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Old 26th August 2019, 07:37 PM   #11
PRR is online now PRR  United States
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> which will be a phaser

Without looking at the actual phaser: I'm quite sure the "500mV" is nominal, basically your 5mV needle figure times 40dB typical preamp gain. Actual needles exceed 30mV@1kHz on LOUD parts (so 3V out of the preamp) and of course down to zero or vinyl hiss. I bet the phaser is all-the-same up to 4V or 8V input. This is not like fitting a swimsuit! More like a one-size-fits-most poncho.
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Old 26th August 2019, 08:07 PM   #12
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Quote:
Originally Posted by wiseoldtech View Post
..."purity of tone" by using the time-tested two transistor style preamp....
I've been working with 2-Q RIAAs for decades. It is pretty easy to show that this form does not have enough gain to be "real good".

Consider first: 47k input, Gv@1kHz=100(40dB), and assume a 47k load. Gain at <50hz is 10X from 1kHz so 1,000. Since Zin and Zload are the same, this requires a Current Gain of 1,000.

Because transistor parameters vary part-to-part and time and temperature, a NFB plan is highly favored. But this wants an additional gain of 10X to ensure "large" NFB. So Current Gain of 10,000.

Yes, we can pluck two transistors with hFE>100. However we need DC feed and base bias networks, and we want good DC stability. We use much of hFE in the infrastructure. An RIAA NFB plan of reasonable Z becomes a hard load in the treble (tho we typically have ample gain up there). Also the assumed 47k load is no longer standard, 22k and 10k inputs are getting common.

The 2-Q plans tend to be sloppy in the bass, with hFE=300. Even with hFE=900 they do not shine.

I have moved (since ~1977) to 3-Q plans. Usually implement the second stage as a Darlington so as to preserve your "purity of tone" by having Q2 Q3 work in the same direction. Macintosh had their own version(s), a nice plan was published in Audio Amateur.
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Old 26th August 2019, 08:17 PM   #13
ubergeeknz is offline ubergeeknz  New Zealand
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Quote:
Originally Posted by gsantosk8 View Post
Thank you guys, all the sugestions will be considered. The thing is, I need about 500mV on the output to for the next stage, which will be a phaser, yes, I'm going quadraphonic!
http://www.saturn-sound.com/images%2...-%20pt%202.jpg
As shown on the image, the next stage requires 500mV, so, I run a simulation and obtained the following outputs at 1KHz:

3.5mV @ 1KHz --> 402.395mV
4mV @ 1KHz --> 459.879mV
4.35mV @ 1KHz --> 500.119mV
4.5mV @ 1KHz --> 517.302mV
5mV @ 1KHz --> 574.849mV

Having those results in mind, and considering a RIAA preamp has a difference of about 40dB between 20Hz and 20KHz, will this circuit do the job and give out the required voltage level on the audible band?
Yes, plenty of output. Depending on your cart you can always reduce or increase the gain as detailed in the instructions.
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Old 26th August 2019, 09:33 PM   #14
wiseoldtech is offline wiseoldtech  United States
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Quote:
Originally Posted by PRR View Post
I've been working with 2-Q RIAAs for decades. It is pretty easy to show that this form does not have enough gain to be "real good".

Consider first: 47k input, Gv@1kHz=100(40dB), and assume a 47k load. Gain at <50hz is 10X from 1kHz so 1,000. Since Zin and Zload are the same, this requires a Current Gain of 1,000.

Because transistor parameters vary part-to-part and time and temperature, a NFB plan is highly favored. But this wants an additional gain of 10X to ensure "large" NFB. So Current Gain of 10,000.

Yes, we can pluck two transistors with hFE>100. However we need DC feed and base bias networks, and we want good DC stability. We use much of hFE in the infrastructure. An RIAA NFB plan of reasonable Z becomes a hard load in the treble (tho we typically have ample gain up there). Also the assumed 47k load is no longer standard, 22k and 10k inputs are getting common.

The 2-Q plans tend to be sloppy in the bass, with hFE=300. Even with hFE=900 they do not shine.

I have moved (since ~1977) to 3-Q plans. Usually implement the second stage as a Darlington so as to preserve your "purity of tone" by having Q2 Q3 work in the same direction. Macintosh had their own version(s), a nice plan was published in Audio Amateur.

Interesting about your Darlington arangement.
I assume that increases the output dramatically?
Most 2Q preamps do sound quieter as compared to say, the FM or Aux selector, and of course this is partly due to low cartridge output (2-2.5 mv).
I've lowered the Q1 emitter resistor to about half the original value (560 to 270 ohms) in order to boost output of Q2 with good results.
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Old 26th August 2019, 09:41 PM   #15
MarsBravo is offline MarsBravo  Netherlands
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Amplification overall @ 1 kHz = 115.
500mV / 115 requires 4+ mV... @ 1kHz
That's a typical MM/MD output before RIAA, so all signs green.
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Old 26th August 2019, 09:46 PM   #16
gsantosk8 is offline gsantosk8
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Quote:
Originally Posted by PRR View Post
> which will be a phaser

Without looking at the actual phaser:
http://www.saturn-sound.com/images%2...%20cct%201.jpg

http://www.saturn-sound.com/images%2...%20cct%202.jpg

Thank you, if you care to see, there you go. But, this was just a reference, I'm actually gonna implement this other circuit.

http://1.bp.blogspot.com/-a99d5AHTZw...oder-lores.jpg

I just thought of the 500mV as a reference, as showm on the comments of the circuit.
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Old 26th August 2019, 09:53 PM   #17
MarsBravo is offline MarsBravo  Netherlands
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Quote:
Originally Posted by PRR View Post
> which will be a phaser

Without looking at the actual phaser: I'm quite sure the "500mV" is nominal, basically your 5mV needle figure times 40dB typical preamp gain. Actual needles exceed 30mV@1kHz on LOUD parts (so 3V out of the preamp) and of course down to zero or vinyl hiss. I bet the phaser is all-the-same up to 4V or 8V input. This is not like fitting a swimsuit! More like a one-size-fits-most poncho.

I would like to promote these two PRR-quotes as basic DIY-rules by default:


PRR quantumrule ONE:
This is not like fitting a swimsuit!

PRR quantumrule TWO:
More like a one-size-fits-most (q?) poncho.

These rules apply to all DIY... experiments.
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Old 26th August 2019, 09:58 PM   #18
MarsBravo is offline MarsBravo  Netherlands
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Quote:
Originally Posted by PRR View Post
I have moved (since ~1977) to 3-Q plans. Usually implement the second stage as a Darlington so as to preserve your "purity of tone" by having Q2 Q3 work in the same direction. Macintosh had their own version(s), a nice plan was published in Audio Amateur.
Circuit's? Serious important issue alongside Lipschitz tbt!
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Old 5th September 2019, 07:56 PM   #19
gsantosk8 is offline gsantosk8
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Quote:
Originally Posted by EssB View Post
That is Rod Elliot's P06 RIAA preamp from Hi-Fi RIAA Phono Preamp

If you're using LT Spice you can use the 'e' component (voltage dependent voltage source) with a Laplace function in the value parameter as in the image below.
So, by using this source, I should expect a flat responce over the audible band? And, is this the same as playing the 7th and n8th track of this record?
The Ultimate Analogue Test LP - Δίσκος βινυλίου για Δοκιμές
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