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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sat 12, 2017 11:42 pm 
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john8750 wrote:
...Just kiddin of course Flip. I will not make that mistake again. I will build a 12" 3 way system. Should I look for the best sensitivity, as close to 100dB as possible? I will match the crossover to the speakers. You guys had some formula to figure the inside area, so I will ask for help on that....
Finding quality 100 dB woofers is going to be quite a chore these days and not cheap. Everything nowadays are lower efficiency, except for some esoteric, and expensive, specialty jobs.

You need to read some (competent) DIY speaker sites to see how they design speakers because it's quite involved.


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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 1:09 am 
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john8750 wrote:
Thanks for all the speaker info men. I have a few 3-way components in mind, so will start there and let you know. Also will check for more info.
The test speakers I build was a total joke. As someone said, "you are flying blind" A true statement. Search for article on this forum, Test Speakers.

Peter, I do want to build a PP 300B amp. I like that schematic except I have a few thoughts about it.
First is the fact that that schematic is more than likely offered by a manufacture of the transformers. It seems to be built around their transformers, at a high price.
Secondly, the first thing illustrated is the specs. These specs show an impossible watt output ( according to the tubes description , 8watts ) I am not sure about this, but would like to know for sure. And, the THD seems to be listed as to good to be actual.
And the third situation is about the preamp IC. Almost all other amps of this type use a tube. Although I'm not certain, I would like to use all tubes, and no coupling transformers.
What do you think Peter.

I would use Edcor transformers.
I don't know how they calculate the wattage.. but they are using a whopping 500V on the plate and as Flip said they
are using class AB2
...which means they are drawing grid current.
But for me ...I would just try to use class Ab1 with 3-400v plate.

The coupling transformer is a good element because it is automatically providing the inverted signal .. AND it is passively boosting the op-amp output voltage so as to get a wide (50v ?) swing on the grid.
50v would be too much swing for the opamp to do by itself... it's rails are just 26 v apart, as it only uses +/-13v vcc
We could get more swing out out of an op275 cause it's rails are 40v apart as it has +/- 20v vcc
But still ...it can in practice only do about 37v PP ... so that still isn't the full 50v that the 300b needs for full grid swing... as I understand it.

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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 1:12 am 
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john8750 wrote:
... Secondly, the first thing illustrated is the specs. These specs show an impossible watt output ( according to the tubes description , 8watts ) I am not sure about this, but would like to know for sure. And, the THD seems to be listed as to good to be actual.
And the third situation is about the preamp IC. Almost all other amps of this type use a tube. Although I'm not certain, I would like to use all tubes, and no coupling transformers....
The output watt isn't "impossible." As I previously stated the amp is operating Class A2, positive grid drive, as opposed to the common Class A or AB. That's where the extra power is coming from. Again, the 300b isn't rated for positive grid drive, and neither is the 2A3, so they're living somewhat on the edge of practicality.

The TDA2030 is an obsoleted power amp, which provides the power to drive the grids positive. The same thing can be done with tubes, albeit at greater cost (unless, perhaps, you count the cost of their interstage transformer). One can only speculate on the design decisions but that may be why there's no negative feedback, because it's problematic wrapping NFB around two transformers.

They don't give at what power level that THD number is rated at but it's not "too good to be true," especially if it's at 1 Watt. By their nature PP amplifiers cancel the large 2'nd harmonic in the OPT and, so, have lower THD numbers than their SE counterparts, with the uncanceled 3'd harmonic then being dominant.

While, compared to, say, 30 Watt, 50 Watt sounds like a 'lot more' it's really only a 2.2 dB increase in perceived power (it takes 6 to 10 dB to double volume) and, IMO, not worth the cost.

That's in addition to my dislike of solid state in the audio path of a tube amplifier. It just seems counter to the point of building a tube amp in the first place.


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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 1:46 am 
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john8750 wrote:
Flipperhome wrote:
...That's a Goldwood Speaker https://www.parts-express.com/goldwood- ... m--290-335

"These Goldwood low frequency OEM woofers or drivers are ideal for the customer who is looking for inexpensive replacement woofers"

Of course you know that you need more than just a woofer. Designing speakers is another whole ball game and you can't expect "Hi-Fi" performance but just slapping any ole thing together.
Would this be a better choice Flip? I don't mind buying new woofers if they are better.
https://www.parts-express.com/dayton-au ... r--295-320
I always liked the Daytons at partsexpress. They have a smooth frequency response (to 1 kHz or so), better than average sensitivity, and quite respectable free air resonance. IMO they're a good comprise between cost and performance, but that's just me.

You can get a 5 Hz better low end and an extra 1.5 dB with the Dayton 15 inch woofer but is it worth it for almost twice the cost?


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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 2:19 am 
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Flipperhome wrote:

That's in addition to my dislike of solid state in the audio path of a tube amplifier. It just seems counter to the point of building a tube amp in the first place.

But if you feed an ALL tube power amp from a CD or Mp3 player... solid state is still in the signal path... so it just depends on how soon you add it. But.. it'll still be there.
Right?

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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 2:25 am 
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Flipperhome wrote:

The TDA2030 is an obsoleted power amp, which provides the power to drive the grids positive. The same thing can be done with tubes, albeit at greater cost (unless, perhaps, you count the cost of their interstage transformer). One can only speculate on the design decisions but that may be why there's no negative feedback, because it's problematic wrapping NFB around two transformers.

So Flip:
They use the transformer to boost the opamp to a 50v swing right?

Could the op-275 be used in front that interstage transformer ?

And if I drop the plate to 300V... or maybe 400v where would a good AB1 bias point be?

If I could do this with that interstate transformer or some easy & simple (non tube) way to get enough grid swing.. I might build it.

Is there an opamp that would be able to do that wide of a grid swing?
How about something like an opa454 ?? ... would it have good fidelity?
http://www.ti.com/product/OPA454

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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 2:55 am 
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I see another way to get greater voltage swing from an opamp.
Bootstrap it.
Im not sure i fully understand how this works but it seems like a simple idea.

( This bootstrap article is from way back in 1999 so ... maybe nowadays it's better to find a high quality audio opamp with wide output swings like that opa454 opamp? )

ref:
http://www.proaudiodesignforum.com/imag ... 3_1999.pdf

Image

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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 3:08 am 
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Pbpix wrote:
Flipperhome wrote:

The TDA2030 is an obsoleted power amp, which provides the power to drive the grids positive. The same thing can be done with tubes, albeit at greater cost (unless, perhaps, you count the cost of their interstage transformer). One can only speculate on the design decisions but that may be why there's no negative feedback, because it's problematic wrapping NFB around two transformers.

So Flip:
They use the transformer to boost the opamp to a 50v swing right?

Could the op-275 be used in front that interstage transformer ?

And if I drop the plate to 300V... or maybe 400v where would a good AB1 bias point be?

If I could do this with that interstate transformer or some easy & simple (non tube) way to get enough grid swing.. I might build it.

Is there an opamp that would be able to do that wide of a grid swing?
How about something like an opa454 ?? ... would it have good fidelity?
http://www.ti.com/product/OPA454
The grids need to be driven by in excess of 140 Vpp.

It's not AB1. It's A2.

The op275 doesn't have the power to drive the grids in A2. It takes a power amp.


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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 3:15 am 
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Pbpix wrote:
Flipperhome wrote:

That's in addition to my dislike of solid state in the audio path of a tube amplifier. It just seems counter to the point of building a tube amp in the first place.

But if you feed an ALL tube power amp from a CD or Mp3 player... solid state is still in the signal path... so it just depends on how soon you add it. But.. it'll still be there.
Right?
Not if you play records, or tape, with a tube preamp like Little John.
Right?

But even with a CD player your logic doesn't hold. It's akin to saying if your going to ruin it in one place then you might as well double ruin it. Using that logic why do any tubes at all? Might as well just build a solid state amp and be done with it.


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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 3:17 am 
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Howdy John,

john8750 wrote:
The test speakers was a disaster. I had some fun but the only thing I learned is that I had no idea about what I was doing.
Please explain a little further about what to look for in a good speaker for my amp. Not sure that I understand. Is a 12" 3-way with high sensitivity what I need?


Here's a link to a discussion on this subject: http://audiokarma.org/forums/index.php?threads/high-efficient-speakers-that-run-on-low-watt-amps.696223/

I've only read about his stuff and have no practical experience with it, so consider me the blind leading the blind on this subject. Well, I do know a bit about it, but I've always considered myself to be a total noob, unless I've actually tinkered around with such things. Even when I know a subject very well, I still like to consider myself a noob, go through the basic thought processes as a noob, and approach everything this way, no matter the subject. Doing this keeps me curious about these things, and I always like to see if I can figure out a new way of doing things that might improve performance and such. (Shrug.)

73,

Randy AB5NI

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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 3:26 am 
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Flipperhome wrote:
Pbpix wrote:
Flipperhome wrote:

The TDA2030 is an obsoleted power amp, which provides the power to drive the grids positive. The same thing can be done with tubes, albeit at greater cost (unless, perhaps, you count the cost of their interstage transformer). One can only speculate on the design decisions but that may be why there's no negative feedback, because it's problematic wrapping NFB around two transformers.

So Flip:
They use the transformer to boost the opamp to a 50v swing right?

Could the op-275 be used in front that interstage transformer ?

And if I drop the plate to 300V... or maybe 400v where would a good AB1 bias point be?

If I could do this with that interstate transformer or some easy & simple (non tube) way to get enough grid swing.. I might build it.

Is there an opamp that would be able to do that wide of a grid swing?
How about something like an opa454 ?? ... would it have good fidelity?
http://www.ti.com/product/OPA454
The grids need to be driven by in excess of 140 Vpp.

It's not AB1. It's A2.

The op275 doesn't have the power to drive the grids in A2. It takes a power amp.


I wasn't asking about A2 though.

Something less.

Like AB1.

Could an op275 drive that transformer if not in call AB2 or A2?

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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 3:42 am 
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westcoastjohn wrote:
Yes, I remember that book. Gary W. do you remember me lending it to you in 1999? :x


Yeah, it was a good book. I also enjoyed the other books that they put out, such as the book on how to design power supplies. The only problem I ever had with their books is that they always recommended their own components when building things. I guess you really can't blame them for doing that, though :D.

73,

Randy AB5NI

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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 3:46 am 
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ab5ni wrote:
Howdy John,

Here's a link to a discussion on this subject: http://audiokarma.org/forums/index.php?threads/high-efficient-speakers-that-run-on-low-watt-amps.696223/

I've only read about his stuff and have no practical experience with it, so consider me the blind leading the blind on this subject. Well, I do know a bit about it, but I've always considered myself to be a total noob, unless I've actually tinkered around with such things. Even when I know a subject very well, I still like to consider myself a noob, go through the basic thought processes as a noob, and approach everything this way, no matter the subject. Doing this keeps me curious about these things, and I always like to see if I can figure out a new way of doing things that might improve performance and such. (Shrug.)

73,

Randy AB5NI

Attachment:
Rodrigues - speaker salesman_jpeg.jpg
Rodrigues - speaker salesman_jpeg.jpg [ 109.58 KiB | Viewed 184 times ]


That's not a horn. THIS is a horn.

Attachment:
he11bl011000.jpg
he11bl011000.jpg [ 112.66 KiB | Viewed 184 times ]


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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 4:07 am 
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Howdy Flip,

Quote:
Finding quality 100 dB woofers is going to be quite a chore these days and not cheap. Everything nowadays are lower efficiency, except for some esoteric, and expensive, specialty jobs.


You can say that again, which is why I suggested that he might want to look into some of the AM/FM/Phono consoles from the 60's. He should be able to find numerous consoles in his area for damn-near-dirt prices on craigslist and eBay. Not only that, he could restore the electronics and put them up on eBay and get most of his money back, and he might even make a profit.

Quote:
You need to read some (competent) DIY speaker sites to see how they design speakers because it's quite involved.


That it is, dude, and then some!

John: Another thing you're going to want to do is use 3/4-inch particle board. As far as building a house or furniture goes, it's complete and utter garbage; however, the folks in the homebrew-speaker department like it a lot, mainly because it's very dense. Some guys even build there enclosures out of cement/concrete :D.

73,

Randy AB5NI

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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 4:15 am 
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Howdy Flip,

Flipperhome wrote:

That's not a horn. THIS is a horn.

Attachment:
he11bl011000.jpg



Damn! Now that is a nice setup, Flip! Is that the setup you are using, dude? I really love the vaulted ceilings and all of the wood. The acoustics in that room must be amazing.

73,

Randy AB5NI

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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 4:28 am 
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Howdy Flip,

Flipperhome wrote:
Not if you play records, or tape, with a tube preamp like Little John.
Right?


I sometimes wonder if it really matters at all where the input signal is coming from, as long as the input is of decent quality. I'd imagine that WAV and FLAC files will sound really great when amplified correctly. OTOH, I don't think I'd ever use put an MP3 into that pipeline -- that's for sure! :D

73,

Randy AB5NI

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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 5:30 am 
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ab5ni wrote:
Howdy Flip,

Flipperhome wrote:
Not if you play records, or tape, with a tube preamp like Little John.
Right?


I sometimes wonder if it really matters at all where the input signal is coming from, as long as the input is of decent quality. I'd imagine that WAV and FLAC files will sound really great when amplified correctly. OTOH, I don't think I'd ever use put an MP3 into that pipeline -- that's for sure! :D

73,

Randy AB5NI



Yes it does matter. The only way to get a true reproduction nowadays is off of vinyl. IMHO. And I cant say I like everything that's been digitally re-mastered. It just don't sound the same.

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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 5:45 am 
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You guys
Could this circuit be modified for CCS and NFB? I like this circuit.
I need your help here. Without you I wont even try any 300B.
I am getting better educated on speaker building. The 15" is just to big. But I want the 12" with 6/8" mid and a good tweeter. I know that the best I can afford is still not the best.
For now, I would like to settle on the amp schematic. So I can order the iron stuff.
I will duplicate the Little Prince for the preamp, so the 300B will need to be all tubes. The power supply maybe not.
http://www.oestex.com/tubes/Circuits/AW ... ircuit.jpg

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If I did something right, I made a mistake.


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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 6:36 am 
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john8750 wrote:
You guys
Could this circuit be modified for CCS and NFB? I like this circuit.
I need your help here. Without you I wont even try any 300B.
I am getting better educated on speaker building. The 15" is just to big. But I want the 12" with 6/8" mid and a good tweeter. I know that the best I can afford is still not the best.
For now, I would like to settle on the amp schematic. So I can order the iron stuff.
I will duplicate the Little Prince for the preamp, so the 300B will need to be all tubes. The power supply maybe not.
http://www.oestex.com/tubes/Circuits/AW ... ircuit.jpg

Hi John:
So what exactly is it you 'like' about it in particular... you didn't say why.
Explain please.
and btw...
What's with those weird value resistors???
.05 and .25 and .01 ?
What the heck is that all about????????????

is that ohms? or some drafting shorthand for k ohms or megohms????
And especially for 1939... it just doesn't seem to make sense.

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 Post subject: Re: A new 300B amp project
PostPosted: Aug Sun 13, 2017 6:54 am 
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Pbpix wrote:
I wasn't asking about A2 though.

Something less.

Like AB1.

Could an op275 drive that transformer if not in call AB2 or A2?
No. Primary impedance is 30 Ohm.


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