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MiiB

Member
Joined 2005
raidho.dk
This last circuit does away with the risk of frying the cart....I like that...as it also removes any adjustments from the input.....
I like your servo that sense at the output and injects before the buffer better
I see the change of gain with different carts, but I don't see it as a problem as is is possible to change gain with by jumpering different RIAA networks.
 
S

sampler

Member
Joined 2010
mvaudiolabs.com/
Well, today I have listened to op amp version. Servo worked as expected so it was dc coupled. At first glance everything was ok, plenty of gain, but after couple records I realized that something was gone, something that was so appealing about this circuit - ultimate transparency and micro details. Clearly OP275 is not up to the task here, even though it is really not a bad op amp, jfet (or bipolar hybrid, I should check...) input and so on. So I reverted back, mmmm.... much better :)
I sim'ed current mirrors with helper transistors and if multisim is not lying, output impedance raised from 320k to 717k, so this gives me nice RIAA caps values and good bump in gain. This could be enough, I'm going to check it now.
About your last transconductance circuit. At first look I have some doubts. I think input pair would not conduct, it would just float, and grounding sources would leave only one current mirror working, but maybe I'm wrong, I will check it later.
 
Joachim Gerhard

Joachim Gerhard

Member
Joined 2009
suesskindaudio.de
Maybe post 2961 works when you float the cartridge between gate and source of the input Fet, ground not connected. At the source there should still be nearly zero DC.
Anyway, nice that you can get more gain with the helper transistors. In the Opamp version you could try to flip the leads at the cartridge. Maybe the phase inversion results in the strange sound you get. Anyway, if you get it going without the Opamp thats more elegant.
 
RCruz

RCruz

Member
Joined 2006
Paid Member
sampler said:
It's dead quiet Joachim, only broadband noise (2mV/div in foto). Yes, you are right, in my case resulting gain is ~52dB. With 6Ohm cart. that would be way much more. I attached circuit as build and some sims, any tricks and tips would be appreciated. I really like it, I'm even considering upgrading my preamp for more gain if that's the last resort.
I see you started new thread for nobrainer. That looks elegant/interesting too, I may give it a try, just were did I put those low noise 2sc/2sa...
Click to expand...

Hi Sampler

What is the 100k trimmer (R3) needed for in your Starless version ?
 
Joachim Gerhard

Joachim Gerhard

Member
Joined 2009
suesskindaudio.de
No, output impedance is over 700kOhm so the 1Mohm resistor is not right. Sorry, that the schematic appears on page two. It has reasons that are hard to explain.My drawing program tries to put known component names to the semiconductors. Because it uses only weak artificial intelligence it has no idea about what i use. Removing the not used names shifts the component names up and down, creating 3 pages. I do not think that you need spoon feeding, just read EVERYTHING i post here and you will be able to make the best phono stage in the word in a minute. The Opamp has gain. I try to help sampler to get enough gain with his DL103 into my transimpedance input. "I am not perfect, but i am perfect for you "
Grace Jones.
 
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RCruz

RCruz

Member
Joined 2006
Paid Member
I am reading... carefully :)

I really like your design.... Would it work with a benz ACE M (0.8mV output) ?

So IOP2 is the servo and compares DC offset with GND, feeding the difference to the other opamp. That 1u (C1) must have a big impact in the final voicing... what type do you use ?
 
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Joachim Gerhard

Joachim Gerhard

Member
Joined 2009
suesskindaudio.de
What impedance does the ACE M have ? What schematic are you referring too ? Using a servo is a two side sword. It will not have much impact on the treble response so some authorities like Malkolm Hawksford ( my "father" ) uses a simple TL071. By 1kHz the gain has rolled off. Others claim that they can even hear the opamp used. For the cap i usually use Wima MKT. I f i want to scare the demons away i use EVOX-RIFA PPS:
 
Joachim Gerhard

Joachim Gerhard

Member
Joined 2009
suesskindaudio.de
When it is the schematic with the helper transistors you will get 64dB of gain with your Ace M. That should be more then enough. Gain can be changed by changing the components in the RIAA. For example if you half the values of the resistors and double the caps you get 6dB less gain. It also works the other way around.
I like the parameters of your cartridge. That gives a good combination of low distortion and decent noise performance into my circuit.
 
RCruz

RCruz

Member
Joined 2006
Paid Member
That is new concept for me. I mean modifying the Riaa values to set gain. I will do that because I only need 48 ~50dB gain.

Acording to my calculations, using C7 = 20n I need R16 = 15k9; C8 = 6.86n; R15 = 1M and output impedance of the first stage (the one with the wilson mirrors) should be 122k8.

Can you verify my calculations ? What about R17... can it stay as 1k ?
 
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