Amps and Sound SE-84

[mike stehr]

I wasn't referring to the circuit. I tend to believe the limiting factor of a circuit is the implementation not the circuit as much. Small power supplies of output transformers that are not idea are limiting. Larger/better output transformer would allow the SE84 to go deep (frq response) without distortion but there is no room :-). I generally use bigger iron for that reason but opted for a more balanced approach this time. The SE84 is meant as a great all around solution/ office amp.

So general rules for me... Output iron with largest cores possible (less prone to saturation, etc.) and largest power supply possible... Ive seen difference robust power supplies make. The SE-84 limitation was not price but size. As it is... it required me to use tools to hold thing in place during the final assembly as my hands were getting cut.

If I were not trying to build based on repeatable results/ ability to scale up if needed. The RH84 circuit is wonderful. There is a gentleman here who built an example with truly awesome attention to detail using turrets.

Another thing to keep in mind about output transformers is how tightly coupled (wound) the windings are. The tighter the winding, the more extended the high frequencies. So it's kind of a balancing act....you want a large core for extended low bass without saturation, plus tightly wound/coupled windings for good high frequency extension. I'm sure you are aware of that.

I've been taught to not really trust advertised output transformer specifications/measurements from commercially made OPTs. Notice that is really never a standard set of measurement parameters. Some manufacturers are good about it and show -1-3dB rolloff of high and low frequencies. Many show or just list -6-10dB rolloff. So if a OPT is 6 to 10dB down at 20kHz, and more than likely ringing, that could effect the bandwidth below 20kHz. If it's ringing, it will more than likely show 10kHz or even lower depending on the quality and build of the OPT I'm guessing.

So it's always a good option to bench test a OPT using simulated primary and secondary loads monitoring square waves with a scope. This will give a guy a good idea of the low and high frequency response, and how it will effect the circuit it's used with. The upper harmonics of a 25kHz square wave will start rounding off the top left edge of the square, but a good OPT should still be holding a good square wave at 25kHz. If it looks like a rounded triangle wave by 25kHz, that could be a problem. Feedback can beat down ringing of a OPT, and extend response.

For example, the little Magnavox SEP EL84 console I just freshened up. The output transformers for the 8601 series maggotbox are the size of a 1 henrie choke. In circuit without feedback monitoring square waves, these OPTs ring badly, akin to someone having a heart attack. But monitoring/noodling with fdbk resistors, (6.8K) along with compensation caps, a good high and low end response can be achieved. With proper feedback, the little maggotbox OPTs can extend to 40kHz. The EL84 cathodes are shared, and the cathode bypass cap is 100uf, to give a slight boost at 30Hz.

For nearfield listening, the little Magnavox amp has well balanced tonality with my Cornwalls. With strong bass, and is plenty loud.

When I was breadboarding the RH84 circuit, I used James universal output transformers, (6123HS?) along with poly caps for cathode bypass. That circuit was the best sounding SEP EL-84 that I could come up with. But I wasn't going to waste a nice pair of universal OPTs for a single ended 6BQ5 amplifier...I'll use those for the triode projects...So I built the amp with the little Grundig output xformers.

It sounds just as good if not better than the little maggotbox amp.

I'm no audio engineer, so take these comments with a grain of salt.

Thanks for the Kudos on the RH84 amplifier. I think you and Dave got a good thing going. Nice looking work!

Mike

[justinsweber]

Mike,

Id never call my self an engineer. I have great partners who aid with that... Im just good at putting it all together.

I full agree about the bigger is not always better adage, though I don't do poorly made or performing outputs.

Ived used some iron that was massive... 12lbs each. They sounded nice in the circuit, but when the same circuit and parts were used with the Iron I use regularly it was a night and day difference. Big looks great but requires additional bracing and is no guarantee for performance. Sometimes you just have to build it to test.

[joessportster]

Dean i sent you an email concerning the amp

Joe

[Deang]

Thanks, now Dave and Justin will remember that it's sitting over here -- I was hoping they'd forget about it.

[joessportster]

I am sorry, did not mean to interfere with your EXXXXXXTTTTEEEEEENNDDDEEEDDDDDDDD, listening test / Audition , I was also trying to give Justin and his work a bit of a bump on the sly

[Deang]

lol.

All I can say is that's it real hard to remember that you're listening to a $900.00 amp while you're listening. It's really smooth and laid back, and like I said, rich with a lot of texture. By "texture", I mean the soundfield is deep and nicely projected -- it does that tube layering of the sound thing pretty good.

[Guest David H]

I am sorry, did not mean to interfere with your EXXXXXXTTTTEEEEEENNDDDEEEDDDDDDDD, listening test / Audition , I was also trying to give Justin and his work a bit of a bump on the sly

What do you mean listening test, I thought Dean was breaking it in for me!

I am going to need this well broke in.

Dave

[justinsweber]

I was never one to believe about break in... But I have come to accept that amps, crossovers, drivers and tubes all sound dramatically different and improved when they have hours of use on them. I try pretty hard to give most of the amps 10 hours of playing before they leave. Even with that, I know they will require another 20-50 before they settle into their own sound. The SE-84 was built in a run of 6... Im down to my last 2 being on the shelf. Im trying to get to a place where I have at least 1 of everything all built and boxed but kinda a pain when you're have more than 1 product.

[Guest David H]

I was never one to believe about break in... But I have come to accept that amps, crossovers, drivers and tubes all sound dramatically different and improved when they have hours of use on them.

The break in comment was a (Joke): A story with a humorous climax. Some use this same description for sex.

I am true believer in break in, then again I am an auto mechanic by trade. Every new engine needs break in.

As for audio gear, not so much.

Dave

[joessportster]

Its a known fact that tubes need to get to optimal operating temp to sound there best, wouldnt that same idea explain breakin. ie.... all the components inside an amp need to settle in after use, seems logical that caps, resistors, iron etc... would need some use to sort of find there stride / equalize out

I was never a believer in the theory either, till i started using headphones, They reveal so much more for me it's much easier to hear subtle differences

Edited February 17, 2014 by joessportster

[joessportster]

Warm up is different than break in. Any electronic sound gear needs to fully warm up to reach final sound. It can take an hour or more for some gear, especially those with heavy transformers. Getting all the parts inside to their operating temperature takes time.

Break in for tube amplifiers involves the OPTs. They are wound with many layers of interwoven magnet wire and all of that settles with applied heat. That might take 50 hours or even more. Depends how hot you get them and for how long. Tubes of course are like candles, which begin dying the moment you light them, so there is a quick downturn initially followed by a long shelf and then a quick decay at the end. Kind of like 3 stages of different sound.

And then of course we have the very real phenomenon of breaking in the user's ears. This is absolutely real and is just not avoidable. We adopt a new reference after many hours of listening. Sometimes we even accept errors as being normal.

Thats what i said , I agree 100 percent breaking in user ears. When i first tried headphones I hated them, now I have adjusted and rather like them USER BREAK IN for sure

[Guest David H]

Its a known fact that tubes need to get to optimal operating temp to sound there best, wouldnt that same idea explain breakin.

Warm up I understand perfectly, capacitors, resistors and other solid state devices charge fairly quick. By the time the amp is warmed up, you are getting most of what you are going to get from the amp. Anything else is a bonus. Whether it be break in, satisfaction, atmospheric anomalies, whatever the phenomenon may be, if you hear it and like it - its all good.

Dave

[Guest David H]

Warm up is different than break in. Any electronic sound gear needs to fully warm up to reach final sound. It can take an hour or more for some gear, especially those with heavy transformers. Getting all the parts inside to their operating temperature takes time.

Break in for tube amplifiers involves the OPTs. They are wound with many layers of interwoven magnet wire and all of that settles with applied heat. That might take 50 hours or even more. Depends how hot you get them and for how long. Tubes of course are like candles, which begin dying the moment you light them, so there is a quick downturn initially followed by a long shelf and then a quick decay at the end. Kind of like 3 stages of different sound.

And then of course we have the very real phenomenon of breaking in the user's ears. This is absolutely real and is just not avoidable. We adopt a new reference after many hours of listening. Sometimes we even accept errors as being normal.

Ok, Marks answer is better. And no-one is surprised.

Dave

Edited February 17, 2014 by GotHover

[joessportster]

ng normal.

Ok, Marks answer is better. And no-one is surprised.

Dave

I would get insulted, if i didn't agree

[justinsweber]

Its a known fact that tubes need to get to optimal operating temp to sound there best, wouldnt that same idea explain breakin.

Warm up I understand perfectly, capacitors, resistors and other solid state devices charge fairly quick. By the time the amp is warmed up, you are getting most of what you are going to get from the amp. Anything else is a bonus. Whether it be break in, satisfaction, atmospheric anomalies, whatever the phenomenon may be, if you hear it and like it - its all good.

Dave

:-) I don't want to start cable, tube or cap debates... But use and enjoy :-).

[joessportster]

Its a known fact that tubes need to get to optimal operating temp to sound there best, wouldnt that same idea explain breakin.

Warm up I understand perfectly, capacitors, resistors and other solid state devices charge fairly quick. By the time the amp is warmed up, you are getting most of what you are going to get from the amp. Anything else is a bonus. Whether it be break in, satisfaction, atmospheric anomalies, whatever the phenomenon may be, if you hear it and like it - its all good.

Dave

:-) I don't want to start cable, tube or cap debates... But use and enjoy :-).

I completely agree, I stay out of those debates, a few years ago i was dragged into the Push Pull /SET debate and learned i cannot change any ones mind on there gear choices and beliefs. I just keep those opinions to myself, unless asked a specific question. My beliefs on amps is what drives me to look at your product.

[joessportster]

Dean when you post impressions with headphones can you also post dimensions especially height (its not on the web site, it says 10 x 6" no mention of height

Joe

[justinsweber]

True dems are 11.5" x 8.5" the wood base add 1.5" and the hight is between 6" and 7" if I recall. They are all boxed for shipping. But that should be pretty close

[joessportster]

True dems are 11.5" x 8.5" the wood base add 1.5" and the hight is between 6" and 7" if I recall. They are all boxed for shipping. But that should be pretty close

Thank you sir,

I have to figure out if i can adjust my shelf, i only have 5.5" clearance right now. I will shoot for 9" give it some breathing room

[justinsweber]

^{Dean can give you an exact measurement.. I have them all boxed up. If needed, I can unbox.}

^{The power transformer is just under 4" tall and the chassis is 2.5"... as long as you have 7" youre good.}