Foil is already 1.8um. I have tried thinner, 1.2um, but it is too weak, it breaks from nothing.
I have mic SUT 1:37 and preamp input SUT 1:2.5/5/10.
1:10 audibly impacts frequency response, makes sound tinny.
Whatever you do you here you cannot fool the laws of physics. Ribbon is moved by energy of acoustic waves. You cannot get more energy from the same waves using SUT. SUT just increases wave's (that are already in electrical form) amplitude. You cannot increase SUT ratio infinitely. Intrinsic resistances/impedances of input stage, SUT itself, and a cable, will react back to ribbon as mechanical resistance to its mechanical oscillations, more energy will be reflected from ribbon back to air, not transferred to electricity, and all this will make sound tinny and dull.
Though you can increase picked up energy by setting wider baffles around the ribbon, this will increase signal, but also will effectively reduce HF threshold. That is why many ribbon mics are not the brightest ones.
0.5mV is it what LOMC gives?
Perhaps not the same type of noise measurement you are referring to, but for reference purpose, the GT Vipre has an equivalent input noise (EIN) of -129dBu (600 Ohm source, A-weighted), according to this article.
The Vipre has a lot of gain.
The EIn, equivalent input noise, at -129 dB is related to this gain. (max 73 dB)
It has + 30dBm as Vout.
In the case of MM7 the sn is related at less gain so the sn, not the EIN, will reach.less or more, the value I think.
The EIN is the value of residual signal in output divided for the gain, filtered B.
Bye
Walter
The EIn, equivalent input noise, at -129 dB is related to this gain. (max 73 dB)
It has + 30dBm as Vout.
In the case of MM7 the sn is related at less gain so the sn, not the EIN, will reach.less or more, the value I think.
The EIN is the value of residual signal in output divided for the gain, filtered B.
Bye
Walter
That doesn't make sense. A 600 ohm source by itself produces -125dBu noise, or -126dBu A-weighted...
That's acheivable if your source feeding the first tube is >500mVrms and <300 ohms, say. You can usually assume somewhere between 0.5uV and 1uV EIN for the first tube (unweighted). Really careful selection might get you down to 0.3uV. If you're lucky.
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Could anybody explain me the topology from this?GT Vipre said:
Disregard please.
I found the schematic. It is mu-follower with NFB. So is it really that quiet or it is some marketing trick? I see Merlin doubts.
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Got strange issue. During measuring V at U2/U1 plate, I heard loud buzz, then pop, then volume dropped many times. Preamp still works quite good with headphones as a load (50R), but plugged into mixer line input (Z 10K) and sound card (Z 3k3) it lacks like 40dB of gain. Noise is also very quiet.
Visually all parts are OK. No flash, no smoke, no excessive heat. Anode V are OK. I switched tubes from socket to socket, all same.
Can tubes be spoiled by the loud signal? Like cathode oxide layer has been evaporated?
Visually all parts are OK. No flash, no smoke, no excessive heat. Anode V are OK. I switched tubes from socket to socket, all same.
Can tubes be spoiled by the loud signal? Like cathode oxide layer has been evaporated?
It seems that the Zou is very high.
Check the circuit.
Less 40dB means that you lost a signal of 100 times!!!
The quite at 50 ohm means that the signal was killed!!!
One questiog
The calculation you sent of total gain if optimistic.
I can't understand again why you don't use a 1:40 trafo (32dB of gain) instead 1:5 (13 dB).
In this way you can arrange an active stage less noisy that receive a clear signal from input trafo.
Walter
Check the circuit.
Less 40dB means that you lost a signal of 100 times!!!
The quite at 50 ohm means that the signal was killed!!!
One questiog
The calculation you sent of total gain if optimistic.
I can't understand again why you don't use a 1:40 trafo (32dB of gain) instead 1:5 (13 dB).
In this way you can arrange an active stage less noisy that receive a clear signal from input trafo.
Walter
The puzzling is that it is quieter but still quite loud in headphones (50Ohm).
But in higher Z line input of sound card (3k3 Ohm) it is very quiet.
I think I have to check all passives, caps and Rs first. Did not have time yet.
I know it is optimistic. But the preamp worked. Only flicker noise was the issue.
SUT has 2 primaries and 2 secondaries. I've made it switchable to following ratios: 1:2.5, 1:5, 1:10.
In 1:10 sound (frequency range) was already impacted - low LF and HF.
You are talking about 1:40!? Not realistic.
As I wrote already, you cannot transform energy of sound waves, gathered by a ribbon, too much. Intrinsic resistances and impedances of cables, SUTs, and tube, will eventually dump the ribbon making it sound tinny.
I don't think so.
A MC cartridge with 2 ohm impedance and 0,09 mV ( as Ortofon MC30 p.e.) is quite the same and with 1:40 it sounds great.
As mentioned with 6C45 the input capacitance is very high so the freq. answer will be limited.
With a 1:40 and a first stage with a secondary close by a 33kohm you will have reflected on primary about 20ohm enough for your mic.
With a EF184 triode connected ( or similar) you will have 35 dB of gain + 32 dB of trafo = 67 dB
But you need a CF as after the first tube to lower the output impedance around 180 ohn as 6H30 so the connection with a low Zin will be easier
Walter
A MC cartridge with 2 ohm impedance and 0,09 mV ( as Ortofon MC30 p.e.) is quite the same and with 1:40 it sounds great.
As mentioned with 6C45 the input capacitance is very high so the freq. answer will be limited.
With a 1:40 and a first stage with a secondary close by a 33kohm you will have reflected on primary about 20ohm enough for your mic.
With a EF184 triode connected ( or similar) you will have 35 dB of gain + 32 dB of trafo = 67 dB
But you need a CF as after the first tube to lower the output impedance around 180 ohn as 6H30 so the connection with a low Zin will be easier
Walter
I can confirm this with an experiment I did. Get some variable voltage power supplies and set up a simple tube gain stage where you can adjust B+ and bias by turning knobs on the power supplies.
Next a put a clean 1KHz signal into the stage and connect the output to my distortion meter. I twiddle the power supply knobs until i see a minimum value on the distortion meter. The minimum always occurs just before the tube explodes. OK, I don't allow that to happen but the top end of the envelope is the place to be.
BTW a typical THD distortion meter is nearly useless for measuring the THD of a good modern amplifier because the new amps are so good the meter will always read "0.000 THD". But for tests like the above where you measure amplifier components what are run with no NFB the meter is very useful for measuring parts.
Got strange issue. During measuring V at U2/U1 plate, I heard loud buzz, then pop, then volume dropped many times. Preamp still works quite good with headphones as a load (50R), but plugged into mixer line input (Z 10K) and sound card (Z 3k3) it lacks like 40dB of gain. Noise is also very quiet.
Visually all parts are OK. No flash, no smoke, no excessive heat. Anode V are OK. I switched tubes from socket to socket, all same.
Can tubes be spoiled by the loud signal? Like cathode oxide layer has been evaporated?
I would suspect a passive component before a tube. Transformers can develop a shorted turn, caps can develop leakage paths and resisters can open circuit.
It is more likely that a tiny spec of polyester film inside a capacitor melted than the oxide layer on a tube.
Also check your SOLDER joints. Just this morning I was embarrassed to have someone find a cold solder joint in something I built. We both tested this thing for hours looking at the signal on a scope. It would work for hours perfectly then all of the sudden the signal drops to near zero. I visually checked and re-tested and it starts working again. I check the connects one at a time with an ohm meter, they are all good. The problem was that solder joint to a gold plated output connector. Visually using a 10x magnifier the joint was perfect but the pin had not been heated enough.
quite the same with what? With the ribbon or with the ribbon+micSUT 1:37 ?
It was not limited. I've tested. HF rolloff was -2.19dB at 20kHz
I do not know impedances of my SUTs, but as I said, audibly even 1:10 did not sound good (with 12AX7 input tube, mu-follower).
Per Lundahl told me the same when I asked him about another SUT with 1:20 ratio. He knows impedances of his traffos, and advised me this LL1935.
I can measure FR at 1:10 again with 6S45P-E when I'll fix the preamp.
Adding to my previous reply, I also do not think that you can compare a phono cartridge with a mic ribbon because cartridge stylus is driven by a groove that walls are much more stiffer than air is. I doubt that MC can be dumped by a load on SUT secondary, even if you short it. Groove will make stylus to oscillate overcoming Lorentz force that is reflected back from SUT secondary load. Mass of cartridge head will easily prevent its possible co-oscillations with stylus. So coils will anyway move relative to magnets.
Air is not that stiff, and not that massive. So it can be reflected much easier when Lorentz force will resist ribbon movements.
That is why SUT secondary should be minimally loaded and there is a limit to SUT ratio because it is impossible to remove completely the intrinsic resistance and impedance on the secondary side .
Hi,
Surely not just attributable to Miller capacitance on its own?
Is such an early roll-off acceptable for a mic?
Why not use a cascode as the first stage? That would at least not suffer too much from Miller effect and, most importantly lift the input signal above flicker noise levels (hopefully).
Ciao,
Surely not just attributable to Miller capacitance on its own?
Is such an early roll-off acceptable for a mic?
Why not use a cascode as the first stage? That would at least not suffer too much from Miller effect and, most importantly lift the input signal above flicker noise levels (hopefully).
Ciao,
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