Simple RIAA phono preamps

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#61
Re: Re: Re: Re: Bugle!

Optical said:
gotcha
so what did you do with these diodes? did you put them across the power supply?
Click to expand...
Have a look at this schematic.
At the output of first amp, there is an arrow and a constant current (2 mA) symbol.
The constant current diode was placed there,
to the negative supply. Makes the OP run in Class A.

Nicke schematic

I think it is a modified version of Linear Tech'
application for LT1115 + LT1010.
see LT1115 datasheet
 
#62
Re: Re: Re: Re: Bugle!

Optical said:
so what did you do with these diodes? did you put them across the power supply?
Click to expand...

This part isn't really a diode. It's a FET with a buitl-in source resistor and the gate in connected to the other end of the resistor. This forms a classic current source made of a FET. This current source is connect between the output and the negative rial = the outstage goes in class A more than it would.

Check here but if you will see it more clearly look here.
 
#63
Re: Re: Re: Re: Re: Bugle!

peranders said:


This part isn't really a diode. It's a FET with a buitl-in source resistor and the gate in connected to the other end of the resistor. This forms a classic current source made of a FET. This current source is connect between the output and the negative rial = the outstage goes in class A more than it would.

Check here but if you will see it more clearly look here.
Click to expand...

So if you can not find those seldome used CC-diodes,
you can use a JFET transistor and a resistor, just as well.
That makes you able to change to desired current,
within the JFET's limitations.
 
#64
Re: Re: Re: Re: Re: Re: Bugle!

halojoy said:
So if you can not find those seldome used CC-diodes,
you can use a JFET transistor and a resistor, just as well.
That makes you able to change to desired current,
within the JFET's limitations.
Click to expand...

Right, but since you are from Sweden you can easily buy these from ELFA. Check art no. 70-095-09 and forward. Note that they are rather expensive, 1-2 USD.
 
#66
Re: Re: Re: Re: Re: Re: Re: Bugle!

peranders said:
Right, but since you are from Sweden you can easily buy these from ELFA. Check art no. 70-095-09 and forward. Note that they are rather expensive, 1-2 USD.
Click to expand...

Right, I know. I have almost complete collection of ELFA catalogue,
for some 10-12 years back.
I wouldn't know much of components without ELFA.
Optical might find them diodes, too, in NZL or AUS.
But if not he can use a JFET instead.
 
#67
wow, thats a really cool idea.. Is the change in the output actually audible though?
i guess it cant be a bad thing though!

i cant find any constant current regulators in my area, so a jfet transistor and a ~100ohm resistor would suffice?
 
#68
Optical said:
wow, thats a really cool idea.. Is the change in the output actually audible though?
i guess it cant be a bad thing though!

i cant find any constant current regulators in my area, so a jfet transistor and a ~100ohm resistor would suffice?
Click to expand...

hook up the JFET + resistor to a 12-15 V supply.
By messure the voltage across the resistor you get
the current.
Current=Voltage/Resistens I=U/R
change the resistor til you get 0.002A = 2mA

Start with a 1 Kohm resistor
2 Volt/1000 ohm= 2 mA
lower the resistor for more current
 
#72
peranders said:


I have tested it and I can't hear any difference...but I think you can lower the cross-over distortion somewhat, but how much?
Click to expand...

I think the idea is to have sufficient bias to get rid of the cross-
over distorsion entirely. That assumes you do not load the opamp
to heavily, except for the bias current.
 
#73
peranders said:


I have tested it and I can't hear any difference...but I think you can lower the cross-over distortion somewhat, but how much?
Click to expand...


I have tried it with AD797 and LM6172 and that is the reason I used it with the OPA637.I would always use a constant current source with an opamp,it is worth it IMHO.

By the way,I can recommend my phono stage.It sounds really good,I have no problem with noise despite the "high"(compared with a AD797 or LT 1115) noise of the OPA637.

Nicke
 
#78
Re: Re: Bugle!

peranders said:


Yes, check the resistor values of the feedback. Way too high! Almost any RIAA of class has values from 5-10 ohms, max 100 ohms (MC) to 100-220 ohms, max 470 ohms (MM). High values generates noise.

OPA2130, ugh! noisy! NE5534 has 12 dB lower noise!

To have resistors in series with the non-inverting input are also totally unneccessary, adds noise only. The opamps are FET-type = very low input bias current => Resistor matching means nothing in order to reduce offset voltage. Since OPA2130 is a FET amp, this resistor choice can reduce distortion but I think it's more wise to have low resistor values instead, then the distortion will be low
Click to expand...


Mostly true, but...

The NE5534 has fet's at the inputs. See:
http://www.semiconductors.philips.com/acrobat/datasheets/NE_SA_SE5534_A_2.pdf

If you choose to keep the resistor values in the feedback as low as sugested in the quote above the value at the noniverting input can be propotionally lower.

If you decrease the resistor values with a factor 100 I suggest you either put in a lot more batteries or put in a good quality powersource. I expect the lifetime of the batteries to be decreased with a factor 100 as well.

By the way the schema of the bugle seems pretty simple an can be built cheaply. (NE5534 costs 1,50 Euro, better opamps mentioned in this thread cost much much more)How can equipment that's according to you be sold for such high prices?

Peranders, do you hav the schema of a Nad PP1 and MTech?
 
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