Edster's Moondogs are feeling better... (longish post)

[Erik Mandaville]

...and sounding just fine!

Ed's packages (one big box for the amps; another smaller one for the tubes)arrived on Friday in perfect condition. The UPS guy had even covered them with a sheet of clear plastic in case of rainy weather (in Houston, that can happen almost without notice).

And as far as the packing! I told Ed that I didn't think anyone could beat my mom's packaging ability, which would have been the envy of ancient Egyptian embalmers! The amps were extremely well protected and double boxed. Boy, they are nice looking amplifiers, and the stain and light finish formed a great contrast to the brass chassis plate. I have always preferred lighter wood to darker, and the wood I ordered with my Moondog kit was the bird's-eye maple. I like Ed's stained walnut better, as did my wife.

I'll briefly list what was done:

All B+ and filament voltages were just about spot-on. That was good to find.

I replaced the one bad coupling capacitor in one amp, and then changed the corresponding cap in the other amp, as well. Ed sent two capacitors for this.

The rest of the wiring looked to be in generally good shape, but I noticed that the output transformer secondary windings had been wired for 16 ohm speakers. I rewired the outputs for an 8 ohm load. One more voltage check, and everything looking good, I put the amps into my system to listen. Because I use BNC connectors on my cables, I had to look around for some RCA terminated coax, and found a pair in my big box of wired. After letting the amps warm up for about 15 mins., I put in a CD (Narada acoustic sampler). Great sound! They were very transparent and had an almost 'liquid-like' quality that I much preferred to my own (mylar coupling cap....ahem...)Moondogs. At normal listening levels, everything sounded fine, but turning the volume down or off revealed excessive buzz and hum. And! there was a bit of intermittent performance, where the sound would cut-out or drop in volume for a second, and then come back on again (which led me to believe the coupling capacitor may not have been the only problem) The amps went back to the work room for a very careful going-over.

I found two ground bus connections that were loose and hadn't been soldered. Fixed those. I also noticed that the 2A3 AC filament supply hadn't been twisted as it should have. I disconnected the old leads and added a new twisted pair on each amp with 18 AWG solid capper wire (Ed: You'll be able to tell this by the red insulation on the wire). The shielded cable from the RCA jack to the grid of the first 6SN7 was also problematic: The first builder had twisted the braid so tightly that virtually all the strands of the silver shield had been torn, and the braid was hanging to the ground tab on the jack by just a couple of strands. The RCA jack to circuit ground was superficicl at best. The ground wire, itself, was not making contact with the ground bus, but was held in place by a little solder (The solder was what was making contact in this crucial ground connection.) Not good, since solder is a poor conductor.

All input and and output jacks were very loose, so I took off the backplate and tightened those with an open-ended. wrench. The amps went back into the listening room, where I first tested them without the preamp (AES AE-1) connected and the inputs shorted. They were now very quiet -- no buzz or other strange noises -- only a slight, low level hum, which was only audible with my head inside the La Scala bass bins. For SET amps and very sensitive speakers, a little hum is normal. I hooked the preamp back up, and background noise, as it was on my Moondogs when they didn't have volume controls, was a bit louder. We listened to Ed's amps all afternoon and into the evening. My wife liked the sound so much, she at one point turned to me to ask why ours sounded a bit different -- a little less real, less palpable, and more sterile.

As soon as I'm done with this post, I'm off to my workroom where my Moondogs are now awaiting a removal of the volume controls. I've gone through this before, and have been trading a slight roll-off at frequency extremes for a quiet background behind the music. The gain of most tube preamps is really more than the couple of volts the Moondogs need to push them into clipping region, but I have them 25 feet from my preamp -- I need this extra gain. Passive preamplification can be the way to go with short interconnects, but won't do the trick in my situation. I installed the volume controls to have some flexibility over the strength of the signal going into the amplifiers. This has been working, but the music seems to lose a bit of its polish and shine.

I will also be installing the same kind of Jensen capacitors that Ed has in his. Kelly H. told me about these, and I was stubborn and obstinate about the fact that I thought they would sound dull and lifeless. 'Dull and lifeless' couldn't be further from the truth. They are outstanding, and I was very wrong about that impression. I have Hovlands and Solens in my preamp, and I found that combination to sound quite good with the Jensens in the amplifiers. I also am not one who believes in the 'break-in' of wire, cable, and other passive electronic parts. Rather, I think people are the element in the equation that changes. I'm not saying I'm correct about this, and I know many would argue to the contrary. It's just my opinion, and I know I will get more used to the sound of the Jensens as time goes on. As is, I love it!

It was a great weekend, Ed! Thanks!

Erik

[sprocket]

Hello Erik

I hear many folks stating their suspicions about "component break-in". I'll offer this observation

(not my own). Of all internal components, the capacitors may be the most sensitive to any break-in

process. Some report the thermal cycling of serveral hours on followed by several hours of off time

will properly break-in the capacitors. This corresponds with mosts people's listening behavior

amyway.

RB

[jt1stcav]

Good work, Erik (and a good read as well). I know that Ed's a happy camper once again to have his Moondogs up and howling to his Klipschorns!

[leok]

Erik,

Nice job. One could probably count on fingers and toes the number of people, in the world, who would do such conciencious and skilled analysis and rework. Something about how good Klipsch speakers sound driven by good electronics that adds motivation. Thanks for posting the interesting report.

Also interesting about your perception of the caps. I had metalized polyprop. in my pp amps and the switch to Jensen copper foil pio was an education in how much difference a cap can make.

leok

[@silverfox@]

excelent post erik!!.

could'nt help but recall the origonal post by esterdo, and the origonal diagonist by the tech who obviously did'nt seem to know squat about the amp.a tremendous amount of loving care way put into soulving not only supposed pproblem but with previous knowledge solvinging issues that were from inseption.

stimulating post a job well done!!!!!

[Deang]

Excellent work Eric, Ed is going to be so happy --

As far as caps go -- sometimes I think it's a good idea to mix things up a bit. I have the Jensen copper PIO's in my Cary preamp, and what appears to be RelCap MIT metallized polypropylenes for the coupling caps in the Quicksilvers (I say "appears", because the caps are wrapped in light yellow instead of white, with the Quicksilver logos on them -- but I certainly know what the MIT's look like).

All of these caps are fine products, and each have their own signature. I think maybe keeping things mixed up prevents the overall signature from shifting too far in one direction.

Changing the parts in my RF-7 crossovers, and the experience of listening to the signature smooth out over a month -- forever convinced me of the idea of 'break-in' as it relates to caps.

[edster00]

I just want to thank Erik (and his wife) for all the time and effort that went into checking out the Moondogs so thoroughly. My decision to send them to Erik was because of his familiarity with the circuit, heck I'll bet he could build a pair of 'em with one hand tied behind his back. Erik is a great guy to talk to on the phone also!

I can't wait to get them back in the system and give the K-horns a good workout!

[Erik Mandaville]

Thanks, you all, for encouragement and kind words. I left an important part out, however -- that was how Ed and I had an even better conversation talking about ice cream! Turns out he likes to stir his up a bit and let it soften before partaking...me too. I very much enjoyed our phone chats, Ed!

I've got my own amps in the system, minus the volume pots. Things are MUCH improved, and I found the 25 long interconnect was contributing (static, RFI, etc.)to background noise. So I've done away with that! I always prefer to have longer interconnects than speaker cables, and now have an interconnect just under 3 feet.

Ed's amps had an outstanding power supply electrolytic, which was a monster! Also great teflon sockets, etc. I want to save up for that stuff, and rebuild mine with either ceramic sockets.

I've gotta get those amps packed up again to ship tomorrow.

Erik

[jazman]

Erik,

Glad to see your report and your efforts putting Ed's Moondogs back in service. I had often wondered why you had installed the volume pots to your Dogs, but now I see it was due to your preference for long interconnects. I know it's a loaded topic, but I found could hear the difference a high quality interconnect makes between the Dogs and preamp. Just something for you to consider. I am fortunate to have a pair built by an equally knowledgeable builder which have provided trouble free performance, but I always read your post. One improvement I have often considered is installing the rechargeable NiMH battery bias he had used but have not wanted to possibly add a small degree of complexity though there is some benefit.

Last, what do you think of Ron Welborne's new battery powered preamp design and kit?

Klipsch out.

[Erik Mandaville]

Jazman:

On the volume control issue -- tube amps generally tend to be of fairly high input impedance, which contributes to their high sensitivity. Most are also setup to deliver full output with only a very small signal...in the case of the Moondogs, just a couple of volts or so. That's the reason lots of Moondog (or similar SET) owners can get by without a preamp, and use either the fixed or variable outputs on the CD player to go straight to the amplifiers. I did this for awhile, too, and made provision on the Moondogs for a volume control (which is basically a passive preamp installed on the amplifier. Although this had worked fine for awhile, I honestly enjoy and prefer the sound imparted by a tube preamp. The problem there, is that many preamps are of rather high gain. In other words, it's not at all difficult for a powerful preamp to create distortion and noise by overloading an amp's input and driver stages. Since a volume contrl is a voltage divider, it offered the flexibility of having greater control of the strength of the input going into the amplifier. Lots of vintage amps have input level controls, which is where I got the idea. In the end, what happened was that noise levels went down dramatically, to where background noise was virtually non-existent. But having Ed's amps here gave me the chance for a very direct comparison between the two, with Ed's coming out easily on top in terms of performance and sound quality. This better performance comes at the slight cost of increased noise generated by the preamp/amp connection. Adding another power supply into the mix can always present problems of one kind or another.

Battery powered ultrapath linestage: Having experimented with an ultrapath output on my amps (which Leo had done, as well -- and has gone the next level to parallel feed output), I can see the merit of using the approach with line level signals. I have a copy of the original schematic for the ultrapath linestage, as it was printed in Vacuum Tube Valley. The design is by Jack Eliano (who also designed the DRD amps now being offered by Welborne Labs). The battery supply is of course one of the key elements, and the reason why the preamp has been reported to be so quiet. It's one of the things that led to the experiment I did with using a battery supply on the Moondog 6SN7 heater supply. Probably an even better thing to try would be to use the battery supply on the directed heated 2A3. The one other way I plan to lower the noise floor of the amps is by using 6A3 instead of the 2A3. I have a couple of 3 amp. 6 volt filament supplies, as well as the parts to build to full-wave bridge rectifiers and filter section. I would be able to use DC on the output tube filaments. 6A3s are also generally quite a bit cheaper than 2A3s, so that would be an added advantage!

I've never heard the Ultrapath BP, but have read favorable reports. One also needs to be willing to deal with the sort of tweakiness of the battery supply. I bet it's a great-sounding preamp, with a lineage that dates to when tubes werea also used in the automotive industry. That's kind of neat, I think.

Erik