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Spinning Ray Brown

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Posted on January 13, 2017 at 15:46:49
SteveBrown
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Location: Portland, OR
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An old PP EL84 amp I built by recycling iron from a Heath aA151, driver uses a Gary PimmCCS in the shared cathodes. No feedback and UL transformer connection. Directly driven by my Carrivaggio phono stage. Very sweet. Simple is good.

 

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RE: Spinning Ray Brown , posted on January 13, 2017 at 18:40:15
vinnie2
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Location: North Carolina
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 If I were going to listen to a PP amp instead of SET, it would be an EL84 amp. I have always liked their sound. Hey, maybe I should try an triode connected EL84 SE amp ......
Nice job on the build!

 

RE: Spinning Ray Brown , posted on January 13, 2017 at 18:59:37
SteveBrown
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Location: Portland, OR
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 You know I've built dozens of SE amps and a dozen pp. I've learned that my efficient (97db) speakers need a bit of muscle to get going (JBL 2226 on bottom). The pp almost seem to do that better than SE. And I'd agree, el84s are really nice. Good punch but also great tone and texture. Sound stage is excellent.

 

RE: Spinning Ray Brown , posted on January 14, 2017 at 01:03:47
Frihed89
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Posts: 15703
Location: Copenhagen
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 Audio Note makes a marvelous series of EL-84 PP and SE amps. If this is any indication, I'd try it.

 

No feedback and UL transformer connection, posted on January 14, 2017 at 05:59:21
Chip647
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 You can get better sound from using some feedback. One of the selling points of triodes is that they do not require feedback to be linear. However, UL pentodes do need feedback. You should at least try it. However, you may be digging the distortion from not having it.

 

RE: No feedback and UL transformer connection, posted on January 14, 2017 at 08:09:15
SteveBrown
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Posts: 2454
Location: Portland, OR
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 You seem to have made the assumption I didn't try it. I did. DIdn't like it as well as naked. Perhaps someplace in between would be good - which I have not experimented with. UL of course, gets close to triode.

 

What's the driver tube? (nt), posted on January 14, 2017 at 12:16:29
dhieber
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 nt

 

RE: No feedback and UL transformer connection, posted on January 14, 2017 at 13:24:37
Chip647
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 Ok, just watch out for pleasing distortion. UL ain't triode.

 

5965 (nt), posted on January 14, 2017 at 14:34:15
SteveBrown
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Posts: 2454
Location: Portland, OR
Joined: November 14, 2002
 nt

 

RE: No feedback and UL transformer connection, posted on January 14, 2017 at 15:39:04
PakProtector
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 and linearity is not reasonable output impedance.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: No feedback and UL transformer connection, posted on January 14, 2017 at 19:21:02
Eli Duttman
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Posts: 10455
Location: Monroe Township, NJ
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 Precisely! The (IMO) inadequate damping factor will be problematic with many speakers. A few speakers may mate tolerably well.


Eli D.

 

RE: No feedback and UL transformer connection, posted on January 14, 2017 at 19:41:54
SteveBrown
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Posts: 2454
Location: Portland, OR
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 Well.. the driver is kind of a cross between an El Cheapo and a Baby Huey, as for output you know, on my speakers the bass sounds really solid. I'm using 97db JBL 2226 - more of a mid-woofer, likely not much below 40hz but sure sounds solid to me. One thing I've found with these speakers is they need a bit of power - more than a 2A3, but not a lot more. Very enjoyable and my point in the original post wasn't to garner criticism, though I'm not surprised it did, but rather to encourage us to all sit down and listen to some MUSIC. I do have a vintage Leader distortion analyzer and maybe next week I'll put her on the bench but I can't believe at the 3 to 5 watts I'm asking that I'm getting much more than a couple % of distortion.

 

RE: No feedback and UL transformer connection, posted on January 15, 2017 at 03:42:52
PakProtector
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 errr...not being critical( too much...LOL), just trying to take exception of the simplistic FB statement made by chip.

I built an open loop amp around the Dyna A441 outputs once. Sounded pretty good with the tertiary winding feeding the screens. Sounded even better with a fixed g2 voltage and the cathodes riding the screens. On a wide variety of speakers the CFB rigging was The Way To Go, but on a few, open loop U-L was a little bit better.

Then I hit upon the Plate-to-Grid implementation we called E-Linear. Not looked back, and built several full pentode amps of that topology.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: No feedback and UL transformer connection, posted on January 15, 2017 at 07:55:45
SteveBrown
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Posts: 2454
Location: Portland, OR
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 Hi Douglas, I remember this being discussed in the DIY forum a number of years ago - in fact found some posts I guess from you ca 2003. Wow, time flies. In the schematic I saw it used 6AU6's and EL34's. Might be fun to give it a try. I'm in kind of a mood to experiment. It's probably buried in that old post, but to resurrect it a bit, can you discuss the relationship between the coupling cap and the feedback resistor from EL34 G2 to plate of 6AU6? How are values chosen?

 

RE: No feedback and UL transformer connection, posted on January 15, 2017 at 12:53:09
PakProtector
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 That FB resistor as you call it is just the plate load for the 6AU6. I'd rather select a signal pentode that has a higher plate/g2 current ratio...the 6AU6 is rather poor, though I have had them work very well. Using the power tube's screen tap just sets the ratio of plate signal delivered to the signal tube. Plate to grid FB, and with pentode OPT's it can be done with a voltage divider too...the screen tap is just convenient...:) The type EL84 turns out to be a very fine signal pentode.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: No feedback and UL transformer connection, posted on January 15, 2017 at 14:45:43
Eli Duttman
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Location: Monroe Township, NJ
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 IIRC, the 6BQ5/EL84 was used, on occasion, as a video O/P device. Adequate and then some bandwidth there. ;>)


Eli D.

 

take exception of the simplistic FB statement made by chip., posted on January 15, 2017 at 16:58:20
Chip647
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Posts: 2649
Location: The South
Joined: December 24, 2012
 OK How about

"The use of global negative feedback does several things: it flattens and extends the frequency response, it reduces distortion generated in the stages encompassed by the feedback loop, and it reduces the effective output impedance of the amplifier, which increases the damping factor. All of these things affect the tone in some manner.
The flattened, extended frequency response obviously changes the tonal character by removing "humps" in the output stage response and producing more high and low end frequencies.

The distortion reduction makes the amp sound cleaner and more "hi-fi", up to the point of clipping, with less output-stage generated noise.

Perhaps the main difference for the "feel" in a negative feedback amplifier, as opposed to a non-negative feedback amplifier, is the increased damping factor produced by the negative feedback loop. The decreased effective output impedance causes the amp to react less to the speakers. A speaker impedance curve is far from flat; it rises very high at the resonant frequency, then falls to the nominal impedance around 1kHz, and again rises as the frequency increases. This changing "reactive" load causes the amp output level to change with frequency and changes in speaker impedance (a dynamic thing that changes as the speakers are driven harder). Global negative feedback generally reduces this greatly. This can be good or bad, depending upon what you are looking for. Negative feedback makes the amp sound "tighter", particularly in the low end, where the speaker resonant hump has the most effect on amplifier output."

http://www.aikenamps.com/index.php/what-is-negative-feedback

 

RE: If it's pleasing, it ain't distortion nt, posted on January 15, 2017 at 19:55:59
kitch29

 

??? nt, posted on January 15, 2017 at 20:42:13
Tre'
Industry Professional

Posts: 17294
Location: So. Cal.
Joined: February 9, 2002
 .
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: If it's pleasing, it ain't distortion nt, posted on January 16, 2017 at 00:19:35
Eli Duttman
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Posts: 10455
Location: Monroe Township, NJ
Joined: March 31, 2000
 I'll quote Frank VA. "You like distortion, you have bad taste." ;>D

Either it's HIFI or it's not. High fidelity, get it.

Everybody is entitled to their own opinions and, in their own "castles", do pretty much what they please. Just DON'T go calling distortion HIFI. It may be euphonic, but it's not high fidelity.


Eli D.

 

I consider UL as.feedback I would have to listen before passing judgment-nT, posted on January 16, 2017 at 06:41:39
Cleantimestream
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 !
The Mind has No Firewall~ U.S. Army War College.

 

to be clear..., posted on January 16, 2017 at 08:10:11
Tre'
Industry Professional

Posts: 17294
Location: So. Cal.
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 The term "distortion" is a technical term.

Anything coming out of a circuit that wasn't part of the input signal feeding that circuit, no matter how pleasing it might be to you or anyone else, is distortion.

If, in your opinion, as long as it's pleasing to you then you don't care if it's distorted or not then just say so.

But you can't go around redefining the term "distortion" simply based on your own personal preference. It's inaccurate and it shows ignorance.



Tre'




Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: to be clear..., posted on January 16, 2017 at 14:21:56
SteveBrown
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Posts: 2454
Location: Portland, OR
Joined: November 14, 2002
 To make this work, we must also question the level of distortion, below which, we have "fidelity". NO amplifier, even instrument amp, is perfect, so where is it "good enough"? And again, I'd say at the output levels I use, I'm guessing distortion is actually very low. In this amp I've also eliminated two prior pre-amp stages and thus, eliminated the distortion from them. Introducing feedback isn't something I'd see doing to help distortion at the end of the day. I might do it to improve damping factor, however.

 

RE: to be clear..., posted on January 16, 2017 at 15:10:36
Eli Duttman
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Posts: 10455
Location: Monroe Township, NJ
Joined: March 31, 2000
 If you are at or below 0.3% THD, when full power is produced, you definitely are good to go. Only folks with the very best hearing can(?) detect that, when the driving signal is a pure sine wave. Under 1% is probably OK, when a complex music waveform is present.

IM distortion is another matter, as it is much more irritating than harmonic distortion.


Eli D.

 

Thanks (nt), posted on January 16, 2017 at 15:20:31
SteveBrown
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Posts: 2454
Location: Portland, OR
Joined: November 14, 2002
 nt

 

Multiple kinds of distortion..., posted on January 16, 2017 at 16:55:35
SteveBrown
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Posts: 2454
Location: Portland, OR
Joined: November 14, 2002



I attempted to measure output power and distortion (distortion on my old Leader LDM 171). I got 7.6w out just prior to clipping. And IF I used the distortion meter correctly, it was about 2.3% distortion. Of course that made me suspicious that I was doing something wrong. Power was too low, distortion was too low. I figured 7 to 8 watts was what I'd get with triode wired EL84's so I took a peak under her skirt and sure enough, sometime long ago I converted to triode. As for the distortion reading, I'm not at all sure I did that correctly, seems like you should put a test signal in both the amp and analyzer but the instructions don't say anything about that. I also don't know if the amp should be on a dummy load, but I assume so. Anyway, distortion is suspect to say the least.

 

RE: Multiple kinds of distortion..., posted on January 16, 2017 at 18:34:16
Tre'
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Posts: 17294
Location: So. Cal.
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 "seems like you should put a test signal in both the amp and analyzer"

No, you just match the frequency with the distortion analyzer. You did it right.

You have to deduct the distortion of your generator to get an accurate number. It's complicated but the manual should walk you through it.

IMO 2.3% is high considering that it's a PP circuit and all the even ordered distortions should be canceling.

IMO 2.3%, made up of 3rd and 5th and (God forbid) 7th, will sound much worse than 2.3% of 2nd.


BTW My objection to kitch29's post was his redefinition of the term "distortion". To me he said that "as long as it sounds good to the listener then it can't be described as distorted".

That's just not true. What if the listener has no idea what the recording should sound like? Personal preference for a particular type of sound is not the same as low distortion.

Tre'



Have Fun and Enjoy the Music
"Still Working the Problem"

 

Very Nice!, posted on January 16, 2017 at 22:18:23
amandarae
Audiophile

Posts: 2591
Location: So.Cal
Joined: November 30, 2004
 I too have an El 84 project(restoration) on the works. Hope mine will sound as nice as your build looks. Great job!

 

RE: Spinning Ray Brown , posted on January 16, 2017 at 22:29:46
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
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 Dave
Did you use a film cap off the GZ34 in that beautiful amp as you did in one of your other amp projects?
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Spinning Ray Brown , posted on January 17, 2017 at 06:04:41
SteveBrown
Audiophile

Posts: 2454
Location: Portland, OR
Joined: November 14, 2002



Hi Mike, yes I did. It's the Solen tucked down by the rectifier. The enclosed fil transformer is for a negative supply for the CCS's.

 

RE: Multiple kinds of distortion..., posted on January 17, 2017 at 06:07:44
SteveBrown
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Posts: 2454
Location: Portland, OR
Joined: November 14, 2002
 Thanks. My signal generator is an old and cheap one, and I don't have a manual, but I'll take a look on line and see what I come up with.

 

Thanks! (nt), posted on January 17, 2017 at 07:18:08
SteveBrown
Audiophile

Posts: 2454
Location: Portland, OR
Joined: November 14, 2002
 nt

 

RE: Multiple kinds of distortion..., posted on January 17, 2017 at 07:20:11
Tre'
Industry Professional

Posts: 17294
Location: So. Cal.
Joined: February 9, 2002
 The manual for the distortion analyzer should describe the mathematical process for accounting for the generator distortion.

Run the generator straight into the distortion analyzer to get your base line distortion and then work from there.


Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Spinning Ray Brown , posted on January 17, 2017 at 07:20:27
SteveBrown
Audiophile

Posts: 2454
Location: Portland, OR
Joined: November 14, 2002
 Oh, and you'll notice one of the coupling caps is not like the others - I ran out of the 0.1uf 400v Kimbers I was using. I don't think they're even made anymore. Probably some day I should make them all the same. I've got a bunch of those Russian K40Y guys but would have to shoe-horn them in somehow.

 

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