[ACM investiupgradifications] All things MICROPHONE

[rodabod]

Oliver Archut's 47-inspired mod:

http://recforums.prosoundweb.com/index.php/m/0/26173/96/13216/#msg_num_14

Oliver is now selling these transformers:  http://www.compasspointstudios.com/bulldog/bulldog-tnc_upgrades.html

The circuit designs all look fairly standard, and seem to be typically cathode-biased. The transformers could be good on a budget though. From what I understand, the BV8-inspired model is made from off-the-shelf lams and is built to be machine-made to save cost.

 

[spica]

Has anyone tried ordering just the boards from Oliver?  I have sent a couple emails requesting two boards but haven't received a response.  Maybe they don't want to just sell the boards? 

Did it take a while to get a response when you ordered transformers as well?

Thanks.

 

[rodabod]

I haven't ordered any transformers yet. Still not sure if I should splash out for a "proper" BV8 or not. It depends on how well this BV8-inspired model specs.

You could make the circuits shown on the original boards though. It's not too tricky.

 

[0dbfs]

Has anyone tried ordering just the boards from Oliver?  I have sent a couple emails requesting two boards but haven't received a response.  Maybe they don't want to just sell the boards? 

Did it take a while to get a response when you ordered transformers as well?

Thanks.

I didn't get a response at first either but was persistent (hopefully not a pain!) and oliver and I ended up playing email and phone tag for a day or so until we connected up and completed the transaction. The t49 trafo's and bulldog boards were at my door within a couple days. I ordered all the parts last week which are at home now so i'm expecting to dive into modding the mic's this coming weekend. There is at least one trace-bridge on one of my boards that i'll have to fix but i'm looking forward to putting them together.

He mentioned that the lady who normally processes their orders is out so you may have to be a little persistent to get through.

I think his direct email is oliver@his-company...

Hope that helps.

Cheers,
j

 

[spica]

Thanks, gents. 

I made a G7 circuit for one of my mics a while ago but some of the connections are a little too close for comfort to the metal mic supports and it fits ackwardly in the body so I wanted to wait for something more legit. 

I ended up buying a pair of the Cinemag-CM2461NiCo BV8 transformers a while ago so will be using those with Dale's M7 capsule.  It should be a pretty quick project to assemble, so hopefully I'll be able to post some sound samples with that configuration in the near future. 

Cheers.

 

[spica]

Noob question regarding the heater wiring for the EF86 tube:

Are the heater pins (4 and 5) tied together and connected to the 6.3V supply or does one go to ground as it appears in the G7 schematic (are 4 and 5 connected internally?)?  Most of the other tube types I've tried to cross reference do not have a heater connection going to ground, but those are for other tube types. 

Thanks.

 

[clintrubber]

In general w.r.t. ACM-1200-mic:

don't those various circuit- & transformer-upgrades neglect the probably weakest
point ? (the capsule) Or is the used capsule actually considered to be not too bad, relatively speaking ?

Bye,

 Peter

 

[Rossi]

In my experience, the order of Far Eastern OEM Condenser Evils is:

1. Circuit (Most of them are bad designs to begin with, and usually they're built quite clumsily.)
2. Capsule (Some are better than others, but few are really good.)
3. Transformer (Some are weird designs such as the "ever popular" 1.87:1 type, others aren't as good as European or American iron, but imho, Chinese iron is manageable, *if you built a decent circuit around it that's designed for whatever transformer the mic's got*.

 

[mushy]

Meh... It doesn't seem great but doesn't seem awful.  What I will say is that trying to create a U47 or an M49 with this capsule would seem to be a bit of a fools errand.  I think they were modeling it more after a CK12.

My own progress report:  I've got one that I've modded up with a Dale M7, some of the circuit changes I found here and elsewhere (lots of trial and error), a JAN 5751, dropped the B+ voltage a bit, and Oliver's T47 transformer.  I really like the results so far, but I have yet to really put it to the test.  On my second one I'm going to follow the Bulldog mod to the letter (mostly) and compare both pre and post capsule change.

I've learned more about capsule design, tube bias, amplifier design, impedance, voltage dividers, etc in the last month or two than I ever thought possible. 

Thanks guys.

 

[rodabod]

Some people seem to like these capsules. Personally, I hate them.

The majority of the sound of the mic is in the capsule. A good example of this is the variety of Oktava models sharing the same capsule that all sound similar. I have dound that replacing the electronics of Chinese mics does not change the character massively, however, replacing the capsule alone does.

 

[Rossi]

Perhaps I should point out that I wasn't talking about the particualar models at hand, I didn't even take part in this groupbuy.

I recently fitted an SE M1C with a Dale M7 - it sure made it sound better, but basically it still sounded crap. It wasn't until I reworked the circuit completely that it sounded like the Dale M7 capsules I'd used before. So, yes *in a decent design*, such as the Oktavas, the sound is mostly in the capsule, but many of the Chinese OEM circuits are so bad, you won't get decent results even with a good capsule.

Among the Chinese capsules I've encountered, there were a few that sounded okay or even good with dedicated circuit (which usually entails filtering). I have a SE 2200A whose capsule actually sounds nice - but you really wouldn't have guessed, because the stock circuit was crap. I put in a new circuit with some filtering, and it really sounds pretty good now, even with the stock transformer.

That's not to say you can make any Chinese mic sound better by just putting in a better circuit. But you do need a better circuit in order to hear if the capsule is okay or total crap. Also, transistors, caps and resistors are cheap. See how far a few bucks can get you before you order new capsule or a new transformer.

 

[rodabod]

Perhaps I should point out that I wasn't talking about the particualar models at hand, I didn't even take part in this groupbuy.

Same here. I am only talking about the 32mm Shanghai model found in cheaper mics. The 34mm edge-terminated models tend to be good (still bright), and the 797 models can be great.

 

[Rossi]

Those Chinese capsules are quite confusing. The SE 2200A I have has a 32mm capsule, the SE M1C (I actually have two which I bought just for the body/grill) has a 34mm capsule. Weird. That particular SE 32mm sounds good with a proper circuit. I think I'm going to give the 34mm a try, too. It *looks* quite well made, but that doesn't say much, of course. Some of the no-name ultra cheapo mics have capsules with wrinkles in the diaphragm. It would be interesting to know how the various Far East capsules differ from one another. A lot of them look quite similar.

 

[clintrubber]

In my experience, the order of Far Eastern OEM Condenser Evils is:

1. Circuit (Most of them are bad designs to begin with, and usually they're built quite clumsily.)
2. Capsule (Some are better than others, but few are really good.)
3. Transformer (Some are weird designs such as the "ever popular" 1.87:1 type, others aren't as good as European or American iron, but imho, Chinese iron is manageable, *if you built a decent circuit around it that's designed for whatever transformer the mic's got*.

Interesting for the DIYer that the circuit (involving lowest BOM) is actually still in the equation. I mean, many circuits are [NL]geschoept[/NL]/Schoep'ed; how hard is this to get it right ? A topology shouldn't be too hard to clone, so it'd be layout & parts-quality then ?

 

[Rossi]

It's perfectly possible to screw up a Schoeps type circuit; in fact you can see done it in almost any Chinese mic using that circuit. Bad FET bias, polarization voltage all over the map etc. It's not a very engaging circuit for a LD mic anyway. It is a good SD mic circuit, though, if you just follow the original.

 

[spica]

Finished mine yesterday with Dale's M7, the T47 circuit, a EF86 tube (ElectroHarmonix) and a Cinemag Bv8 replacement transformers (which I had bought awhile ago so I decided to skip Oliver's).

A few initial observations are:

1.  It is pretty quiet.  I haven't done any kind of real measurements, but the noise floor is not at all bothersome with a quiet source.

2.  It is VERY dark.  I  EQ'ed in about 10 dB of high end (10k very broad Q)) to get it to where I thought I'd like it.  A bit too much low end as well.  Maybe this is a combination of the capsule being darker than the stock capsule?, the circuit being designed around a brighter capsule and compensating for it?  Perhaps the circuit doesn't like being connected to my Cinemag transformer? 

I'm not too sure where to start to flatten it out.  Maybe I'll try a G7 circuit.  Any suggestions? 

 

[rodabod]

Rp will be sitting in the ~25K region at that current/voltage which is a bit high for your output transformer.... but you did say you had too much bass.

I'm not sure about the ack of HF though. Those capsules are not that dark really. Do you have a spare capcule to try?

 

[Rossi]

2.  It is VERY dark.  I  EQ'ed in about 10 dB of high end (10k very broad Q)) to get it to where I thought I'd like it.  A bit too much low end as well.  Maybe this is a combination of the capsule being darker than the stock capsule?, the circuit being designed around a brighter capsule and compensating for it?  Perhaps the circuit doesn't like being connected to my Cinemag transformer? 

I'm not too sure where to start to flatten it out.  Maybe I'll try a G7 circuit.  Any suggestions? 

Dale's M7 is fairly balanced with a slight presence boost. I wouldn't call it dark or bass heavy. The stock capsule is likely to be brighter, but not in a pleasant way. You might want to try your capsule in a different mic, or maybe try the other side of it. Front and back usually sound a little different anyway.

Of course you could have made a mistake in the circuit. Most of the time, if something doesn't work it's a silly mistake. Make sure you have no unwanted connections on your pcb, check your wiring, measure your resistors etc.

 

[Gus]

What I often do if I am adjusting a microphone circuit or installing a different circuit is to not change the capsule in the microphone before testing the adjusted/new circuit.  Sometimes I even do that with transformers.  If you do things a step at a time and test take notes you can often figure out what does what in a microphone.

If you can try the old capsule with the circuit to se if it is a capsule related sound change.  Also make sure all your connections to the  grid and capsule have no leakage paths caused by solder flux, dirt, dust etc.  Make sure that area is very clean

Search here and at prosoundweb Klaus's forum about EH tubes in microphones.

 

[mushy]

Check your decimal places on those caps. Especially C5. I can't tell you how many times Mouser has sent me the wrong thing.