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Old 10th January 2003, 10:47 PM   #31
lohk is offline lohk  Europe
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So probably better buy Rod's PCB, will you ?
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Old 11th January 2003, 05:47 AM   #32
corbato is offline corbato  India
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Thumbs up NE5532 RIAA

Hi miguel2

I tried the single power version with terrible results. Avoid that !! Build the split power version and employ a proper regulated (LM313+LM337) supply. And, please, no "wall-warts".

Last night I rigged up the Elliot pre-amp with my main system – an early 70’s Sonodyne Class A. (The usual RIAA phono stage is a rebuilt SHURE M60 Box that my father bought in the 60's - Very natural and airy, so I know how Vinyl sounds).

The Elliot pre-amp can get quite strident in the upper frequency band, though the bass is quite plentiful and smooth without being boomy. Noise is virtually non-existent while Hum is zero. What I do notice is a lot of crosstalk. I think that can be attributed to the less than perfect construction practices followed in my Vero board quickie. I also believe if “audiophile” caps were to be used, the pre-amp may sound less harsh.

peranders and lohk are both right on your RIAA issues. It’s very important to match the components - not only to the specified value but also between channels. I have no means of measuring the RIAA response but the 'Golden Ear' test sounds ok imho.

As lohk has advised, it is very important to have a Ground plane earthing in this case. I wasted 3 veroboard before my pre-amp started working as promised and without oscillating. I have switched between NE5532 and OPA 2134 without hearing any audible difference.

I would strongly suggest that you try out this pre-amp with a variety of programme material before finalizing it as your main phono stage. You will be surprised.

All the best.
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Old 11th January 2003, 06:22 AM   #33
Electrons are yellow and more is better!
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Quote:
Originally posted by miguel2
I used the NE5532. The circuit is on the bottom of the link on Corbato's message.

I cannot say I matched the RIAA curve because I have no way to measure it (I blew my soundcard some time ago measuring my preamp distortion ). I mixed carbon film and metal film resistors, but I think that is not the reason. And ordinary parts everywhere. I also mounted everything on a veroboard.

Don't know if the NE5532 has some tendency to oscillate, but the sound seemed to tremble....
Miguel, you didn't do everything right, I'm afraid because NE5532 is dead silent and it's hard to get oscillating. Do you maybe have a picture of you amp? Maybe we can straigt things out?
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Old 11th January 2003, 06:29 AM   #34
Electrons are yellow and more is better!
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Default Re: NE5532 RIAA

Quote:
Originally posted by corbato
I tried the single power version with terrible results. Avoid that !! Build the split power
When you use single power supply, it's important that the "fictive" ground becomes very fixed to the minus pole of the battery (your real signal ground) otherwise you will get problems. It's nothing wrong technically to use single supply voltage.
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Old 11th January 2003, 02:47 PM   #35
miguel2 is offline miguel2  Portugal
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Hi,

Thank you all for your support. I have to say that the single supply version I built is no more... Just dessoldered all the components to get the veroboard (and components) for the dual supply version.

I do have some doubts about the carbon resistors (5%?), and as my multimeter is a piece of crap I cannot measure their value with the accuracy I wanted. So I will substitute all these by metal film 1%. (My chinese multimeter has great looks but I believe an accuracy worse than 1%)

Klaus,
Although the caps values are ok, I will check those resistors and check if it goes ok. I will not buy Rod's PCB simply because p-2-p is more fun (I built a Zen v4 like that).

Corbato,
Thanks for testing it on your main system.
I found another "wall wart", from an old printer, opened it and saw that it is only a transformer. I have converted the 25VAC into -15 -0- 15 VDC with a phantom earth. Same as NAD PP1. See

http://www.audioxpress.com/reviews/media/AE300GG.pdf

For now it stays unregulated, but I will use some regulation IC if everything goes right. Are the regular 7815 / 7915 any good for this purpose?

Peranders,
As you can see, I can not post the picture of the first trial... It did have some hum and the sound seemed to tremble so maybe something was not well. I will check those components values. I will also try to improve the layout. The board I am using is around 12 x 8 cm, so space is at premium (2 channels and PSU). Not that it has to be like that, I just found that board in the bin.

Miguel
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Old 11th January 2003, 05:11 PM   #36
corbato is offline corbato  India
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Hi

peranders
Quote:
When you use single power supply, it's important that the "fictive" ground becomes very fixed to the minus pole of the battery (your real signal ground) otherwise you will get problems. It's nothing wrong technically to use single supply voltage.
yes..but why bend backword to achieve that when the darn opamp is designed for a split supply. BTW when I was searching for a suitable preamp to build, I came across your design. Someday...SOMEDAY...I'm going to build it.
miguel2
Quote:
Are the regular 7815 / 7915 any good for this purpose?
They are but the 78xx series I believe is noisier compared to LM317/337. The NAD PP1 power supply is el cheapo and the only reason it is that was is to use the 'wall wart'. i'm surprised beacuse a proper power supply would'nt have been more costlier.

cheers

You really don't need to order Rod's PCB. The layout is pretty simple and yes more fun if done the PP way. I built mine in a 2"x3" vero board so that it could be housed inside my TT. However, I do intend to make a PCB in the days to come and get some proper caps. I'm begining to like this design.
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Old 11th January 2003, 06:55 PM   #37
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Quote:
Originally posted by corbato
yes..but why bend backword to achieve that when the darn opamp is designed for a split supply.
In real life NO opamp is designed for a special supply type. The only thing that differs is the input common mode range which can be practical if it is in a certain way.

Every opamp can be used in single or dual supply but some types are easier to use in certain applications.
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Old 11th January 2003, 06:59 PM   #38
Electrons are yellow and more is better!
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Quote:
Originally posted by corbato
They are but the 78xx series I believe is noisier compared to LM317/337. The NAD PP1 power supply is el cheapo and the only reason it is that was is to use the 'wall wart'. i'm surprised beacuse a proper power supply would'nt have been more costlier.
Don't forget how the noise is measured! You can't compare the noise if you don't have the exact circuit. If you add caps it's no problem to use 78xx and 79xx.
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Old 13th January 2003, 07:33 AM   #39
Werner is offline Werner  Europe
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Feeding opamps one can live with 78**/317/etc.

The rising output impedance of such regulators, when combined with the typical 47-330uF caps at their output/close to the opamps, gives rise to a resonance smack in the audio band.

But if you can live with a non-zero supply impedance at LF, and opamps with a decent PSRR should allow this, the following solution is feasible:
-put a small capacitor after the regulator, say a 4.7-10uF
-then insert a series resistor, 100m-1 Ohm.
-only then put the opamp supply caps of about 100uF.

The result is a fairly quiet, non-resonant supply line, with the added benefit of good noise filtering.

For those interested, Maplin are presently clearing out Rubycon ZA and ZL low-imp caps at very very very silly prices.
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Old 17th January 2003, 01:39 PM   #40
miguel2 is offline miguel2  Portugal
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Ok. Finally finished this Rod's RIAA amp. It has now an unregulated split supply of -16 - 0 - +16 V. I managed a nice 3D pp mounting so I can say that all the stuff is properly placed in around 3 x 5 cm. There are no changes from Rod's schematics. On power up there was no smoke . So connected it but heard a lot of hum from speakers. After some arrangement of those crappy aligator clips I could get rid of the hum and could listen more carefully.

There is no trembling now, but the upper frequencies are clearly distorted like ssssss. Bass is ok but not very strong. I was feeding my ZenV4 through a voltage divider (had no potentiometer at hand) and attributed this apparent weakness of bass to the lack of a linestage pre. Maybe these NE5532 are not capable of driving directly a ZenV4 .

Anyway I have to finish that line preamp now to confirm this. For that I need to solve this irritating earth problem, as hum is quite high when I connect it to the power amp. One question: I have the inputs/outputs of this pre bolted to the aluminium chassis. So I have no earth cables soldered to the I/Os, as the chassis will do the job. But to which point of the earthing cable do I connect the chassis: to the point nearest the xformer or the other one, where I have the earth of the cathodes?
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