Advice on Peluso p67 mod?(Love the Du67 project! I should have done that!)

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Please also check these two resistors marked on the pictures.
Are these two the same  - 100k resistor - brown - black - black - orange - gold ?

It would have more sense if the one be 10k.
 

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ln76d said:
Please also check these two resistors marked on the pictures.
Are these two the same  - 100k resistor - brown - black - black - orange - gold ?

It would have more sense if the one be 10k.

They are both the same color code.  Which looks like Brown, Black, Black, Orange, Brown.  This checks out as I measured one of them and it is 97.5k ohm, which is supposed to be 100k ohm.  Both look identical to me.
 
Measurements taken immediately after powering on.

6.04 VDC between ground and Yellow

179.5 VDC between ground and Brown

76.5 VDCbetween ground and Blue

.015 VDC between ground and Green

.015 VDC between ground and Black

 
Alright!  Look at that!

Now, would it be a huge headache to swap the transformer to implement the NFB circuit?

I'll give you c7 in a bit.  The mic is hot and on a session right now...
 
Hey,

little bit weird but possible.
Please check is it as on the schematic.

If you compare this schematic to the U67 schematic - these are completely different microphones.
Whole deemphasis circuit is much more than traansformer with feedback.
Look at these noodles on u67 schematic - on your board simply is no place to make this circuit.

My opinion!
It never was  U67 and it probably never be.
But!
P67 circuit isn't bad, it use good tube and minor changes should change a lot.
I would make this microphone sounding best as possible and if you still want something close to the U67, you can build another mike using even kit and then use peluso capsule for the project. Then you can put new capsule to the p67, let say M7 (or D7), K47 or even chinese k47 (yes,even with this - microphone should sound better).
Better to have two good microphones than one and not used red PCB with the tube :)
What do you think?

 

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Ok, so here's basic mod.
Ask if anything is confusing :)

Another things is voltage!

Please check again between blue and ground for two side pattern switch settings.
And also between  two 2M resistors - refered to ground.
 

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ln76d said:
Hey,

little bit weird but possible.
Please check is it as on the schematic.

If you compare this schematic to the U67 schematic - these are completely different microphones.
Whole deemphasis circuit is much more than traansformer with feedback.
Look at these noodles on u67 schematic - on your board simply is no place to make this circuit.

My opinion!
It never was  U67 and it probably never be.
But!
P67 circuit isn't bad, it use good tube and minor changes should change a lot.
I would make this microphone sounding best as possible and if you still want something close to the U67, you can build another mike using even kit and then use peluso capsule for the project. Then you can put new capsule to the p67, let say M7 (or D7), K47 or even chinese k47 (yes,even with this - microphone should sound better).
Better to have two good microphones than one and not used red PCB with the tube :)
What do you think?

All interesting points!  Hmmmmm.  I will definitely build a 67 at some point.  I am at a decision point now, though.  The p67 can be modded, but not to be like a 67. So either I can sell it and use the money for kits, or mod it and do a kit at a later date(I have an m49 kit coming now, can do a 67 later)

I have decided to mod it simply because we have come this far and you have kindly put in this work, and though it won't be modded to the degree that I had hoped, it would be rude to not mod after you've kindly worked so hard.

Question - the transformer almost looks like AMI.  Do you think it is?  If not, could I put in a similar cinemag or AMI and improve the sound there as well?

The changes you have proposed, can you tell me a little of what they will do?  Are they static EQ curve adjustments?  More than that?  I can read a schematic on a basic level, but cannot conceive what they will change.
 
Part 1

Transformer isn't ami, it's a chinese transformer (theoretically made for Peluso specifictions - they all say that :D ).
It is probably same as advanced audio microphones.
Really, you don't need to change it for ami, if you will even hear the difference it's not worth the money.
What's AMI? AMI for me is a lot of stories and theories (really fascinating) but it will not blow your mind, believe me.
You want hear real difference try some (even east) German made old transformers.
Currently "diy" kit around market looks similar to the audiophile market - etiquete, brand, name.
Really don't go that way :)
Remember that even if someone call  kit, board, capsule, enclosure  like u47, m49, c12, M7, k47.
It doesn't mean that it will be the same as original unit. It even can be not similar in the sound (different tubes, transducers, transformers etc - different everything).
Did you thinking, buying P67 that it's same as u67?
Many people think it is only because enclosure is similar (little bit retarded) capsule is similar, name is similar and bullshit stories from manufacturer and all the believers.
It's not even in the same league.
Same is with the kits, many of the parts etc.
Do you need good microphone or microphone (even shitty) with a fake etiquette, pretending something which isn't?

 
Part 2

you can do the mod, you don't have, i don't mind, i don't care.
I have fun with this ;)
My advice - make mod, try it, try with different capsule - still don't like it?
Restore original circuit (mod is realy simple - you don't have to cut PCB traces or change anything complicated).
Sell it!
What you can lose?
20$ for parts?
You already lose money buying this microphone and probably lose more selling it.
Maybe after mod it would be great mike?
If you don't try you will never know :)
Good microphone isn't fake etiquette but properly tuned circuit - and yes it can be made even with chinese compnents if you know what you are doing.
 
Part 3

I'm not the best in expalining circuits, especially in the language which i barely know.
Also I'm a practitioner, not a theoretician but i will try ;)

EQ - the only eq (theoretically only)  in this microphone is C5 2.2nF. It is simple LPF made by capacitor from the plate to ground.
It's also good for radio frequencies etc. If you will decide to try other capsule than k67 you can remove capacitor or change value to the smaller one.

Most important here is capsule input connection!
My favorite is without any capacitor in the path, but for multipattern is hard to make, when you already have PSU and don't want to build another.
In original design (which is popular in many microphones, even neumann but better made) 100pF capacitor (sometimes 1nF or even 10nF) acts like eq and when the capacitance is higher cutoff frequency is higher also, microphone lose sensitivity and overall sounds much worse in whole spectrum. It's overbrighted and yucky.
The same capsule can sound completely different with different input configuration.
Look to my S16 project in this postion i have to use 3.3pF - and it sounds a lot better than 1nF but for cardioid i used configuration without this capacitor at all!
Changing input configuration you should hear the difference which wouldn't give you any fashionable transformer, tube etc.
For tuning circuit low end response you have thre points.
First - output capacitor before transformer - in your circuit - really important to overall sound balance.
Too big capacitance can boost output (mostly in not noticable range) and dull microphone in the whole range.
Some use even 4.7uF-10uF - what for? How sh*tty is that microphone that you need to use so high capacitance here?
470nF Siemens MKT which is already here is pretty good - if you want to improve try old MP capacitors 470nF-680nF range.
Overall 500nF range is enough aand the best.
Second - capacitor between two plate resistors to ground - here 10uF - for original circuit maybe it is a good value...
You don't want electrolytic here and also so big! 2uF is enough - find some good MKT 250V.
Third - cathode capacitor - original 47uF - this is the place where you final can tweak low end response.
Assuming that first and second are already choosed, if you will decide to adjust first plate resistor (i will not surprise if 10k would be good option)  - now is time to set the value of cathode capacitor.
There's probability that even you don't need electrolytic cap. Again - check my S16 - in this postion am using 3.3uF MKT and it's enough! 6AK5 is really similar to the 6028/408a tube.
If you will need electrolytic - i will start from lower values - for tests any electrolytic - if you will find final value - i will try to bipolar electrolytic. After set i will add 1uF film capacitor  in parallel for example as in schematic. It's for lower esr of final capacitance. At cathode 10V-16V capacitors are enough - so cheap and easy to source.

There's also fourth - added by me 1nF at the input grid of the tube. We are not considering it as a filter - 1nf for low end cut in not useful range and forget about it. In this configuration it need to be used to keep away DC polarisation voltage from tube input. Good styroflex capacitor or ceramic C0G/NP0 (also COG/NPO). No silver mica or MKP.

Other  mods - changing polarisation voltage value, adjusting plate resistance mentioned before (with this sometimes is need to adjust polarisation voltage, if tube suck more current), Changing plate resistors and cathode resistor for different type (no, not metal film even dale) - want improvement find carbon beyschlag or draloric.
Changing capsule for these which doesn't need EQ.
Changing transformer - really last thing here - or mybe different ratio? This could be nice :)
Changing tube - after all circuit tuning and test i would go for few different brands 6AK5 and try them.
I'll be testing soon 5654 which is military higher quality version of 6ak5. It will be NOS made for French army.
Since it was for French army, they probably have a loooot of unused tubes, if you know what i mean :D :D :D







 
For your future "m49" if you want make c version, check my something a'la m49 thread.
If you will use 5840/EF732 (valvo for example - great tube), you will need to change cathode resistor at first point.
 
ln76d said:
Part 1

Transformer isn't ami, it's a chinese transformer (theoretically made for Peluso specifictions - they all say that :D ).
It is probably same as advanced audio microphones.
Really, you don't need to change it for ami, if you will even hear the difference it's not worth the money.
What's AMI? AMI for me is a lot of stories and theories (really fascinating) but it will not blow your mind, believe me.
You want hear real difference try some (even east) German made old transformers.
Currently "diy" kit around market looks similar to the audiophile market - etiquete, brand, name.
Really don't go that way :)
Remember that even if someone call  kit, board, capsule, enclosure  like u47, m49, c12, M7, k47.
It doesn't mean that it will be the same as original unit. It even can be not similar in the sound (different tubes, transducers, transformers etc - different everything).
Did you thinking, buying P67 that it's same as u67?
Many people think it is only because enclosure is similar (little bit retarded) capsule is similar, name is similar and bullsh*t stories from manufacturer and all the believers.
It's not even in the same league.
Same is with the kits, many of the parts etc.
Do you need good microphone or microphone (even sh*tty) with a fake etiquette, pretending something which isn't?

All very interesting!  I wouldn't know how to go about an old transformer, so I probably wont go that route...

I did indeed think the p67 was a u67 clone, as the marketing seems to allude to.  Funny that it isn't nearly the same!  I will say, it does actually sound really nice sometimes.  I just think it could have slight improvements...
 
ln76d said:
Part 2

you can do the mod, you don't have, i don't mind, i don't care.
I have fun with this ;)
My advice - make mod, try it, try with different capsule - still don't like it?
Restore original circuit (mod is realy simple - you don't have to cut PCB traces or change anything complicated).
Sell it!
What you can lose?
20$ for parts?
You already lose money buying this microphone and probably lose more selling it.
Maybe after mod it would be great mike?
If you don't try you will never know :)
Good microphone isn't fake etiquette but properly tuned circuit - and yes it can be made even with chinese compnents if you know what you are doing.

Interesting!  You have convinced me.  So I can solder the components in on top of other components to achieve the mod?  Thats easy.
 
ln76d said:
Part 3

I'm not the best in expalining circuits, especially in the language which i barely know.
Also I'm a practitioner, not a theoretician but i will try ;)

EQ - the only eq (theoretically only)  in this microphone is C5 2.2nF. It is simple LPF made by capacitor from the plate to ground.
It's also good for radio frequencies etc. If you will decide to try other capsule than k67 you can remove capacitor or change value to the smaller one.

Most important here is capsule input connection!
My favorite is without any capacitor in the path, but for multipattern is hard to make, when you already have PSU and don't want to build another.
In original design (which is popular in many microphones, even neumann but better made) 100pF capacitor (sometimes 1nF or even 10nF) acts like eq and when the capacitance is higher cutoff frequency is higher also, microphone lose sensitivity and overall sounds much worse in whole spectrum. It's overbrighted and yucky.
The same capsule can sound completely different with different input configuration.
Look to my S16 project in this postion i have to use 3.3pF - and it sounds a lot better than 1nF but for cardioid i used configuration without this capacitor at all!
Changing input configuration you should hear the difference which wouldn't give you any fashionable transformer, tube etc.
For tuning circuit low end response you have thre points.
First - output capacitor before transformer - in your circuit - really important to overall sound balance.
Too big capacitance can boost output (mostly in not noticable range) and dull microphone in the whole range.
Some use even 4.7uF-10uF - what for? How sh*tty is that microphone that you need to use so high capacitance here?
470nF Siemens MKT which is already here is pretty good - if you want to improve try old MP capacitors 470nF-680nF range.
Overall 500nF range is enough aand the best.
Second - capacitor between two plate resistors to ground - here 10uF - for original circuit maybe it is a good value...
You don't want electrolytic here and also so big! 2uF is enough - find some good MKT 250V.
Third - cathode capacitor - original 47uF - this is the place where you final can tweak low end response.
Assuming that first and second are already choosed, if you will decide to adjust first plate resistor (i will not surprise if 10k would be good option)  - now is time to set the value of cathode capacitor.
There's probability that even you don't need electrolytic cap. Again - check my S16 - in this postion am using 3.3uF MKT and it's enough! 6AK5 is really similar to the 6028/408a tube.
If you will need electrolytic - i will start from lower values - for tests any electrolytic - if you will find final value - i will try to bipolar electrolytic. After set i will add 1uF film capacitor  in parallel for example as in schematic. It's for lower esr of final capacitance. At cathode 10V-16V capacitors are enough - so cheap and easy to source.

There's also fourth - added by me 1nF at the input grid of the tube. We are not considering it as a filter - 1nf for low end cut in not useful range and forget about it. In this configuration it need to be used to keep away DC polarisation voltage from tube input. Good styroflex capacitor or ceramic C0G/NP0 (also COG/NPO). No silver mica or MKP.

Other  mods - changing polarisation voltage value, adjusting plate resistance mentioned before (with this sometimes is need to adjust polarisation voltage, if tube suck more current), Changing plate resistors and cathode resistor for different type (no, not metal film even dale) - want improvement find carbon beyschlag or draloric.
Changing capsule for these which doesn't need EQ.
Changing transformer - really last thing here - or mybe different ratio? This could be nice :)
Changing tube - after all circuit tuning and test i would go for few different brands 6AK5 and try them.
I'll be testing soon 5654 which is military higher quality version of 6ak5. It will be NOS made for French army.
Since it was for French army, they probably have a loooot of unused tubes, if you know what i mean :D :D :D

LOL.

Wow - that is allot of info!  I need to digest it.  I appreciate you writing in English!  Otherwise we wouldn't have gotten very far!!!

Lots to think about...
 
ln76d said:
For your future "m49" if you want make c version, check my something a'la m49 thread.
If you will use 5840/EF732 (valvo for example - great tube), you will need to change cathode resistor at first point.

I bought Dan's kit for the 49 - I think it works for either revision.  Though I have no idea which one I should make.  Perhaps C?  I was wondering what tube I should try.  I can't afford an ac701k so its got to be something else anyway...
 
achase4u said:
Interesting!  You have convinced me.  So I can solder the components in on top of other components to achieve the mod?  Thats easy.

No, not exactly :)

You need to rewire capsule, change few parts.
Back to the original circuit is soldering all the old parts to their place.

achase4u said:
I appreciate you writing in English!Otherwise we wouldn't have gotten very far!!!

Thanks :)
That's funny, because i never learned that language :D
Forget about grammar - i have no idead about english grammr ;D

achase4u said:
I did indeed think the p67 was a u67 clone, as the marketing seems to allude to.  Funny that it isn't nearly the same!  I will say, it does actually sound really nice sometimes.  I just think it could have slight improvements...
Same is with these kits clones...
This circuit after mod, truly would be best for different capsule.
If you will try k47  - you can call it U47, because it has nothing to do with it as these U47 clones :D :D :D

achase4u said:
I bought Dan's kit for the 49 - I think it works for either revision.  Though I have no idea which one I should make.  Perhaps C?  I was wondering what tube I should try.  I can't afford an ac701k so its got to be something else anyway...

I think that C version is easiest to get something similar to m49 if you don't have original components.
5840/EF732 is pretty good and most known substitute.  There's no replacement (AC761 is even more rare than AC701).
Am using Valvo EF732. My schematic is something like C but without low end filter and cathode resistor is more adequate for this tube.
 
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