Mullard 3-3 Pics and Review

[JoeTele]

Thought I'd post the final pics and thoughts on the 3-3. It's all done, stable, and I'm enjoying it like crazy. This is my first experience with tube hifi (and, for all practical purposes, hifi period). After 4 guitar amp builds, where the point is distortion in varying degrees, it's neat to hear how tubes do clean music reproduction. Most of all, it's an experience akin to vinyl in that the "inconvenience" by modern standards is part of the magic. It's great to flip that crisp, metal switch, see the big amber pilot light go on, and of course wait the necessary time for those tubes to glow orange! In the end, all of the power supply resistors and caps are back to stock values, with the exception of the first dropping resistors, changed to accommodate the 5AR4 in place of the EZ80. It's funny because after a few hours of music through it, it actually cooled off. The cathode had been hovering around 29 volts but stabilized at about 26.5 when I measured after some initial play. With that and going back to the stock screen resistor values, it stabilized at 13.5 watts of EL84 plate dissipation rather then 15.5, which is where I was at first power-up/listen. Pics are attached. It's largely inspired by the one in the original plan (particularly the stovetop knobs) and the copper chassis was my own idea. The speaker was supposed to be a hammered brown Rustoleum, but I had no idea how MDF digested paint and my filling job wasn't as good as I thought. No biggie, though. Perfectly presentable in my dimly lit apartment. Though I didn't go into this with audiophile intentions, I couldn't help but come strive for a creative idea to connect the amp to the speaker, so I rigged a set of nuts, bolts, and washers to clamp the speaker wire directly to the OT secondary leads, exposed on the back side of the amp, and soldered the wire directly to the terminals of the full range driver on that side, with added strain relief on the back of the speaker box.

Overall the sound is incredible. The major caveat is the stereo to mono conversion, which impacts some recordings more than others, and is what it is. That aside, I'm completely blown away by the big, full warmth and clarity that the little amp can push out that single box/driver, and the way the sounds bounce around inside the box. It's really got me doing more focused listening to/appreciating music rather than just having it as background to other activities. I could go on for quite awhile about how it handles different styles, as I listen to many, 3 things jump out at me.

1. One of my all time favorite albums is Miles' In a Silent Way. There is a lot of space around the instruments and I'm hearing things for the first time through the amp, especially in the low registers, such as subdued but omnipresent rumblings of the electric synths.

2. Modern R&B and Hip/hop. Not what I listen to most, but given the unrepentant digital hi-fi nature of many such recordings, I would not necessarily have expected this setup to be the best delivery system. To the contrary, the clarity and definition is top-notch (minus, of course, stereo to mono losses which can skewer the relative levels of voices and instruments) and the system adds a nice woody warmth on top of it. The vocals often sound like they are being recorded right in the box.

3. Acoustic music/Bluegrass. Absolutely breathtaking. This set-up was made for acoustic music and acoustic music for it. If this were all or most of what I listened to, my perfectly respectable Klipsch powered satellite speakers and subwoofer would be on Craigslist. Great acoustic tone is as important to me as great tube amp tone (I recently sold a Santa Cruz and bought a Huss and Dalton if that's any indication) and there are songs I could listen to over and over through this amp. One that comes to mind is a progressive, gypsy-esque Tony Rice tune called Port Tobacco, which has some of the coolest, complex interplay between guitar, mandolin, and upright bass I've heard, and they all shine through. Here, even stereo to mono losses are more than made up for by instrument tone.

Honorable mention also to Wagner overtures, preludes, etc.

One final observation is that the simple but very useful treble/bass tone stack invites tweaking for different albums.

So, thanks again for all the help! Happy to answer any questions, but at this point you've probably read way more than you cared to anyway

Joe

[dorrisant]

Very nice Joe!

[strelok]

The major caveat is the stereo to mono conversion, which impacts some recordings more than others, and is what it is.

You could always build another!

[rp]

That amps looks terrific, totally retro cool. You actually went for the volume and tone controls. I would have figured everyone entering from the digital era would have used the volume on the ipod or computer, either the analogue or the s/w digital. Neither of which sounds good, source is best left up full especially digital and gain done analog on the preamp/amp end, though it is nice to be able to lower the volume from the computer. Nice to have the option. I would have skipped the tone controls especially w/ 3Ws and 4” driver. Might want to try bypassing them to see if you hear any more clarity, if so you can always add a switch. If you used carbon pots, film pots are a noticeable improvement. Alps Blue Velvet is the econo hifi standard.

Given your sonic satisfaction, you need to build the second pair and go stereo - you know you wanna, or will real soon. BTW just a thought, if you think this could happen in the future, you might want to buy the 2nd driver now and set it on the shelf. From what I’ve gathered, Fostex often drops or changes models to mk2/mk3 etc. You’d definitely want the pairs to match.

After the stereo pair you get to build something like this http://diyaudioprojects.com/Speakers/Fo ... -Speakers/

Been my dream. I’ve never had the chance living in little apts. Friend just bought a vast house in the burbs of Cleveland, huge property around it. I may go stay out there just to do all those things I could never do in NYC, or Italy, like build a big SET tube & horn system, and build and play a 100W stack as loud as I f’ing like when I like.

Little tangent: Since you discovered that good kit enhances musical pleasure I’ll note that good Hifi isn’t BS, though there is a whole lot of BS in that industry. As in any high profit luxo endeavor, you must put on a whole lot of show to hustle the rich out of their lucre but that doesn’t mean it’s BS through and through. Like in photography resolution is a drug, once you get it you always want more. When was the last time you watched a VHS on a 25” 480p TV? Try it, you won’t believe how God f’ing awful it was, and yet it was fine before we knew better. That’s what generic hifi is: 480 and VHS compared to watching a Blueray on a 55” 1080p flatscreen. Funny, people think good hifi is nonsense even for music they adore, but run out and buy the latest 4K Flat Screen to watch MSNBC or play video games.

Trick to good hifi is high resolution in an organic holistic whole (like real live music) not disembodied detail floating out in an unnatural 3D space. Get everything right, resolution, tonality, imaging and pace, rhythm and timing (PRaT) and you’ll catch the hifi bug. I could never sing or even attempt bluegrass harmony till one day I bought a used Naim NAIT II and Rogers LS2 speakers to use will living abroad for a year. Suddenly I could hear the lead and harmony lines distinctly, follow them easily. My timing on guitar took a great leap forward, so much so that friends wondered if I’d done the Robert Johnson devil at the crossroads deal.

I left tubes behind after discovering the PRaT thing, sold off my tube C-J gear and HiFish speakers for “flat earth” BBC style NAIM SS gear and Spendors. I think ss is better for Rock or anything that has a hard driving rhythm, so even acoustic Bluegrass qualifies. SS seems to help drive a Fender bass better, it’s a dampening thing I think. Tubes are fantastic for classical chamber and small ensemble music, music where the timing floats more than charges. Horns or small single drivers are fantastic for open dynamics of classical. Jazz is a toss up but the ability of tubes to float a throaty sax up in your face is pretty f’ing cool. I’d love to spend an afternoon w/ Coltrane complete Village Vanguard box and some large horn or single driver speakers and some single ended triode amps or a simple Williamson triode PP. I’d sadly written this all off many years ago. But the internet and forums really got me curious again and raised my confidence level. With forums you can pretty much get walked through a build or a troubleshoot these days. Pretty hard to screw up compared to when you just went at this stuff blind and blew money letting the smoke out.

BTW That must be a fine Huss and Dalton to replace a SCGC. Curious, was the SCGC giving you any stability problems or just liked the H&D better? I had to get mine re-topped, a little too lightly braced. Could have sold it during the dry months but would have felt bad. Freaked me out but I’m over it I guess, sounds even better but still not trouble free. IMO best stick with 50y/o seasoned guitars if you have the choice.

Thanks for the Fostex report. Get the other stereo pair made - that mono stuff is driving me nuts!

[dcribbs1412]

Congrats Joe
great looking build!

D

[JoeTele]

Interesting point about the tone controls. I may try bypassing, but I actually use them quite often so I'm guessing they'll stay. Being that this is my first Hifi build, I'll probably just keep it as is, mono and all. The vibe of the whole is just bigger than the sonic deficiencies. I will probably build a stereo in the future though and start with a fresh set of speakers, though the more I look into it, the more the whole idea of full range drivers appeals to me. I think I'll look to build something just a little more powerful so I'm not limited to 93db+ speakers/drivers. I get what you're saying about distilling the good from the bs in hifi audio. Here is a great video about that if people haven't seen it: https://www.youtube.com/watch?v=m7ERMu825m4

I'm sure if I went through mine band by band I could pick out plenty of frequency specific weaknesses (and have to some degree) but like you say, it's the organic totality and immediacy of the sound that is exactly like looking at that 1080 HD tv for the first time.

The Santa Cruz was amazing, but it was a mahogany dread (Vintage Artist) and I wanted rosewood. It just, imho, is far more difficult to find a rw acoustic that does rw well. Mahogany just seems more forgiving so I started with that. Also, the SC had enough overtones that a friend who works with acoustics for a living remarked that it would be an exceptional fingerstyle guitar. That's just not what I was after, at least not now and to me H&D have all the impeccable build of Collings et all but are more woody.

[strelok]

You could always add a bypass switch if you want to keep the option available. Could do it as a push/pull pot if you don't want to add another hole. A simple SPDT would work, with, say, a 56k resistor in series to compensate for bypassing the bass pot. Then you could do something similar with the treble.

The thing with negative feedback is its never truly negative. That is, the signal being fed back is never really 180 degrees out of phase with the input. The reason for this, aside from the very slight propagation time, is mainly due to phase delay of the various components encompassed within the loop. Anything encompassed by the loop with a capacitive or inductive impedance, namely transformers and capacitors, will introduce phase delay that varies in its amount with frequency. When this phase shifted signal is fed back into the input it introduces high order harmonics that are interpreted by the ear as loudness, brightness and/or harshness.

Fwiw I work for a Hifi company that builds tube amps and pre-amps with no negative feedback anywhere in the circuit, aside from the smaller amps which have about 1-2db, so practically none at all. For a while I didn't get the whole audiophile thing, then after working there for a year, while listening to the test system it finally clicked. I had been listening to the test system while working late quite loud, around 85-90db for at least an hour or two. I suddenly realized that my ears hadn't gotten fatigued in the slightest, normally more than half an hour at that level I have to turn things down, but not in this case. Just some food for thought on the effects of heavy NFB in a hifi context, and keep in mind this is in comparison to SS amps that generally use lots of NFB.

If you where to bypass the tone controls you'd remove some of the phase delay in the loop. Now I'm not saying you should or you must like it better that way, but just a suggestion to experiment with. I do recommend experimenting with it though Also I'd need to run the numbers to find how much NFB the Mullard uses so I'm not claiming it suffers terribly by these effects, just as something to try.

Also if you're interested in doing something slightly more powerful for a stereo setup, the Dynaco ST70 or ST35 are excellent places to start, as well as the higher powered Mullard amps.

[JoeTele]

strelok,

How much power are you able to get with no negative feedback in a hifi circuit? I'm not looking for much more loudness than I have with the Mullard (which actually came in right around 3.5 watts) and a 93db speaker, just the ability to get as much with (possibly) a less sensitive one, though I suppose having 2 channels for stereo is already going to give things a boost. Upon getting into hifi, I was immediately attracted to the single ended tetrode philosophy and I know that lack of negative feedback is part of it's appeal. Are you working from circuits that are out there or are they proprietary?

Thanks!

Joe

[strelok]

Generally you'll get more gain however it won't be as clean. I wouldn't recommend running a pentode circuit without any NFB for HIFI and/or running UL mode. Generally you want at least a little, maybe 5-10db. Pentodes generally aren't all that linear, which is why we like them in our guitar amps so much, most everyone will tell you a guitar amp with triode outputs or pentodes running in triode mode are rather boring or unexciting to listen to. Triodes are very smooth sounding and if you're over driving the power section chances are that's not what you're going for.

If you want the same volume with a less sensitive speaker you'll need a bigger amp. Unfortunately there really isn't much in the way of getting around this. Certainly not while maintaining performance.

The SET has some great ideas behind it, but its not without its drawbacks. Namely efficiency. A 40w triode (like the 300b/2A3) can generally be expected to put out about 7 watts and you can expect the power consumption to be around 200 watts total for a pair of monoblocks. They also tend to be big and heavy (for their output power) and require a beefy driver section to drive large power triodes.

However the upside is you get an amp, that while relatively dismal in performance in comparison to any modern amplifier on the bench, has harmonic content within the range that the ear finds pleasing/tolerable. Namely second and a bit of third. As I somewhat alluded to earlier if you were to take that same SET without any NFB and start adding it in. You'd see those 2nd and 3rd harmonics get "squished" up the spectrum to the higher order ones. The overall THD has gone down. However they're now in a region that the ear is much more sensitive to, as they are no longer musically related to the fundamental frequency. This is why amps with lots of NFB can sound harsh, bright, or just loud in comparison.

This is one of the great caveats of NFB that is quite often overlooked in hifi amp design. Especially SS stuff where you have a ton of gain at your disposal in a small package so why not use up a lot of it on making the amp supposedly more linear by adding in a ton of NFB. The other problem is that when these bench specs are taken, they are looking at voltage linearity which is fine for a voltage amplifier. However when talking power amps you must consider the power linearity as well. This a whole huge topic that I won't delve into super deep but you can find more on it by searching around if you wish.

The circuits we use are somewhat proprietary, however I can tell you that they're all triode based, and are output transformerless using a bridge/circoltron topology.

[JoeTele]

OK so I'm interested in stripping some of the controls in the 3-3. I did some listening/experimenting and decided the treble and volume can go completely. Things don't sound shrill with the treble maxed out, and I can cut at the computer eq if need be. Trying to boost bass with the computer is more problematic though, and the amp does not sound great with the bass added by the nfb network turned all the way down. Would there still be value replacing the pot with a fixed resistor at my preferred value (about noon on the pot)? Could the effect be achieved with fewer components?

Also, very basic: could someone explain why that nfb bass boost works at all? It seems that any frequencies that encounter the bass pot and .1uf cap are going to hit the same 6.8k/390pf junction that is there in the version with no tone controls, regardless of whether they go through the pot or around it and through the cap.

Thanks!

Joe

[martin manning]

You could certainly replace the pot with a fixed resistor. You might want to experiment with different values for the 0.1uF cap, though. The 6k8//390p is going to start increasing the NFB up around 60kHz. That's not about audio frequencies, more likely about suppressing oscillation.