[Avro_Arrow]

I don't think the difference in tolerance is going to make any difference...it does not need to be an exact value.
The power bypass cap (the one right behind the power connector) is the same height as the power connector.
The 10,000uF power cap (the one between the power connector and power switch) that Judge Buff is using is
as tall as the tube so you will not be able to use the top plastic cover if you install this mod. 
Also installing the Bias caps is going to make the bottom plastic useless as well. You end up
with an amp that sits up on little legs.
You can set the Bias for 17 volts on the anode of the tube for each channel. After listening for a while it seems to
give the best sound even if it does not give the largest voltage swing. Anywhere between 15 and 17 volts at the 
anode seems to work well.
 
Here is a picture of mine...I have not installed the upgraded electrolytics yet, they will have to wait for my next
order. I have upgraded the MOSFET to IRF510, Changed the Bias adjust to 2K multi turn pots, replace the power
bypass cap with 1uF Film and installed the Bias caps (they are on the bottom of the board).
 

 
Quote:

The difference in those caps is the original is 5% tolerance and the new link you posted has a 10% tolerance.
 
On another note, my amp started making noise in the right channel. I thought it was a tube pin problem but it turned out to be a bias problem. I had 7 volts in the right channel and 8 volts in the left at the output cap. I readjusted to 12.04 volts which was the closest I could get. What a difference now. Not only is the noise all gone but the dynamics have opened up dramatically. The sound stage is way out there now and I can hear things I couldn't before. I guess the mods even make it better.
 
I'm gonna buy those 10% caps and get my order filled. I don't think a 5% tolerance will make a difference for the bypass cap.
 
Also A_A, you mention that the big PS filter cap just fits. Does it fit through the plastic cover where the original pops out of? Or does it just fit the board?

 

[Judge Buff]

 
Quote:

Also A_A, you mention that the big PS filter cap just fits. Does it fit through the plastic cover where the original pops out of? Or does it just fit the board?

The diameter of the PS reservoir cap on my board can't be "fatter" (diameter) than 22mm. The 10K Nichicon KZ just fits between the stock switch and the PS jack.
 

 

[Joe Presto]

I've been using this amp sporadically, but since hanging it on the wall next to my bed with blu-tac, it's getting far more use!
 
I used a guide on the Rock Grotto Audio Forum (link) to set the bias, however regardless of the bias, these is an ever present hiss/static; would replacing the bias trim pots help alleviate the problem, or could there be another cause?

 

[xtlee]

A_A, I used the Bias method you mentioned back in this thread. Adjusting the trim pots so the voltage at the output cap is half the supply voltage. What is this method compared to the 16-17v at the cathode method?

 

[Judge Buff]

Quote:

I've been using this amp sporadically, but since hanging it on the wall next to my bed with blu-tac, it's getting far more use!
 
I used a guide on the Rock Grotto Audio Forum (link) to set the bias, however regardless of the bias, these is an ever present hiss/static; would replacing the bias trim pots help alleviate the problem, or could there be another cause?

My guess is it's your power supply (adapter). The Bravo adapter is notorious for being noisy. A larger PS cap may quiet it some.

 

[Avro_Arrow]

Setting the Bias Point is really a compromise between what is best for the tube and what is best for the output stage.
The output stage is a voltage follower and the Bias point for this is usually set to 1/2 the supply voltage as measured
at the + side of the output cap. If you were building a Szekeres this is how it would be adjusted. The Bias point for the tube
is a little more tricky. Because the greater the difference in voltage between the cathode and anode the better the tube works,
you want to keep the anode as high as possible while still allowing enough room for the voltage to swing. Somewheres up around
3/4 of the B+ voltage is where the Anode voltage is set. The design notes I saw for this amp stated that the desired Bias
point was .65 to .7 of the supply voltage. This would give you between 15.6 and 16.8 volts at the Anode. If I remember
correctly, when I had my amp set for 1/2 supply at the output cap, I had about 15 volts on the Anode. Right now,
with my Anode up around 17 volts, I get 13.5 volts at the cap so it's not a big difference. I'd just go with whatever sounds
best to you somewhere in this range.
 
Maybe someone with a better understanding of tubes can give a better explanation of how to bias the tube...
 
Quote:

A_A, I used the Bias method you mentioned back in this thread. Adjusting the trim pots so the voltage at the output cap is half the supply voltage. What is this method compared to the 16-17v at the cathode method?

 

[Joe Presto]

Quote:

My guess is it's your power supply (adapter). The Bravo adapter is notorious for being noisy. A larger PS cap may quiet it some.

Thanks JB! I tried a different tube, can, 3.5mm adaptor and powerplug last night and that setup seemed to generate less hiss, I'll have to see which components made a difference, but I'll see if I can get a new power supply too. Either way, I think I'll be needing a soldering iron soon!

 

[pj_rage]

I got my bravo v2 two days ago, but got a chance to listen yesterday.  I'm very impressed with this little amp!  The output power is jaw dropping.  It drives the K702 and DT880/600s with absolute ease and PLENTY of power left over.  I really can't go above 10 o'clock on the volume knob with either of them (10 o'clock being pretty darn loud).  It sounds nice and clear with a good soundstage too.  I didn't expect it to be so powerful or to sound quite as good as it does.  I have a bagful of goodies on the way from mouser as well per AA's recommendations, so it's likely it will sound even better.  I also have a number of 12AU7 tubes here for my EF1 that I'll be able to play with, but even the stock tube doesn't sound bad.
 
One thing that irks me a little bit is that it seems that the channel balance isn't quite perfect.  It's very close, but seems to favor the left channel slightly.  I don't think it's due to a low volume setting, as I'm pretty well away from the lower points when noticing it, at about 9:00-9:30 on the knob.  It's most noticeable with the K702, and a little less noticeable with the DT880/600s.  Perhaps the parts I'm changing out will help, if not I think I'm going to try to look into this further and see what might be the cause.  It is slight, but I would like to correct it nonetheless as it's a little bit annoying to think/worry about for an otherwise good sounding amp.

 

[mcnoiserdc]

Quote:

I got my bravo v2 two days ago, but got a chance to listen yesterday.  I'm very impressed with this little amp!  The output power is jaw dropping.  It drives the K702 and DT880/600s with absolute ease and PLENTY of power left over.  I really can't go above 10 o'clock on the volume knob with either of them (10 o'clock being pretty darn loud).  It sounds nice and clear with a good soundstage too.  I didn't expect it to be so powerful or to sound quite as good as it does.  I have a bagful of goodies on the way from mouser as well per AA's recommendations, so it's likely it will sound even better.  I also have a number of 12AU7 tubes here for my EF1 that I'll be able to play with, but even the stock tube doesn't sound bad.
 
One thing that irks me a little bit is that it seems that the channel balance isn't quite perfect.  It's very close, but seems to favor the left channel slightly.  I don't think it's due to a low volume setting, as I'm pretty well away from the lower points when noticing it, at about 9:00-9:30 on the knob.  It's most noticeable with the K702, and a little less noticeable with the DT880/600s.  Perhaps the parts I'm changing out will help, if not I think I'm going to try to look into this further and see what might be the cause.  It is slight, but I would like to correct it nonetheless as it's a little bit annoying to think/worry about for an otherwise good sounding amp.

can you please do me a favor?
If so, How do you compare your mk III with the bravo v2 for HD600?
I'm asking because I may be upgrading and I'm affraid I won't get any advantage

 

[Avro_Arrow]

My channel balance is a little off too. My guess is the constant current source for the tube isn't balanced exactly. None of the parts I changed improved the channel balance.
I just set my balance one click off center on my sound card. The channel balance could be related to the tube as well, I guess, I have not tried any different tubes yet either.
 
The channel balance at very low volume is the fault of the volume pot and is common in this part.
 
Quote:

I got my bravo v2 two days ago, but got a chance to listen yesterday.  I'm very impressed with this little amp!  The output power is jaw dropping.  It drives the K702 and DT880/600s with absolute ease and PLENTY of power left over.  I really can't go above 10 o'clock on the volume knob with either of them (10 o'clock being pretty darn loud).  It sounds nice and clear with a good soundstage too.  I didn't expect it to be so powerful or to sound quite as good as it does.  I have a bagful of goodies on the way from mouser as well per AA's recommendations, so it's likely it will sound even better.  I also have a number of 12AU7 tubes here for my EF1 that I'll be able to play with, but even the stock tube doesn't sound bad.
 
One thing that irks me a little bit is that it seems that the channel balance isn't quite perfect.  It's very close, but seems to favor the left channel slightly.  I don't think it's due to a low volume setting, as I'm pretty well away from the lower points when noticing it, at about 9:00-9:30 on the knob.  It's most noticeable with the K702, and a little less noticeable with the DT880/600s.  Perhaps the parts I'm changing out will help, if not I think I'm going to try to look into this further and see what might be the cause.  It is slight, but I would like to correct it nonetheless as it's a little bit annoying to think/worry about for an otherwise good sounding amp.

 

[pj_rage]

I'll let you know if changing tubes helps the balance.  Do you have any other thoughts for parts to check/change to balance it better?  Which side does yours favor before changing balance settings on your computer?  If it's also left, maybe there is a problem with the design that we can fix.
 
I actually haven't tried this amp with the HD600s yet as I don't listen to those as much.  I'll try a little tonight between the two and report back.  I did try the bravo vs MKIII a little bit with the DT880/600s and there is definitely a difference in sound signature, the MKIII being warmer.  I think I preferred the MKIII, but (outside of the channel imbalance) in the end it may come down to personal preference.  "Better" or "upgrade" IMO is a tough unless there is a glaring problem that is there on one and not the other, which I didn't particularly notice, but I'll listen more closely and try specifically with the HD600 too.

 

[pj_rage]

Changing tubes seems to have cleared up the imbalance issue!  Sweet!  Must be poor QA or something with the cheap tubes.

 

[pj_rage]

Now that I've gotten rid of the imbalance, I'm enjoying this amp even more.  I've been using a GE Great Britain 12AU7 (mullard short plate) and it sounds great.   I can't believe what you get for ~$50-60 shipped.  This has to be one of the best bargains in headphone amplifiers.

 

[mcnoiserdc]

Quote:

Now that I've gotten rid of the imbalance, I'm enjoying this amp even more.  I've been using a GE Great Britain 12AU7 (mullard short plate) and it sounds great.   I can't believe what you get for ~$50-60 shipped.  This has to be one of the best bargains in headphone amplifiers.

hi!
Still waiting for the comparison with hd 600 between bravo tube and mk III

 

[pj_rage]

I did briefly listen to both with the HD600 (stock cable) and D4 DAC.  The MKIII I thought had a little more spacious and natural soundstage, had more bass and lower mids, and was a little warmer and maybe even more laid back overall.  The differences between the two were slight and not huge, and may be more impacted by tubes than anything else (the MKIII has stock power tubes and M8100 drivers, the bravo had a GE Great Britain (short tube mullard) 12AU7).  The bravo has way more power even with the MKIII at max gain, but the MKIII has absolutely no problem driving the HD600 way beyond what your ears (and probably the drivers) can take too.
 
Probably the most noticeable difference to spot was the bass, which had more quantity on the MKIII, but they really are pretty close sounding overall.  I don't know how good you are with listening critically or whatever, but at first listen, they do sound pretty similar (not a night/day in-your-face difference in my opinion).  I had to A/B a bit to really start to notice the differences.  Maybe I don't have golden ears, or maybe I suck at listening critically, or maybe they really are just that close?  I'm not sure.
 
Really, I thought both sounded very good.  I might imagine that some people would prefer the bravo and some would prefer the MKIII - that is, they both sound very good to my ears, but I'm not sure one or the other is "better", just different.  My preference was the MKIII, but not by a alot.  I think this says more about the bravo than the MKIII anyway.  If you already own the bravo, I think it's a tough decision whether or not to get the MKIII.  The MKIII definitely looks much better / cleaner / more professional, and is better put together, and IMO does sound a little better too.  But the bravo has insane power output, is kind of cool to look at as well, is very cheap, and sounds surprisingly good in my opinion.
 
I don't know if that helps, but there ya go

 
I kind of wanted to given another listening session before saying much because I didn't listen very long to make those conclusions.  I'll try to listen again this weekend and I'll let you know if any of my opinions change.