Wave Form

[brucetassin]

Hello.
Just by looking at this wave form, what can say about the performance of this 12AX7 phono preamp.
Thanks for any comments.
Bruce

 

[rayma]

what can say about the performance of this 12AX7 phono preamp.

Not much. Instead, build an inverse RIAA circuit, and check the preamp's
frequency response with a square wave input.
http://www.hagtech.com/pdf/iriaa2.pdf

 

[nigelwright7557]

Do a frequency sweep with your sig gen and see how it falls off at top and bottom end.
It should go down to a few hertz and up to at least 20Khz.

 

[Gofer]

It is clipping badly for a start.

 

[DF96]

That might depend on what sort of music it was playing. It looks like clipping, but maybe that happened in the studio?

 

[dhaen]

As mentioned, the clipping appearance may not be the preamp, especially since the clip point seems to vary.
It shows a small amount of channel separation.
The waveform shows symmetry, so 2H distortion is probably reasonable.

All these are guesses. It's not possible to deduce sortcomings of a waveform without reference to the source. And even then, there are better methods of faultfinding.

 

[brucetassin]

Hello,
So now for full disclosure ...

I bought this kit on eBay

NEW E834 RIAA MM Amplifier Kit Base + Power Supply Kit + Transformer | eBay

The pre seems to have too much gain.
I have another pre that I used to compare the ear 834 kit with.
(see wave for below)

The pre schematic with voltages I measured.

The power supply that came with the kit.

What can I do to calm down this pre?

The music track is the same song, turntable, cartridge.

 

[rayma]

The pre seems to have too much gain.What can I do to calm down this pre?

Remove the RIAA components, and replace with more standard values to the input cathode.
Like this circuit: https://www.youspice.com/spiceproje...-simulation-projects/riaa-tubes-preamplifier/

 

[brucetassin]

Thanks Rayma for your suggestions. I will give this some serious consideration.
I don't have an RAR reader so I can't get a good view of the schematic you suggest.

I did some research on the EAR834 pre amp and found many good reviews, that's the main reason I choose this kit, cost being second. All of the resistors in the kit are 1% and capacitors seem to be good quality so I'm surprised the pre behaves as it does. I am using 7025/12AX7LPS tubes.

Thanks again

 

[rayma]

I don't have an RAR reader so I can't get a good view of the schematic you suggest.

Try this.
https://www.youspice.com/wp-content/uploads/2015/04/RIAAamplifier.jpg

 

[brucetassin]

Some one suggested I was unsafe as I did not show a transformer and fuse
in the schematics. I do have a transformer and fuse as can be seen in the
photo. The transformer can also be seen in the eBay link.