With fake log pot, combined impedance of pot and resistor is app. the value of resistor from wiper to ground (15k). Therefore, if output impedance of input stage is app. the value of series output resistor (in case of ESP preamp 1500 Ohms) fake log pot is 10 times that which means 15k.
My schematic is classic that uses log pot. It uses usual value of series output resistor in the input stage, 100R. Since there are no log pots with 1k value, and not even 5k, it's usual to use 10k value.( It should be at least ten times the value of series output resistor.) Than, you need to define input rersistance of the output stage which should be 5-10 times log pot value. Anything from 50k to 100k will do.
I hope that my explanation was sufficient.
My schematic is classic that uses log pot. It uses usual value of series output resistor in the input stage, 100R. Since there are no log pots with 1k value, and not even 5k, it's usual to use 10k value.( It should be at least ten times the value of series output resistor.) Than, you need to define input rersistance of the output stage which should be 5-10 times log pot value. Anything from 50k to 100k will do.
I hope that my explanation was sufficient.
yes, that settled the issue. gain is now exactly at 4. thanks a LOT for sharing your knowledge.
i still have to read up on the input from ivan but for now my breadboard circuit is up and running and the performance is fantastic! i usually have problems with RF interference in my apartment which can only be solved by putting my amps inside a metal chassis. for some reason the P88 doesn't pick up any of that. the sound is ... well ... just super clear and transparent.
i'll order another pot for balance and update my circuit next week. for now i can only thank you guys for your help!
best,
michi
Congratulations!
. now, if you have the time and patience, I think you should build it on your own designed PCB based on the comments here and enjoy the sound. I am sure it will be a very good experience. use good quality coupling caps e.g.kemet SMR or wima.regards
Prasi
yes, I'll definitely keep experimenting with this design and report back.
i currently have wima polyester caps on my breadboard. yesterday i read in douglas self's book that polyester usually gives more distortion than polyprop. i guess i'll try wima polyprop or the kemets you recommended next. let's see if it makes a (audible) difference. 63VAC rating should be enough, right?
i currently have wima polyester caps on my breadboard. yesterday i read in douglas self's book that polyester usually gives more distortion than polyprop. i guess i'll try wima polyprop or the kemets you recommended next. let's see if it makes a (audible) difference. 63VAC rating should be enough, right?
In my experience coupling caps make big difference in sound quality, but what one will prefer depends mostly on personal taste. I do not like polypropilene better than polyester although their specs are somewhat better! Even ordinary polarized elcos can be used successfully (and are used in many great sounding industrial Japanese amps).
Whenever they are in the signal path they make a difference. Initially I used 1uF polyester and 200k to ground at the output of P88 but noticed that the sound is overly bright and checked things on the scope. Sinus, triangle and square showed considerable loss of low frequencies. Than I removed that cap from the signal path. Now the sound was too soft and lacked brightness for my taste but scope waves were perfect! You must tune the preamp to your taste, find the right values by trying different values untill you are satisfied. I think that at the output you need at least 10uF. You may use elco. I measure the offset at the output before orienting elco. If offset is positive connect + side of the elco to the output of opamp.
For audio signal level coupling, the best type of electrolytic is a non-polarized type such as from Nichicon's Muse ES range which is well known but other manufacturers produce good equivalents too. That way, you don't have problems when offsets drift and the caps don't form properly because the DC offset is too small, as happens when devices are running in and passive component values change a little. I understand that the true non-polarized type is not the same as the low cost bipolar types (sometimes also called non-polarized and vice-versa) which are used for speaker crossover networks - don't waste your money on substituting them for the real thing.
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So I finally put the whole P88 circuit including volume and balance control AND a P06 RIAA on the same breadboard. It looks a bit messy but works a treat. I'll experiment with different capacitors in the next few weeks although I do not see a lot of room for improvement - because it's already great. The RIAA could be a bit more accurate as i have rather large differences between channels. I mostly used 10% caps so that really doesn't come as a surprise.
What did come as a surprise is the RF immunity of this circuit. I've had massive problems with various amps in the past as they always seemed to pick up RF noise unless they were in a properly shielded enclosure. For some reason my messy P88/P06 breadboard circuit without an enclosure doesn't pick up any RF at all.
What did come as a surprise is the RF immunity of this circuit. I've had massive problems with various amps in the past as they always seemed to pick up RF noise unless they were in a properly shielded enclosure. For some reason my messy P88/P06 breadboard circuit without an enclosure doesn't pick up any RF at all.
Hi Mixi,
I follow this treat with interest because I am in the process to build this preamp with RIAA. and P104 Muting Circuit
Do you plan to change the schematic to be able to accommodate the moving coil cartridges and cartridge loading, see Note : Hi-Fi Phono Preamp (RIAA Equalisation) Rod Elliott - ESP (Original Design)
"There is some debate on the Net about cartridge loading impedance, with various suggestions that reducing the standard load from 47k to something lower (even as low as 10k) provides benefits. While this is plausible, I've not run any tests so cannot confirm or deny that there may be an advantage. If this is something you wish to try, I suggest that it be done at the phono RCA input socket (along with the capacitor if you want to try that too)"
Did you use ivanlukic schematic with the change that Prasi ask you?
"Originally Posted by prasi,
can you try setting up a 100R at the output of first stage instead of 1k5 and ALSO instead of 15k to ground, a 100k to ground like Ivan's schematic?"
I follow this treat with interest because I am in the process to build this preamp with RIAA. and P104 Muting Circuit
Do you plan to change the schematic to be able to accommodate the moving coil cartridges and cartridge loading, see Note : Hi-Fi Phono Preamp (RIAA Equalisation) Rod Elliott - ESP (Original Design)
"There is some debate on the Net about cartridge loading impedance, with various suggestions that reducing the standard load from 47k to something lower (even as low as 10k) provides benefits. While this is plausible, I've not run any tests so cannot confirm or deny that there may be an advantage. If this is something you wish to try, I suggest that it be done at the phono RCA input socket (along with the capacitor if you want to try that too)"
Did you use ivanlukic schematic with the change that Prasi ask you?
"Originally Posted by prasi,
can you try setting up a 100R at the output of first stage instead of 1k5 and ALSO instead of 15k to ground, a 100k to ground like Ivan's schematic?"
Glad to see this thread pop up as well. I am in the process of building the ESP P88 pre-amp.
I'm using "ugly" construction with no PCB and it looks like it will be simplest to use one dual op-amp per channel rather than one per stage. I was wondering if that would cause problems or have benefits, but it sounds like it's fine either way.
I just finished the P05 power supply circuit yesterday and saw a solid +/-15VDC from the regulated outputs. I used a 16VAC wall wart transformer as suggested by Rod Elliott.
Hopefully this weekend I can start building up the audio parts of the circuit.
-Neil N0FN
I'm using "ugly" construction with no PCB and it looks like it will be simplest to use one dual op-amp per channel rather than one per stage. I was wondering if that would cause problems or have benefits, but it sounds like it's fine either way.
I just finished the P05 power supply circuit yesterday and saw a solid +/-15VDC from the regulated outputs. I used a 16VAC wall wart transformer as suggested by Rod Elliott.
Hopefully this weekend I can start building up the audio parts of the circuit.
-Neil N0FN
the p05 is on my list as well. i currently use the muffsy power supply which seems to be similar.
yes, using dual opamps is fine and possibly cheaper. from a performance perspective i don‘t think it will make any difference. earlier in this thread somebody mentioned channel crosstalk in dual opamps but the issue seems to be negligible. i have tried the opa2134 and ne5532 so far and they both work fine.
rod elliott suggests the use of polyester caps but other sources say that polypropylene causes less distortion. again, probably only makes a difference on the measuring bench.
Hicoco: I believe you‘ll need another amp before the p06 to be able to use MC carts. Something like this: head amp. For cartidge loading I‘ve only used 47k and I think I‘ll stick with it. I have never read a reliable claim that it should be lower - unless specified by the cartridge manufacturer of course.
yes, for the p88 i followed prasis advice successfully. but now i have it set up with 10k balance and 100k volume (both linear) and use the resistors from the original configuration.
all in all i can say that both circuits are very beginner friendly (i consider myself a newbie) and there‘s a lot to learn from them. get a breadboard and experimenting with various resistors and caps will be a breeze.
hope that helps.
yes, using dual opamps is fine and possibly cheaper. from a performance perspective i don‘t think it will make any difference. earlier in this thread somebody mentioned channel crosstalk in dual opamps but the issue seems to be negligible. i have tried the opa2134 and ne5532 so far and they both work fine.
rod elliott suggests the use of polyester caps but other sources say that polypropylene causes less distortion. again, probably only makes a difference on the measuring bench.
Hicoco: I believe you‘ll need another amp before the p06 to be able to use MC carts. Something like this: head amp. For cartidge loading I‘ve only used 47k and I think I‘ll stick with it. I have never read a reliable claim that it should be lower - unless specified by the cartridge manufacturer of course.
yes, for the p88 i followed prasis advice successfully. but now i have it set up with 10k balance and 100k volume (both linear) and use the resistors from the original configuration.
all in all i can say that both circuits are very beginner friendly (i consider myself a newbie) and there‘s a lot to learn from them. get a breadboard and experimenting with various resistors and caps will be a breeze.
hope that helps.
Hi Ivan, my understanding is that you use 10k volume pot.. and 100k resistor (R6) correct? , do you use a Balance pot ? and if yes which value?
Thank
i am asking because I have a doubt and i am confused with the post #61
Evan want to ad a second LPS RK27 pot, he left enough room on the pcb to accommodate it's footprint 28mm x 26mm and added three solderpads that suit ALPS RK27 pin layout