M49 Oliver Archut alt version

[HerbertR]

Hi, does anyone know how to modify the OA M49 Circuit using instead of 5840W Tube as standard the 6S6B Tube? The 5840 are sounding super but noise is little bit higher than from other Mics I own. I tested different "40h burnt in" 5840 Tubes like Raytheon, Philips, Thompson.... the difference between their Noisefloor is huge. Not really happy with that. Also the Tube-Microphonic is very high, very sensitive against touching. So I want to try the 6S6B Tubes. I think the regulated Filament Voltage should work without any adjustment, current is higher and needs to be checked for sure. HV Anode 120V can get easily adjustet via the Ra Resistor. What about Gridresistor and delf Cathode? Any suggestions what to modify?

 

[mhelin]

You don't need to change anything, I think someone tested already the 2.2k cathode bias OK. The grid resistor (100M) is on the safe side, too.

 

[mhelin]

You might want to try the 6205 (might be less noisy than 5840) and connect it's supressor grid to plate, too, to make a super triode. If you want to experiment try fixed bias with two series 1n4148 diodes from cathode to ground (instead of the resistor and cap) and a 1G grid resistor, and maybe a little bit lower heater voltage (less electrons so less noise and lower grid current which allows for greater grid resistor and better THD at low end)...

 

[HerbertR]

I ve tested 6S6B Tubes in the OA M69 Circuit. Noisefloor is a little bit lower but the Sound is not as good as with the 5840. I dont like them. Not as warm as with 5840 Tubes, less silk, Outputlevel is also a little bit lower with "standard" OA Resistors like from the schematic.

Lowering the Heatervoltage (0,15mA current) from my 6,5V DC Filament Voltage to 6,0V via a additional 3,3Ohm Dropingresistor in the PSU after the Voltagregulator caused an smooth audible increasement of the HF Response, more Silk, more air coool, very cool! Also LF Noiselevel is better now.
I ve ordered low noise Raytheon Mil Grade 5840 Tubes from Royer Labs. They test every Tube. Very excited about them to test, import from US to EU will be really expensive. Currently the Thompsom 5840Tubes I ve tested are less noisiest

 

[Recording Engineer]

A 5840W in 49 circuit without local feedback has been great-sounding and quiet. A 6947 in a 49b circuit has been great-sounding and quiet. A 5718 in a 50b circuit has been great-sounding and quiet, but truly does need an hour of warm-up it seems. Had high-hope for the 6533 in that one, but nope! Anyone have any thoughts on 5718 vs 5703?

 

[Purplenoise]

A 5840W in 49 circuit without local feedback has been great-sounding and quiet. A 6947 in a 49b circuit has been great-sounding and quiet. A 5718 in a 50b circuit has been great-sounding and quiet, but truly does need an hour of warm-up it seems. Had high-hope for the 6533 in that one, but nope! Anyone have any thoughts on 5718 vs 5703?

Haven’t compared to 5703 but I have used 5718 in my m49 and 251 style mics. I find the sound smoother than 5840 and phaedrus ac701. For my personal taste the 5840 sounds a little “glassy”. I find the 5718 smoother in high end and high mids but not lacking in detail.

 

[Recording Engineer]

Haven’t compared to 5703 but I have used 5718 in my m49 and 251 style mics. I find the sound smoother than 5840 and phaedrus ac701. For my personal taste the 5840 sounds a little “glassy”. I find the 5718 smoother in high end and high mids but not lacking in detail.

I know exactly what you mean. In the mics I mentioned, for lack of better words, I find the 5840 mic naturally-glassy, the 6947 mic naturally-dry, and the 5718 mic silky-smooth.

 

[Parabola]

I have now tried 49c with 6S6B and 5840. I think the 5840 with K47 capsule sounds incredible and much better than the 6S6B. @HerbertR, please let us know about the Raytheon low noise 5840. If the noise is lower this would be very interesting. I am also now curious about the 5718. With the 5718, are you all using M7 or K47?

 

[rock soderstrom]

If the 5654/6AK5w/E95F would fit in the M49 body, that would be my choice. The 5654 is the better 5840.

 

[kingkorg]

Lowering the Heatervoltage (0,15mA current) from my 6,5V DC Filament Voltage to 6,0V via a additional 3,3Ohm Dropingresistor in the PSU after the Voltagregulator caused an smooth audible increasement of the HF Response, more Silk, more air coool, very cool!

How interesting. I'm not a tube guy, what is the mechanism behind this? How does this happen to high end?

 

[SparkleBear]

I’ve used many 5703 in these circuits and find them more pleasing to my ears versus the 5840. Also a lot less pricy!

 

[Parabola]

If the 5654/6AK5w/E95F would fit in the M49 body, that would be my choice. The 5654 is the better 5840.

Interesting. Could you elaborate on this? Depending on the body, this tube could fit. But I'm curious why you think it is "the better 5840". Are you able to speak to any sound similarities/differences? Thanks!

 

[rock soderstrom]

Interesting. Could you elaborate on this?

Ok, here's my humble opinion.

I compared some 5840 with 5654/6AK5W/E95F directly in identical mic preamp and mic circuits.

My experience are as follows:

5840 and the 5654 are technically almost identical and can be directly interchanged without circuit modification. (is also mentioned in some datasheets).

The socket of the 5654 is big advantage over the 5840, especially for microphones! Anyone who has ever changed directly soldered tubes (during selecting for best tube) knows the difference, especially with PCB mounting. It is not only easier and faster but also much better for the sensitive High Z areas.

Look at the solder pads after the fifth tube!

There are also sockets for the 5840 but they are not of the same quality as the better ceramic 7pin sockets. The socket also makes the 5840 lose a lot of the size advantage over the 5654.

In direct comparison, the 5840 was on average more microphonic than the 5654. That was my impression with the tubes I had available. Whether this is true for all tubes I can't say....

The same applies to the noise floor, also here the 5654 types had slight advantages. I had two 5840 which were first good and then after a few weeks became increasingly noiser.

Due to the limited number of test tubes this result is not scientific, whether this can be generalized I do not know.

Ultimately, I found purely subjective that the 5654 sound better, I like the high-frequency response better. This was true for all manufacturers, the tendency was always the same and much more consistent.

For me the 5654 family is the best overall package and due to the small design ideal for LDC microphones. Very consistent good performance, they have never disappointed me so far. They are also still very available and really cheap for the performance.

 

[TLRT]

Ok, here's my humble opinion.

I compared some 5840 with 5654/6AK5W/E95F directly in identical mic preamp and mic circuits.

My experience are as follows:

5840 and the 5654 are technically almost identical and can be directly interchanged without circuit modification. (is also mentioned in some datasheets).

The socket of the 5654 is big advantage over the 5840, especially for microphones! Anyone who has ever changed directly soldered tubes (during selecting for best tube) knows the difference, especially with PCB mounting. It is not only easier and faster but also much better for the sensitive High Z areas.

Look at the solder pads after the fifth tube!

There are also sockets for the 5840 but they are not of the same quality as the better ceramic 7pin sockets. The socket also makes the 5840 lose a lot of the size advantage over the 5654.

In direct comparison, the 5840 was on average more microphonic than the 5654. That was my impression with the tubes I had available. Whether this is true for all tubes I can't say....

The same applies to the noise floor, also here the 5654 types had slight advantages. I had two 5840 which were first good and then after a few weeks became increasingly noiser.

Due to the limited number of test tubes this result is not scientific, whether this can be generalized I do not know.

Ultimately, I found purely subjective that the 5654 sound better, I like the high-frequency response better. This was true for all manufacturers, the tendency was always the same and much more consistent.

For me the 5654 family is the best overall package and due to the small design ideal for LDC microphones. Very consistent good performance, they have never disappointed me so far. They are also still very available and really cheap for the performance.

Better test the tubes in separate tester where you can use alligator clips for connecting submini tube wires(I use this method for testing too)

 

[rock soderstrom]

Better test the tubes in separate tester where you can use alligator clips for connecting submini tube wires(I use this method for testing too)

Nice test rig, good idea with the crocodile socket!

That makes sense if you want to test many tubes but most will rather test in the microphone which they are building. There are, as described, tube sockets a real advantage.

 

[Spencerleehorton]

the second design of the PSU i have done is noisey and im going to have to revisit, noticable hum from the original design.
doesnt help that i have tried to cram everything into a small case!!!
May build a better turret board but i think its poximity of transformer, might try and change other transformer for toroidal and see if it improves, otherwise its going to have to be a bigger case!!!!

 

[Spencerleehorton]

I have opted for a complete rebuild on the PSU and im reverting back to the passive M49b design as it works and is quiet, nothing else seems to play ball!!!
If anyone knows of a reasonably simple PSU design which is quiet please fire away

 

[Khron]

Capacitance multipliers?

 

[rock soderstrom]

If anyone knows of a reasonably simple PSU design which is quiet please fire away

Maybe this fits your needs.

.' DIY project: A handy power supply PCB for small tube amps like preamps, buffers or microphones.

 

[Spencerleehorton]

I’ve just made a turret version of the passive psu and have all the components, it’s a tried and tested design that’s works, no one else I have spoken to has used the gyraf g7 design.
I have got two toroidals a 18v and a 30v, should be able to get close to the 20vac and 120vac with 18vac into the 30vac which should put out about 135v as it’s the same ratio as the 9v and 15v as per the gyraf g7 psu.
Just will then need to tweak the trimmers or alter the node resistors.