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How to extend the low end rolloff on vintage 87
Old 2nd September 2018
  #1
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MYN's Avatar
How to extend the low end rolloff on vintage 87

I built the Poctop D87 from VintageMicrophonePCBKit and I think it sounds pretty great. My one criticism is that I'd like it to have a bit more low end extension. I know the capsule I used is fully capable of a more full bottom end, so I'm guessing there's a capacitor here that controls the low end rolloff that could be changed to achieve what I'd like. I'm just not savvy enough to know which cap so I thought I'd ask the folks here for some advice.

I've asked at GroupDIY, but those cats are seemingly more interested in keeping their cards close to the vest and not giving direct answers. Hey, I'm all for the "experiment and learn" thing in DIY, but sometimes I just need a direct answer to a question and not a riddle or vague roadmap.

I'm attempting to attach the schematic to a vintage 87 here, as the D87 is based upon that.

Old 4th September 2018
  #2
There are 470 pf polystyrene caps in the head assembly. I used Rel Cap 1000 pf/600V RT polystyrene. That buys an extra octave of low end. Then there is a tantalum cap across the source resistor to the jfet, change that to 22 or 47 uf. Lastly, there is a 1 uf tantalum coupling cap from the jfet drain to the output transformer, increase that to 3.3uf poly at 63 volts, they fit.
Old 4th September 2018
  #3
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Brian M. Boykin's Avatar
Quote:
Originally Posted by Jim Williams View Post
There are 470 pf polystyrene caps in the head assembly. I used Rel Cap 1000 pf/600V RT polystyrene. That buys an extra octave of low end. Then there is a tantalum cap across the source resistor to the jfet, change that to 22 or 47 uf. Lastly, there is a 1 uf tantalum coupling cap from the jfet drain to the output transformer, increase that to 3.3uf poly at 63 volts, they fit.
Do you come to your values through exact math, from your years of experience of changing parts and measuring their affects, or a little of both?

I’m a pretty systematic person and “experimenting and using your ears” isn’t the most scientific reproducible way to do this stuff. It seems parts should be selected first by their appropriateness based on math and function, second by measured results, and last by the ear test.

Brian
Old 4th September 2018
  #4
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Quote:
Originally Posted by Jim Williams View Post
There are 470 pf polystyrene caps in the head assembly. I used Rel Cap 1000 pf/600V RT polystyrene. That buys an extra octave of low end. Then there is a tantalum cap across the source resistor to the jfet, change that to 22 or 47 uf. Lastly, there is a 1 uf tantalum coupling cap from the jfet drain to the output transformer, increase that to 3.3uf poly at 63 volts, they fit.
Wow. Thanks Jim! I have a pair of high end 1000pf/600v polystyrenes from a D-12 build that I can try. It appears on the D87, that C8 across the bias resistor is already 22uf, but I'm willing to try getting a 47 and upping it and also upping that 1uf at C8.

I know you're busy, but one last clarification. Can the 470p's be switched to the 1000p's independently of the other changes or should all 4 caps be changed at once?
Old 5th September 2018
  #5
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gyraf's Avatar
 

The 470pF in the head has nothing to do with low end, leave those alone. We're talking a 0.34Hz highpass into the 1G Ohm..

Same with the rest of these esoteric suggestions - they are all sub-audio-range already.

If you're sure that you really lack low end in the amplifier (have you measured it?), the obvious place to look would probably be the transformer - it requires high primary inductance to pull low frequencies through with the relatively high amplifier source impedance. The AMI/Cinemag transformer clones might not be optimal..

Quote:
Originally Posted by MYN View Post
I've asked at GroupDIY, but those cats are seemingly more interested in keeping their cards close to the vest and not giving direct answers.
..Hmm.. There is a 148 pages long (!) help thread on the subject, which your question indicates you didn't read (if I'm guessing your local username right). I honestly don't think that anyone would keep information from you on purpose, it's simply not policy over there..


Jakob E.

Last edited by gyraf; 5th September 2018 at 01:07 PM.. Reason: sp
Old 5th September 2018
  #6
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Brian M. Boykin's Avatar
Quote:
Originally Posted by DrAudiospecific View Post
cap size adjustments isn't nuclear science. because after a while people like Jim and me can reduce the math in our heads and come up with an appropriate values. And yes, most are 20+ years of experience that can do this.

Another thing you should investigate is construction of materials and construction techniques that go into building the electronic parts. because they directly effect performance, and not one perfect type of part is superior to another, however, the circuit might dictate a cheaper part working better in one section of the circuit.
Thank you. I’m slowly working my way through “Optimizing Op Amp Performance” by Jerald Graeme. There’s obviously a math to this stuff but I reckon you guys that have been doing this for so many years nlknow which direction to go and by about how much to put you in the ballpark of where you want to be. I’m a professional fire fighter by trade, I can look at a burning structure and have a pretty good idea what the fire load is, how much water flow I’m gonna need, manpower and hose on the ground. My goal is to look at a circuit design and be able to do the same.

Brian
Old 5th September 2018
  #7
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MYN's Avatar
Quote:
Originally Posted by gyraf View Post
The 470pF in the head has nothing to do with low end, leave those alone. We're talking a 0.34Hz highpass into the 1G Ohm..

Same with the rest of these esoteric suggestions - they are all sub-audio-range already.

If you're sure that you really lack low end in the amplifier (have you measured it?), the obvious place to look would probably be the transformer - it requires high primary inductance to pull low frequencies through with the relatively high amplifier source impedance. The AMI/Cinemag transformer clones might not be optimal..



..Hmm.. There is a 148 pages long (!) help thread on the subject, which your question indicates you didn't read (if I'm guessing your local username right). I honestly don't think that anyone would keep information from you on purpose, it's simply not policy over there..


Jakob E.
Thanks for your input Jakob. Yeah, my username is not the same on GDIY as it is here. I asked about the low end extension earlier this year and also again last year with no takers. I don't necessarily imply that people are keeping info from others on purpose, but for someone like me who has less experience than others, I have sometimes gotten responses to other questions that are a little too vague and follow ups sometimes get answered and sometimes get ignored, so it's definitely not all Kumbaya over there 24/7.

I've read through that 148 page thread more than once and kinda studied it in the two years before I finally built my D87s and it helped me a lot. But this one question, about if there is a cap change that can open up the low end a bit more (as I have noticed is possible in a schoeps circuit), has eluded answer over there. So, your assumption that I didn't read it based upon my question is incorrect and defensive. I posted here because I got tired of waiting for answers. There are questions posted in that thread from others that have never, ever been answered in the years it has been in existence.

And yes, I'm using a Cinemag 13113, so maybe that is the answer. I really, really like the sound of my D87's. I just wish they had a bit more bottom end.
Old 5th September 2018
  #8
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I feel your pain MYN. I feel like Danielson most of the time and Mr Miaggie is throwing out riddles. However, more times than I can count, through my relentless reading and studying the lightbulb has gone off and I find myself thinking “that’s what he meant.”
Old 6th September 2018
  #9
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MYN's Avatar
Thanks Brian. Yeah, trying to solve the riddle of whether or not some kind of cap swap or swaps can increase the low end on Dany Bouchard's D87 seems to be elusive.

On his D847, the Neumann 84 circuit modified to use with an LDC capsule, the tantalum coming off the source resistor to the fet is the one said to increase the bottom end and to do so, the recommended change is from 4.7uf to 22uf. Now, what I've been told is that the 84 circuit is very similar to the vintage 87, just without the HF EQ. So, on the D87, the standard BOM already calls for the 22uf at that same cap which comes off the source resistor to the fet, which seems to align with what Jim Williams is saying above.

But yes, it's a riddle...
Old 6th September 2018
  #10
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gyraf's Avatar
 

When you wish for a bit more bottom end - COULD it be that you actually wish for slightly more proximity effect, i.e. lowend-when-closemiking?

If this is the case, then you could simply polarize the microphone slightly towards hypercardioid (i.e. a bit more in the fig8-direction) - this is an effective and common way to achieve "that sexy proximity effect" by simple means..

Yes, I've used the trick myself on occasions where I needed to spice up a slightly boring-sounding mic.

Just remember that this does not add to low end in omni and distance-miking - so if you're primarily doing orchestral work or such, it won't help.

Jakob E.
Old 6th September 2018
  #11
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MYN's Avatar
Quote:
Originally Posted by gyraf View Post
When you wish for a bit more bottom end - COULD it be that you actually wish for slightly more proximity effect, i.e. lowend-when-closemiking?

If this is the case, then you could simply polarize the microphone slightly towards hypercardioid (i.e. a bit more in the fig8-direction) - this is an effective and common way to achieve "that sexy proximity effect" by simple means..

Yes, I've used the trick myself on occasions where I needed to spice up a slightly boring-sounding mic.

Just remember that this does not add to low end in omni and distance-miking - so if you're primarily doing orchestral work or such, it won't help.

Jakob E.
Jakob,
That may exactly be it. I do commercial VO. It's all I do and proximity effect is my best friend. I recently picked up a TLM 107 for character voice work and found that in HyperC it's got the kind of 'oomph' in the low end I like for narrations.

So, if that is a possible solution, how would I go about it? I have one D87 that's multi-pattern, and one that's just cardioid only which I wouldn't be able to switch to Hypercardioid.

I've come to the conclusion that, as built, my D87s sound as they should. Last year, I built a 3rd one (with an AMI tranformer) that I gave to a friend of mine who is a producer/label owner in NYC and he shot it out against a Grammy-winning producer friend's prized vintage u87i in Philly and said the difference in the two was that the D87 was just a touch darker up around 10k. I talked to him about it again this morning to ask specifically if he remembered if the low end on the D87 was different and he remarked that below 600hz, the mics sounded identical. So, kudos to Dany Bouchard for nailing this circuit and I think it's possible that there hasn't been a clear answer how to extend the low end because probably nobody else has really wanted to... yet. Don't get me wrong, I think this mic sounds really great as it is. I may just be too used to the low end I get on my transformerless mics.
Old 6th September 2018
  #12
I used the 1000 pf/630 volt Re-cap polystyrene film caps because Rel-Cap doesn't make 470 pf. Rel-Cap is one of the last polystyrene film cap manufacturers and they make fabulous stuff. Usually I use a 47 uf el cap for the gain shunt along with a small film bypass cap. The 1 uf output cap is too small, there is excess phase shift from that. A Wima 4.7 uf/63V mylar will do well there along with a small poly film bypass cap for air.

Don't expect a lot of depth from that design, it's not really there with that capsule and transformer design.
Old 6th September 2018
  #13
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Thank you again, Jim. I really appreciate your expertise and input. You seem to be very right about the limitations of this circuit, and I'm going to hunt down those caps and try it on one of my D87s to see if I like it better for my particular needs.
Old 7th September 2018
  #14
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So what low end are you really after? What are you recording with it? In most applications, excessive low end is just a big nuisance.
Old 7th September 2018
  #15
Most of my mics go down to lower than 20 hz by design. I like the depth and tightness of the low end when the phase shift is removed. I like to feel the low end on recordings, it adds energy. A HPF removes any unwanted low end. Those are reasons I don't own a U-87. I consider those mid range mics as they lack both lows and tops above 16k hz. They do make a fabulous voice-over mic.
Old 7th September 2018
  #16
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MYN's Avatar
Quote:
Originally Posted by Radardoug View Post
So what low end are you really after? What are you recording with it? In most applications, excessive low end is just a big nuisance.
True. In a lot of cases, low end is something you have to fight off with a stick in a mix, but what I'm looking for is not necessarily excessive low end, but just a touch bit more low end extension than I'm currently getting. I should probably clarify that, for the purposes of my original post, I'm talking about tuning a mic for a very specific need. I do voice over and only voice over. No music, so my needs differ slightly. Nearly all of my daily booking work is done on a 416 shotgun because it's either a radio/TV commercial or narration (like an explainer) that needs to cut through (or more appropriately, sit atop) a music bed with clarity and presence. The 416 is great for me for commercial/promo work because it has a certain sound, but it's not optimal for character work (or even some high energy car commercials) because it just gets a wee bit hairy when you're really shouting into it from three to six inches away.

So character voice work, or narrations such as PSA's that I know will not have a music bed, requires a different mic for my particular voice. Mostly, I voice in the "young adult" range where the main focus is in the mids and high mids, but there is a certain amount of subtlety I feel gets lost when you lose too much bottom end, and subtlety is often what sells the performance. It's why some voxers like a 47 style mic for dramatic narrations because of that low end heft, but the 47 sound doesn't really work for my particular voice. Last week, I had a 3 day lockout job for a "youthful" character voice for an educational/edutainment video game and I knew that nearly everything was going to be without underscore so I went with a TLM-107 that has a nice full range and bottom end because I felt that, even though it was a voice that centered around upper mids, without that fuller low end, the performance lacked the kind of one-on-one friendly energy/intimacy that the narrator character needed to have to guide kids through the journey. Without music, I tried to use the subtle low tones in my voice to fill out the soundscape and the client really loved it.

Again, I understand where you're coming from and apologies for the long-winded reply. My deliverables are all naked voice tracks, not mixes or stems so they have to have a certain sound on their own and this kind of work is generally done with no (or very little) EQ or processing. While the 87 is a fantastic all-arounder for most purposes, what I'm trying to do with this particular mic of mine is to create a more tailored sound for a specific purpose for my voice only. I don't have the usual radio-guy or big VO guy voice, more of a regular dude voice, so sometimes getting that little bit of extra oomph that I'm not currently getting even with proximity effect on this mic would make it a little more dialed in for what I'd personally like for some of the work I do.
Old 7th September 2018
  #17
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MYN's Avatar
Quote:
Originally Posted by Jim Williams View Post
Most of my mics go down to lower than 20 hz by design. I like the depth and tightness of the low end when the phase shift is removed. I like to feel the low end on recordings, it adds energy. A HPF removes any unwanted low end. Those are reasons I don't own a U-87. I consider those mid range mics as they lack both lows and tops above 16k hz. They do make a fabulous voice-over mic.
I think that's why I like your tranformerless design, Jim. The U87 is pretty awesome for VO, especially on voxers who have a lot of that natural VO guy resonance and texture that really pop out in the lows and low mids. For someone like me who leans more contralto/tenor but can go lower when needed, it may be that the 87's natural design restrictions can't really pull out those low growly tones from my voice as much as I'd like, and as much as tranformerless mics are able to. My intent on posting here was to learn something and I think so far I have. Thank you.
Old 7th September 2018
  #18
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Thank you for the detailed explanation, now that we know what you are trying to achieve we can home in with suggestions. Firstly, although your mike is modelled on the 87, it is not a Neumann. Further, there were several variants of the Neumann U87. Your mike is none of them.
You obviously know what you want in a mike, and have tried several, and you do have others that work better for you. So dont try and turn a pig into a cow. Just do your auditioning, and when you find the microphone that works best for you, buy it. This is your primary tool for your job. Dont try and find a cheap solution, find the right solution and pay for it.
The reason that Neumann U47s cost a fortune, is that the market has decided they really like them. I'm not saying you should use this mike, just that some mikes work better than others, some mikes work better for a lot of people than others.
Old 7th September 2018
  #19
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MYN's Avatar
Thanks Doug. Since Dany Bouchard based this circuit design (vintagemicrophonepcbkit.com) on the 87i (rev 16) schematic, it was why I was asking in reference to said schematic. Luckily, I already have a good arsenal of mics for work so at this point it's more of a "what if" kind of exploratory project since I enjoy modding and building mics and occasionally Dr Moreau-ing the random pig-cow to see what happens.
Old 7th September 2018
  #20
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ruffrecords's Avatar
C7 would be my bet. That and the transformer primary impedance determine the low end -3dB point. Try doubling it to 2.2uF or doblt again to 4.7uF for extra low end.

Cheers

Ian
Old 8th September 2018
  #21
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Quote:
Originally Posted by ruffrecords View Post
C7 would be my bet. That and the transformer primary impedance determine the low end -3dB point. Try doubling it to 2.2uF or doblt again to 4.7uF for extra low end.

Cheers

Ian
Thanks Ian! That goes with what Jim Williams is saying and now that you put it that way it makes sense. I bought a couple of your phantom power pcbs a couple months ago though I haven't built them quite yet, so I know you know your circuits.
Cheers!
Old 8th September 2018
  #22
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Quote:
Originally Posted by MYN View Post
Thanks Ian! That goes with what Jim Williams is saying and now that you put it that way it makes sense. I bought a couple of your phantom power pcbs a couple months ago though I haven't built them quite yet, so I know you know your circuits.
Cheers!
No problem. Good to hear from you. I am surprised you got no answer at groupDIY; it is a normally a very friendly and helpful place. I do not normally read the microphones section so I missed your question.

Cheers

Ian
Old 8th September 2018
  #23
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Originally Posted by ruffrecords View Post
No problem. Good to hear from you. I am surprised you got no answer at groupDIY; it is a normally a very friendly and helpful place. I do not normally read the microphones section so I missed your question.

Cheers

Ian
No worries, Ian. Glad you were able to respond here. It just seems like the Neumann Vintage U87 Clone Build Thread for Dany's D87 doesn't bristle with the kind of activity it once did. It is really only the discussion of the lack of global inventory of good 2N3819 fets that has recently sparked it back to life.
Old 9th September 2018
  #24
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Originally Posted by MYN View Post
No worries, Ian. Glad you were able to respond here. It just seems like the Neumann Vintage U87 Clone Build Thread for Dany's D87 doesn't bristle with the kind of activity it once did. It is really only the discussion of the lack of global inventory of good 2N3819 fets that has recently sparked it back to life.
I checked out that thread - it has been going for a long time - over 2000 posts. I sometimes get posts to my old poor man's EQP1A thread I started several years ago. Let me know how you get on with the mods to the mic.

Cheers

Ian
Old 9th September 2018
  #25
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This actually makes sense. I’ve been playing with the cheap Chinese knockoffs to learn for a couple months now. I just read up on a lot of this last week researching ribbon mics and preamp selection and the 10x rule. I’ve read a lot of material about the history of recording and the telephone companies influence. Seems there are several conditions that could be contributing to the lack of low end extension. Component selection in the circuit, impedance mismatch, proximity affect, and te transformers themselves. If it were me, and correct me if I’m wrong, I’d start with matched impedance if it’s off, then circuit components, play with proximity affect all along the way and end with the transformer. That’s what the systematic person in me wants to do.

Brian
Old 10th September 2018
  #26
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Quote:
Originally Posted by DrAudiospecific View Post

These vintage microphones (u87, ELA-M251, c12) are not in the design parameters of modern transformer-less mic pre-amps and interfaces. Most are totally out of the range of that ill conceived 10X rule too. The main reason was the phantom blocking capacitors being undersized because its the assumption that mics are 1K ohm impedance, so a 22 uf caps are used instead of the 68-100 uf caps that would be in.
.
Thee is nothing wrong with the 10X rule.

Phantom blocking capacitors are not sized based on the assumption that the mic impedance is 1K; it is based on the assumption the mic impedance is significantly less than 1K Most mic pres today are 1K5 or more nominal input impedance.

As ,long as the mic pre input impedance is significantly greater than the mic source impedance then it is the mic pre input impedance that primarily determines the low end 3dB point So with a 1K5 mic input impedance (which is low by today's standards), a 250ohm source and 22uF input caps, the -3dB point is 8Hz.

Cheers

Ian
Old 10th September 2018
  #27
Quote:
Originally Posted by ruffrecords View Post
So with a 1K5 mic input impedance (which is low by today's standards), a 250ohm source and 22uF input caps, the -3dB point is 8Hz.
Cheers
Ian
And the low end phase shift kicks in at 80 hz. Roll off at 2 hz and it remains below 20 hz = not an issue. 100 uf caps will solve that.
Old 10th September 2018
  #28
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Where does your 80Hz come from?

Why not 800Hz or 8K, if we're pushing it already?

Any magical universal cutoff, you want to share?

Jakob E.
Old 10th September 2018
  #29
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Quote:
Originally Posted by Jim Williams View Post
And the low end phase shift kicks in at 80 hz. Roll off at 2 hz and it remains below 20 hz = not an issue. 100 uf caps will solve that.
Absolutely right but the OP was interested in low end response of his mic. The point is the mic pre is not a factor.

Low end phase response is yet another good reason for used a transformer input mic pre. Transformer inductance actually increases as frequency drops thus maintaining better phase response than a capacitor.

Cheers

Ian
Old 10th September 2018
  #30
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Quote:
Originally Posted by Jim Williams View Post
And the low end phase shift kicks in at 80 hz. Roll off at 2 hz and it remains below 20 hz = not an issue. 100 uf caps will solve that.
10 times 8Hz. Phase actually starts to change a decade above the -3dB point.

Cheers

Ian
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