[holland]

follow up would be great, very curious myself.

 

[sceleratus]

I just checked FedEx status.  Jack will have them today.
 
He said the following:
"We will spec the amp before and after so you will have a record of what it is capable of."
I'll have a Blueprinted amp when it comes home.
 
Nervous......

 

[holland]

Originally Posted by sceleratus /img/forum/go_quote.gif
 
"We will spec the amp before and after so you will have a record of what it is capable of."
I'll have a Blueprinted amp when it comes home.
 
Nervous......

 
Yeah, I would be too.

 

[sceleratus]

First and foremost, I want it to sound like it did before it became a bug zapper.   I love listening to my baby sing.
 
But everyone here Loves Numbers.  Having a benchmark from an independent source with a good reputation is cool.   Like taking your 57' Chevy with a 383 stroker to the track.  If it's a dog, ya still love her.   (No self respecting rodder would ever send their ride out for someone to repair it....  I failed.)
 
It'll be fun to post them.
 
Nervous...

 

[muskyhuntr]

I don't know that you failed.  You have designed and built one of the nicest enclosures on this forum, period!  Also note that you are diving into some what uncharted territory by converting an amp designed for speakers and modifying it for head phone use.  Not an easy task, even for the most skilled builders.  Indeed, I just finished reading through a rather long and interesting thread where a number of individuals are attempting to scratch design from scratch, something similar.  I believe they spent about 30 pages just discussing the output transformer and even had a number of mfg's joining in the discussion.  Not easy!   Both you and the people on that other forum are aiming for the best that can be accomplished.  I think you both will succeed.
 
Jim
PS. I admire your perseverance,

 

[sceleratus]

  I don't know that you failed.  You have designed and built one of the nicest enclosures on this forum, period!  Also note that you are diving into some what uncharted territory by converting an amp designed for speakers and modifying it for head phone use.  Not an easy task, even for the most skilled builders.  Indeed, I just finished reading through a rather long and interesting thread where a number of individuals are attempting to scratch design from scratch, something similar.  I believe they spent about 30 pages just discussing the output transformer and even had a number of mfg's joining in the discussion.  Not easy!   Both you and the people on that other forum are aiming for the best that can be accomplished.  I think you both will succeed.
 
Jim
PS. I admire your perseverance,

Thanks Jim.
 
Tom Christensen deserves the lions share of the credit.

 

[holland]

  Thanks Jim.
 
Tom Christensen deserves the lions share of the credit.

 
A build is very personal.  It's multiple things all lumped together.  The circuit is a part of it, everything else is not.  Don't sell yourself short.  It was a good build, and as you have seen, the build can make or break a design.
 
It'll all work out.  Everything in the box is replaceable.

 

[sceleratus]

Thanks Holland,
 
My minds going in 10 directions wondering where the problem lies.
I'm hoping for "stupid simple", or will I have to build a new board.  No matter.
 
I'm very pleased that I was able to pull this build off.  I fancy myself good at design (enclosure) and logistics.  It really did come together and the sound was fantastic. 

 

[sceleratus]

The problem:
 
Something failed on the Maida regulator that produced the buzz/hum.  I do not know specifically what it was.  I did look through my build and saw that I used the wrong value for R-3.  I used 10Ω.  It should have been 15Ω
 
Jack measured the amp prior to working on it and sent me the following:
 
"Distortion specs at 2 watts into 50 ohm load, 2khz at 2.2v input, 
.194% THD IMD at 2.2v input, 2.4%, this is very good.
4.43v to 8.48 watts symmetrical clipping. This is a good amp."
 
Post fix he sent me the following:
 
"We just dived into the amp and its much better and the hum is gone and draws 1/2 an amp less from the line. 
The - 50-53db noise floor, is now -55-56 db with the choke and caps.  
 
This is the limit for this circuit due to this -56db is the top of the switching noise, so can't go lower than that.  Switching noise is a hiss,  this can be heard now if you strain your ears."
 
I decided to have Jack re-work the OPT's so they will support speakers as well as HP's.
 
I am looking into some high efficiency speakers that are 85dB / 1W / 1m.  I am just learning about them but Jack said they will work great with the amp.  (Solist, LINN, Zu)  When he finishes modifying the OPT's to 8Ω, I will put an R12 in parallel and an R50 in series to the HP outputs and switch between speaker plugs.  Since I'm a nonconformist I like the Neutrik "SpeakOn" speaker connection system.
 
I hope to have the amp back by the end of the week.
 
I've been converting my friends vinyl collection to digital.  I really like the sound and am smitten with his turntable.  I'd like to build the phono pre amp and I am looking at designs.  This one from GlassWare Audio Design looks interesting but I wouldn't know a good one from a bad one.  I think the only reason I like it is that it has 8 valves, so it must be better.
 
When I recut the back panel I will put input jacks for a phono pre amp and a 4pole rotary.

 

[holland]

That's great news!  85dB isn't too sensitive, but should be good enough with 10W.  I have 89dB bookshelf speakers on a 5W amp, and it's loud enough but might not be so for high dynamic range pieces.
 
I heard some of your clips, they came out great!  It makes me want to delve into vinyl as well.
 
Choke and cap?  He updated the regulator and added a choke?  Chokes are nice, but can be big.  With output resistors you won't hear the noise with headphones, in addition to additional reduction going to 8 ohms on the OPT.
 
Glassware/TubeCad makes good stuff.

 

[sceleratus]

As you all know Jack is Old School.  I think they invented the term after him.
 
He said the problem was in the regulator and as such I built another one.  However he preferred a "simpler approach" and replace it with caps and a choke.  He had the amp, I know practically nothing, I deferred to him and said do it.  My understanding is there isn't a HV regulator anymore.
 
Speakers:
The Zu Audio "Soul" are 99dB. The Sonist Recital3's are 93dB and the LINN Majik 109's are 88dB  That's where I've been looking so far.  Also found "The Horn Shoppe"  interesting and thrifty.   The speakers will be in a "music room" of which I am in the acquisition negotiation process.  The room is 19' x 15' with a 11' vaulted ceiling.... along the long edge.  I think nice clarity is the most important criteria for me.
 
I am dying without that amp.

 

[muskyhuntr]

Great news!  Glad it's all sorted out.  Do you have any specifics as to what happened to the regulator?  What part/parts? 
I am very interested in the sound with the 8 ohm transformers and how your phones sound with the resistor network.  Looking forward to a full report.
 
I cannot comment on the Tubecad phono boards.  I will say that I am in the process of casing up one of his preamp designs.  This is going to be a 2 case dual mono design.  I am not far enough along to comment on the sound, but I have run square, triangle, and sine waves through and they look very good on the scope.  His boards are about the best I have seen offered.  Thick and rugged.  Most are adaptable to different tubes, voltages, caps, etc.  If you decide to go this route, also consider his power supplies, also first rate. 
 
An update on my DG 300b.  All power supply boards are now built and tested.  Amp board is also built but I installed 2 resistors of the wrong value and need to replace them.  Have the 6n6p tubes.
Unfortunately, I am going to have to put this project on hold for a while, at least until I finish up a few other projects.
 
Jim

 

[tomchr]

  The problem:
 
Something failed on the Maida regulator that produced the buzz/hum.  I do not know specifically what it was.  I did look through my build and saw that I used the wrong value for R-3.  I used 10Ω.  It should have been 15Ω
 
Post fix he sent me the following:
 
"We just dived into the amp and its much better and the hum is gone and draws 1/2 an amp less from the line. 
The - 50-53db noise floor, is now -55-56 db with the choke and caps.  
 
This is the limit for this circuit due to this -56db is the top of the switching noise, so can't go lower than that.  Switching noise is a hiss,  this can be heard now if you strain your ears."

 
In the Maida Regulator, R3 = 10 Ω is the correct value. This is listed on the top level assembly schematic. If you install a higher value here, you'll get hum for sure as the current limiter will start to kick in.
 
Which changes did he make that resulted in a 2x reduction in power consumption? Did he dial back the bias current in the 300Bs to 50~60 mA?
 
What switching noise is he measuring? May I see the spectrum? The only noise I measure on the output of my amp is 60 Hz and harmonics thereof induced by coupling from the power transformer to the output transformers.
 

The noise floor is -110 dBV. The highest spurious is below -80 dBV. The only thing in the amp that switches at audio frequencies is the rectifier bridges, so I'm curious to see a spectrum measurement of the noise.
 
~Tom

 

[sceleratus]

Here's a Post I made on "Post Pictures of your Build"
 
I'm going to have my back panel re-cut to accommodate some changes.  Rather than 0.09" silicon bronze I'll use 0.07 T6061  AL-LEW_MINI-YUM
 
Aquatech water cuts the panels straight from my Adobe Illustrator file.  They have a fixed fee for anything up to 24" x 48".    Since I only need 6" x 16" I was going to buy a 24" x 24" piece.  I guess I could cut 3 more, but why.
 
So why am I posting?  I thought if any of ya'll might want a panel cut it would only cost the postage if it'll fit in the remainder of 24x24 otherwise add the difference between the cost of a 24x24 and a 24x48 AL sheet.  I have not purchased the material yet.  The pieces in the photo below were from a 24x24.  I'm only cutting the small one.  Including the perimeter, there are close to 90 things cutout.
 
Or if a couple guys have small pieces we could do that...
 
PM me if interested.  If needed, I'll help with getting your layout into Illustrator.
 
 

 

[sceleratus]

Unless I hear something, I will have the panel cut Tuesday.
I could hold off a few days if there is interest.