[Listen2this1]

Quote:

Originally Posted by joneeboi /img/forum/go_quote.gif I'm all for biasing up to 150mA, but I just don't have any clue how many mVs I need to hit that mark. I'm running ~24.5Vs so I can easily hit that 150mA mark, I just don't know how carefully I should tread. There's got to be something I can consult wrt to this matter. The MAX website says 264mV for MOSFETs will give me 120mA. Does this transfer over for BJTs? I checked the MAX site, Steinchen's dB site and the M^3 site but I couldn't find anything.

Joneeboi, I learned this calculation the hard way. If you are using a 2.2ohm resistor for RB10/11 you will use the multiplier of 2.2 for your calculations. ie: if you are reading 200mV on a Dmm you would divide this by 2.2 and get 90.9mA. You will be making these readings from TA2-L/R to TB-L/R, Not to ground.

Hope this helps

 

[IcantHearU]

Quote:

The MAX website says 264mV for MOSFETs will give me 120mA. Does this transfer over for BJTs? I checked the MAX site, Steinchen's dB site and the M^3 site but I couldn't find anything.

Joneeboi,

DB Bias
Measurement Points:TB1L or TB2L tu TA2L, TB1R to TB2R with TA2R
Adjustment Device:RB12L, RB12R
Acceptable Values:66mV - 110mV (30ma - 50ma)
http://www.diyforums.org/MAX/MAXsetup.php

That's from the MAX site - the setup and biasing page
Although not as high as you're going, I'm sure the math still holds true - (mAx2.2=mV)

 

[pinkfloyd4ever]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif My first foray into Black Gates on a Millett MAX: [size=xx-small](click for a larger pic)[/size] Panasonic FM's all around, Wimas, etc. 1" or less parts all around 1000uf 25V BG NX's in CA2 680uf 35V BG NX's in CA7 BJT's - 2SC2238/2SA968's

YUMMMYY

Quote:

Originally Posted by tomb /img/forum/go_quote.gif The relay is sounding pretty harsh in the left channel, but I've measured both turn-on and turn-off and the offset is within previously seen values - it just sounds bad. Maybe the caps need to break-in some more. If it continues like that, I may replace the smaller electrolytic with a 10uf 25V tantalum - something Amb recommended over on Headwize in the E12 thread - and see if that helps. I may have a not-so-good relay.

would it make sense or even be possible to use 2 10uf tantalums in parallel? Seems like that might be a little faster than 1 20uf? Maybe; I'm just guessing, I don't actually know What i'm talkin about

Quote:

Originally Posted by tomb /img/forum/go_quote.gif 3. 3rd config - high cost, audiophile special: Black Gate NX's at CA2 and CA7, hefty caps at CA4 and CA5 2SC2238/2SA968 BJT's This seems to be the Audiophile special. To my ears, it's as flat and detailed as a solid state amp - nothing exagerrated, but nothing lost. I think the BJT's add to this effect a lot, since they have always been listed as the ultimate neutral and extended response BJT's. The only downside that I can see to this combo so far is the slight fuzziness in the Black Gates. That may decrease with further running - as pabbi has indicated. Or, it might be corrected immediately with a pair of those PIO caps. I will try them by next weekend and let you know.

sounds like that is in fact the one for me. Damn tho, I hope everywhere doesnt sell outta BG's before I get a chance to buy em...def next on the list to buy when I get the money to spare. Should be by late Dec (after I get x-mas money), do I have anything to worry about?

Quote:

Originally Posted by ruZZ.il /img/forum/go_quote.gif So anyone have a good recommendation on rca jacks from pcx, not on the looney expensive side?

Ha, aren't those mutually exclusive?

 

[pinkfloyd4ever]

Quote:

Originally Posted by jerrygp /img/forum/go_quote.gif Thank you vixr...sometimes the solutions are simple. The reduction in the diameter of the lead is not an issue. I am going to experiment with different Kiwame resistor values to see what effect they have, but volume levels are decent now with my HD580's and my old untrained ears may not notice any decrease in upper frequency harshness.

Ya I've been wondering about this too, because at $1 each they're not cheap. I'd like to be able to use the full range of the pot but I have no idea what values would work best with my cans (ya I know somewhere b/t 10-150 ohms). For now (meaning at least for a yearish) I just have an MS-1 & some KSC-75s, which are both 32 ohms, correct? But when/if i get new cans I might wanna change em...crap. Goodbye money, hello ton of $1 resistors that I'll end up using exactly 2 of...

 

[amphead]

Well Pabbi, that was not where the problem lies. QB2R & QB3R are my next possible culprits.

 

[amphead]

Pabbi, So now you have 2sc3421 in the right DB. I have replaced QB2R & QB3R. I had to create a jumper to ground for QB2R, because the ground plane does not make contact on one of its pins that is supposed to be grounded. Checked for tube bias voltage in the right channel. You now have 23.4V. So I biased the right tube to 13.7V. Checked the right DB bias and it was 25mv. Brought it slowly up to 30mv to match the left DBs. Plugged in my phones. YEEAAOOOW! Its a slammin, killing machine! Another MAX Lives!

Articulate vocals, crushing bass and all around great sound. With Cerafine(CA7), Silmic II(CA2), Sprague .47uF bypass caps all around.

 

[adfinni]

Quote:

Originally Posted by pabbi1 /img/forum/go_quote.gif Tom, the Black Gate bloom really is a wonderous thing - you wonder what all the fuss is about, they turn dull, then downright icky, then wham - where did that come from? It is a truly mysterious experience, but something you just have to experience to join the believers. In fact, I didn't go BG mainly because this is an office rig, and I just travel too many weeks to live through all the bloom cycles I would be faced with. So, I thought the Cerrafines would suit my application better. This was not an economic decision for me.

Agreed here, they sounded ok when i first ut my amp on and biased it, actually better than my old millett hybrid. Left them running in for a week and they sounded a bit better, plus they sounded quite good at the meet. Plugged everything back in last night and my amp does just sound 'icky'. perfect wording there pabbi.

This is with about 120-130 hours on them, so il keep them running in, and will eventually try some vit-q's in ca8 + ca9 position combinations.

 

[tomb]

Quote:

Originally Posted by joneeboi /img/forum/go_quote.gif I'm all for biasing up to 150mA, but I just don't have any clue how many mVs I need to hit that mark. I'm running ~24.5Vs so I can easily hit that 150mA mark, I just don't know how carefully I should tread. There's got to be something I can consult wrt to this matter. The MAX website says 264mV for MOSFETs will give me 120mA. Does this transfer over for BJTs? I checked the MAX site, Steinchen's dB site and the M^3 site but I couldn't find anything. edit: Also, I'm running with the top of the Hammond enclosure removed, so the greenhouse effect will be avoided.

Others have given you the formula. What's happening is that the current across the transistors (the bias, IOW) is determined by the voltage across the 2.2 ohm output power resistors. Since I = V/R, then I(ma) = V(mV)/2.2. Or:
mV measured = Desired Current Bias * 2.2.

You may be taking a mile after getting an inch, though. Yes, you are correct from Amb's table that perhaps 150ma should be possible with 24V and 1.5" heat sinks (actually 155ma, interpolating correctly from your 24.5V). However, keep in mind that those are for TO-220 MOSFETs. MOSFETs have that positive temperature coefficent, making them more stable and much more tolerant of heat + high bias. The TO-220, with its full metal back and tab will also have better heat transfer characteristics than the TO-225 of the MJE's.

So, to be conservative and safe, 100ma should be easy to obtain. Higher than that could be risky, IMHO. So, tread carefully.

 

[fordgtlover]

Tomb

those BGs look absolutely stunning.

The BJTs are mounted on the Mosfet side. Are they a different package to the usual ones? (demonstrating an absolute lack of knowledge of BJTs)

 

[Televator]

Quote:

Originally Posted by amphead /img/forum/go_quote.gif YEEAAOOOW! Its a slammin, killing machine! Another MAX Lives!

good work amphead, good fortune pabbi! another MAX lives!!(it was a close call, but some first aid revived it without too much problems

)

 

[tomb]

Quote:

Originally Posted by Listen2this1 /img/forum/go_quote.gif Tomb In position CA4/5 they are Muse 470uf 35v, In position CA2 it is a Muse 1000uf 16v. The output trannies are the ones direct linked from the BOM. I was wanting to get some of the Toshiba's but then you had that shipping problem, so I went with the ones from the link. I am currently using Rca 12fk6 tubes. Bias is staying really stable.

You should be getting fantastic bass, based on your parts selection. I'm somewhat at a loss to suggest things that could help - you should already be there. However, here are the guesses in no particular order:

1. You might try some upsized power caps instead of the ES's in the CA4 and CA5 positions. Those positions aren't necessarily supposed to affect the bass, but perhaps the fact that the ES's are bi-polar is messing up the application at that point. Those caps are supposed to ensure decoupling between the V+ and Ground, which maintains the voltage differential. Bipolar caps will let current flow in either direction, perhaps defeating the entire purpose of caps at those positions.

Use some regular power caps - FM, FC, UPW, or UHE's, 1000uf minimum. I like those 1800uf 35V Panasonic FM's here. They're not very expensive and are 1" in height - very potent.

2. You might try the Nichicon FG 1000uf 35V at the CA7 positions. It's an audio grade cap that's only 1" high and is inexpensively available at Handmade Electronics. I'm not sold on this, though, because I've heard nothing but good reports from Grado owners all the way back to the old revMH Millett Hybrid - using a 470uf for the output cap. The difference between a 470uf and a 1000uf combined with Grados may only be 5Hz within the audible frequencies, so I doubt that this would have a noticeable affect on increasing bass, but there it is. Plus, bipolars (ES's) in this position would be superior, whereas the FG would not.

EDIT: If you don't have height restrictions, there are many possibilities - 1000uf 50V KZ's would be an excellent choice. There's also the 1000uf 50V Elna Silmic RFS's at DigiKey. For that matter, you can try a simple power cap such as the Panasonic FM, as long as it's bypassed with the WIMA. The FM would be well under 1", too. Lots of possibilities ...

3. Have you verified your source? Perhaps it has a bass rolloff that you've never really tested until you built the MAX.

Quote:

Should the mje253's run warmer than the mje243's?

Not in principle, but anything located on the center two sinks will run hotter. That's the nature of the tradeoffs in designing the board - the middle two sinks don't have enough air space between them and will run hotter. This is as it should be, given the design.
Quote:

Also I am using the Grado 325i's, I know they are slightly on the bright side, this is why I am wanting a little more bottom end.

Again, you should not be experiencing a lack of bass, even with the lower impedance Grados. There is nothing particularly deficient with the MJE's. They may not slam as with the 2SC3422's, but they are not going to be lacking in bass.

 

[tomb]

Quote:

Originally Posted by fordgtlover /img/forum/go_quote.gif Tomb those BGs look absolutely stunning. The BJTs are mounted on the Mosfet side. Are they a different package to the usual ones? (demonstrating an absolute lack of knowledge about BJTs)

Thanks.

Actually, that's demonstrating a very good knowledge about BJT's.

It just so happens that there are a few pairs with reversed pinouts. The 2SC2238/2SA968's are one of those pairs.

 

[tomb]

Quote:

Originally Posted by pinkfloyd4ever /img/forum/go_quote.gif Ya I've been wondering about this too, because at $1 each they're not cheap. I'd like to be able to use the full range of the pot but I have no idea what values would work best with my cans (ya I know somewhere b/t 10-150 ohms).

to be honest, I'm not sure "the full range of the pot" is a realistic expectation. I can't even get above 1/2 volume with Sennheisers on a portable PIMETA with a gain of ~4. The rest of that volume travel should be reserved for those instances where you might have weak sources such as an iPod, etc., IMHO - but maybe that's just me.
Quote:

For now (meaning at least for a yearish) I just have an MS-1 & some KSC-75s, which are both 32 ohms, correct?

Actually, the KSC75's are 60 ohms, but they are so efficient that the volume travel needed maybe less than the Grados (Allessandros).
Quote:

But when/if i get new cans I might wanna change em...crap. Goodbye money, hello ton of $1 resistors that I'll end up using exactly 2 of...

It will take 150ohms to get anywhere close to what you're describing. Remember that you can always run leads to the resistor pads and connect them to a DPDT switch. That will give you two choices of resistance.

Also, you want to be using a 12FK6 if you're not already. That tube has the lowest inherent gain (7).

 

[joneeboi]

Hello all,

I bring yet again power supply woes to the Wise in Millett. I was already going to get the www.mpja.com wallwart that tomb recommended and that others have already employed, except that when I plugged in a set of KSC75s with impedance adaptor (DMM showed ~130ohms per channel), a low frequency hum was very apparent. The volume knob doesn't affect it, so my guess is that it has to do with the 60Hz hum from the wallwart I have right now. You can hear the hum putting your ear next to the wallwart, and now I have the fun of having it being transmitted through the audio chain. Yeah!

Now my question is whether I should go with the mpja wallwart or go with a higher quality one in a separate and matching Hammond case? Is there a workaround for this hum? Is anyone else noticing a hum? It's almost inaudible with my SR60s, and it was okay with my KSC75 at its regular impedance. Will a higher quality toroid eliminate this hum? Hum hum hum hum hum hum hum. Stupid hum.

 

[tomb]

Quote:

Originally Posted by joneeboi /img/forum/go_quote.gif Hello all, I bring yet again power supply woes to the Wise in Millett. I was already going to get the www.mpja.com wallwart that tomb recommended and that others have already employed, except that when I plugged in a set of KSC75s with impedance adaptor (DMM showed ~130ohms per channel), a low frequency hum was very apparent. The volume knob doesn't affect it, so my guess is that it has to do with the 60Hz hum from the wallwart I have right now. You can hear the hum putting your ear next to the wallwart, and now I have the fun of having it being transmitted through the audio chain. Yeah! Now my question is whether I should go with the mpja wallwart or go with a higher quality one in a separate and matching Hammond case? Is there a workaround for this hum? Is anyone else noticing a hum? It's almost inaudible with my SR60s, and it was okay with my KSC75 at its regular impedance. Will a higher quality toroid eliminate this hum? Hum hum hum hum hum hum hum. Stupid hum.

You have a problem with your PS on the MAX board, and it is the source of the same trouble you've had all along. There is no reason that you can't get 27VDC and you will not have any hum with a properly constructed PS section on the MAX board.

Give us some pics of the PS section only - that's the big sink, the rectifiers and the four caps - top, bottom, and side facing the LM317. There's something wrong.

EDIT: By design, every walwart used for the MAX will have hum, because the MAX uses only AC walwarts. It's the purpose of the onboard PS to remove all of that hum - the ripple, too - until it's completely inaudible and effectively the same as that using a STEPS-like power supply.