U67 circuit

[gary o]

For my own learning out of spare parts I soldered together a point to point version of the u67, as per common schematic, I'm using a u87ai capsule and grill. I have various Mallard Marconi and Mazda valves to audition. I'm using a Max Kircher transformer . As a reference I have my u87ai mic I also have a violet design vin 67 lollipop capsule... The VIN 67 is a k67 style capsule in a lollipop head and is designed to sound like a u67 microphone when used in conjunction with a flat amplifier body, I have various bodies I use it with. I have never used a real u67 but have an idea what it should sound like. After reading many many threads I have read the max transformer may sound a little darker than others, A friend gave it to me, He picked it up cheap from eBay, I think it may have been taken out of a microphone thought to sound too dark.... I have built into my experimental mic a switch to switch in c17, switches for S1 and S2 on original schematic and a switch to switch in the tertiary winding on transformer. When all switches are set up as original u67 the mic does sound a little dark, ribbonesque you might say quite a bit darker than my vin 67 lollypop but in the same ballpark, not unusable but I don't think it's right probably due to transformer as everything else is as u67 well as close as I can get . For fun I auditioned about 25 C9 capacitors .47 .5 and 1uf, I chose the brightest sounding one to compensate.It is a sprage .47. I feel I have quite a good way to test the sound of the mic all be it unscientific. I am a singer so I choose a song , set up a mic pre and compressor, I'm quite good at singing the exact same verse over and over .I sing the verse, quickly solder in a different capacitor or component and sing the verse on another track and A and B the takes, I only really record vocals so only need cardiod. Im enjoying this circuit I have more experiments to do.

 

[vintagelove]

I've heard that Max transformer is darker as well. Though I will say, I have that vin67 cap, which is awesome btw, but I wouldn't call that dark. It's actually kinda perfect... but... I wouldn't be surprised if your diy 67 with that transformer was a little darker than that vin67 capsule on a flat body (what are you using it with? I have an 80 something year old Telefunken 301/2 and a global pre).

Either way, sounds like a cool project. What are you using for the body of the mic? How does it attach to the capsule?

 

[kingkorg]

For my own learning out of spare parts I soldered together a point to point version of the u67, as per common schematic, I'm using a u87ai capsule and grill. I have various Mallard Marconi and Mazda valves to audition. I'm using a Max Kircher transformer . As a reference I have my u87ai mic I also have a violet design vin 67 lollipop capsule... The VIN 67 is a k67 style capsule in a lollipop head and is designed to sound like a u67 microphone when used in conjunction with a flat amplifier body, I have various bodies I use it with. I have never used a real u67 but have an idea what it should sound like. After reading many many threads I have read the max transformer may sound a little darker than others, A friend gave it to me, He picked it up cheap from eBay, I think it may have been taken out of a microphone thought to sound too dark.... I have built into my experimental mic a switch to switch in c17, switches for S1 and S2 on original schematic and a switch to switch in the tertiary winding on transformer. When all switches are set up as original u67 the mic does sound a little dark, ribbonesque you might say quite a bit darker than my vin 67 lollypop but in the same ballpark, not unusable but I don't think it's right probably due to transformer as everything else is as u67 well as close as I can get . For fun I auditioned about 25 C9 capacitors .47 .5 and 1uf, I chose the brightest sounding one to compensate.It is a sprage .47. I feel I have quite a good way to test the sound of the mic all be it unscientific. I am a singer so I choose a song , set up a mic pre and compressor, I'm quite good at singing the exact same verse over and over .I sing the verse, quickly solder in a different capacitor or component and sing the verse on another track and A and B the takes, I only really record vocals so only need cardiod. Im enjoying this circuit I have more experiments to do.

Please, please, please try to do something more scientific. Vocal is not the best way to test a mic for various reasons. Low spl, won't push the components. Poor harmonic content, many subtle variations will remain hidden. Soft transients. Short transients. Poor low end content. Poor content above 10k.

At least you can record a take with a more transparent mic, and play it back through a speaker recording the same exact take at same exact spot changing the components.

No matter how close you sing every take there will always be more variation in your performance than in some components. Position, intensity, your vocal cords warm up, dry out, plosives, silbilants etc. You will be just fooling yourself. This is exactly how most myths came to be.

When it comes to capsule/source interaction literally a millimeter in distance can make more difference than a capacitor type. Humidity of the air and temperature...

Huge part of tube sound is how it performs noise wise. You can't test the noise unless you have same exacy source level.

 

[gary o]

I've heard that Max transformer is darker as well. Though I will say, I have that vin67 cap, which is awesome btw, but I wouldn't call that dark. It's actually kinda perfect... but... I wouldn't be surprised if your diy 67 with that transformer was a little darker than that vin67 capsule on a flat body (what are you using it with? I have an 80 something year old Telefunken 301/2 and a global pre).

Either way, sounds like a cool project. What are you using for the body of the mic? How does it attach to the capsule?

Hi VL I love my Vin 67 I use it with home made U47 M49 Elam251 C28A &KM83 circuits, it sounds great with everything really, sounds great in U67 in flat mode with tertary winding diconnected via my switch.

Im using home made Neve pre amp & La3a for this evaluation.

Dont laugh but I use chocolate tin as body and I fabricate capsule mount from things like blank CD spindles, its real DIY no spending money ha.If I really like a circuit I try I sometimes buy a real body to give it a home.
I usually well in fact ALWAYS find the circuit makes small difference to sound of a mic, A flat circuit that is.... I have various capsules I try in each circuit I build and always find favorite capsule sounds best in every circuit, no 2 capsule 2nd best everytime and so on, thats why I thought this would be interesting circuit to play with.Maybe I can make a cheap capsule sound good & this is proving to be the case. I have a china K67 capsule that sounds dare I say it as good as my U87ai head, woohoo.

 

[gary o]

Please, please, please try to do something more scientific. Vocal is not the best way to test a mic for various reasons. Low spl, won't push the components. Poor harmonic content, many subtle variations will remain hidden. Soft transients. Short transients. Poor low end content. Poor content above 10k.

At least you can record a take with a more transparent mic, and play it back through a speaker recording the same exact take at same exact spot changing the components.

No matter how close you sing every take there will always be more variation in your performance than in some components. Position, intensity, your vocal cords warm up, dry out, plosives, silbilants etc. You will be just fooling yourself. This is exactly how most myths came to be.

When it comes to capsule/source interaction literally a millimeter in distance can make more difference than a capacitor type. Humidity of the air and temperature...

Huge part of tube sound is how it performs noise wise. You can't test the noise unless you have same exacy source level.

Hi thanks well this is for my own use I just record vocals you see,my own usually, if I cant hear a difference then it isnt worth my time if that makes sense. I enjoy what Im doing and getting all scientific takes the fun out of it for me. I actually feel guilty spending time DIY ing I should be making music really. But sometimes in the winter I feel the need to experiment, Im just looking for a mic to inspire me to sing more thanks.

 

[kingkorg]

Sure

Hi thanks well this is for my own use I just record vocals you see,my own usually, if I cant hear a difference then it isnt worth my time if that makes sense. I enjoy what Im doing and getting all scientific takes the fun out of it for me. I actually feel guilty spending time DIY ing I should be making music really. But sometimes in the winter I feel the need to experiment, Im just looking for a mic to inspire me to sing more thanks.

Makes sense. I started this way exactly, however i ended up chasing my tail. In the end whatever works for you is the way to go. I feel often inspired by the gear i make/mod, and it's often the mics with quirks.

 

[gary o]

I have learnt the hard way about the honeymoon period, when I have made something a mic, a pre or compressor in my case & for a while that piece of kit is the best sounding kit I have... also to try to just use my ears.In this case I have china K67 on my U67 circuit when I put the U87au on my brain says the must be better ! My ears are saying you know what for my vocal recording I dont think it is ... scary

 

[dmp]

Wonderful to see DIY like this around here. Way to go Gary
I'd recommend checking that all the windings are good on the BV12. You can just use a multimeter to check the DCR of all three windings on each bobbin. My suspicion is a lot of those trannies had open windings, which is why so many builders had mics that didn't sound right, dark (but a few did! The lucky ones that didn't get defective transformers). I had built a u67 and m269 with bv12s and found that both had at least one open tertiary winding on a bobbin.
I know its a fun challenge to spend as little as possible, but add one of Moby's BV12s to your pallet when you can!

 

[gary o]

Wonderful to see DIY like this around here. Way to go Gary
I'd recommend checking that all the windings are good on the BV12. You can just use a multimeter to check the DCR of all three windings on each bobbin. My suspicion is a lot of those trannies had open windings, which is why so many builders had mics that didn't sound right, dark (but a few did! The lucky ones that didn't get defective transformers). I had built a u67 and m269 with bv12s and found that both had at least one open tertiary winding on a bobbin.
I know its a fun challenge to spend as little as possible, but add one of Moby's BV12s to your pallet when you can!

Thankyou DMP I need that encouragment....I got my Max BV12 from friend who got real cheap on fleabay & I suspect it was from someone who thought it broken or too dark. I could not find pin out diagram anywhere so did the DCR measurments and looked ot photos here on official ioadioMk67 build thread to work out pin out. When I measured with my meter what I think (from photos) is the tertary winding white to brown on U67 schematic I have no reading ? So I thought I guess makes sense thats why it was sold cheap> I re constructed the mic I connected the seemingly dead tertary winding via a switch & wah la its seems to work, when switch open bright sound too bright switch closed much darker sound....this shouldnt happen should it ?
As it stands I have a mic that I think is well within the U67 ball park using my U87ai & Vin 67 capsule on a M49 circuit to compare, the U67 is darker than both which makes sense, Im going to change values of R18 to 22K R4 to 2M2 R5 to 5meg and switch out C17 As per the slightly older U67 schematic just to see how she sounds.

 

[dmp]

Yeah, if you get no reading on the pins then the winding is open.
I'm working to setup and rewind the bad coils. Shouldn't be too hard. I'll post once I've done it.

 

[gary o]

Maybe there something wrong with my meter as you say open circuit & yet in circuit it takes out the highs....I will follow with interest your rewind, good luck.