Oh Sh#7! Eddie Current Studio B

Additional information to add context to post #175

Acoustic measurement setup using a calibrated recording 94 dBSPL = -16 dBFS
ACO Pacific 7046 mic capsule on Josephson C617 mic body
Mic distance to Studio B power supply transformer is 50 cm
Mic distance to LG refrigerator (out of view) is 4 meters
LG refrigerator, HVAC and all other sources of ambient noise OFF for Studio B power supply acoustic noise measurement


MixPre 3 ii is totally silent to avoid contaminating the ambient
MixPre 3 ii records 32 bit float and has a residual noise floor of -10 dB SPL with mic pre gain set to 26 and 160R dummy input.

Red trace is MixPre 3 ii preamp residual noise with 160R dummy input and gain set A=26
Green trace is room ambient when all ambient noise sources have been silenced, extraordinarily quiet.
Visitors to our house find the quiet eerie until some ambient sound occurs such as HVAC turning on.

Studio B power supply hum at 50 cm with AC mains 120 Vac: 42 dBC SPL


LG refrigerator running extra quiet mode at 4 meters: 45 dBC SPL


Comparison of the two previous measurements:


One of our requirements for refrigerator was low ambient noise. This particular LG is much lower than any other we researched.

When the refrigerator is running in extra quiet mode, Studio B power supply hum (at 120 Vac) is completely masked and rendered inaudible at the location of the mic capsule shown in the setup picture above.

One way to quiet the minimal mechanical hum is to use a variac and lower the mains voltage to below 115 Vac.

 

thank you all for the information, I will check if the transformers need to be tightened and check the wall voltage to see what it is.

 

My preferred input tube is a NOS 5 star GE5670 with square getter and black plates. I found the WE396a far too warm and compressed and the Bendix 2C51 to be a bit too laidback and relaxed for my taste. The 5670 is cleaner and more linear than both and I think synergizes best with my chain. I don’t hear any magic the others have that the GE is missing either.

 

When I saw the 1st post the other day mentioning the Bendix, I swapped from the WE to a Bendix 2C51 (for the 1st time since putting the WE in). I'll use this for a few months and see how we get on. So far, it is pleasing and clear. (My faulty memory of) the difference is much smaller than changing the 300Bs.

To be clear, I have zero desire to roll tubes. I want to listen, and it is surely a pleasure with the Studio B.

 

Are you near an industrial park or something? I've never seen voltages swing that high on our grid.

Perhaps your next DIY project should be to build yourself a nice AC voltage regulator. I've seen it done with autoformers, or digitally.

 

Old neighborhood, but nothing industrial particularly close. 130 is rare, but 125 is very common.

 

I have recently replaced my 5670 with a 396a and upgraded the 5ar4. It greatly improved depth. tonally the bass and mids are richer/wetter (which I prefer) more space around the whole sound scape. using the genelex 300b at present will experiment with different 300b when I have the cash. I bought the tubes from Vintage Tube Services in Michigan. I have bought tubes from Andy for the last 25 years. An honest source that knows his stuff. I am not associated, friends with or associated with him in any way have just always been pleased with his tubes and prices. Only slight problem he is slow to ship them.

 

What 5AR4 did you upgrade to? I've been very happy with my setup with Gold Lion 300Bs and also Gold Lion new production 5AR4, but still always tempted to upgrade the rectifier. WE396A are great for that richer, warmer sound, particularly the square getter version.

 

the 5AR4 is a NOS sylvania (gz34 on the box, the 396a is a tungsol 2c51 I was surprised with increase space, especially going from flat(did not hear this until I put new tubes in) to have depth. I am not a tube master type, I found and trust Andy to steer me in the right direction, so far its been good. When I have some money save will try different 300b's, probally the EM Labs 300b solid plate for a different sound compare to genelex 300b.
best

 

I am getting a him from one ear of focal elex when my studio b is turned off? when I plug my fostex rp50"s in I do not get the hum, any thoughts on what this is and why its happining?

 

Output transformers may pick up stray magnetic fields. See this post for an example.

Focal Elex are approximately 10 dB SPL more sensitive than the Fostex T50rp when both impedance and dB/mW sensitivities are included in the calculations. The hum is probably low level in one and below masking threshold in the other. The side upon which it is heard there is possibly a transformer or other magnetic source nearby as demonstrated in the post linked above.

 

Thanks, I will experiment with this and see what I find

 

presto it was my bifrost 2 moved and hum is gone, thank you

 

Studio B is both a good and a bad amp. Good in that engagement factor is incredibly high. Listening to Cannonball Adderley Sack 'O Woe bass solo imparts the incredible richness from the wood resonance in the upright bass, as an example. Studio B is bad in that such immersion diminishes curiosity to spend time evaluating other amps.

 

Which version?

 

The Definitive Cannonball Adderley track 6.

 

Speaking of double bass, this is worthy: https://www.ecmrecords.com/shop/1619621465/overpass-marc-johnson

 

I have a preorder thanks to your previous recommendation on one of the other threads.

 

Cannonball CD on order, I should spend more time with classics.

 

I missed this the first time I read it... I also have a Sylvania 5AR4/GZ34. If it is gray plates with either 4 or 7 notches in the plates, then it's really a relabeled Mullard (should also say GT. BRITAIN after the 5AR4/GZ34 label). Apparently mullards were relabeled as all sorts of brands and the notches are the tell tale

-------edit-------