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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 29, 2017 4:52 pm 
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john8750 wrote:


Increasing frequency does not increase volume.
If that is true, then the prince John is flat up to at least 11khz.

Increasing freq only effects the amps ability to respond linearly after a point.

So for instance if you apply 400hz @ 100mv AC rms to the input you may see about 10v AC rms on the output plate into an 8 ohm dummy load.
And if you increase the input toward higher 120-150mv the output signal should also continue to raise until further increases cause the output to start to flat-top.
Then you should just back off the input until the output signal looks perfect w/no distorted shape.

If that point is 10.5v AC rms (or whatever) ... then that's the maximum un-distorted power your amp can deliver.

If ( keeping the input frequency fixed at 100mv or whatever) you do this test at 400hz and then again at 1khz, and 5khz, and 10khz and 15khz etc... on up to 20khz... you may begin to see the maximum Peak to peak (or ac RMS on a meter) output signal drop a bit as you increase the frequency. But ordinary True ACRMS meters cannot read the AC voltage properly as you keep increasing the frequency beyond maybe 400hz.
You'd need a very high quality Bench or lab meter to read AC at those frequencies.
So you will need to watch the scope signal to seethe PP envelope start to drop down indicating the highest point where the amp can still deliver maximum voltage.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 29, 2017 9:38 pm 
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john8750 wrote:
I think I understand now.
The shape of the waveform from the input through the amp should match the output. I adjusted the output trace amplitude and overlaid the input trace. Increasing frequency does not increase volume.
If that is true, then the prince John is flat up to at least 11khz. Above my hearing.
Thanks Peter. I want to be accurate.
Increasing or decreasing frequency in the range of 20-20kHz shouldn't affect volume and that's what you're testing, to see if it does. If it does then the frequency response is not "flat" over the audio range. That's what "flat" frequency response means.

Usually, the frequency response is measured at 1 Watt out. Testing the frequency response at 'maximum' (undistorted) power is the "power bandwidth" and is a harsher test. Often the 1 Watt frequency response will be wider because, at 'max power', the OPT will saturate on the low end or be slew rate limited on the upper end. In your case, because of the OPTs you're using, the "power bandwidth" should be from 20-20kHz (at least) while the 1 Watt frequency response may extend from 10 Hz to 30 or 40 kHz.

The 1 Watt output frequency response is the one we're really interested in because that's what you actually 'hear'.

It's good that it's flat to 11 kHz but that's (almost) trivial to achieve. You need to test it on up to 20 kHz to know if it's working right. There's nothing wrong with doing 50 Hz increments but that's unnecessarily often (unless you're looking for a specific problem). The easiest way to jut take a reading at 20 kHz and the work down in, say, 1 kHz increments if there's a problem (like if it shows 'low' at 20 kHz and you need to find the -3 dB point).

Remember that - 3 dB in power is (half power but) .7 the voltage. +- 1 dB (which is considered real flat) would be +- 12% in voltage.


Last edited by Flipperhome on Dec Sat 30, 2017 1:38 am, edited 1 time in total.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 30, 2017 12:24 am 
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Flipperhome wrote:
the 1 Watt frequency response may extend from 10 kHz to 30 or 40 kHz.

A typo? did you mean 10hz to 30 or 40khz?
Just asking, because there are lots of things I don't understand.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 30, 2017 1:36 am 
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kc5gym wrote:
Flipperhome wrote:
the 1 Watt frequency response may extend from 10 kHz to 30 or 40 kHz.

A typo? did you mean 10hz to 30 or 40khz?
Just asking, because there are lots of things I don't understand.
Oops, yes, I meant 10 Hz. Thanks. I'll edit that.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 30, 2017 3:17 am 
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kc5gym wrote:
Flipperhome wrote:
the 1 Watt frequency response may extend from 10 kHz to 30 or 40 kHz.

A typo? did you mean 10hz to 30 or 40khz?
Just asking, because there are lots of things I don't understand.



Hang around Mark. I know very little about the scope. There guys make it all sound easy.
Except that dB thing.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 30, 2017 3:23 am 
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OK Flip. I did the 20khz down to 1khz. The two traces stayed in perfect alignment. When I change frequency's, it wiggles
just a little. But noticed that both traces wiggled, so guess that's normal?
I need to read about the dB now.
Soon, I will move the Blumoon out to the shop for a scope test.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 30, 2017 3:25 am 
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Flipperhome wrote:
kc5gym wrote:
Flipperhome wrote:
the 1 Watt frequency response may extend from 10 kHz to 30 or 40 kHz.

A typo? did you mean 10hz to 30 or 40khz?
Just asking, because there are lots of things I don't understand.
Oops, yes, I meant 10 Hz. Thanks. I'll edit that.




Oh great Flip. Now I'm confused :roll: :lol:

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 30, 2017 5:22 am 
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Listening to the Blumoon right now. Beautiful music from the mp3. Phono needs some work yet.
The Little Prince really controls this amp. The Bass needs some push. Plenty of highs though.
I need a more sensitive speaker for the den where this amp will be. And we, Flip, will build another
Little Prince, with the added MP3 amp section.
I am telling you all, the Little Prince could be on the market, absolutely awesome.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 30, 2017 6:53 am 
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john8750 wrote:
Flipperhome wrote:
kc5gym wrote:
A typo? did you mean 10hz to 30 or 40khz?
Just asking, because there are lots of things I don't understand.
Oops, yes, I meant 10 Hz. Thanks. I'll edit that.

Oh great Flip. Now I'm confused :roll: :lol:
What are you confused about?


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 30, 2017 6:54 am 
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john8750 wrote:
Listening to the Blumoon right now. Beautiful music from the mp3. Phono needs some work yet.
The Little Prince really controls this amp. The Bass needs some push. Plenty of highs though.
I need a more sensitive speaker for the den where this amp will be. And we, Flip, will build another
Little Prince, with the added MP3 amp section.
I am telling you all, the Little Prince could be on the market, absolutely awesome.
Thanks.

What do you mean when you say the phono needs work yet?


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 30, 2017 6:56 am 
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The best speaker, for the price. Pioneer TS-976M $44.98 at Walmart. 6X9 28-32khz. 93dB.
4ohm. I figure two in series for each box. That's a little over a hundred bucks, plus building material.
No worry, the Little Prince will contour almost any speaker. Should fill my small den room easily.
Could even build four boxes with one speaker in each. Wire two in parallel for each channel.
https://www.walmart.com/ip/Pioneer-TS-9 ... r/46473571

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 30, 2017 7:00 am 
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Flipperhome wrote:
john8750 wrote:
Listening to the Blumoon right now. Beautiful music from the mp3. Phono needs some work yet.
The Little Prince really controls this amp. The Bass needs some push. Plenty of highs though.
I need a more sensitive speaker for the den where this amp will be. And we, Flip, will build another
Little Prince, with the added MP3 amp section.
I am telling you all, the Little Prince could be on the market, absolutely awesome.
Thanks.

What do you mean when you say the phono needs work yet?



I need to balance the tone arm, and tighten the head shell, its loose.
Very easily doable. I will have to take it out to the shop for work. I am gettin
to it. Then, the little prince will need to be there also. Its like back and forth.

OMG- did you think I meant the phono section in the Little Prince wasn't working :?:

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 30, 2017 6:47 pm 
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john8750 wrote:
I need to balance the tone arm, and tighten the head shell, its loose.
Very easily doable. I will have to take it out to the shop for work. I am gettin
to it. Then, the little prince will need to be there also. Its like back and forth.

OMG- did you think I meant the phono section in the Little Prince wasn't working :?:
Oh, I see. The turntable needs work.

It didn't make sense that it would be the Little Prince but it sure sounded like it. :lol:


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 30, 2017 6:49 pm 
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john8750 wrote:
The best speaker, for the price. Pioneer TS-976M $44.98 at Walmart. 6X9 28-32khz. 93dB.
4ohm. I figure two in series for each box. That's a little over a hundred bucks, plus building material.
No worry, the Little Prince will contour almost any speaker. Should fill my small den room easily.
Could even build four boxes with one speaker in each. Wire two in parallel for each channel.
https://www.walmart.com/ip/Pioneer-TS-9 ... r/46473571
I don't believe that frequency spec and I've had bad luck with 'car speakers'. They just don't have the balance of 'real' speakers.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 30, 2017 11:21 pm 
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Flipperhome wrote:
john8750 wrote:
The best speaker, for the price. Pioneer TS-976M $44.98 at Walmart. 6X9 28-32khz. 93dB.
4ohm. I figure two in series for each box. That's a little over a hundred bucks, plus building material.
No worry, the Little Prince will contour almost any speaker. Should fill my small den room easily.
Could even build four boxes with one speaker in each. Wire two in parallel for each channel.
https://www.walmart.com/ip/Pioneer-TS-9 ... r/46473571
I don't believe that frequency spec and I've had bad luck with 'car speakers'. They just don't have the balance of 'real' speakers.



I hear that Flip. That was a thought from a quick look last night. I like the sensitivity, if that is correct. But must agree, hard to believe. But also cheap enough for an experiment. And only a simple box for a test.
Could I power one 4ohm speaker with an 8ohm output?

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sun 31, 2017 2:18 am 
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john8750 wrote:
Flipperhome wrote:
john8750 wrote:
The best speaker, for the price. Pioneer TS-976M $44.98 at Walmart. 6X9 28-32khz. 93dB.
4ohm. I figure two in series for each box. That's a little over a hundred bucks, plus building material.
No worry, the Little Prince will contour almost any speaker. Should fill my small den room easily.
Could even build four boxes with one speaker in each. Wire two in parallel for each channel.
https://www.walmart.com/ip/Pioneer-TS-9 ... r/46473571
I don't believe that frequency spec and I've had bad luck with 'car speakers'. They just don't have the balance of 'real' speakers.



I hear that Flip. That was a thought from a quick look last night. I like the sensitivity, if that is correct. But must agree, hard to believe. But also cheap enough for an experiment. And only a simple box for a test.
Could I power one 4ohm speaker with an 8ohm output?
Nope. you need two per channel to get 8 Ohm.

I guess you're shooting for 'max output', in other words as large an SPL as you can get, but if you just want to 'try' something having to get 2 per channel seems a waste and a 6x9 isn't the best 'shape' to begin with.

A really good speaker system is going to cost big bucks but if you want something 'for the shop' I'd be tempted to get the GRS 8FR-8 https://www.parts-express.com/grs-8fr-8 ... w--292-430 . It's supposed to be rather decent and if the highs aren't there (can you hear above 10k?) a simple cap crossover tweeter can be added.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sun 31, 2017 4:07 am 
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Great choice Flip. And a great price. I should have checked further. Out of stock till Feb. should be about the time I would like to get them anyway. That's why I wanted a full range speaker, no crossover. I can hear up to 11khz. But I am a basement type Man. Highs don't thrill me like bass does. But the Little Prince gives me exactly what I want. With any type speaker.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sun 31, 2017 8:37 pm 
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john8750 wrote:
Great choice Flip. And a great price. I should have checked further. Out of stock till Feb. should be about the time I would like to get them anyway. That's why I wanted a full range speaker, no crossover. I can hear up to 11khz. But I am a basement type Man. Highs don't thrill me like bass does. But the Little Prince gives me exactly what I want. With any type speaker.
Once upon a time I thought about building a "full range' speaker system with the famous Pioneer B20FU20-51FW, referred to as the "BOFU" in the DIY community, but they've discontinued that speaker. The GRS 8FR-8 is supposedly a (near) replacement for it. Even the BOFU really needed a tweeter, though. Whizzer cones just don't 'whizz' well enough. :wink:

Here's the response curve for the BOFU (the GRS 8FR-8 doesn't have one). https://www.parts-express.com/pedocs/sp ... -44291.pdf You can see that speaker specs usually consider a 12 dB range for their 'frequency response'. In the case of the BOFU, that's +3 dB to -8 dB. Some others figure if it wiggles at all that's a 'response'.

Note, the lower graph has the impedance plot and at 20 kHz is up around 40 Ohm.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sun 31, 2017 11:04 pm 
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Flipperhome wrote:
john8750 wrote:
Great choice Flip. And a great price. I should have checked further. Out of stock till Feb. should be about the time I would like to get them anyway. That's why I wanted a full range speaker, no crossover. I can hear up to 11khz. But I am a basement type Man. Highs don't thrill me like bass does. But the Little Prince gives me exactly what I want. With any type speaker.
Once upon a time I thought about building a "full range' speaker system with the famous Pioneer B20FU20-51FW, referred to as the "BOFU" in the DIY community, but they've discontinued that speaker. The GRS 8FR-8 is supposedly a (near) replacement for it. Even the BOFU really needed a tweeter, though. Whizzer cones just don't 'whizz' well enough. :wink:

Here's the response curve for the BOFU (the GRS 8FR-8 doesn't have one). https://www.parts-express.com/pedocs/sp ... -44291.pdf You can see that speaker specs usually consider a 12 dB range for their 'frequency response'. In the case of the BOFU, that's +3 dB to -8 dB. Some others figure if it wiggles at all that's a 'response'.

Note, the lower graph has the impedance plot and at 20 kHz is up around 40 Ohm.



So I will need a tweeter at about 5khz. I have already selected a tweeter, they suggested. I like the average SPL at around 90dB. Should be easy for the 300b to drive. They also suggested a 4uf cap as the only crossover component needed. And a box 36" tall-10" square. Made of MDF, 1/2", or 3/4". A port 3"X5.75". Don't remember if it was a front or rear port.
What about a front square folded port?
I will get more info. Parts express goes into great detail about building enclosures for their speakers. I sure would like to do it right this time.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sun 31, 2017 11:21 pm 
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What type tube is this?
Attachment:
IMG952017123195120154.jpg
IMG952017123195120154.jpg [ 93.85 KiB | Viewed 401 times ]

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