Building Started...

[rlyach]

Well, my kit arrived and so far I have spent the last couple of days prepping the transformers. I am going for a clean look. I used scotch brite, then 000 steal wool, then a buffing wheel. I also painted the power transformer laminations gloss black. Now I can start the actual build. I can't wait to hear it.

 

[Grainger49]

Randy,

They look like a satin finish.  Really nice!

To keep them that way spray some clear on top.  The metal used for end bells will rust over time.  I'm not sure that the chokes have the same problem.

 

[rlyach]

Thanks for the heads up. Unfortunately this is closer to a mirror finish (very smooth) and when I tried to clear coat it the paint beaded up and looked awful. I have settled on a hard coat of wax. Since I live in AZ where the humidity is very low I think this should be enough.

 

[jimiclow]

Excellent work Randy!
What other upgraded parts are you putting in? I'd suggest upgrading the pot to at leat an Alps.  I find those STP's hard to rewire. Those screws that hold the OT/choke are little short.

 

[rlyach]

Yes, I notice the screws were a little short, but I have a large collection of screws in my garage. I did not want to finagle in power supply chokes so I settled in on Mills 12W matched resistors for the power supply and cathode bias. I will go with a single resistor sized for the 2A3 (270 ohm for the power supply and 1200 ohms for the cathode bias). That way I should get better matching between channels. I have also purchased a set of Jantzen Superior Z-Caps for the coupling and parafeed caps. I have read a lot of reviews and these were very highly rated. I did not want to spend the money for the Mundorf silver in oil caps. I had not considered the pot. I assume you are referring to the volume pot and not the hum balance pots. I will look to see if I can get one quickly. If not, I may just go with the kit. I will measure the pot I have to see how well matched the left and right channels will be. If you have a part number for the alps POT I would greatly appreciate it. I forgot to mention that I also purchased a matched set of JJ 2A3-40's

 

[jimiclow]

I get my pots from mouser. They're the 'pcb' mount type but I have a 3-island pcb that I cut and mount the pot on it. It's hard to find Alps with eyelets. Ebay has them but most are fake.
http://www.mouser.com/Search/m_ProductDetail.aspx?ALPS/RK27112A00AK/&qs=sGAEpiMZZMtC25l1F4XBUyOcKw5CnqLBt7NWCgOxelA=

For a neater build, I put heat-shrink wrap on the tip of each stripped wire.
I also upgraded all electrolytics in the PS to 105C panasonics. Areas around the power resistors can get very hot especially in mine because it is configured for 45 use. My coupling are vcaps, parafeed mundorf.

 

[rlyach]

Thanks for the part number. I will measure my pot when I get home. Perhaps this will be a future upgrade. It does not seem too difficult to change in the future.

 

[rlyach]

Just for fun I measured the audio taper that came with the kit and I bought a Radio Shack Alps audio taper and compared them. The results are attached. As you can see, the BH supplied POT gives more error at very low volumes. What really surprised me was the mismatch error between the channels. I guess I expected better matching. Which POT should I use?

 

[Grainger49]

Nope, the below post is not reading the graphs right.  I don't see where tracking, measuring the right channel versus the left channel is depicted.  What matters is the the two channels read similar or the same at a given setting on the pot.  The absolute resistance is irrelevant. 

RS seems to track much better at the bottom and goes whacky at 80%.  The point would be channel to channel tracking.  Unless you expect to play above the 3:00 position the better tracking is the RS pot.

 

[rlyach]

Grainger,

What do people think about the gold point mini-V stepped attenuator? It is very expensive but I imagine the tracking is much better.

 

[Grainger49]

Yes, higher priced products all are better tracking devices.  Do a search on Goldpoint mini-V and you will find a number of posts.  The best pot in my house is an Alps Black Beauty, no longer made. 

 

[Quattrofish]

I have just started on my build as well and am very interested in this discussion, as I know next to nothing about these components.

A friend has offered me a 24-step attenuator similar to this one left over from another project:
http://www.ebay.com/itm/24-Step-Volume-Control-500K-A-Dale-resistor-Stereo-/220950860306?_trksid=p3284.m263&_trkparms=algo%3DSIC%26its%3DI%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%26otn%3D21%26pmod%3D330684912924%26ps%3D54

Apparently these track perfectly left-to-right.  Is that true?  Would it be an upgrade from the volume control provided in the kit?  Would I be better off with an Alps unit? 

 

[Grainger49]

The stock volume control is not a bad control at all!  Especially with the Stereomour, which is for speakers.  Poor tracking at low volume settings is most noticeable with headphones.  Every record I play has a slightly different center image.  They all move +/- a foot from dead center.  So even with perfect tracking you would need a balance control to recenter the image for each recording if that is most important to you.

It seems to be most important to my brother.  When he listens he keeps asking me to adjust the balance so soloists are dead center.  I have come to tell him that he gets one centering per listening session.  Then he has to live with whatever balance the recording engineer recorded.  I think he was just trying to aggravate me by making me tweak the balance.  He is my younger brother.

 

[rlyach]

Well, the engineer in me finally won out. I could not live with the mismatch error. So, I ordered a Goldpoint mini-V and a Goldpoint selector switch. I hope to preserve the signal integrity as far as possible. Since I went to the trouble of getting matching resistors, caps, and tubes, to skimp on the attenuator seems wrong. This is my first build and I hope to get many years of listening out of this system. Thanks for all the help and advice.

 

[jimiclow]

Get the knobs too since they're different from the stock. The goldpt uses 6mm while the stock is 1/4.

 

[rlyach]

jimiclow,

Thanks for the info. I ordered a couple of knobs as well. I was not aware of the size difference. 

 

[Paul Joppa]

It is unclear to me what exactly is being plotted, so I can't comment on that.

However, I will say that a major virtue of switched attenuators is that they have excellent tracking. Normal pots are quite poor; linear ones claiming 10% and audio-taper usually being worse. Premium pots specifically intended for audio rarely spec better than 5%. But switched attenuators almost always use 1% resistors.

The disadvantage of switched attenuators is cost. Reliable switches are expensive, and switches with many positions are likewise expensive; the combination of both  is expensive indeed. Goldpoint products seem costly relative to potentiometers, but among available switched attenuators their products are remarkably affordable.

In our experience, even cheap switch contacts have no sonic problems - even the crappiest switch sounds good as long as it continues to work at all. This does not appear to be the case for the sliding contacts of potentiometers, though there is little available data beyond anecdotal evidence of the form "brand A sounds better than brand B."

None of the above addresses the effects of the resistive element. There, you get into subjective assessments that don't correlate well with things that are measured and/or quoted in specifications. A search of the web will provide a variety of opinions ...  :^)

 

[rlyach]

Paul,

Thanks for weighing in. The graph shows channel to channel matching over the entire resistance range of the kit POT and an RS Alps POT. I set the pot and measured the resistance of each channel and then moved on to the next measurement point. The % error is the difference between the channels as calculated against the average of the channels. The db error is calculated assuming a 2V signal and looking at the Vout error of the pot. At very low values of resistance (high volume) the error is small in the db scale. At low volume levels a large % mismatch will lead to a large db difference between the left and right channels. I hope I explained the graph adequately.

 

[Doc B]

None of the above addresses the effects of the resistive element. There, you get into subjective assessments that don't correlate well with things that are measured and/or quoted in specifications. A search of the web will provide a variety of opinions ...  :^)

Yes. The Goldpoint populated with Dale resistors is fairly widely regarded to sound better than the miniV with surface mount resistors. I imagine the resistance value tolerances are similar. And I concur based upon our recent adventures designing the BeeQuiet attenuator, the resistor type seems to have a lot more influence upon the sound than the switch contact material. Of course then there is the added twist of which form of attenuator is chosen, series, ladder, shunt, etc. Like anything else in audio you can analyze this stuff into the ground and still never have a clue about what sounds good until you actually start cutting, trying, and listening. And of course like anything else on the internet there is an excess of opinion on the subject and a startling percentage of those opinions posted are from insane people. Which I see as all the more reason to just buy some parts and try stuff myself.

 

[Paul Joppa]

Hey Randy-

Perhaps it's the residual of Valentine's dinner  :^)  (yes, homemade wine was involved...), but this is still not clear to me.

Assuming R1 is the series part of the pot resistance, and R2 is the shunt to ground, then if I understand you correctly:

"% error" = 2*(R2A-R2B)/(R2A+R2B)

However, the absolute resistance is not the same as the attenuation of the pot.

I still don't know what exactly is the "Vout error" that goes into the dB calculation.

Vout/Vin=R2/(R1+R2)

and there is no consideration of R1 in the above "% error" expression. I would suggest that:

dB error = 20*log10(R2A/(R1A+R2A)) - 20*log10(R2B/(R1B+R2B))

but I can't tell whether that is what you used.

I know this is a picky and technical question, but I sense that you are a technically inclined person, so I am pursuing it - let me know if I am getting overbearing; it's something I am unfortunately prone to do!

best,
-Paul J.