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Old 4th April 2014, 06:18 PM   #941
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In an attempt to retribute Mooly's help, I upload here the Tone Controls but using NE5532 and I've added several electrolityc capacitors. Other than that, the schematic is the same as Mooly has uploaded.

The file NE5532.txt should be located in the same folder as the .asc schematic.
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Old 3rd March 2015, 06:20 PM   #942
Mooly is online now Mooly  United Kingdom
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Default More on the active volume control debate.

Some of you may remember the debate on the active volume control and whether or not it could introduce higher than expected levels of distortion at high attenuation levels.

Well this thread provides some real test data which is very interesting,

TI Active volume control board...tipd136
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Old 3rd March 2015, 07:15 PM   #943
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If anyone is still worried about this issue as regards my preamp, permit me to quote from Small Signal Audio Design, second edition, p367:

"Going back to the loading on the inverting opamps at low volume, we have 383 Ω at Mk 1, which is 766 Ω per opamp and no cause for alarm. However, I have heard doubts expressed about a possible rise in distortion at very low volume settings below this, because the inverting amplifiers U1:B, U2:A then see even lower load impedances. The impedances may be low, but the current to be absorbed by the inverting stages is actually very limited because almost the whole of the pot track is in series with the input at low settings. To prove there is not a problem here, I set the volume to Mk 1 and pumped 20 Vrms in, getting 1.6 Vrms out. The THD residual was indistinguishable from the GenMon output of the AP SYS-2702. In use the input cannot exceed 10 Vrms as it comes from an opamp.

To push things further, I set the volume to Mk 0.2, (ie only 2% off the endstop) and shoved 20 Vrms in to get only 300 mVrms out. The THD+N residual was 0.0007%, composed entirely of noise with no trace of distortion. I then replaced the 4562s in the U1:B, U2:A positions with Texas 5532s (often considered the worst make for distortion) and the results were just the same except the noise level was a bit higher giving a THD+N of 0.0008%. There is not a problem here."
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Old 3rd March 2015, 07:43 PM   #944
rsavas is offline rsavas  Canada
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One day (winter) on my list of audio diy projects, is to make/design the active volume ckt (basically the Elektor 2012 pre-amp) including the new var freq tone control ckt (why did Elektor, not use this?), using motorized pots such as Bourns PRM16, relays, etc.
Mother, me being next in line :-) has to get up on her walker to adjust/turn off the old Pioneer SX-950, this just not right :-) The new 50" Panasonic flat screen has lousy sound/volume.
If I ever manage to do it, I'll post it here for everyone to build/use.
We are getting close to be able to have affordable colour graphic LCD, (FT800(EVE), AVR xmega (Arduino) to run/control it, from an Android &/or a IR remote device too.
It blows my mind that we are still using ne5534a and this was used in my second pre-amp design back in college,1979. I used a ne5533 that never caught on for some reason. A monumental step from the previous LM381A design.
So I'll pair up some ne5534a with my si4770 radio design. :-)

Can someone answer a nagging ? I have, why do the majority of today's new bjt opamp's have higher current noise than the old ne5534a?

Cheers
Rick

Last edited by rsavas; 3rd March 2015 at 07:48 PM.
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Old 3rd March 2015, 07:50 PM   #945
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Quote:
Originally Posted by rsavas View Post
One day (winter) on my list of audio diy projects, is to make/design the active volume ckt (basically the Elektor 2012 pre-amp) including the new var freq tone control ckt (why did Elektor, not use this?),
?
They didn't design it, I did, and as the emphasis was on very low noise, a simple Baxandall tone-control was more appropriate. I also wanted to show off the new split-drive tone-control technology I had thought up.


Quote:
Can someone answer why the majority of todays new bjt opamps have higher current noise than the old ne5534?
Presumably because they are optimised for low voltage noise, which is almost always what counts. An MM cartridge input is the notable exception, and the 5534 matches that impedance much better than, say, an LM4562 with its higher current noise.
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Old 3rd March 2015, 07:52 PM   #946
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yes, the ~1 nV/sqrt(Hz) class of low noise op amps are only low noise with low source Z

but this does seem to be the most touted for audio recently
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Old 3rd March 2015, 08:15 PM   #947
rsavas is offline rsavas  Canada
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Wow, did not expect such a fast answer :-)
I have to get/read/test the LA article to see what the noise spec's are on the new var freq tone control. It is a great ckt to use. I do not think that one needs a parametric/SV eq/filter, although I have one that I put into the old pre-amp.

More ?'s, if you not mind.

1) why do you stay away from a jfet first stage in the design for a MM cartridge?
The issue, that was raised, something about an bjt opamp has varying/non-linear i/p cap, against a high Z source, causing IMD.
It was written about this in a few places, one being the Amber 3501 THD analyzer that I have. They used a 2sk146 dual.
Bogus :-)
I'll post the circuit, I'd like you thoughts on it, a mess for me to figure out :-)
2) how can you tell from bjt data sheet what the current vs voltage noise, I assume you have to look at those NF curves plotting source R :-)

Cheers
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Old 4th March 2015, 06:03 PM   #948
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Quote:
Originally Posted by rsavas View Post
1) why do you stay away from a jfet first stage in the design for a MM cartridge?
It is very difficult to improve significantly on the noise performance of the 5534A with an MM cartridge. A J310 FET would in theory give an improvement of 1.7 dB, but hybrid discrete-opamp circuits can be rather tricky. I have deployed thousands of them but I am still wary of issues with HF stability.

Quote:
The issue, that was raised, something about an bjt opamp has varying/non-linear i/p cap, against a high Z source, causing IMD.
Other way round. JFET opamps have the capacitance to substrate problem.
BJTs are not free of CM distortion but there is usually less and the mechanism is quite different.

Quote:
It was written about this in a few places, one being the Amber 3501 THD analyzer that I have. They used a 2sk146 dual.
Bogus :-)
I'll post the circuit, I'd like you thoughts on it, a mess for me to figure out :-)
Pretty standard instrumentation amplifier made from two JFET-opamp hybrid circuits.

2) how can you tell from bjt data sheet what the current vs voltage noise, I assume you have to look at those NF curves plotting source R :-)
Cheers[/QUOTE]

Yes. You rarely get plots of vn and in vs Ic on data sheets. I don't know why.
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Old 6th June 2015, 01:40 PM   #949
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Quote:
Originally Posted by nickds1 View Post

Specifications
Test conditions: supply voltage 17.6 V; all measurements symmetrical; tone control defeat disabled.
Test equipment: Audio Precision Two Cascade Plus 2722 Dual Domain (@Elektor Labs)
THD+N (200 mV in, 1 V out) 0.0015% (1 kHz, B = 22 Hz 22 kHz)
0.0028% (20 kHz, B = 22 Hz 80 kHz)
THD+N (2 V in, 1 V out) 0.0003% (1 kHz, B = 22 Hz 22 kHz)
0.0009% (20 kHz, B = 22 Hz 80 kHz)
S/N (200 mV in) 96 dB (B = 22 Hz 22 kHz)
98.7 dBA
Bandwidth 0.2 Hz 300 kHz
Max. output voltage (200 mV in) 1.3 V
Balance +3.6 dB to 6.3 dB
Tone control 8 dB (100 Hz)
8.5 dB (10 kHz)
Crosstalk R to L 98 dB (1 kHz)
74 dB (20 kHz)
L to R 102 dB (1 kHz)
80 dB (20 kHz)

Apparently absent, possibly the most important spec: source impedance.

Max output voltage on the low side compared to inexpensive competition.
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Old 6th June 2015, 02:50 PM   #950
MarkS is offline MarkS  United Kingdom
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AP2700 Source Impedances
Balanced 40 ohms, 150 ohms or 600 ohms.
Unbalanced 20 ohms or 600 ohms.
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