UPDATE 11/14/22

While trying to decide how we're going to handle the silk screen issue, I couldn't wait any more...

So I have built the actual production bench sample.  The production sample is the unit that will be copied when we start building them.  So a lot of pressure to get the layout as sane as it can be.

First, here is the prototype that we've all been listening to all summer and at DECFEST2022...



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Remember this unit has been drastically modified at least 6 times.  And the voltage regulator tubes are on the inside, hardwired to the circuit.

Some of the changes I made include moving the power switch to the back, moving the voltage regulator tubes to the outside, and the voicing switches to the front.

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Using inexpensive 300B tubes for initial testing ; )

Steve

Beautiful

Any chance of a “real flame” look for the Sarah in a couple of years?
Earlier in this thread I saw that a 5670 tube was used (I think), was a WE396a tried?
 Thanks, your buddy dawg, Ralph

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JMO but I think you are better off with a ZBIT than balanced inputs on your amp. It is very close pricewise and gives you the flexibility of putting it anywhere in the signal chain, should you decide to get e.g. a CSP3 type preamp in the future. Also, the ZBIT has gain control while I don't think the input on the amp does.

Hi BlackBess,

We won't be offering it that way, with the custom paint, however at some point in the future we might do one and auction it off.  I have Denis, my senior tech who retired earlier this year who is interested in building these fancy paint job amps at home in his spare time.  We've already done two so far.  I plan to keep that gig going as long as he wants to stay busy.  So some day you may see one.  Make sure you are on our customer appreciation list.  You can find it on the contacts page:  https://www.decwareproducts.com

-Steve

I have both zbit and zrock with se84ufo2 and using the Pontus2. I long for nothing more and nothing less, it's perfect!

I think the zrock likes 4 volts or less input.

UPDATE - FATHER MURPHY

Murphy's Laws were drafted after Murphy died.  It's a list.  There are several versions of it on the Internet.  The one I grew up with said for example; Rule # 7 - Any tool dropped while working on a car in your garage will automatically roll to the exact dead center of the vehicle so as to become out of reach from all four sides.

The set up - it takes one.  It's what pages Father Murphy who is now an evil spirit who especially likes to mess with audiophiles.  So the set up is this...

I made an assembly video of the amplifier being built for the newer techs on our team.  This of course means I have to make it without mistakes... this was the first ring.  Naturally long before it was even finished, a mistake was made and filmed.  I put in a 47K resistor where a 100K resistor goes.  I decided to leave it in the video as a teaching tool.  At the same time I bragged in the video about how I measure everything as I go, so I found it right away.  This was the second ring.  Then I realized if they watch the video without listening to my important commentary they would build the amp with the wrong resistor at which point I would know they didn't listen to the video.  This is playing chess with Father Murphy.  Score Father Murphy zero, Steve one.  This was the third ring.

Not to foreshadow or anything but never play chess with evil spirits.

When firing up the amp for the first time, I checked all the voltages and they were perfect.  I smiled.  This was ring number four, and Father Murphy one, Steve one or so I was about to find out.

I put the amplifier on the scope and couldn't get any kind of substantial output from it.  Like a half a watt, yet everything was working perfect. This is how I know the ringing had been answered.  He's awake, he's here now, and this is where the punishment starts.

I noticed that I forgot to connect the input jacks to ground.  That was of course because I had already posted a picture in the forum before the amp actually worked.  Father Murphy two, Steve one.

I fixed the jack and took new pictures so I can fix the video, and it makes perfect sense why I couldn't get a signal out of it since there wasn't really a signal going into it.

Lesson one, Murphy NEVER works in single shots. If he has to show up to your gig, you can bet it's going to be worth his time as pure entertainment.  I imagine it is the same satisfying feeling that I used to get when I was five and used to tease my younger brother about pooping his pants.  It was so much fun.

I hook everything back up and virtually nothing has changed.  This seemed impossible by I remember he works in threes, so I just started looking for problems.  Damn, this means real troubleshooting.  I quickly discover that the signal going through the stages is but a fraction of what is should be and find out it's a partial short to ground at the input of the amplifier, which is in mono due to the scope and signal generator being hooked up to both channels, so the problem was on both sides.  This whole thing was impossible.  Literally I had to start taking things apart... could it be a bad input switch, or cable, or something I can't see in one of the jacks?

After taking everything apart I determined it was actually the cable, the brand new perfectly installed cable had an 80 ohm short.   I completely removed it and measured it again, and it was fine.  Murphy three, Steve one.

I re-installed it to see if I was loosing my mind and measured it again.  80 ohms to ground.  I should have known, Cables is one of Muphy's favorite tools of torment.  When a cable starts to go bad it either opens or shorts, and does it intermittently.  Since the cable is flexible, it depends on how it is bent as to if it will work right or not.  Murphy four, Steve one.

The cable was something different I found laying on my bench.  It looks like the excellent cable we normally use on the outside, but has only one conductor and is built more like a coax.  I couldn't see any reason why it wouldn't work as well or better so I used it.

Now with the one bad cable removed there was only the other side to investigate and it had a similar issue of about 150 ohms to ground.  I removed it and replaced it with our regular cable to match the first side. Murphy five, Steve one.

The odds of two cables doing this just from being soldered into place (by someone who can solder) is pretty high. Murphy six, Steve one.

And for the check mate, I wired the 12AU7 as a 6922 so that only half of the heater worked.  So that's on the video too.  Murphy seven, Steve one.

This is another excellent testimony of why big manufactures use circuit boards with cable connectors.  Make it so a monkey can't screw it up and they'll all probably work the first time.

Anyway, I wrote this true story to make myself look bad so he would leave.  That's how it works.   Now it is time to test the amp and see if it works.


Steve

Not that I really care all that much if it's 4 watts or 7 watts, what gets me excited is what's happening at 1 watt, which is where we all listen.

Check this out...  at one watt the distortion is 0.3%














That's the calling card of the Audio Gods...

So why the discrepancy between two supposedly identical amps?  Well, I may have used my General Instruments 1840-A to measure it the first time, which is an inductive load using transformers... but it's not a 3 watt difference, so there is some magic to figure out.

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Looks as if you may be using 75C1 tubes there (an 0A2 variant)? Those are cool sounding tubes--Will and I have used them, I'm using a pair in my Monoblocks currently.

This is the Sarah 300B Logo.  It will live on the power transformer so it can be seen from a distance.

Fantastic touch, this!

Steve,

Can you remind me— What was the total harmonic distortion at 1 watt in the prototype at Decfest? Trying to compare and understand the difference with the new and successful tweaking of late.

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I measured it originally into an 8 ohm inductive load and at 1 watt it was closer to 1%.  This recent measurement I did of the newer amp is into the standard 8 ohm resistive load.  I measured the original amp dozens of times into the resistive load as well, just don't remember the exact numbers.

Steve Deckert wrote on 11/21/22 at 04:58:23:

Thanks--those are nice tubes, I use them now as replacement for 0C2 tubes in my SE84UFO3 Monoblocks (under the chassis). Does this mean these could be rolled with 0A2 and 0B2 tubes?

Over the years I have purchased three pairs from eBay.

It's an interesting tube. Some years back when I was using a Torii a mention of the tube by Will led me to experiment with it. My take is that it has a tiny bit darker sound than the other 0C2 types I had used, yet quite a transparent, lively sounding tube.

Hey Lon, I found a US source with eBay - thanks.  Then, of all places, I found it on the Decware website as well.  One of those "right under your nose" things.

Thanks Steve for the THD stats. It appears (to state the obvious) that Sarah is now both objectively and subjectively better compared to the close to final prototype we heard at Decfest last month. Exciting!

Over on the Hoffman forum Decware is getting insulted and practically laughed at on a thread about the 300B amp. I have been trying to defend and fend off with little success. Sigh. I just feel sorry for those who close their mind to the possibilities of sound we can enjoy because of Steve's vision and hard work.

Agreed. I just hate to see the ignorance and viciousness and lies.

But in this here and now I should expect it.

No it's not my first day. I was neither surprised nor naive. I just hate them calling Steve an amateur with sloppy workmanship and some sort of evil money-grubber for charging a deposit on a long wait list.

Lon,

Some of those people were on this forum and polluted the earlier pages of this thread and others. I am very glad they are no longer on this forum...I have no time in my life for ridiculous nonsense like that, and certainly won't be spending any of it on that other forum.

Michael

That's kind of like my exposure to the Hoffman site these days.
I check out jazz news, any Beatles remaster news, contact with a couple of (additionally, fed up) old timers, but very rarely do I even glance at equipment BS those folks post about. Most of that is either nonsense, hearsay or flat out BS from people who have no clue as to what they are talking about.

That place has lost my interest as well.

Popped in here for a few minutes yesterday and THIS place was a little pissy.
Puts me off. And, I'm not weak or milquetoasty!

Even though I have been around this site for about eighteen years, I still think of these as some of my early days.
I am just getting to the point, with my new situation this year, where I can enjoy and appreciate more of what is here for all.