OP amp phono preamp gain
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 6th October 2015, 03:37 PM #1 stevovee   diyAudio Member   Join Date: Feb 2009 OP amp phono preamp gain Just wanted to double check that I am calculating this gain right. There are two gain stages so the first one has (3320/150)+1 or 23.1333 gain and the second gain stage has the same so multiplying these tother 23.13*23.13=534.9969 and then converting this to dB using this calculator Decibels to Voltage Gain and Loss convert calculation conversion amplification amplifier electronics - sengpielaudio Sengpiel Berlin gives me a gain of 54.5dB am I doing this correct. The reason I ask is that I just tried an off the shelf phono that is supposed to have 40dB of gain but seems to have much more than my DIY phono that I am calculating has 55dB
 6th October 2015, 03:53 PM #2 stevovee   diyAudio Member   Join Date: Feb 2009 realized i forgot to attach the image of the phono preamp design.
rayma
diyAudio Member

Join Date: Apr 2011
Quote:
 Originally Posted by stevovee gives me a gain of 54.5dB am I doing this correct.
Yes, for low frequency gain. Then in the midband you lose 20dB due to the RIAA network,
so the nominal signal gain is 34.5dB. So, the other preamp has 5.5dB more gain.
This one will likely have much better RIAA response and lower noise, though.

Last edited by rayma; 6th October 2015 at 05:07 PM.

 6th October 2015, 04:56 PM #4 AndrewT   R.I.P.   Join Date: Jul 2004 Location: Scottish Borders If you need the extra gain, then put it all into the first stage. Try 75r instead of 150r. But don't put in too much, or you'll use up all the gain bandwidth product. __________________ regards Andrew T.
 7th October 2015, 11:40 AM #5 jcx   diyAudio Member   Join Date: Feb 2003 Location: .. put at least 1 pole of the RIAA roll off in the 1st amp feedback and you don't have a GBW problem and get dynamic headroom benefit too for mistracking, pops, ticks does cost a extra RC low pass to correct the Zero introduced by the non-inverting low pass filter's transfer function flattening out at unity gain the flat gain blocks with passive RC EQ in the middle is the most demanding of op amp performance compared to intelligent low pass frequency shaping in the feedback network(s) it really seems wrong that those suspicious of feedback amp performance tend to select this worst case topology Last edited by jcx; 7th October 2015 at 11:45 AM.

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