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Old 16th March 2004, 10:14 PM   #1
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Question my RIAA stage. Any comment

HI all

I just finish my LCR riaa stage.
I love it but it`s not still perfect.

I need a better bass, more robust and extended...
that is the only complain i have.

R9,R12,R13 and R11 are inductor DCR

On simulation, I have 1.2 Db riaa accuracy. I just don`t understand why my bass is not as good as my previous riaa project.

PS; I use sealed acid battery for PSU (B+ and heater) I expect my psu to have about 24ohm impedance (12battery in serie, about 2 ohm each)


Thanks
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Old 17th March 2004, 06:51 AM   #2
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Wow, that's what i call impressive!

Are the numbers next to the chokes Henry? 30H may be a bit low for a 417. What types of chokes are you using? They must be pretty well shielded if you don't complain of hum.

Bass? Some people may find 1.2db excessive. What did you use to simulate and calculate the riaa values? Have you tried adding capacitance and chokes in the PS?

I wish i had the guts to build one like that!
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Old 17th March 2004, 09:36 AM   #3
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I wish i had the guts to build one like that
Me too !
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Old 17th March 2004, 02:36 PM   #4
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>Wow, that's what i call impressive!
Thanks,

>Are the numbers next to the chokes Henry? 30H may be a bit >low for a 417.
I run at 16mA. So -3db is 17hz. I don`t use bigger choke because i`m affraid to heve subsonic noise.

>What types of chokes are you using? They must be pretty well >shielded if you don't complain of hum.
With battery supply, i don`t have ANY hum!!!

>Bass? Some people may find 1.2db excessive. What did you use >to simulate and calculate the riaa values?
Orcad capture lite (free on their official website)

Have you tried adding capacitance and chokes in the PS?
Should I?. If I add capacitance, that will be electrolytic one. I tend to don`t use them...

I wish i had the guts to build one like that!
I greatly recommend to build a LRC type. that better to passive RC EQ. I changed the value of mine for fit the output impedance of my first stage (1.8K)

this is the original value from tango EQ.

martin
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Old 17th March 2004, 04:15 PM   #5
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Moving magnet cartridges expect to see 47k, rather than 100k. It won't affect the bass, but it will cause a rise in treble towards 20kHz that could make the bass seem lightweight in comparison.

2 Ohms for a lead acid battery seems very high. Are you sure?
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Old 17th March 2004, 10:15 PM   #6
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Hi,

Could it be you lose bass response because the LCR RIAA isn't terminated?

Cheers,
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Old 17th March 2004, 10:28 PM   #7
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Quote:
Originally posted by fdegrove
Could it be you lose bass response because the LCR RIAA isn't terminated?
I wondered about that, but etalon90 says he ran a simulation on it. Mind you. 1.2dB error is rather large...
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Old 17th March 2004, 10:39 PM   #8
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Hi,

Quote:
Mind you. 1.2dB error is rather large...
Exactly.
I know that proper termination of the 600 Ohm ones is mission critical; put 620 Ohm instead of 600 Ohm to terminate it and you lose the entire RIAA curve along with it.

I see no reason why this wouldn't be the case with a 1K8 cell.

Either way it doesn't take much to find out and if it works fine this would be great news.
After all a 1K8 Ohm load is much easier to drive with valves than a measle 600R, right?

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Old 17th March 2004, 11:54 PM   #9
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Quote:
Originally posted by fdegrove
After all a 1k8 Ohm load is much easier to drive with valves than a measly 600R, right?
This is a common misconception (I've even found it on semiconductor manufacturer's data sheets). 600 Ohm meant driving from 600 Ohm, and terminating in 600 Ohm. In other words, the source actually saw a load of 1200 Ohm. (The source was always made to have almost zero output resistance, so that adding a series 600 Ohm resistor gave constant 600 Ohm output resistance with frequency and level.)
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Old 18th March 2004, 01:26 PM   #10
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Hi,

Quote:
(The source was always made to have almost zero output resistance, so that adding a series 600 Ohm resistor gave constant 600 Ohm output resistance with frequency and level.)
O.K. I see the mistake.

For this particular implementation (LCR RIAA) g' would than be 3K6 which is still a very heavy load for anything but a xformer or CF to tackle, correct?

Which is why we almost invariably see a stepdown xformer after the driving stage in pro gear a la Pultech etc.

Any advice on how to best implement this LCR correction without resorting to esoteric xformers?

TIA,
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