Advent 300 Receiver Preamp

[Norman Nicolai]

I recently acquired an Advent 300 receiver as a throw in on another vintage audio purchase. When I hooked it up I discovered that the tuner was missing a channel, as the previous owner had warned me. Not a big deal since I essentially got the Advent for free. 

The Advent 300 is a low powered receiver (15 watts per channel) that was sold in the late 1970’s. It’s not noted for very much, other than it’s preamp, designed by Tomlinson Holman, who later went on to develop the LucasFilm THX sound system. The 300 receiver was a Henry Kloss product, which meant it was a good value product, not noted for outstanding quality of workmanship. The preamp, however won rave reviews at the time, far outperforming other preamps at its price point, and giving some state-of-the-art preamps a run for their money. (BTW, hat tip to JKent here. I had read about the Advent 300 preamp in the past, but a mention by Kent regarding the 300 got my gears turning about using it’s preamp separately.)

I hooked up the 300 to some KLH Model 17’s and was surprised at how good it sounded. That’s when the light bulb went off. What would happen if I used the preamp in the 300 and bypassed the preamp in my main basement receiver, a HK3490? The HK3490 is a solid state, high current amp putting out 120 watts per channel. It used to be part of my main system before I purchased a number of vintage tube receivers. It’s now relegated to my basement collection, accompanied by 2 turntables, other receivers, power amps and multiple speaker sets. The basement is sort of my “lab”, probably like a lot of other audio enthusiasts.

The results were better than I imagined, especially with the phono stage using my Technics SL-230 with an Ortofon 2M Red cartridge, and stacked Advents. I think the Advent preamp is giving me enhanced bass and more detailed, clearer midrange and high frequencies compared to the preamp in the HK3490.

I have not done an A-B test yet using the HK3490 preamp, but that will come later when I can set that up. Besides, I’m pretty sure how that will turn out. In the meantime, I’m enjoying listening to my vinyl with my newly enhanced basement audio system. 

Final thought: even though the preamp was designed by Tom Holman, the 300 is still ultimately a testament to the genius Henry Kloss, who managed to create audio magic with so many things that he touched.

[Jordac]

I have the advent 300, too. I agree; it sounds super sweet. My advent started to lose power in one channel , so I took part in David Eaton’s “swap” program. Basically, you send in your old one in with $300, and he turns around a recapped/refurbished/amazing unit with your original faceplate. Kind of expensive, but he does good work, gives helpful advice, and I really *needed* my little Advent . The advent’s phono stage is almost cultishly good, but lower quality build, as I understand. This guy has a whole thing set up devoted to Advent 300, and he turns them around as good as, if not better than original.

https://davidreaton.com/advent/model_300_receiver_main_page/300_repairs/

 

[Norman Nicolai]

Jordac, thanks for the in the info on David Eaton. I contacted him early this morning and he got back to me within a couple of hours. 

If anyone else reads this and has information on David Eaton's work, please feel free to chime in. 

Thanks!

 

[Norman Nicolai]

Just a follow up. After talking to a couple different audio repair shops that I deal with I decided to ship the 300 to David Eaton in St. Louis. He was the most expensive option, but also promised the most extensive restoration plus the fastest turn around time since he would swap out my existing 300 for an already restored 300 sitting on his shelf. He also guaranteed that the exchanged 300 would sound at least as good, if not better, than a new 300. 

I just got the exchanged unit back from him today and anxiously set it up to my bench speakers, a set of Optimus Pro 77's. The package also contained a binder with a user's manual and sets of schematics, a nice touch. Well, it worked for about a minute. Then, when I went to boost the lower frequencies by tuning the Bass knob, the potentiometer felt glitchy and a a few seconds later a large booming sound came from the speakers. I powered down the unit, waited a few minutes, powered up, and the same thing happened, this time immediately.

I sent an email to David Eaton with a video showing the scratchy Bass control, since you can actually hear the scratchy potentiometer. He replied immediately, apologized, and told me to send it back to him for another unit.

So, what happened? Even though it was packaged carefully, it was probably damaged during shipment. In the meantime, I still can't wait to get my Advent 300 hooked up again as a preamp to my more powerful HK 3490.

I'll post again with a report when I get the refurbished 300. Still can't wait.

[Norman Nicolai]

I got the new exchanged Advent 300 today from David R. Easton. I plugged it into my bench speakers briefly to confirm that it's working. So far, I have been able to determine that the FM section works fine but did not have the time to check the Aux or Phono functions because of lack of time. I will report out as soon as I get time, probably tomorrow.

[Norman Nicolai]

Had more time today and put the rebuilt/exchanged 300 through its paces. I used it as both a receiver with some KLH 17's and an FM tuner/preamp with my HK3490 and KLH 6's. Sounded pretty good both ways. The 300 power amp only puts out 15 watts per channel but still impressed hooked up to the KLH 17's. With the HK3490 it sounded even better run through my KLH 6's. 

But...  (There is always a but)

I am having a problem. I'm getting a background FM signal at low volume from my speakers regardless of whatever input is selected, FM, Phono, or Aux. The FM signal is NOT the same as what I have the FM tuner set at. The volume control does not amplify the background signal. If I touch the wire straps on the back of the unit that connect the preamplifier to the power amplifier, it magnifies the strength and volume of the signal, as if my body is an antenna. If I use the 300 as a tuner/amp only, the problem persists.

If I didn't know any better I would think there is a pirate Carrier Current radio station operating in my area, but I'm not getting the same problem on any of my other equipment.

Anyone ever encounter a similar issue? Help!

[ar_pro]

No problems specifically with the Model 300, but RF leaking into audio stages is something that used to be not uncommon. 

Your first instinct to consider the possibility of an unauthorized broadcast is a good one; way back in the '70s, RF interference was usually someone in the area with a beefed-up CB radio,  but now it could be anyone running a linear amplifier in a pirate setup. Has the station used call letters or announced a frequency? Try checking the broadcast with an AM/FM portable to see if they're for real.

Also, try sliding your tape monitor switch back & forth, just to be certain of good contact, as RF loves to enter through switches.

If no luck, try contacting one of the many Ham radio websites & forums, since those guys have a ton of experience, and love solving issues like this.

[JKent]

ar_pro gives good advice but my first thought would be to contact David Eaton. I assume he stands behind what he sells.

[ar_pro]

Absolutely - speak with your seller first!

The 300 was a unique product - a great-sounding low-powered receiver from the era when major manufacturers were waging wattage wars.

My wife had one of these in college, matched with a set of Large Advent speakers, and a Thorens turntable; it was a fine little system for not very much money.

 

[Norman Nicolai]

Just an update on where I am with the Advent 300.

I contacted David Eaton and did not hear back from him for a few days. In the meantime I posted the problem on another forum and got many, many suggestions. Among the suggestions:

Many non-specific suggestions that it was a grounding issue, but no suggestions as to how to resolve the grounding issue.

I had a couple of suggestions to use ferrite plugs and I ordered some from Amazon since they were very cheap.

A number of people suggested changing the orientation of the receiver or placing it in an entirely different location, which is not exactly feasible right now since space is limited in my small cottage.

The most interesting suggestion was to place a pyramid shaped Shungite tile on the receiver...

I did hear back from David Eaton after a couple of days and his suggestions were to
1. change the plug polarity.  
2. use double shielded RCA cable for the power amp/preamp connecting straps. 
3. reorient the receiver   
4. shield the receiver.

My solution: I decided to get the double shielded RCA cables from Amazon, along with some ferrite shielding plugs from the other forum suggestion.

The upshot: After ordering the parts the problem pretty much disappeared on its own after about 4 days. One day, BEFORE getting the ordered parts and installing them, I turned the Advent 300 on, and the RF/phantom FM station was completely gone! What happened, whether it’s an atmospheric condition change, a power source resolution, or improved grounding on its own, I have no idea. 

In the aftermath, I’ve installed the directional double shielded RCA cable (It looks really high tech...) and the ferrite plugs (very low tech looking) and I have my fingers crossed that the problem does not re-emerge.

The Lesson: Damned if I know. Maybe, be more patient before freaking out and asking for help? 

In any event, thanks everyone for your help and input!

 

 

[JKent]

When I take my car to the mechanic the noise goes away.

When I go to the dentist the tooth stops aching.

Same phenomenon 😄

Enjoy the receiver.

[Norman Nicolai]

It's back. The radio station signal leaking into all the inputs on my Advent 300 is louder than ever. I can hear the signal very clearly now and have been able to identify it. The signal is from a radio station with its broadcast towers about a mile from my house, WNSW, 1430 AM. For those of you familiar with Clifton, NJ, it's the former WPAT towers on Broad St. in the southern end of Clifton, just at the border from Bloomfield, where I live.

The signal is so loud and so clear, I hear the AM signal better on my FM only Advent 300 than on the Pioneer SX-626 AM tuner in the adjacent room!

I've got a feeling that atmospheric conditions might dictate when the signal migrates to the Advent. The last time it happened I was having trouble with FM signals I usually capture easily. I hope it is an intermittent problem that happens infrequently. 

If anyone has any new ideas, I'm all ears.

Thanks.

[genek]

Do you get this if there's nothing at all plugged into the amp inputs?

You could try shielded RCA caps in the the unused input jacks.

[JKent]

Did you mean RCA shorting plugs?

https://www.takefiveaudio.com/contents/19-rcainputshortingplugs

I've made them and it's pretty easy to do.

[Norman Nicolai]

Thanks, genek. Based on what you suggested I was able to further isolate the problem. It's coming from the FM section. If I unplug the FM antenna from the receiver, the background radio station disappears completely. I started by disconnecting all the inputs, Phono and Aux, but the background AM station was still there. Once I disconnected the external FM antenna, the receiver went silent on all inputs. I have an attic FM antenna that connects to the Advent via a 20 ft coax cable. As I wrote earlier, I'm about a mile from an AM transmitter and that is the signal I'm getting. Tomorrow I'll downsize to a dipole to see if that works. I really only listen to two FM stations out of NYC so I may not need the attic antenna.

Thanks again, genek. But I have to confess that when I got the email that notified me of your response to my post, I saw that you were a Moderator. My first thought was that I had posted something inappropriate, but could not imagine what!

It's late and I will post tomorrow when I try a couple of antenna solutions.

Thanks.

 

[genek]

The problem with shorting plugs for RF interference is that the signal wire is still exposed to the interference. What I was referring to was a cap, basically a metal shield that fits over the plug rather than going into it.

https://www.audioquest.com/accessories/audio-enhancements/noise-stopper-caps/rca-noise-stopper-caps

However, there's not a lot you can do about one radio station overpowering another in your tuner. If you're lucky enough for the offending station to not be in the same direction from your home as the stations you want, you could try a more highly directional antenna.

Another alternative is to see if the stations you want to listen to stream their sound online. If so, you could bypass your tuner altogether and feed the sound to your Aux inputs. I haven't used any of my tuners other than the radio in my car for years now.

[Norman Nicolai]

Latest update:

The dipole FM antenna works adequately and so far there is no interference from the local 1430AM station. Obviously, I don't have the same selection of FM stations to choose from, but I only listen two or three FM stations anyway, and all of them are coming in reasonably well with the dipole.

The previous attic antenna I was using was omnidirectional. The interfering AM station is due north of my location and all the FM stations I am interested in listening to have their transmitters atop the Empire State Building in NYC, which is ENE of my home. I think the next step is to purchase and try a directional FM antenna, like genek suggested.

Any input on specific antennas would be appreciated.

Thanks, all!

 

[ar_pro]

Try describing your problems to this bunch - be sure to include the relevant info, and that you're a stone's throw from an AM transmitter:

https://www.antiqueradios.com/forums/viewforum.php?f=2

or 

https://www.antiqueradios.com/forums/viewforum.php?f=13

[dxho]

That 20 ft coax could be picking up some signal.

Here's way more information than you probably need, but the
coiled-coax balun might help.

http://ham-radio.com/k6sti/balun.htm

 

[Jordac]

I hope you got things figured out! 

[Norman Nicolai]

Update:

I moved the Advent 300 down to the basement which is sort of my workshop/man cave. I have a lot of vintage equipment down there and I am constantly patching in different turntables, receivers and speakers to see which combination sounds best. Right now, I'm only using the preamp section of the Advent receiver and it's connected to the power amp portion of a Harman Kardon HK3490 receiver. I am not using the FM tuner and it is disconnected from my coax cable antenna. I'm using a Rotel RT 850 tuner for my FM listening through the tape monitor function on the 300. The Rotel seems to pull in the stations that I listen to frequently with far less static and background noise than the Advent 300. 

I'm pretty sure the AM radio station interference was coming from my attic omnidirectional FM antenna hookup and coax cable link. Now that the receiver is in another location and the FM section is disconnected from the coax cable entirely, the problem is dormant. 

So, I don't think I solved the problem. I just eliminated it with a work around. Frankly, I was hoping to use the FM section in the 300. It had a good reputation in some reviews that In had read. But between the AM radio station interference, the background hiss and inability to pull in local stations when there was no AM interference, I'm kind of disappointed. At least the Tomlinson Holman designed preamp works well, which is the main reason to own an Advent 300.