D-EF47 Tribute To Oliver Archut U47 Build Thread.

[Purplenoise]

This is true. Some tube datasheets include information for what drop in transconductance can be expected. For example, the 5840 datasheet says with 5.7V heaters, you can expect a 10% drop in transconductance.

The interesting thing is that low transconductance can also be a sign of a dead tube. For example, EF800 datasheet says if initial transconductance value drops to 5.4mA/V, that's a dead tube (EoL).

I wonder if with lower heater voltages / operating proportionally at a lower transconductance 1. really increases tube life as some believe; and 2. if a tube that was considered EoL on standard voltages would be usable at lower heater voltage.

Assuming an EF800 and the drop being proportional (and it isn't always), then a 20% drop would be 6mA/V, which is still within a good range. If one of the tubes I receive isn't great, I'll try and measure the transconductance at lower heater voltage and see what comes up.

I believe Oliver came up with the 5.05v setting mostly to bring the impedance closer to a vf14...or closer to what a 6.5:1 transformer wants to operate optimally. Some say that ef800 tubes work better with a 12:1 ratio transformer. It would be interesting to see if for example at 5.05v you get more low end than 6.3v. If you do the experiment I would be very curious about your findings.

 

[guitar4444]

Hi Group,
can anyone please tell me? I've previously built 2 of the  the IOAudio MK 47 with the dual 6028 tubes from the kits wuth Chungers bodies if I remember rightly. Back when the bodies were a complete Chinese mic and cases etc.
I'm finding tyhem to be noisier than I would like. I want to replace the boards for the D-EF47 and use as many parts as possible and same bodies.
So I'm wondering
Will the boards fit in the same bodies? (the ioaudio47 boards fitted perfectly)
Can I use the same transformer or do I need new trannies?
Any other differences that would make it difficult to change?

thanks for any help.

cheers Greg

 

[Hank Dussen]

I have a bit of hum that's gone when I lift pin 1 from the output XLR.
I tried lifting the ground at different places but only at pin 1 of the output XLR seems to completely eliminate the hum.
My XLR cable have no connection between pin 1 and sleeve.
When I use an XLR cable that HAS a connection between pin 1 and shield at the input side this also eliminates the hum.
Whats' going on? This seems to be a groundloop problem.
Is it a problem if I keep pin 1 disconnected? Or if I connect it to the chassis instead?
Should I ground my cables at the input side?

 

[JMPGuitars]

I believe Oliver came up with the 5.05v setting mostly to bring the impedance closer to a vf14...or closer to what a 6.5:1 transformer wants to operate optimally. Some say that ef800 tubes work better with a 12:1 ratio transformer. It would be interesting to see if for example at 5.05v you get more low end than 6.3v. If you do the experiment I would be very curious about your findings.

I definitely plan to test it, but it's probably gonna be a couple week or so before my tubes arrive. They were shipped by boat (probably powered by a mouse on a wheel) from Germany.

 

[Purplenoise]

I definitely plan to test it, but it's probably gonna be a couple week or so before my tubes arrive. They were shipped by boat (probably powered by a mouse on a wheel) from Germany.

It’s been two months since my order of a haufe transformer is been sitting at the post office in Germany...the slowest shipping of all European countries

 

[Delta Sigma]

I have a bit of hum that's gone when I lift pin 1 from the output XLR.
I tried lifting the ground at different places but only at pin 1 of the output XLR seems to completely eliminate the hum.
My XLR cable have no connection between pin 1 and sleeve.
When I use an XLR cable that HAS a connection between pin 1 and shield at the input side this also eliminates the hum.
Whats' going on? This seems to be a groundloop problem.
Is it a problem if I keep pin 1 disconnected? Or if I connect it to the chassis instead?
Should I ground my cables at the input side?

From your power supply PCB, how many paths to the chassis are there? Did you connect the 0V terminal at the power transformer side to the chassis? Did you connect the 0V terminal on the microphone side to the chassis? Is your pin 1 connected to the power supply chassis or to the PCB?

My grounding preference for Dany's boards:
[list type=decimal]
[*]IEC (wall A/C) ground connected to chassis where the wall A/C enters the chassis
[*]the 0V bus on the transformer side of the PCB not connected to the chassis
[*]the 0V pin on the 7 pin connector (inside the PS) connected to both the 0V terminal on the PCB (mic cable side) as well as to chassis ground using the 7 pin mic connector mounting screw. I put a toggle switch on this ground conenction so I can open a loop if I get one.
[*]0V inside the mic connected to the mic body
[*]mic body bonded to 7 conductor cable shield
[*]7 conductor cable shield connected to PS chassis at the same 7 pin connector mounting screw[/list]

Even if the 0V toggle switch is open, the 0V buss is bonded to the PS chassis via cable shield.

 

[Delta Sigma]

Hi Group,
can anyone please tell me? I've previously built 2 of the  the IOAudio MK 47 with the dual 6028 tubes from the kits wuth Chungers bodies if I remember rightly. Back when the bodies were a complete Chinese mic and cases etc.
I'm finding tyhem to be noisier than I would like. I want to replace the boards for the D-EF47 and use as many parts as possible and same bodies.
So I'm wondering
Will the boards fit in the same bodies? (the ioaudio47 boards fitted perfectly)
Can I use the same transformer or do I need new trannies?
Any other differences that would make it difficult to change?

thanks for any help.

cheers Greg

Should be the same audio transformer if you're using a BV.08. I haven't built the MK47 so I'm not too familiar with it. My guess is your biggest cost would be the power supply. Did the MK47 use a U47 style power supply (105V, no separate heater)? You may need a new power supply B+ transformer, heater transformer, choke, PCB (included with mic PCB) and components.

 

[Hank Dussen]

From your power supply PCB, how many paths to the chassis are there? Did you connect the 0V terminal at the power transformer side to the chassis? Did you connect the 0V terminal on the microphone side to the chassis? Is your pin 1 connected to the power supply chassis or to the PCB?

My grounding preference for Dany's boards:
[list type=decimal]
[*]IEC (wall A/C) ground connected to chassis where the wall A/C enters the chassis
[*]the 0V bus on the transformer side of the PCB not connected to the chassis
[*]the 0V pin on the 7 pin connector (inside the PS) connected to both the 0V terminal on the PCB (mic cable side) as well as to chassis ground using the 7 pin mic connector mounting screw. I put a toggle switch on this ground conenction so I can open a loop if I get one.
[*]0V inside the mic connected to the mic body
[*]mic body bonded to 7 conductor cable shield
[*]7 conductor cable shield connected to PS chassis at the same 7 pin connector mounting screw[/list]

Even if the 0V toggle switch is open, the 0V buss is bonded to the PS chassis via cable shield.

Thanks. I'll check your suggestions and let you know the outcome.

 

[JMPGuitars]

It’s been two months since my order of a haufe transformer is been sitting at the post office in Germany...the slowest shipping of all European countries

Crap. I'm not that patient. I think I'll get another tube to hold me over waiting for the ones from Germany. My order has said pre-shipment since 1/20.

 

[Purplenoise]

Crap. I'm not that patient. I think I'll get another tube to hold me over waiting for the ones from Germany. My order has said pre-shipment since 1/20.

My previous orders from Germany took about a month...I hope my haufe is not lost or something haha...ughhh

 

[JMPGuitars]

My previous orders from Germany took about a month...I hope my haufe is not lost or something haha...ughhh

I ordered some EF80s from California while I was expecting the EF800s from Germany to take forerver...they're both getting delivered today.  :

EDIT: They both arrived. CA got here 45 minutes before Germany. lol

 

[JMPGuitars]

I think I have a gremlin.

Before connected the mic, my voltages were set perfectly at the PSU using dummy loads.

I also made sure there were no shorts on the cable I made...and after connecting it, I verified no shorts again, and also good continuity from B+, H+, pattern in the PSU to their respective spots in the mic, with no issues.

But, my B+ won't go above 63V now with the mic connected. H+ is currently set to 5.09V.

Thanks,
Josh

 

[Delta Sigma]

I think I have a gremlin.

Before connected the mic, my voltages were set perfectly at the PSU using dummy loads.

I also made sure there were no shorts on the cable I made...and after connecting it, I verified no shorts again, and also good continuity from B+, H+, pattern in the PSU to their respective spots in the mic, with no issues.

But, my B+ won't go above 63V now with the mic connected. H+ is currently set to 5.09V.

Thanks,
Josh

My first guess is a wrong component. This should be fairly easy to troubleshoot by continuity, voltage and component value checks. Gives you an opportunity to learn the circuit.

Keep in mind that you cannot measure B+ in a Hi-Z section (Capsule).

 

[JMPGuitars]

My first guess is a wrong component. This should be fairly easy to troubleshoot by continuity, voltage and component value checks. Gives you an opportunity to learn the circuit.

Keep in mind that you cannot measure B+ in a Hi-Z section (Capsule).

All components were tested and verified before installing. Reading a schematic is no problem for me.

B+ is being measured at both the PSU cable connections and the mic PCB where B+ is marked.

I will verify components again for the hell of it, since I've got nothing better to do with this.

 

[JMPGuitars]

I tested the voltages in my mic, and everything is dead on, except anything tied to the B+ line. I pulled the tube, and that had no effect on B+ either. I reverified the mic cable, and I think now I need to explore the PSU some more as I think that's the source of the issue.

UPDATE: There's definitely something in the PSU. In omni B+ is perfect, but in cardioid it drops 50%, and then pattern is only 50% of that (which I assume is expected).

Is that voltage drop expected in cardioid? I'm assuming it's not correct. My relay is the 48V version, and with the dummy load the PSU is only feeding 24V to the relay with the 12K resistor installed.

Thanks,
Josh

 

[Delta Sigma]

I built mine in one of Dany's bodies so no relay. I used a relay in my M49 but I powered it off H+.

How is the relay implemented? Is there a resistor and the relay hanging off the B+ or just the relay? Let's say the relay coil is roughly 8K. It would draw 6mA when energized at 48V. That means you'd need a 9.5k resistor (roughly so 9.1k or 10k) in series with the coil.

If it's just the relay, it's probably too much load. Not sure Dany's design, but I prefer to measure the current drawn by the relay, then put a matching resistive load from the supply (B+ in your case) to 0V when the relay is de-energized.

In other words, your pattern switch would switch between the relay. To use my above example of an 8k coil, your switch would switch the B+ from the relay to an 18k resistor to keep the B+ from changing.

Hopefully my math is right and all that made sense.

 

[guitar4444]

Can anyone please tell me if the IOAudio BV-08 as supplied in the IOAudio MK-47 kit will fit in the D-EF47 boards without any mods?
thanks for any help
cheers Greg

 

[FarisElek]

Can anyone please tell me if the IOAudio BV-08 as supplied in the IOAudio MK-47 kit will fit in the D-EF47 boards without any mods?
thanks for any help
cheers Greg

Any BV-08 will work.

 

[JMPGuitars]

Oops. Looks like I was the gremlin. The mic I built before this was the M49b, and I made the mistake of wiring the transformer the same way for the EF47. Once I realized my mistake, I fixed the transformer wiring, and this thing is FANTASTIC. It's by far the best build so far regarding SNR and output level. This mic gets plenty loud in the mid 20s on my input gain knob, whereas my M49 has to go into the high 30s or 40s to compete. The U87 around 50.

This mic is dead quiet, no noise issues or anything. I'm looking forward to trying different tubes in it. Right now I have an NOS EF80, but I will also try some EF800 tubes and see if one is really favorable compared to the other.

I won't be experimenting with the voltages until I can convince my tube tracer to test these tubes.

Thanks,
Josh

 

[Purplenoise]

Has anyone tried an ef184 in this build? Are they all microphonic or is it possible to find acceptable ones? Thanks.