AES AE-25 DJH Super Amp

[Budnick123]

A friend has just purchased an AES AE-25 Super Amp from eBay. Both he and the seller did not realize at the time that it was the DJH version of the AE-25. Unfortunately, the amp didn't come with the biasing meter that was supplied when new nor the manual. My buddy is irritated by that since finding info for this particular version is not very easy and the differences between it and the regular and Signature versions are enough for my buddy to think that he can't use the same biasing procedure the Signature uses. He also sees that the tubes on the amp look tired, so he would really like to find out what the biasing procedure is if he ends up keeping it verse sending it back to the seller. Though, I suspect the seller probably never had the meter and didn't know that it originally came with one. For anyone wanting a biasing meter for their Cary or AES amp, and don't know how to make something that would work using a multimeter, you can currently get the Cary MA-300 meter from carydirect.com for $100 or musicdirect.com for $85. By the way, I have a regular AES AE-3 preamp (they did make a DJH version of that as well) and brought it over to my buddy's house so that we could have a listening session. They are both high quality pieces that sound very good on their own or together. Back to the amp. From what I could find on the internet, the regular version is auto biasing and the Signature version seems to have some info which is easy to find on the internet. I could not find the user manual for the DJH version. Given that it has a single output for a 1/4" phone connector and one adjustment for biasing all four tubes, my buddy knows that they are all biased at the same time. I found the biasing procedure for Cary amps on the caryaudio.com website in their FAQ section. It seems to differ from what is needed on the AE-25 Signature and DJH models because it only has one jack for both channels instead of a jack for each channel making my buddy unsure if it applies to his unit. After doing some searching on the internet, I found some info on the Audio Electronic Supply AES AE-25 DJH (Dennis J Had) Super Amp, which I copied and pasted from the now defunct superamp.com website. I found the below info using the WayBack Machine and digging through the old superamp.com website. It is presented as being a letter by Dennis Had. I cannot confirm this, but I don't know why it wouldn't have been his words given it was on one of his business's websites. It does provide the biasing current for the various types of tubes you can use in the amp but not the procedure on how to prepare the amp before making bias adjustments. Hopefully this info is helpful to those with the amp but not the manual and maybe, some individuals with the manual can add more info to complete the knowledge base for biasing the AES AE-25 DJH version.

Dear Audiophile Friend:

I have spent countless hours designing the Super Amp and this VERY special DJH version. My associates at Cary Audio have, on numerous occasions, asked why I was spending so much time with this product. If I may, I would like to give you the history of the DJH Super Amp.

The Super Amp started life as the model AE-25 stereo amplifier offered for the last two years by Audio Electronic Supply. The original AE-25 amplifier utilized a pair of EL-34’s in a basic push-pull configuration. At $800, in factory built form, I felt it was good but not quite approaching the magic of the single-ended triode sound. In fact, I would have to put it in the category of a good amplifier but clearly worthy of improvement. I may sound harsh by this description but once again I am accustomed to Cary, CAD-805 sound. This original AE-25 had EL-34’s, push pull, feedback and good specs. However, I felt, with much work, it could be improved. I wanted to make the AE-25 come closer to the music. I needed it to become an exceptional sounding amplifier.

For those of you not aware, I am a triode-crazed audiophile. Do KT-88’s or EL-34 tubes have any merit? They sure do! Simply take a look at the curves when connected in the triode mode. Looks similar to the good ole 300B or 2A3 for that matter. Even the 6L6 looks like a great tube when run in the triode configuration. So, off I went spending enormous amounts of time to create some realistic musical excitement. As I developed the Super Amp I soon discovered that I was enjoying it much too much. I mean, it was push pull in design. I was able to develop some nice triode parameters utilizing an extremely sophisticated output transformer design. I was on my way with the “fun factor”.

As I continued to design and listen, my wife, Donna, proclaimed, “you are producing some super sound tonight honey”. That’s it …. I'll call this the Super Amp. Super sound needs a super amp. Thus the name was born. Super Amp!

The first public showing and listening session of the Super Amp occurred on January 23, 2000, in Charlotte, North Carolina at the Charlotte Audiophile Society meeting. The raves and thumbs up approval were overwhelming. Several members even placed orders with me at the meeting, which was the ultimate compliment. I have been crazed with this lil ole amplifier since the first showing.

For the technically minded, a review of the circuit is in order. The DJH version of the Super Amp operates in a class A/AB mode. The output stage KT-88 tubes are fixed biased, with an equal negative bias voltage to ensure maximum linearity. Utilizing this bias network will permit the user to try many different types of output tubes if desired, a tweakers delight, if you will. Some of the choices may range from EL-34’s, 6550’s to 6L6’s. One might even wish to listen with 6V6’s. All these output tubes will present their own sonic signature, thus allowing the proud owner the ability to change the sonic character of his or her amp at their whim. There is a bias adjustment required when listening with these different types of audio tubes in the DJH Super Amp. The output power is 35 watts through each channel in the triode mode, utilizing KT-88’s, EL-34’s or KT-90’s. You may wish to operate with KT-66’s, 6L6’s or even 6V6’s. The output power with these lower dissipation tubes will yield from 20 to 25 watts output power. Speaking of output power, the DJH Super Amp has a peak envelope power of 57 watts into an average loudspeaker load.

There are a number of significant differences between the DJH Super Amp and the basic Super Amp. First, as mentioned above, a separate adjustable bias voltage supply. This is a two stage bias supply that even incorporates a filter choke in the supply. Secondly,channel independent B plus supplies utilizes film and foil power supply capacitors. The front-end driver stage 6922’s have separate left and right channel regulated B plus power supplies. A current source for the 6922’s is provided by separate EL-84 tubes. The power transformer in the DJH version is almost twice the size and capability of the standard Super Amp power transformer. To top off the ingredients, Jensen copper foil and oil coupling capacitors carry the audio signal from the 6922’s to the output stage KT-88 final output tubes.

Please remember to initially set the DC bias on the DJH Super Amp at 200 ma. DC current with the KT-88’s, EL-34’s or KT-90’s. Using 6L6’s, KT-66’s or 6V6’s the bias should be set at 160 ma. DC current.

In concluding, I am most fortunate to be able to do what I love. I consider my work to be a privilege and I take it very seriously, while never losing sight of the "fun" factor. I hope I have conveyed this fundamental principle through the DJH SuperAmp. I am honored to be able to contribute, in some small way, to your enjoyment of sound and music.

THE END

 

[Budnick123]

In terms of sending it back, my buddy gets anxious when things aren't working out perfectly or the way he hopes and expects. So he immediately looks for ways to back out. He really shouldn't be buying stuff on ebay for that and other reasons, but he has the addiction like so many of us. With tubes, he figures that the getter is a good indicator of age. One of the tubes has a faded or worn out looking top getter. All that and no power cord is enough for him to at least want some money back. He figures whether it is showing or not, if the item came with something brand new, and it is necessary when operating the item, then it needs to come with it or otherwise state said item is missing. Perhaps he should have done some research in advance and asked some questions before purchasing, but reality rarely gets in the way when Jonesing for something new . Thank you for the update on biasing procedure.

 

[kward]

In the manual here: https://www.caryaudio.com/wp-content/uploads/2017/05/SuperampMKII_manual.pdf

it says to adjust the output tube bias for a reading of 200 mA as read from a DC current meter. Somewhere on the amp is a 1/4" plug that you insert and connect the two ends to a DC current meter. Then adjust the bias potentiometer until 200 mA (plus or minus 15 mA) is read. Done.

What is difficult about this for your friend? Maybe his amp didn't come with the 1/4" plug to measure bias? Maybe he doesn't have a DC current meter? You can get a cheap (good enough) digital multimeter from Harbor Freight Tools, and even if he doesn't have the bias plug, one can be fabricated from a blank phone jack, some wire, a soldering iron, and a little solder.

This isn't really hard but may take just a bit of soldering skill to fabricate the necessary jack so that bias can be measured. If by chance he got the schematic, that will answer all questions about how to fabricate the bias plug.

I wasn't sure from your writeup in your opening post if he has the Mk 1 or Mk 2 version, but I suspect the biasing approach is the same for both.

In the absolute worst case, a technician can pop the bottom plate off and have a look at how the bias plug is to be wired.

 

[kward]

Here is a screen shot from the page in the manual I linked to above that shows the rear panel layout. You will notice the bias jack is on the left of the power inlet, and the bias adjust pot is on the right of the power inlet.

 

[kward]

So my educated guess on this is that the output stage bias is a reading for all four output tubes combined. It therefore appears matched output tubes are necessary since there is apparently no individual bias adjustment per tube on this amp.

I suspect the bias phono jack is a mono jack (meaning, not stereo). So if these assumptions are correct, it's about dead nuts simple to wire up a blank male end of a phono jack for this purpose. Two wires of about 8" in length would be needed--one wire connected to the "signal" lug of the male phono jack and another wire connected to the "ground" lug of the male phono jack. To measure bias (apparently), set the meter to read on the 500 mA DC scale, plug the phono jack into the bias jack, connect the meter leads to the wires coming out of the phono jack, turn the amp on, wait for it to warm up for say 10 minutes, then adjust the bias potentiometer until +200 mA or -200 mA is read on the meter. (ignore the sign positive or negative on the meter--just look at the number itself and adjust to 200 mA). 200 mA may read as 0.200 Amps depending on how the readout of the meter works, or it may read "200."

The meter reading will bounce around a bit. It's not critical to get it "exactly" to "200"--anywhere within 5% of that is fine.

 

[Budnick123]

In the manual here: https://www.caryaudio.com/wp-content/uploads/2017/05/SuperampMKII_manual.pdf

it says to adjust the output tube bias for a reading of 200 mA as read from a DC current meter. Somewhere on the amp is a 1/4" plug that you insert and connect the two ends to a DC current meter. Then adjust the bias potentiometer until 200 mA (plus or minus 15 mA) is read...

Thank you for the follow up. In terms of the amp my buddy has, it is not the amp you are referring to here. There are a number of different Super Amps between Cary and AES. However, I appreciate the info on how to create a simple lead. 20 years ago my buddy would have been on top of creating a lead and such, then do a little trial and error. Now he is not at all interested in doing anything outside of his very small comfort zone. So until he sees something from his amp's user manual, he will not be willing to try it. He no longer solders, but I could certainly use the helpful tip you provided to fashion my own lead should I need to in the future.

 

[Budnick123]

So my educated guess on this is that the output stage bias is a reading for all four output tubes combined. It therefore appears matched output tubes are necessary since there is apparently no individual bias adjustment per tube on this amp.

I suspect the bias phono jack is a mono jack (meaning, not stereo). So if these assumptions are correct, it's about dead nuts simple to wire up a blank male end of a phono jack for this purpose. Two wires of about 8" in length would be needed--one wire connected to the "signal" lug of the male phono jack and another wire connected to the "ground" lug of the male phono jack. To measure bias (apparently), set the meter to read on the 500 mA DC scale, plug the phono jack into the bias jack, connect the meter leads to the wires coming out...

Thank you so much for the follow up from everyone. I will forward the info to my buddy and if soldering needs to be done, I can likely do it for him. I will certainly pass on the information to him to see if he is willing to try it, but he is a bit of a nervous belly at this point in his life. He wants things to be easy. I don't blame him. I would prefer that, too. However, I'm hoping he will be willing to try something mentioned here before giving up on the amp. It is a very nice piece. Well made with quality parts and sounds great. He wants to keep it but get a few bucks back for having to do some leg work to get it up to snuff.

 

[zackthedog]

Thank you so much for the follow up from everyone. I will forward the info to my buddy and if soldering needs to be done, I can likely do it for him. I will certainly pass on the information to him to see if he is willing to try it, but he is a bit of a nervous belly at this point in his life. He wants things to be easy. I don't blame him. I would prefer that, too. However, I'm hoping he will be willing to try something mentioned here before giving up on the amp. It is a very nice piece. Well made with quality parts and sounds great. He wants to keep it but get a few bucks back for having to do some leg work to get it up to snuff.

Ugh. If your friend is at a stage where he wants things to be easy, he should 1) get a nice Arcam integrated amp and 2) not buy tube amps from auctions sites. And believe me, I speak with sympathy. I have a very long-time, very very dear friend who has to change things all the time. He would call and say his latest amp/CD player/speakers sounded terrible, so I would go over and remove the 37 weird tweaks he had installed and get it sounding normal again. See my thread here about the Sophia Electric PP amp he bought--basically it had been trashed by an experimenter. By contrast, I have had the same speakers for 20 years, and moved slowly from DIY SE to PP as my tastes and experience have evolved. He also has introduced me to some very good equipment. And in all fairness, he once said, "But you can change your amps whenever you want! I can't do that." But I'll say this for him-- a loss was a loss and he moved on.

So best wishes for your friend. I wasn't familiar with that amp until now, but Dennis Had is no slouch. I hope you can help to get it working to spec.

 

[liteagilis]

Someone on usaudiomart was selling a home-brew bias meter made in this fashion for like $35. All Cary amps seem to bias in this ‘as sum of all’ way. There’s a video on YouTube of a guy w the bottom cover off of one of these and talking about the bias circuit.

this actually doesn’t seem like much of a problem to me. Hopefully the amp is stock underneath.

 

[s-petersen]

Maybe analog addict can help?

 

[analog addict]

I communicated with Dennis and he said set the bias to 200mA...of course realize that if all four output toobs are running off one bias circuit, not only will you want to use as closely matched toobs as possible, you’ll want to check them on a tester every so often to make sure they stay matched....

 

[Lbow]

I read that the AES AE-25 has an "auto-biasing" circuit. I'd like to see the schematics for that amplifier. From what I know, the sweet-spot bias level is the region just beyond the point when cross-over distortion is eliminated. I imagine a stated factory bias level will be much higher than that point. 200mA will probably be safe for all versions of output tubes the amplifier can use, but in some cases, the 200mA bias level may tend to drive some tubes harder.

When I rebuilt my AES Six Pac mono tube amplifiers, 230mA's was the suggested bias level setting. But when I fed the amplifier a 1kHz signal and scoped the output, 165mA was the sweet-spot.

Since the AE-25 is a stereo amplifier, it would be interesting to supply both channels with the same signal and scope the left and right speaker terminals to see how well matched they are. A stereo amplifier with one bias adjustment for both channels seems limiting IMHO. For starters, individual components would need to be very well matched.

Anyway, keep your eye out on Ebay for these old Bakelite Triplett milliamperes meters too. They look good on the bookshelf when they're not plugged in

 

[Destructor]

I built an AE-25 Superamp in 2001. I wired it in triode mode and used PIO coupling caps. My version is auto biased. It also has a jack on the back but no pot installed. It is the most no fuss amp I have, other than a couple power tubes fading out it has been rock solid dependable.

I recently hooked my AE-25 into my system. After not listening for awhile I was astonished at how good it performs. I was previously listening to my AES SE-1 300B amp for a few weeks. My Ae-25 does sound similar to my SE-1 but with more power and it seems to image better. I use ordinary Shuggie EL 34's and Russian 6922 and 6CG7's.

 

[Budnick123]

The amp my buddy has came with KT-88s by the way. He purchased a meter a seller on eBay made so he no longer needs a meter. I'm not sure what about it allows him to believe it is properly calibrated, but I also did not read the original eBay listing, which may have explained how it was calibrated.

In terms of biasing, he emailed Denis Hadd, who said 120mA for the DJH version of the AE-25. Cary said 150mA DC and confirmed they meant the AE-25 DJH version. Then there is the number I found on the original superamps.com website (see above) from when the amp was new at 200 mA DC using KT-88s. That info was a letter written by Denis Hadd for the company's website. So at this point, my buddy would really prefer getting his hands on the manual or info directly from someone who has the manual since there is no consensus. When my buddy checked the bias, it was around 130 mA. He dialed it down to 120mA for now until he can get the manual. He now seems to be comfortable with how to prepare the amp prior to setting the bias current. I didn't ask, but maybe Denis Hadd and Cary both said the same thing regarding that part of the bias procedure.

Just to review, there were three versions of the AES AE-25 Super Amp (not to be confused with the AES AE-25 amp or Cary's current Super Amp mk II). The entry level model of the AE-25 Super Amp was $1200 and had an autobiasing circuit. The AE-25 Super Amp Signature is the mid level version that was $1500 with a number of upgrades and changes including a bias circuit. The top model at $2000 was the AE-25 Super Amp DJH with much larger transformers, a third choke, and some other goodies. The manuals for the base and Signature versions are available online. The one for the DJH version is not. Cary has a standard bias procedure available on its website and it applies to all Cary's current amps. However, it is different than what my buddy is getting for responses from Denis Hadd or Cary.

Thank you again to everyone trying to help my buddy out. If anyone has the manual for the AES AE-25 Super Amp DJH, I'm sure he would greatly appreciate a scan of it or something.

 

[Budnick123]

Looks like I repeatedly misspelled Dennis Had's name in the above post.

 

[Budnick123]

Made another mistake as well. Probably should have waited to hit "post reply." I called the Super Amp mk II a Cary unit, but it is an AE (Audio Electronic) unit according to the label on it.

 

[Budnick123]

My buddy finally sent me what Dennis Had told him about biasing the DJH version of this amp. According to Dennis Had: "There were two versions of this amplifier. One is auto bias and the other have a bias pot and 1/4 " jack that you adjust for 120 ma. DC current...When you turn on the amplifier cold you need to make sure you are in the 100 to 120 ma range or adjust immediately if more that 150 ma. After a few minutes of playing adjust for the 120 ma. range. it is not critical ... 105 to 130 is fine."
I've not seen any sighting of the DJH version of the AE25 Superamp that mentions an auto biasing version. Just the standard AE25 Superamp. Maybe that is what he meant.

 

[Destructor]

My Superamp shortly after I built it in 2001.

 

[Budnick123]

Nice! Like the MX110, too!