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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Rod Eliot project 88 question
Rod Eliot project 88 question
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Old 12th December 2018, 11:51 AM   #191
starbender is offline starbender
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I'm at page '9 atm.
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Old 17th December 2018, 11:10 AM   #192
starbender is offline starbender
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I etched another pcb and used resistor values from post 30 schematic.

I'm sure it will be ok. In the meantime I'm using protoboard preamp to test and it seems it's pretty good sounding.

I made B1 and BA3 preamp before this one. I used B1 for almost two years and another two years I used BA3 preamp. Both of them is driving pass F5 clone.
As you know F5 gain is pretty low and it needs a sensitive speakers to shine. I'm using 4 ohm 86dB speakers right now and F5 with added gain from BA3 cannot feed enough juice to these speakers.

I always had distance to opamp base preamps and I always thought it cannot be better than any discrete design. But this little thing is impressive as it is..

I tried NE5532 and OPA2134 so far. I'm planning to try OPA2604 and old jfet input type opamps.

Anyone tried any other opamp with this project?
If so, can you please share your experience?

Thanks..
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Old 17th December 2018, 01:21 PM   #193
ivanlukic is offline ivanlukic  Serbia
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I tried several opamps with P88 but I prefer bipolar opamps over j-fets. I tried 4558, LM4562, OPA2134 and NJM2114. I use NJM2114 but it will be difficult to find it. I recommend that you try LM4562.
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Old 17th December 2018, 01:28 PM   #194
starbender is offline starbender
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Quote:
Originally Posted by ivanlukic View Post
I tried several opamps with P88 but I prefer bipolar opamps over j-fets. I tried 4558, LM4562, OPA2134 and NJM2114. I use NJM2114 but it will be difficult to find it. I recommend that you try LM4562.
I removed lots of old opamps from broken cd players, i think i had njm2114. Will try those.

Thanks.
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Old 19th December 2018, 10:01 AM   #195
Mixi is offline Mixi  Europe
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I was planning on posting a summary of possible resistor / potentiometer combinations that people have used successfully. I hope I'll have time to do it in the next few days...
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Old 27th August 2019, 09:57 AM   #196
Mixi is offline Mixi  Europe
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Let's give this thread an update. I just found a rather new P88 projects on the web and I'd like to share it:

Rod Elliott ESP P88 Pre-amplifier – (mis) Adventures in Hi-Fi

nicely done.
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Old 4th September 2019, 05:25 PM   #197
Mixi is offline Mixi  Europe
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Seems I'm the only one in this thread now :-(

I'm in the process of getting started with EasyEDA to make my own PCBs for this pre. I'd need some general advice for PBC layout for opamp based amps. Can someone point me in the right direction or give me some advice? For Example:

1) track width for signal / power
2) general advice for routing signal and power
3) general advice for gnd plane / pour on the pcb

I know one should keep transformers away from audio circuits - what about rectifiers? Say I power the pre from an AC wall wart and have the rectifier / dual power supply in the chassis. Should that be kept away from the audio circuit?
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Old 7th September 2019, 03:54 AM   #198
6L6 is offline 6L6  United States
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Rod Eliot project 88 question
Yes.

As you mention, the transformer is the biggest noise source, but there is also ringing and noise in the rectification.

A properly designed snubber will make a large difference in radiated noise. Mark Johnson did a very good article in Linear Audio about this.
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Old 11th September 2019, 11:35 AM   #199
Mixi is offline Mixi  Europe
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Thanks, i'll read up on the snubber topic. Should the rectification also be physically seperated (shielded, kept at distance) from the amplifier circuit?

Regarding the PCB layout: What are the recommended track widths for power and signal?Can Signal and power cross or is this to be avoided?
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Old 12th September 2019, 07:26 AM   #200
sasmit is offline sasmit  India
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My version of the P88 I made a few years back, still listen to it as my primary preamp. Sound quality is rather good for such a simple design.
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