[nlitworld]

Yep, that looks super easy to make a star ground connection like you're describing. Thanks for the tip! Looks like I'll be busting out the soldering iron this weekend. 

[MosDeaf]

After I attached the purple shield wire from the power transformer to chassis that got rid of the last hint of hum/buzz. I did a listen test after attaching the IEC to chassis & leaving the power transformer still in the IEC as initially directed. Well it's initially directed to leave both wires in the IEC but just doing the safety to chassis & not the transformer I could still hear a hum/buzz with ear to the woofer on my test 2-way speakers. After attaching the transformer shield to chassis as well I can put my ear On the woofer & hear nothing. With ear On the tweeter I can still make out what I call tube hash. But I'm talking ear on the tweeter to hear it. My ears are in their 50's though.

A builder/repair tech friend of a friend told me how to test if the heater circuit is grounded or floating.. or if only one of the heater pins is grounded or floating & to give him the B+ voltage. He said if the amp is designed how he's guessing it is he will show me how to do a heater elevation mod. Said it's like making a 2 resistor junction near the B+ with a small terminal strip or whatever I want to use & then run 2 small wires to the 6.3v inputs with a small resistor in series. Said it should drop the noise floor by at least 10db. He says that's a small estimation as it could be much higher depending on the circuit. I'm happy with the amp as it stands though.. but I'll give it a shot.

I think this is a legit good sounding amplifier.. especially for the money. I did try a handful of other . 22uF caps, even tried raising the value with a couple but those old Russian oil caps were pretty good right out of the gate. I'll give them a few hundred hours before considering something different. But I have to mention that they measured kind of high in ESR on my LCR meter vs newer caps. I gave them a chance anyway & thought overall they were good. I have a quad of V-cap ODAM's I haven't tried in that spot yet. I've used them in other builds & they are more transparent & extended at both ends of the FR. More transparent than adding any character or emphasis anywhere to the sound.

I've also built a couple preamps from tubes4hifi that I had to redo the wiring scheme that they give you..in order to make it quieter. Very good preamps.. even the 9pin SP13. A little tricky when it comes to getting dead quiet. Anyway, I hope that these little changes reduce any of the noise you can detect. Good luck.

[nlitworld]

Yep, I'm excited to bust out soldering iron and try these grounding scheme mods. I've heard several people suggest mods to the preamps to improve ground noise, so it doesn't surprise me that amps need the same. My SP9 preamp needs the same.

[MosDeaf]

I finally got a chance to listen to the amp outside of my testing set up. Something seemed a little off with it.. unless it was something else in that system. The el84 didn't sound as good is the easiest way to describe it.

I went & looked at the ANK build of this PCB & they direct builders to hook the OPT's to the speaker jacks.. not the PCB. I'm wondering if me rerouting the output transformers to the PCB has altered the feedback design in a bad way. Some time this weekend I will reverse it then give it a good listen.

[nlitworld]

I was wondering about that. Keep me posted how that works out. 

I did look at my amp again and wondered if twisting the wires to and from opt should have been done. I didn't twist them at all, but I could easily go back in and do the pcb to opt blue,res,brown wires. The opt to speaker connections I cannot as they are crimped and soldered in place.

Aside from that, I'm excited to explore your grounding mods. Need to finish a couple other projects around the house first, but that is definitely on the table.

[MosDeaf]

Yeah I have a handful of different projects & chores to always get done as well. I'll definitely share my thoughts when switching the OPT's back to the speaker jacks. The music was just kind of flat & the bass just sounded wrong with them hooked to the PCB.

[Bill Baker]

Very nice build. Love the paint job.

[nlitworld]

Parts ordered for ground breaker. Will see how it works out next weekend when I tear into it. Also snagged a few other parts for dac coupling cap upgrade as well. Horray for soldering projects.

[nlitworld]

Very nice build. Love the paint job.

Thanks Bill. I like fun painting projects like this, so it's good I get to keep my chops up in spraying.

[nlitworld]

Parts ordered for ground breaker. Will see how it works out next weekend when I tear into it. Also snagged a few other parts for dac coupling cap upgrade as well. Horray for soldering projects.

So groundbreaking and better star grounding certainly did make the noise less, but it's not exactly 0. Probably 80% better than before. Wouldn't be surprised if the NOS Sylvania tubes I have in there are just a touch noisy. One of these days I need to go back and measure voltages just to see if perhaps there's something else causing that last little bit of hum, like a low B+. But all in all, it's definitely better. Thank you for the tips!

[nlitworld]

So I did decide to open amp up and take some measurements of voltages and think I found part of my hum problem. I may have overdone it on the choke and it's pulling my B+ voltages down too far. The schematic wants it roughly 330V, and I was sitting at 299V using the suggested 22uf cap. Also the bias voltage suggested between 10 and 12v and it was sitting about 9.25.

Checking suggested measurements it recommended changing the first filter cap to 24.2ish to get up to correct voltage, but it only pulled it up to 305.5v. It also pulled bias voltage up to 9.5/9.6ish. Moving in the right direction, but calculating change in voltage vs change in cap size, my first power supply cap likely needs 33uf. Ordered another from Elon so we'll give it a go next week. If anyone is interested in a pair of 12uf Obbligato silver caps for cheap, let me know. Barely used... 

Good news is I'm learning a bunch on how tube amps function and power supply filtering. I figure an applied education lesson at $50ish in tinkering is pretty good deal. I'll post results once I swap those caps out.

[MosDeaf]

Good job 👍 Certainly doesn't hurt to start getting a better understanding of the power supplies.. it's such a vital component of these tube amps.

I haven't had much time to play with mine & I was all excited after switching up the Grounding & better audible improvements on my test system. But when I brought the amp into my music system there is still some audible noise floor. It's better, not bad, but I can't help but want silence.. or close to. But I didn't even try switching out the resistor for a choke yet. I was looking at a 2 Henry 350ma choke. Do you recall which size you went with?

Last time I checked my B+ I was closer 337-339vdc. Bias at 11v

[nlitworld]

Choke I used was a Hammond 193P. Circuit diagram calls for 5H 350ma and that 193P was the closest to without undersizing (5H 500ma). I think since that filter is so filtery, it dropped the voltage though. It is YUGE though. You could probably go less than that, but I didn't know enough to make that designation.

And yeah, I don't demand SS amp dead silence. I'm totally understanding of tube amps having something there, but I don't want to hear it 6ft away.

[MosDeaf]

Thanks for re-sharing the choke that you went with. I'll have to search for something closer to spec.. without raising the resistance too high compared to the 10ohm resistor it replaces.

But in actuality, as far as noise goes, I'm not hearing anything unless I stick my head near-ish the speakers

[nlitworld]

Oh yeah. I went with easily available meeting equal or over specs, but I'm sure there's a lundahl or other one that would meet spec without being 11lb behemoth. Most people would consider the ear to speaker performance good enough, but we are not like most people. We want that last 5% of performance squeezed out of everything. I should have that other cap Wednesday most likely, so I'll keep you posted how that goes.

[nlitworld]

Update: no change in voltage by applying a larger first filter cap. I actually had higher voltages running the 2x 12uf caps than I do the 33uf. Back down to 299v B+ and 9.25-9.5v on power tube test points.

It does sem to be a smidge quieter though. Not sure if there's just less AC noise right now or if ambient noise in the house is just higher. Either way I'm keeping the higher 33uf in there for the moment. I think I'm done tinkering... for the moment. It sounds freakin amazing so I need to hyper fixate elsewhere in my system.

[nlitworld]

I adjusted the position of the choke from the second resistor to the first resistor point making it a clcrc filter. I think there was a typo on their circuit board as to where it was intended. Now rather than just the ecf80 tubes getting filtered power, the whole unit is benefitting.  Voltages seem about the same of 305v B+ and same for the bias points. There was a good difference in black background though. My preamp connected still makes a tiny amount of hum with ear to speaker, but with no input connected it is absolutely dead silent. I'm already eyeballing new preamp options, so I'm calling the amp tinkering done. Last night playing some music to test out, it was sounding very very good. 

Thank you guys for following along and all the help with this build. I've learned a lot along the way.

[MosDeaf]

Yes, there is a 220 ohm resistor & a 10 ohm resistor in the power supply. From my understanding you would want to replace the 10 ohm resistor with the upgraded improvement of the filter Choke. One would want a minimum of a 300mA rated choke for this amp with a stereo pair of el84's.  You can go with a higher amp rating, or higher Henrys rating.. even though I believe 1.8 to 2 Henrys will make a good positive difference in this power supply. It's the DCR rating of the choke that you should pay closer attention to. Anything over a 10 ohm DCR (10ohm resistor you replaced)  is going to drop the voltage lower than what the circuit is spec'ed for. I was able to come across a couple of quality filter chokes not being ridiculously expensive with DCR's around 23ohm, 19ohm. A difference of just a few dropped volts  compared to the 10 ohm resistor being replaced. Not a huge deal...& a Super low DCR choke for an amp like this would probably need thick wire windings which would cost more.

I had initially ordered a filter choke when I purchased the amp.. it had a DCR well over 200 & I never bothered even trying it. I also wasn't even sure of what I needed.  It wasn't until a few weeks ago that I was able to figure out what would work. 

I ended up taking those vintage Russian oil caps & replacing them with some mcap evo silver/gold oils. I had to use a slightly higher value because it's what I had available. .47uF vs the stock .22uF. I didn't notice any difference from the value change but it made a big difference getting rid of that last little bit of noise at the tweeter. Using an LCR meter the ESR of those vintage caps was huge compared to the non-existent ESR of the modern caps. If I use a higher gain preamp with this el84 amp it raises the noise floor. Low gain or solid state preamps or dacs attached straight to this amp & the noise floor is great.

Overall this is a very nice sounding amp. Maybe some pricier or different type of iron/transformers would change the tone but I am very happy with where it stands using the toroidals. You are definitely getting a fuller bandwidth compared to some of the non-toroidal units that only extend down to 40 or 30hz. Good iron costs good money.
This circuit is good. You don't need to use boutique parts to get good results. I have a separate PCB of this amp filled with no-name parts other than some nichicon electrolytics & some budget Audyn Q4 caps. I was very impressed with how it sounded as well.. though I prefer the PCB I populated with some better passive parts in certain areas. I think this amp sounds great.. when listening I never find myself wishing it had more or less of something. Though I always yearn for better dynamics.. dynamic swings that make you jump. But I feel that way with just about every component.

Compared to other kits & builds I don't think this one is very hard. The extra grounding points were an adventure but now I know.
If anyone ever needs a tube preamp & wants to try a kit I always recommend Mellow Tone Kits. They have very thorough build videos on YouTube. They will even tell you which temperature to use, & how to properly solder. I've built a couple of their preamps. Good kits to grow your confidence.. & then you will be tackling all types of projects. Their preamp circuits are very simple, sound, & stable. You can alter the tone just by upping the values on the 1st plate & cathode resistors. Simple circuits you can experiment with & will better help you understand what is actually going on & why. They just recently released a truly balanced preamp kit..& they have a couple amp kits but I've never tried them. I have no affiliation with the designers.

That's my rant for the day. Thank you @nlitworld for making this thread. Your preamp looks beautiful. Maybe one day I will get a nicer looking chassis myself.

[nlitworld]

Yep, replacing the choke position made the amp dead silent. The Hammond 193P I bought is huge, but effective and fits the low resistance criteria. If I plug my phone is as a source, I can't hear any faint noise even with ear on tweeter of my NX-Studios. Problem actually arises from my preamp, so next project I will be looking to replace that. The amp is based on a clcrc power filter, but the preamp is just "c".  Perhaps a Django preamp or a much better design lower gain tube pre than my current one, and definitely hope for a better grounding scheme as that has a good bit of influence as well. We'll see where things go there.

[MosDeaf]

That's a proper monster choke you have. You really did a great job making this amp All it can be..personally I can appreciate the effort you put into your parts choices. I'm currently taking advantage of parts connexion's 20% off sale & grabbing some of my favorite passive parts.

I'm about to look up this Django preamp you mentioned 👍