Does it comply with the RIAA spec ?
If it follows spec there is nothing to do in the riaa stage itself, but you could
turn your bass control up a bit.
Well it's supposed to, but it sounds very bass light to me. I'm going to borrow a friend's phono stage to plug into one of the line level inputs of my preamp and see what it sounds like.
Which components in the EF86 section control the RIAA curve? Is it C1, C2, C4 and R3?
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If the RIAA is flat at least to 20Hz and you are complaining about the lack of low frequency response then we are talking about Power at the bottom end or should I say Drive ?
I have built many preamps and make a point of making sure its flat down to 20Hz , what I found is that exact values of capacitance/ohm-age are required for a high degree of flatness even values of "around 1% " are not really good enough .
JLH actually built up values to make the response a very high degree of flatness--complaints were--- "we cant get those values" or "that's extra work for us " which I don't accept .
I have built many preamps and make a point of making sure its flat down to 20Hz , what I found is that exact values of capacitance/ohm-age are required for a high degree of flatness even values of "around 1% " are not really good enough .
JLH actually built up values to make the response a very high degree of flatness--complaints were--- "we cant get those values" or "that's extra work for us " which I don't accept .
R1, C1, C2, but the tube characteristics in a simple single stage have influence also.
No, gain of the stage may not be sufficient.
Only way to increase the gain "a lot" is to
use a constant current load.
Only way to increase the gain "a lot" is to
use a constant current load.
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AUDIO VALVES: EF86, Z729, CV2901, CV4085, PENTODE – MULLARD MAGIC
Increasing the gain in other ways can incite microphonics in some cheap makes.
Scroll down for gain at different voltages.
Increasing the gain in other ways can incite microphonics in some cheap makes.
Scroll down for gain at different voltages.
Who talked about sand ?
Joke aside I do not see much space in the amp of post 34 for plate chokes ..
Joke aside I do not see much space in the amp of post 34 for plate chokes ..
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It is clear when you look at the circuit that low-frequency RIAA conformity will be poor. The RIAA stage is essentially an inverting op-amp stage with the op-amp replaced with the EF86, but there is nothing in the feedback network that levels off the gain below 50 Hz: if the EF86 had nullor/ideal op-amp properties, the gain would just keep rising as frequency decreases.
That means that the frequency where the gain levels off is inversely proportional to the open loop gain of the EF86 stage, which won't be very accurate. It depends on the EF86 transconductance among other things, which depends on the age of the EF86. A fresh valve will give you more bass than an aged one.
You can tweak the open-loop gain and, hence, the lower RIAA cut-off frequency to some extent by using a fresher or older EF86 or by tweaking the anode or cathode resistors.
That means that the frequency where the gain levels off is inversely proportional to the open loop gain of the EF86 stage, which won't be very accurate. It depends on the EF86 transconductance among other things, which depends on the age of the EF86. A fresh valve will give you more bass than an aged one.
You can tweak the open-loop gain and, hence, the lower RIAA cut-off frequency to some extent by using a fresher or older EF86 or by tweaking the anode or cathode resistors.
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And thats exactly the reason why this is just a mediocre sounding phono stage and not an "excellent one" as Elektor claimed. They could have done better, fulfilling their marketing paroles to deliver high class circuits for the techies and clever people. But they just delivered to them one of the many versions of low quality phono stages of the golden era of tube sound, when expectations for home audio wasn't high end.
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The Riddle of the Sands -- first world war spy drama about the invasion of the UK using barges probably the Frisian Sands.
Das Boot was better.
Das Boot was better.
R5 = 150 kohm and everything else as is, or
R6 = 1 Mohm, R5 = 180 kohm, everything else as is.
Mind you, this is based on very approximate calculations, so you may have to experiment a bit.
By the way, it is essential that the output only gets loaded by R7 and the 500 kohm potmeter. If you would use a lower value for P1 or connect a line input straight to the EF86 without the JFET buffer, that would reduce the gain of the EF86 stage and shift the first cut-off frequency.
I was watching "Das Boot" in 1981 in Berlin UFA Palast. Very long movie. Enjoyed a good sleep in the last half.
The values of post #56 are correct after all; with a more elaborate calculation, I get two extra factors that cancel each other.
You've nailed it, MarcelvdG. When I built he preamp I used a 250k pot instead of a 500k one, after I was advised it would make no difference. I'll change it for a 500k one and see where that gets me.
Thank you.