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The Christiansen "DG" 300B Amplifier Build Thread - Page 40

post #586 of 631
Thread Starter 
Quote:
Originally Posted by Steve Eddy View Post

Don't have to take the Gungnir apart. Just measure between pins 2 and 3 on its output jacks.

se

yup...

I mean't take the amp apart, but I appreciate your concern.

I'll check tomorrow.

 

Thanks

post #587 of 631
Thread Starter 

No DC voltage across Gungnir XLR output pins 2 & 3

post #588 of 631
Quote:
Originally Posted by Steve Eddy View Post


Why are you taking the can and the shield to the chassis instead of signal ground?

se

 

My bad, I was a bit quick on that. Ideally, can should be run to chassis, internal shield to signal ground (though chassis is a common practice). Might be difficult with the wooden case, I just realize.

 

Anyone interested in the finer details could have a look here

 

 

Quote:
 

No DC voltage across Gungnir XLR output pins 2 & 3

 

Thx for measuring.   I must say, short of being with you with a scope and signal generator, it's difficult to see any obvious problems.:confused_face_2: 

 

If it works correctly and silently with rca... maybe leave well enough alone.

post #589 of 631
Quote:
Originally Posted by sceleratus View Post
 

Have a set of Sophia Electric™ Princess Mesh 300B sometime this week.

 

Dude!! Good find. I've been looking for a US vendor of the 300B mesh plate tubes. 

 

I tried the Full-Music 300B/n mesh plate tubes a while back. They are very nice sounding tubes. However, one of the "matched pair" I received had issues with run-away. The plate would develop hotspots even at 380 V, 65~70 mA (27 W dissipation, the tube is rated for 40 W). I patted myself on the back from buying from an eBay vendor with a return policy. 

 

Did you get the input transformer circuit working? It was my impression from your email that you did... 

 

~Tom


Edited by tomchr - 11/19/13 at 10:33am
post #590 of 631
Thread Starter 

Yup.

Got lucky again.  They sound amazing. They are in the sweet spot of the price/performance curve.  US made with a one year warranty and come in a black base.

 

Let's not go into the input trans situation/train wreck/nightmare.  If I'm itching for a project down the road I might try it again.  Honestly my heart wasn't in it.  I wanted to listen to music more than troubleshoot a problem.

post #591 of 631
Thread Starter 

Here is an SPL graph for my music room as measured by FuzzMeasure Pro3 with a Røde mic.

Volume was set to max and the mic was placed head high in the center listening position.

 

It's pretty flat... but not quite my Audeze LCD2 R2's.  :)

I don't think I want absorption panels because I don't have the power to compensate.  Also don't have the knowledge.

Perhaps a bass trap near the speaker corners.....  I think.

 

 


Edited by sceleratus - 11/19/13 at 2:14pm
post #592 of 631
Thread Starter 

Using this cool tool, and looking back on Tom's post ohm Haas Effect here's FuzzMeasure reverberation calculations and graphs from the Haas article.

The room is 2700 cu ft.  At 62 ms I'm somewhere between an auditorium and an opera house.  I'f I'm reading it correctly.

However it looks like times below 35 ms aren't good as they are close to direct sound.

 

This is cool stuff. Time to get that physics degree. 

 

 

 

 

 

post #593 of 631
Thread Starter 

Amp measurement to clipping.

 

3.12 VAC to amp inputs.

10.20 VAC on binding post where the sine wave starts to flatten.  Measured using DMM

There was a 10 ohm 10W resister across the binding posts.

 

post #594 of 631
Thread Starter 

This is a duplicate post I made in "Show pictures of your Build"

 

Does anyone have a design recommendation for a high pass filter?

 

I put in a sub that I had doing nothing.  I cabled it straight off the second RCA's on the Schiit Gungnir DAC.

It works great.  Because I only have 10W max from my 300B, it only required a tiny fraction of volume.  I used FuzzMeasure Pro to capture the room freq levels with the sub and my Thiel CS1.5's  Turns out that 100-120Hz is about right.

 

The High Pass.  It is my understanding that a filter on the Thiels will make them more efficient.  That would be good for me.

 

Any input  will be appreciated.  The BLUE is the room without the sub.

The GREEN is after dialing in the volume, freq, and phase of the sub.

 

This software is a lot of fun.  It recognized my speakers are Thiels from, I guess, the sound signature.

 

EDIT:   Is this just a matter of calculating one resister and one cap?  Where 110Hz is 150 ohm and 10uF ?

 

 

 


Edited by sceleratus - 11/20/13 at 12:04pm
post #595 of 631
Thread Starter 

I need a Preamp...

 

Update.  Tried my friends LINN Preamp.  Sending 1.7V to the amp.

HUGE difference.

 

I bought an Adcom GFP 565 on Audiogon.


Edited by sceleratus - 11/20/13 at 3:16pm
post #596 of 631

It looks like you have a measurement error in the plot without sub (blue trace). The straight line from 3 kHz to the ADC/DAC roll-off at 22 kHz doesn't look real.

 

Getting good in-room measurements is tricky business. 

 

~Tom


Edited by tomchr - 11/21/13 at 1:14pm
post #597 of 631
Thread Starter 

Hope everyone is having a wonderful and safe Holiday.

 

Getting off track a bit, again,  (I can do that because it's my thread)  I got into woodworking mode.....  specifically attempting veneering and marquetry.

I've ordered the parts to make a veneer press and my first project is a shelf for the music room.   The structure is complete and I'm waiting the arrival of the veneer

 

If it comes off, I'll tackle a rack for the amp and gear.

 

post #598 of 631
Quote:
Originally Posted by sceleratus View Post
 

Hope everyone is having a wonderful and safe Holiday.

 

Getting off track a bit, again,  (I can do that because it's my thread)  I got into woodworking mode.....  specifically attempting veneering and marquetry.

I've ordered the parts to make a veneer press and my first project is a shelf for the music room.   The structure is complete and I'm waiting the arrival of the veneer

 

If it comes off, I'll tackle a rack for the amp and gear.

 

 

 

Cool.  Are you going to make a vacuum press?  I looked into veneering a little, but haven't tried it.

 

Nice job on the shelves.  How did you make the curved cuts?  Making curves that nice is beyond my ability.

 

I'm making a couple of cases for my 300b amp project out of curly maple.  I have one partially completed, had a few issues but it looks pretty nice now.  It's going to take a lot longer to make the cases than to build the amp, but I am enjoying the process.  I finally broke down and bought a table saw, which has been very useful.

 

Randy

post #599 of 631
Thread Starter 

Happy New Year Randy,

 

It’s pretty easy to make curves.  I’ve done bending and clamping a thin wood sandwich around a jig but for this project I used a router with a template bushing in the base plate.  It will work for hardwood and mdf.

 

Make a template of the curve you want using a jigsaw and sanding it to refine the edge.  I use double sided tape to make a 3 part sandwich on the bench.  1) A sacrificial piece of MDF. 2) I rough cut one of the pieces to be duplicated with a jig saw. 3) Affix the template on the top allowing for the offset of the bushing.

 

Glide your router bushing along the template.  Repeat as many times as necessary.  I use a rubber roller to spread the glue and clamp everything together.  Rule #1.  You can never own enough clamps.

 

I use the Krieg Pocket Screw Jig to put it all together.

 

I am building a venturi based press from Joe Woodworker

 

I’m going to section the platen so I can use a large bag for smaller projects.  My veneer project is ambitious.  I discovered Paul Schurch.  He’s a master builder.  I went nuts and got his videos and signed up for his 5 day workshop in November.  Take a look at his portfolio.  Amazing.

 

I can't call it furniture but I'm working up to that for an equipment rack.

Keeping my fingers crossed.

 

 

 


Edited by sceleratus - 12/31/13 at 10:15am
post #600 of 631
Thread Starter 

Randy.

 

As you can guess, I'm very fond of curly maple.  Be sure to post some pictures here. 

 

 

Everybody else too.  !


Edited by sceleratus - 12/31/13 at 10:13am
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