Klipsch/Moondog/AES AE-1 = Outstanding Combination

[Erik Mandaville]

A friend recently sent me his ailing AES AE-1 preamplifier (Audio Electronics Supply - DIY division of CARY Audio)to check out and possibly repair. One channel was evidently not working properly. This piece having been built by another individual, I believe it came to me second or third hand; and as such, I was just a little reluctant to use it to feed a signal to my amplifiers. Normally diagnosing an electrical problem would involve listening to the offending component, but I took off the bottom plate and to check out the circuit and wiring without ever having played it. I also didn't have a schematic, which would have been helpful. I believe AES does in fact sell these -- someone on another forum mentioned he thought they cost around $25. Anyway, there were things I could check out without the circuit diagram.

The builder replaced the dual mono volume pots with a good quality stereo NOBLE, and this subsequently left an unsightly hole in the front panel. I initially thought the volume pot wiring was done incorrectly, but closer examination revealed simply the use of a 'shunt type' attenuator circuit. So that was alright. I have always preferred two mono attenuators to a single stereo control, and returned the preamp to its original dual-mono arrangement.

High voltage rectifiers (dual full-wave fed by a single power transformers)had a damaged diode in each channel. Those were replaced.

Regulated DC current is used for the 12 volt filament supply (6SN7 heaters wired in series), the diode ring that forms the full-wave bridge looked very sketchy, and was in serious danger of shorting against the chassis. I installed a new rectifier and filter section.

Several joints were also found to be either cold or altogether unsoldered. Not having any specs to go on, I checked to make sure all high voltage filter capacitors were working, and B+ voltages were within range for the 6SN7, of which this preamp uses a total of four. 6.3 volts is what would normally be imposed on the filaments, but the 12 volt regulators reduced this only minimally -- if nothing else, the tubes will just last for a long while.

I share all of this, because I simply did not approach this repair with the expectation of enjoying the sound of this preamp as much as I did. I have built several designs from scratch over the years, but none based on this outstanding tube (which are also used in the input/driver sections of the Moondogs. I knew that AES offered very high quality kits at comparatively reasonable prices, but was just always interested in building my own. Having put the piece back together and installing 4 JAN tubes (all registerd very strong on my tester) I put it into the system night before last. It took a very short while to discover that this circuit was very, very good, and easily preferred to the other preamps I've constructed. Music, although not euphonic in the least, had 'cleanliness' and liveness to it that wasn't there before. Small details that previously had trouble making themselves heard, suddenly spoke out with outstanding clarity. I don't care for 'liquid warmth' which to me is another way of saying 'dull' (that's just my opinion....), and this preamplifier exhibited nothing of that. It was just really great sounding! The only other thing I might do, and this with the permission of the owner, is increase volume sensitivity a bit by installing a 250K control instead of the 100k now being used (simple, $1.50 carbon pot that sounds just as good as those I've purchased for $35-$50). 250K is more sensitive in that less signal is sent to ground, meaning that the controls don't have to be turned up as high.

This is the first time I've heard a 'CARY product,' and I was enormously impressed by the quality of parts used and overall build of the component. Very good quality center-tapped and potted transformers are also used, which one doesn't find too often in a kit product. I'm also used to the sort of battleship like aesthetics of my own home-built pieces. I have always preferred the form/function relationship, but the AES products have a little of both. They look really nice in an understated fashion.

What a great addition to the system -- the thought of probably having to return it to its owner is one I regret!

Happy Thanksgiving!

Erik

[mobile homeless]

Welcome to a 6SN7 based preamp...bout time! Heh... I havent gone back from my highly modified Cary 6SL7/6SN7 SLP-70 since 1990 although flirting with others is fun. The typical 6SN7 pre can sound A LOT BETTER with tweaks not to mention very different NOS tubes... I started talking up the little AE-3 (and AE-1 which is similar to an SLP-98) a year or so ago as a great cheap preamp with good potential. Several of the forum members have gone this route including Edster00, Chris Robinson, Tbabb, deang, and a few others, believe it or not.

The DJH version has tube rectification with some really nice parts as well. I find the 6S*7 based preamps to offer very musical attributes(when matched with excellent NOS options); it is open, liquid, relaxed, yet with good dynamics and GREAT AIR, and does not sound DULL in the slightest (not so sure that liquid is another way of saying dull either although I guess it can be if taken to its extreme). An excellent 6S*7 pre can bring VERY nice detail while still remaining musical, a delicate balancing act.

A good 6S*7 pre is a great combo with the Moondogs and Klipsch and mates VERY well with solid state amps to give them some tube-like qualities.

kh

ps- Erik, I have been talking to several 2A3 SET buddies and most seem to be saying the optimial range of the 2A3 for the best sonics is higher than 250-275v. Many are going over 300-350v with the DIY offerings, on purpose.

[Deang]

Erik,

The shunt circuit is something Kirk at Cary advocates. However, I had discussion with Dennis Had on the phone about it, and he doesn't like it one bit. He claims there is a perceived increase in bass response because the circuit supresses midrange output. Dennis feels it sucks the life out of the midrange.

[Erik Mandaville]

Hi Kelly and Deang:

Kelly, I must admit to wanting to learn as much as I could about tube audio design, which began with tubes other than the 6SN7. The 12AU7 variants are also very good tubes, as is a surprising sub-mini triode, the 6021. The latter tube is not much more than an inch long, and has been the tube (just a single one) in the preamp I built after an Eric Barbour schematic. That same preamp was used by the staff at Vacuum Tube Valley for some time. Eric Barbour also contributed a recent article, with information on a 6SN7 based preamp, which uses a 5Y3 rectifier. This one is on hold right now for a future project. If you like that tube, you should try building the design. You've never mentioned your experience in building, although you have talked about swapping coupling caps. I think you might enjoy the process of building something of your own.

Anyway, I've got that AE-1 preamp up and running very well, and rewired the volume controls in the conventional fashion. So I guess it's 'bout time' as you say, however, that is really sort of a relative issue, and I've been busy doing restorations of 1920s radios and other similar things. I'm actually fairly familiar with AE-3, and considered that as an option for quite some time. As I said, though, I prefer the challenge of building completely from scratch, and in so doing, learning more about the process of circuit design and implementation.

'Liquid' is a subjective term, which I qualified as (my opinion)

...and Kelly: Great about the 2A3 voltages, by the way...higher voltage can sometimes improve linearity as well. Current production 2A3s can certainly handle voltages in the 300 range or even higher -- I've known that since the time I decided to lower the plate voltages on my NOS 2A3s. So go for it and crank it up!

I'm leaving mine exactly where it is. I would suggest the same for anyone using old 2A3s, and be wise enough to follow RCA specs for 250 volts. My tubes were not cheap, and I would like them to last as long as possible -- I'll swap (subjectively) less dynamics for that any day.

Thanks for your replies and thoughs,

Erik

[mobile homeless]

No, I have never built an amp from scratch. I plan to within the next few months as a friend and I are out to embark on what I call "The Super HF-81" with his unit being built as an amp only affair(with dual vol) while mine will be an integrated with minimum amount of switching involved.

Parts will be carefully selected for a balance between resolution and musical results. Both our chassis will be hardwood as he has acquired an amazing few logs picked up from the bottom of the St. Lawrence River in Quebec. The wood is amazing. Both will feature brass or copper tops plates depending.

The HF-81 is actually NOT a Williamson design per say and is really a very unique amplifier. I have been in love with this homely vintage amp since I first heard it in a little tube/vintage shop on the outskirts of Philly.

Below is a screenshot of "The Super HF-81" page with the drawing of HIS proposed layout. Mine will be a rectangle length-wise with a stereo volume (as opposed to his dual volume passive) and one source selection with on/off toggle.

I will be using all original EICO HF-81 iron including the power trans. My circuit will be the same as the original EICO minus the tone control circuit as well as the extra switching, tape outs, balance etc. I am not sure on the phono either; this might be external. One half of the 12AU7 will not be used when you remove the tone control stage. While Jean-Francois is opting for the passive volume approach with one input, I will keep the preamp stage as I feel this is a good portion of the sound of this little amplifier. One other change in this circuit might be the implementation of a fixed bias for more user control and specific operating points.

I am looking foward to this project to say the least.

kh

[mobile homeless]

See project above.

See your possible preamp below. This the one you are working on?

kh

[mike stehr]

Keep us up to date on that.

Sounds interesting!

Nichicon VX series axial's must not be that bad of a Electrolytic.

I like going in the local commercial electronics supply place here when it's real jammed.

Then ask for mediocre things like 10 different values of resistors, and 10 different small value caps, etc...

The guy will just give me the parts, every time.

[Tom Mobley]

Kelly,

Your super HF-81 is exactly what I've been thinking about doing. I've been analyzing the schematic to see how to leave out all that stuff without changing the basic characteristics of the amp, I'm stuck on the part where the tone controls and half the 12AU7's get dropped. I would appreciate any guidance I could get from you or your Canadian friend on this. The schematic is difficult for me to decipher because of the involvement of the RIAA stuff in the selector switch and the tone controls being being sort of in between the the two sections of the 12AU7. I do however have a close friend with a PhD in EE who spent time on this stuff back in the sixties. He has offered to help with detail of the circuit mods. Apparently there may be issues with dropping out half of the 12AU7, he thinks this will change the way the remaining half operates. Might need to look for a tube that is similar to half a 12AU7, which in turn will inevitibly raise other issues needing to be addressed. He's digging through his old tube books for one. It may be worthwhile to check into creating a sort of dummy circuit for the unneeded half of the 12AU7, just to keep it live.

Are you thinking about retaining any of the physical appearance of the Eico? I've gone around and around with this aspect as I was thinking about marketing a kit for this.

Tom

[Chris Robinson]

This is a very interesting thread for two reasons ... First, I am about to dive into the SET space with a pair of Wright 2A3 3.5 monoblocks, and I have a well-updated HF-81 that I'm enjoying immensely.

For the 3.5's, I have an AE-3 just sitting in the guest room awaiting their arrival. I had mated it previously to the AES "Superamp" (KT-88 design) and the results were disappointing. I think at this point that the problem was with the poor match of the KT-88's and the super-sensitive Klipschorns. I was, admittedly, concerned about the quality of the AE-3. Your comments, however, give me pause to consider that it might just mate up quite well the Wrights ... so we'll wait and see.

I've got a nice quad of 5962 (CBS Hytron Red Base) in place of the 6SN7 which would fit both the 3.5's and the AE-3.

That wood, Kelly, sounds sweet. I'm sure it is very hard to find, and once found, $$. I've heard of entrepreneurs digging up these old buried logs and milling them for mucho dinero. There was something about the water-logged nature that made them special, although I can't for the life of me remember what it was.

Aging is great fun. You make the same new friends everyday and can even hide your own Easter eggs.

[mobile homeless]

Unfortunately, the preamp that Erik is referring to is actually the AE-1, which is pictured above. IT is a different circuit more akin to the Cary SLP-98 while the AE-3 actually shares more with the Cary SLP-50. I have always said the AE-1 was a great preamp used if you can find one as they can go pretty cheap. The unit above was owned by Edster00 for awhile but I believe he sold it. Not sure if this is the unit that is now being worked on by Erik.

I'm still on the look for a phono stage for you.

As for the EICO project, it is really a long time coming. I bought my second one to use the transformers to build an 81 with exposed tubes and minimal switching/functions, in an attempt to hone the circuit. I couldnt bear to tear my secone HF-81 apart so I am actually buying the iron separate (I might sell my spare EICO HF-81 to finance this whole thing). To be sure, Jean-Francois has MUCH MUCH more experience designing amps and as this will not be a "replace the caps and resistors/pot" deal, it's new territory. The fact that we are building different versions should be interesting. As you noted, the wood is going to be something special.

I am looking forward to hearing your take on the Wrights. WE might have a phono stage lined up by then as well.

kh

ps- Tom, see reply in the EICO on ebay post

[Erik Mandaville]

Hi Kelly:

First off, your Eico project sounds really interesting, as does the wood you have found to use for the chassis. Things like that can make for a very personalized touch, and turn out to look awesome. I agree with you on the simplification of the circuit, as well. But each to his own in terms of needs, desires, etc. I hope you'll keep us posted as this project begins to unfold.

Yes, that's the preamp I've been working on, though the front panel no longer has a hole in it. I much prefer a dual-mono volume control set up, and put in two 100k pots I had on hand. High quality resistive elements are good for stereo controls, where more accurate tracking is needed. With two mono controls, one can even help offset differences in tube gain, making close matching between tubes less imporant. The coupling capacitors (large ones, too!) were flopping around loose inside, since the tie point they were attached became unglued -- sort of like the terminal strips on my Moondogs. The wire nut seen in the picture on the yellow 5 volt filament leads (for a tube rectifier not used on this) is just a plain bad idea. If the wire nut happens to cut into the insulation, the leads can short out. Better to cut them to slightly different lengths, bend over the tops, and then simply tape them off with electrical tape (which is what was done). There were also many leads that were far longer than they should be. All that said, I very much respect the first builder for making a great effort. I still have the first amp I put together, and have not changed the wiring becuase it makes me laugh to look at it. What a rat's nest!

Ed has not sold it yet, but the author of the post is interested! Just don't know if I'll be able to afford it!

You all have a good day today.

Hey, Kelly? do you happen to know how your SET friends are taking the B+ reading on the plates of their 2A3s? Plate to ground will give a reading that is about 50 volts higher than what it actually is.

Erik

[Erik Mandaville]

Hey!

I just grabbed a handful of rice crispies, and then thought of this! I haven't actually measured the available space on top of the AE-1 chassis, but there may in fact be room for dual, 5Y3 rectifiers. The AE-1 already uses two separate full-wave rectifiers coming off the single high voltage secondary, and as such also uses two separate capacitor input filter sections. All that might be needed is a power resistor adjustment in order to obtain correct voltages for the preamp. I might bread=board this off the chassis, and just run wires to the load. This might be interesting!

hmmmmmmmmmmmmmmmmmmmmm

Erik

It's not even mine yet, though! Guess I'll have to wait before I pull out my chassis punches.

[edster00]

When I purchased the AE-1 (to use while I was waiting for my Syrah to be built) it was "in perfect working order" according to the seller. When I received the preamp the input selector switch was broken. I contacted Kirk at Cary for a RMA to have the switch replaced and I also paid to have the AE-1 completely checked out to be sure it was in proper operating condition.

When I got the AE-1 back from Cary it didn't work...it sounded great on one channel and nearly no volume in the other. I did everything I knew to do (being soldering iron challenged) to correct the problem but to no avail. About that time I received the Syrah and so the preamp just sat on my workbench. I don't think Kirk did anything to it at all other than replacing the switch.

I eventually sent it to Erik for him to take a look, it is amazing to me he has been able to do so much to it without even a schematic to go by!

Erik,

As I said in previous emails you are welcome to do anything you like to "hot rod" that preamp. I emailed you from my office yesterday, did you receive it?

[Tom Mobley]

Ed,

>>When I received the preamp the input selector switch was broken. I contacted Kirk at Cary for a RMA to have the switch replaced and I also paid to have the AE-1 completely checked out to be sure it was in proper operating condition.

When I got the AE-1 back from Cary it didn't work...it sounded great on one channel and nearly no volume in the other.<<

Yikes, this is really not good. Are there other reports of this kind of service from them? I thought they were supposed to be pretty good? They must not have even powered it up.

Tom

[Tom Mobley]

Kelly,

Why don't you start another thread labeled Super HF-81 or similar, make the first two posts be the ones from this thread along with your post from the "Clean HF-81 on Ebay" thread, I'll put in my replies from here and over there, we'll consolidate the deal into one thread. I'm willing to use my HF-81 as a breadboard sort of thing for the changes, but we may need to recruit some real ears from Phoenix for testing since mine aren't really much good. I've got a set of Heresy's and LaScala's to listen to. The actual work involved in bypassing the tone controls is trivial, move a couple wires.

So, basically, I'm suggesting we make this into an online project, use my existing HF-81 as a breadboard. Once the design is validated on my Eico, build a open tube prototype on a metal chassis, then a finished product with your cool wood, polished copper/brass, all that.

Tom

Or I'll do it (start the thread), if you want to proceed that way. Or, we could take it off-line, but I'd rather do it in the forums, excellent chances of picking up good ideas from the others. There's some very knowledgeable people on here.

[edster00]

Tom,

I had heard nothing but good things about the work done by Kirk at Cary. I was very disappointed that the preamp didn't work when I fired it up. I didn't call Kirk to ask what was up because I had received the Syrah and I waited several weeks between receiving the AE-1 and giving it a listen.