ribbon mics/mic pre impedance

[alphajerk]

so im getting a demo of the vipre from Aspen this weekend. he uses an RCA 44 to demo the input impedance load. it ultimately settles on 300ohms as "best" suited for great gain for the mic.

i have 2 ribbon mics. the Royer R121 and a B&O BM5. the Royer i can get plenty of gain out of with my Flamingo or API pres [the flamingo doesnt state the impedance in the manual, the API 3124 states it is 1500 Ohms]

but i put my B&O BM5 [44bx mod] on the pres and i cant seem to get nearly enough gain. even with the loudest instrument i use [the drums... or maybe amped guitar] i have to crank their gains full on to get enough gain.

so in the royer manual it states.... if the mic is rated at 300 Ohms [the R121 is 300 Ohms], the preamp should have an input-impedance of at least 1500 Ohms. if the preamp impedance is too low, the microphone will lose low end and body.

unfortunately i cant test my B&O BM5 for its output resistance because doing so will blow the ribbons. i dont know what it is. but im curious as to what impedance i should be looking for in a pre considering what the royer manual states for their mic goes agaist what i witnessed for the RCA 44 being demo'd by Aspen. hmmm, i dont know what the impedance is for the RCA 44 either.


does anyone know this answer?

[Tim Farrant]

There is a way to measure the output impedance but it requires some fiddling, bit of temporary soldering with a stereo pot in the mic line, a console or mic pre fitted with VU meter and a loudspeaker than you can point the mic at and play some tone through. It will give an indication only, but should be within 10% or so. Can you handle it ? if so, I will describe the process in next post (rather than it write now which will take ages and I am in desperate need of another beer....!).

Cheers
Tim
Buzz Audio

[alphajerk]

my B&O BM5 is around 200 ohms.

here is a response from stephen sank:
Royer's suggestion is peculiar to their particular coupling transformers. Ordinarily, for a transformer-coupled preamp input, the impedances should be pretty close to equal, hence the 300ohm input being best for the 250ohm(normally) 44 mic. Read the first two pages of the 1955 RCA catalog on my mic literature page for further good info on mic loading. The BM-5 is the most difficult mic I have yet experienced with regard to preamp selection. It is 200ohm output by the spec sheet, so should be mated with a 150-250ohm transformer input, or same or higher transformerless input. I'm not familiar with the preamps you're using(except that I have worked on API consoles, but not used them), so I can only say that so far, only one BM-5 client has told me what he's used satisfactorily with one, which is the Great River. He said it's just quiet enough, with the gain set high enough, to work well with an average level source, but he thinks not enough for chamber music. My feeling is that the mic would do best with a super high quality transformerless input preamp. I don't know who makes one, though. I say this because the BM-5 does not perform much lower level/higher noise going into my home-built "quicky" bench test preamp, compared to the much easier to preamp BM-3/4 mics. So, it seems to me that the mic's transformers are badly loaded down by the proper input transformer loading(i.e., where loading less with a higher imp. transformer would worsen freq resp), but is not loaded down, and sounds great, with a higher impedance transformerless input.

Stephen Sank


i have also contacted david hill regarding this and what my flamingos input impedance is... i got a reply through fletcher of @ 10k ohms [which seems REALLY high], i dont know if it is correct... i got an email from david hill wondering more about my situation and i replied [basically stating what is here on this thread] but have not heard back. i know my APIs are 1500ohm, i get better gain from them than the cranesong flamingo.

i wish i had a vipre here to easily switch the impedance and test it... but then i would have to buy 2 of them if it worked. i have another thing i am going to be testing regarding the impedance once i get my hands on a pre with switchable loads. i will post more afterwards.

the biggest issue seems to be with the loss of low end... but there is also the issue raised in the RCA manual differing from the Royer manual [albiet entirely different designs]... even though my primary use is for drum overheads... i would like to use the mic in situations of lower SPL [like and acoustic guitar for instance... which would require the low end to be "intact"]

[dynamo]

Im quite positive the B&O 50, mono, had a 50 and 200 ohms settings. Not 100% sure but maybe is the
same for the stereo one.
It would be worth for you to give it a shot and check this possibility. You'll be able at that point to fully
squeeze all voltage out of mike with any pre with a minimum of 600 ohms input.
The different impedance setting were kind of popular. RCA 's and also Neumann
offered that option. If you can't set it at 50 ohms i would greatly reccomend something as a Millennia
preamp ( about 3 K.ohms input ) that works great with ribbon and you have even the option of
gain settings up to 78 dB. You really want the load at least ten times the output of mike ( expecially ribbon)
Matching the impedance may have usually sonic benefits but affects also the ouput level and signal to noise ratio
and i guess also the frequency response.
So it really depends from the application. I have a pair of old Manley pre's and
input impedance is 200 ohms...matching a lot of tube mikes and also my Beyer 130's, 88's..
By the way the RCA 44 can be set for 50 or 250 ohms so you need to know how the mike was set for test...
I have mine at 50 going to an EAR pre which is 600 ohms..nice combo.
Is strange that anyway you have this huge difference in level comparing with your Royer in the API..are you sure B&O is
all ok?? you my want to recheck the otput transformer..jo

[alphajerk]

the dynaco50 or fentone model has an impedance of 50ohms as seen here:
http://www.thuntek.net/~bk11/bm3_dk(1).gif

the dynaco100 or BM5 is 200ohms as seen here:
http://www.thuntek.net/~bk11/bm6_dk(1).gif

the RCA manual stated above is here:
http://www.thuntek.net/~bk11/1955cat1.GIF page 1
http://www.thuntek.net/~bk11/1955cat2.GIF page 2
although both of these pages are difficult to read.


i have never heard 10x's the output impedance... i doubt the millenium would fare any better than the flamingo at 3kohms. the royer manual states 5x's but its output might be different than that of my B&O [or old RCA mics]

if i only had a GML pre to test this on... or a vipre.

[chap]

My Royer likes my Vipre set at 600 ohms. Ribbons are pretty picky bastards when it comes to pres.

[David R.]

I thought variable impediance would be all the rage in pre's. Aside from the Vipre, what else has it? I am looking to get the most from my 77dx and a couple of oddball ribbons laying around.

[Dave Martin]

Originally posted by David R.
I thought variable impediance would be all the rage in pre's. Aside from the Vipre, what else has it? I am looking to get the most from my 77dx and a couple of oddball ribbons laying around.

Well, the Great River NV has a switchable input ipedave, and so do 1073's (though you have to do it from the back).

I would guess that there are some other vintage preamps which can be switched (probably internally) where you could bring the switch to the front panel...

[chap]

for ribbons it's tough to beat the Vipre. Variable impedence and high output (76 db?)

[alphajerk]

never tried the vipre on my ribbons. i unfortunately had to put the vipre purchase on hold right now. i did try the chandler EMI pre at 300 ohms and it worked okay... i think i am having issues with my BM5 that no pre can fix, so as soon as i can afford... the BM5 goes in for repairs. i also tried the Sytek's with their transformerless inputs [i had also heard that "helps"...] but they do not have nearly enough gain to be of use, although they are suprizingly super clean even when turned ALL the way up.

im glad you brought back up this topic because i am finding that lower impedance is working far better than higher impedances in a lot of cases and on a lot of microphones. i think variable impedance should become a norm in preamp design now... im finding it indespensible now that i have one preamp with it... and played with the vipre which also has it. it just so much radically changes the sound on the way in... i feel like i need it on all my pre's.

[chap]

At my place, the best results with ribbons are usually achieved with the Vipre, the SLAM! and the TRAC2. They all have different characteristics but share the high dbs that help out the ribbons.
For percussion the Flamingo sounds great too.
cheers

[sordeli]

I have several mics, and the only ribbon mics that I have are a pair of beyerdynamic M160 and the best (or the sound I preffer)set that I found very pleasent is the isa 110 seting, is about a 200 ohm, and this mics has a 200 ohm impedance, I dont like hager settings in the 428 to this application, because it has a thinner colour, just my 2 cents
BTW the ISA 428 is a great unit for the value, and with he digital option works very good, end clocked to a UA 2192, sound AMAZING!thumbsup
any opinions??

[Petimar]

Try out the AEA TRP. A friend brought several B & O's and a 44bx and 77dx over two weeks ago to try on my TRP. He agreed they sounded better than anything he has tried (he has lots of pres).

Get on the Wes Dooley site and look at the TRP manual, there is an appendix called "Ribbon Mics and Mic Pre Amps".

http://www.wesdooley.com/pdf/TRPOwnersManual_1.1.pdf

[Dan]

I've used the 428 with Royers, and Coles 4038s. I've had better luck with higher impedances also. Most often the isa110 setting is the best. The low setting just sounds thin, and not so good.
The 428 is relatively quiet, and has a ton of gain, so it works ok.