.  I was just considering more options.  I was thinking about toning the plate to a warmer color with a tinted shellac.  I see where some have painted the plate.  From the pics I've seen the swirl aluminum looks nice. With tinted shellac could turn the plate any color I like to match the wood base.  Shellac is a hard finish, I'll just need to find out what kind of heat it could take before it gets soft. 

 

[rlyach]

I wouldn't cut it too close with the temperature. Depending on how thick the shellac is it will change the thermal conductivity of the plate, reducing its ability to draw heat out of the system. Your temperature might run hotter than mine, since I have bare aluminum.

BTW Grainger, While my system was playing at full volume I measured the sound pressure at 86db at 10 feet. That is how far my chair is away from the Orcas. This is good correlation with your number. At least I know that I am getting as much out of my "3.5 Watts" as I can.