A Few Small Post-Build Issues

[williaty]

Issue 1:
A couple of the voltages are just barely out of spec. I've created a Google Docs Spreadsheet of the resistance and voltage checkout results to make it easier for you all to look at them. I've got three voltages that are just a little wonky. I'd be inclined to leave them alone, but I'm doing the Speedball in a day or two and want to make sure everything is right before I do it.

Issue 2:
The 6080 tube is HUGELY microphonic. I was hearing footsteps from around the house. I started tapping around the amp with my fingernail and an extremely ginger tap on the 6080 resulted in church bells ringing inside my head and my ears bleeding. Is this normal for the 6080 or is this an unusually microphonic example?

Issue 3:
I have WAAAAAY too much gain. With the 0-position of the pot being set straight down to 6-o'clock, I can't listen to anything above 9-o'clock. In fact, I'm usually listening at about 7 to 7:30. This puts me down on the portion of the pot that doesn't track well. I remember inputs/outputs can be padded to reduce signal level but I have no recollection of how to make smart choices of how to do this. Any suggestions?

Thanks guys!

 

[Doc B]

You did see in that manual that +- 15%  on the voltages is fine?

The 6080 can be microphonic. That combined with your description of a hair trigger volume control has me wondering what headphones you are using. It would seem they are particularly sensitive.

 

[Grainger49]

What source are you feeding the Crack with?  It might have more output than is needed in combination with Doc's suggestion of sensitive headsets above.

Bottlehead has to make the kit so that it will function with a wide range of inputs and headphone sensitivities.  There are things to do if you determine what is causing the problem.

 

[williaty]

Oh! I thought tolerance on voltages was +-10%. I'm cool then!

I'm using Sennheiser HD-600s and the source is a High Resolution Technologies MusicStreamer II+ (2010 model). The MSII+ swings 2.25V FS. Given that I'm feeding it directly from the source files with no volume control on the computer, it's probably getting up close to that on a fairly regular basis, especially with modern recordings that are over-compressed.

 

[Grainger49]

That is a quarter of a volt higher than the CD "standard."  You could put a passive volume control before the Crack if you don't want to modify the crack. 

Most of the Bottlehead volume controls are 100k ohms, not the FP III.  If you put a 220k ohm resistor in series with the wire from the input RCA jack and the volume control it will pad it down considerably.

 

[williaty]

Yeah, I figured I was going to need to pad either the input or the output. Is a single resistor the way to go, or should I make an L or T pad?

 

[Grainger49]

I think the L-pad adds only one resistor per channel.  That is simplest, I like simple.

 

[Viktor]

Are you sayint that the output voltage from the MS2 is too high for the amp? Because I've been running it for about a month without any mods....Should I lower the input voltage or something like that?

 

[Grainger49]

Viktor,

It depends on your system.  If you use the same source and get good volume control then there is no worry.  What Williaty has is a problem that he can only use a very small turn on his volume control.  To make small adjustments at low listening levels, or any listening level, the control should, ideally, be at full clockwise rotation with your lowest input and your highest listening level.  No one gets that ideal situation. 

What most of us have is a good listening level at 12:00 to 3:00.  That works well and for late night speaker listening, or say background listening with a headset, you can make very fine adjustments of the volume control and get what you want.

 

[Laudanum]

Williaty ... here a good link.  It's for a stepped attenuator but would just as well for a rotary pot.  Paul J was discussing this with me a while back ...  http://www.goldpt.com/mods.html

Viktor ... I use an AH Tjoeb 99 CDP as one of my sources.  That unit is spec'd at 3.5 volts output.  It would have to be a "Hot" cd or track to reach that level but I could never listen that loud, not even close, even with my least effieicent phones.  I havent had a single problem with the Tjoeb as a source.  Let you ears be your guide.  As Grainger49 states and as Doc B has mentioned in a related thread ... hot source? ... that's what the volume knob (gain control / attenuator)  is for.

 

[williaty]

Part of the issue is almost certainly that I don't like loud things. I set the music just loud enough to clearly hear the quietest passages and then don't raise it any higher. Loud noises/music just give me a headache. So it's entirely possible that I'm using less of the pot because I'm trying to listen 10dB quieter than most people.

 

[Grainger49]

Try the series resistors I suggested.  If you can find them at Radio Shack that is a good thing.  I suggest getting an assortment pack.  Once you have zeroed in on the needed resistance then you can buy some $5 resistors that are better sounding.

 

[williaty]

I've got a packet of resistors left over from the Sweet Whispers build 10 years ago. I'll see if any of them come up useful.

 

[williaty]

OK, built the Speedball and installed it tonight. Voltages check out ok, but I have two different issues now.

1) The sound is more dry and trebly. Is that something from the Speedball or just how the recordings I'm listening to are actually mixed?

2) With no input, I have a strange very, very quiet rushing noise in the right channel only. This wasn't there before the speedball. Any ideas what this is?


Overall, I'm really very impressed with this amp.

 

[2wo]

1) let it run in for a while. Seems everything new I try sounds dry and trebly at first. If not you can always go back

2) if the noise goes away with the input shorted, or a source connected. don't worry about it...John     

 

[williaty]

To clarify, the rushing noise, or maybe it's a hiss, I dunno, is present with an input connected or with them shorted, but it's at a low enough level you can only really hear it when there's no signal playing. With music playing, it just lends there sort of odd gummy weight to the right channel. That's an exaggeration, it's a subtle effect, but that's the only way I can think to describe it.

It's really weird to listen to right now. There's so many more sounds and details and whatnot that I can actually identify. All the lower sounds are just MUCH better controlled as well. Yet there's this sterile lifelessness, dryness, brittlenees, something, to it that just makes it sad to listen to. It's the same sort of sound you got out of a cheap solid state amp during the late 80s/early 90s when everyone was chasing the "lowest THD ever!" in consumer gear. It's a weird mix of considerably better performance and yet at the same time less good at being music.


I must have screwed something up.

 

[williaty]

OK, a couple of more hours and some frantic searching for different tubes...

Nearly smashed in the back of the junk drawer I managed to find a 12AU7 someone had once given me to make a necklace out of. Thankfully, I'd never gotten around to it!

So, first things first, the odd rushing sound was caused by the Electro-Harmonix 12AU7 included with the kit. I have no idea why it only manifested itself after the Speedball upgrade, but there it is.

Sound wise, well, it's a different mixed bag. Switching to a different tube definitely removed the sterility/dryness. Most of the boogie is back. On the other hand, things sound just a tiny touch... muddled or confused. Let me place that in context by saying it's still more clear and organized than any other headphone amp I've ever heard and is arguably more sorted out than pre-Speedball, it just loses a tiny something in comparison to the EH tube post-Speedball. On the other hand, it's fun to listen to it now so I'm not going to obsess over this.



Oh, the tube I dug out of the back of a drawer, all scratched up? Turns out it's an RCA Clear Top! Started googling for what "A Electron Tube" might be. Added words like side getter, etc. Finally saw a picture and realized that the "RC" had scraped off, leaving a big A next to the stacked "Electron Tube". Nice sounding tube.

 

[Grainger49]

I've got a packet of resistors left over from the Sweet Whispers build 10 years ago. I'll see if any of them come up useful.

I think those are too low a resistance to be useful padding your volume control unless they are the series resistors for matching the SW to your system.

Give the Speedball a break in and all sorts of music.  As for the rushing sound, you have lowered the noise floor to the point you probably hear the tube rush.  Swap tubes and you should find the rush in the left channel.  That is the tube.

 

[Laudanum]

This is kinda why I havent jumped on trying Speedball yet.  Im just really enjoying the Crack as is.  I havent had the itch to upgrade anything other than roll tubes.  Im not sure Im really in search of added detail or clarity as I dont want to move closer to what I may perceive as a more "sterile" or SS sound.  And the background is extremely quiet as is.  The temptation is there more for the ability to be able to roll a couple more tubes and I may end up loving what Speedball does even more, afterall it does seem that the vast majority hail it as improving Crack even further.  But Im finding myself enthralled with an Amperex 12AU7 ( GE and Triple mica 5814's are in the running as well) and a Tungsol 5998 right now.  Im sure I'll probably try it down the road, as it is easily reversible.

 

[Grainger49]

The Speedball is going to reveal more music than noise.  If you have a tube that has some noise when you turn it up you will hear it if you didn't before because it was buried in the noise floor.  There are benefits and problems with improving your system.  As the resolution increases some things are exposed for the nasty things that are there.  A bad tube, or a less involving tube is exposed as such.  Good, involving tubes are exposed as that as well.

So don't throw the baby out with the bath water.  The Speedball upgrade isolates the power supply noise from the audio path.  It should be cleaner but more detailed.  That isn't really SS sound but more revealing sound.