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1V2 phono riaa preamplifier
1V2 phono riaa preamplifier
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Old 7th December 2017, 02:10 PM   #1
dreamth is offline dreamth  United Kingdom
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Default 1V2 phono riaa preamplifier

This is my last project, ready to be assembled:



1V2 phono riaa preamplifier

http://i68.tinypic.com/or709w.jpg
User Media - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting

I am not an experienced user of LtSpice, nor a good designer so please bear with me!
The version i built is with d3a as pentode in constant vg2k mode as in Tektronix vertical amplifier manual.
The model for d3a in triode mode is the Bartola model.

The bss-135 transistors are just models as the real transistors were bsp-135.
I didn't know how to convert the orcad spice models for bsp125 and bsp135 to LT-spice but a romanian mate, G Sabac, helped me with bsp125 conversion to lt-spice and suggested that bss-135 would approximate the bsp-135.He is the one who gave me the bsp-bss library attached in zip format.
I have to thank jazbo8 for helping me with the the model for d3a as a pentode.

V2 can be 160...190v, but with lower voltages a transistor like pzta42 or a swithing transistor like zetex would work better.Even bc337/40 is better than ksc3503 with lower voltages .Unfortunately it's a bit dangerous in tranzient mode to have a bc337,myght work though....

The riaa network i chose is about 10k impedance, but the sym shows that a 600 ohm lcr network can be ok too with increased thd , but very monotonic decay of h2, h3, h4...
You can see that i used a 470 ohm (wirewound LESA) potentiometer in the riaa network(R23-R25) that allows me to modify the response as a mid-high corrector.
I chose c3 100uf to work as a steep ruble filter with R13-R16 which are in fact a 100 ohm wirewound pot, so i can raise the gain too with that.Of course i can change c3 for a higher value and have a better base response.
The two zenners are in fact just one of 150v...
V3 is just a 1.5v battery.It can be replaced with a 1.2v for higher current and lower noise in the input stage.
I still am curious about the partition noise of the second stage , now that i have a fet providing the constant voltage.
Of couse you can modify the values for your preffered response...


The inverse riaa is a slight modification of this:
https://i0.wp.com/www.bartola.co.uk/...AA-circuit.png


1V2 phono riaa preamplifier

http://i66.tinypic.com/18esxt.jpg
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1V2 phono riaa preamplifier

http://i64.tinypic.com/315ohmg.jpg
http://tinypic.com/m/k0iwlx/1

This is part of a slightly bigger project that includes also my Teardrop headphones amplifier , a hybrid project too.I'm going to make a different thread for that too, but the main transformers are in the headphone amplifier box so they would work together.

You have just some pictures of the Teardrop headphones amplifier for which G Sabac put together the BSP-BSS models and made a simulation here:
https://www.elforum.info/topic/12871...nes-amplifier/
Unfortunately you need to register there and translate from romanian if you want to see that thread.

My real amp sticks a bit to the first version though as i found a better monotonic decay in fft response with higher current in the first stage, but took his advice for higher voltage in the first stage.

1V2 phono riaa preamplifier

http://i68.tinypic.com/ea39ly.jpg
http://tinypic.com/m/k0iyrb/1
1V2 phono riaa preamplifier

http://i68.tinypic.com/2i1iohu.jpg
http://tinypic.com/m/k0iyrp/1
This will be discused also in a separate thread .
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File Type: zip proiect 1v2.zip (425.8 KB, 16 views)
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Old 8th December 2017, 12:04 PM   #2
dreamth is offline dreamth  United Kingdom
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As usual i put the wrong simulation and jpeg...It happened because before uploading i tried to make the image smaller so i scrambled both simulation and image.R18 was linked to the wrong point.Actually it worked like that in the sym and the fft seemed to be the same, but h2 was by 3db higher.Not that i fully trust my syms...i don't really know if they are very correct.I barely knew how to load the sym models...
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File Type: jpg 1v2-pentode real.jpg (159.9 KB, 136 views)
Attached Files
File Type: asc 1v2-pentode.asc (7.3 KB, 12 views)

Last edited by dreamth; 8th December 2017 at 12:06 PM.
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Old 8th December 2017, 12:39 PM   #3
jackinnj is offline jackinnj  United States
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1V2 phono riaa preamplifier
Instead of a battery, why not an LED in the cathode of the first stage?

Take a look at the front end of SY's design "His Master's Noise" : His Master's Noise: A Thoroughly Modern Tube Phono Preamp
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Old 8th December 2017, 02:07 PM   #4
dreamth is offline dreamth  United Kingdom
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I was just my option...I have nothing against led's but i allready used batteries and i liked how it works.
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Old 8th December 2017, 02:16 PM   #5
dreamth is offline dreamth  United Kingdom
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This is my second design based on d3a, the first is here:
UNU-pnono riaa mm preamp
I used a battery to bias the second stage there, but i never showed the second stage on diyaudio.It was quite complex and not very effective on low impedances as it was allan kimmel mu stage but built fully with tubes .

Among all the phono stages based on d3a, the one i allways envied is the ""Izzie wizzie ""design and i used his battery arangement for the first stage just to see how it will work like that.
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Old 9th December 2017, 12:58 PM   #6
RajkoM is offline RajkoM  Bosnia and Herzegovina
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Ale Moglia also gave a good idea for pentode with CCS as a driver.
This is applied to a phono preamplifier with a single D3A.
If we add Fet source folower (aka Dutman's idea to RCA phono preamp), we get this:
Simulation looks pretty good.
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File Type: jpg D3A phono.jpg (152.7 KB, 160 views)
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Old 9th December 2017, 05:04 PM   #7
dreamth is offline dreamth  United Kingdom
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1.9v on the red led...i think a green one would be 1.8...1.9 v
Anyway my design works with really cheap transistors and it can go really low with the voltage as it works very close to the saturation of the transistors.I tried to make Allan Kimmel's design pure transconductance mu stage removing any resistor as load .I didn't want to go the ccs way for anode.Voltage source is better for this design as the efficiency can be much higher than the one of any ccs .I will try to go with 100...130v as supply for the first stage to see how it works.
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Old 9th December 2017, 07:54 PM   #8
RajkoM is offline RajkoM  Bosnia and Herzegovina
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All my red LED`s, bought in Burklin about 20 years ago, are 2V.
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Old 9th December 2017, 10:35 PM   #9
sesebe is offline sesebe  Romania
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Looks impressive!
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Old 10th December 2017, 03:54 PM   #10
dreamth is offline dreamth  United Kingdom
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Thanks Bogdan!
I built yesterday the capacitor and resistor network swich for loading the cartridge for both mm and mc carts.
I simulated today with the japanese spice model for d3a and their thd results measure worse by 4...6 db which i trust more :-).
I also spent some hours to simulate a fet input placed in the d3a cathode for an mc cart input and i found a simple way to swich from valve input to fet input so that i will use the d3a grid for mm cart and fet input for mc.I tried with lsk489, but i would use bf862.I can't download today the bf862 model so i will look tomorrow for that.
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