Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › A Super-Simple 6DJ8 Headphone Amp
New Posts  All Forums:Forum Nav:

A Super-Simple 6DJ8 Headphone Amp - Page 20

post #286 of 490
Thread Starter 


Oy, is this thread still alive? Amazing!

Quote:
Originally Posted by yellowjeep View Post

For c102/202 I have Nichicon KW 470uF 63v. I picked these because it was discussed early in the thread that 1000uF was was probably over kill.

[/quote]

 

It was convincingly (i.e. math was involved) argued somewhere that C102/C202 should be 1000uF, I think. It's not too hard to find suitable caps, so I tend to err on the side of caution there, per (dBel's?) advice.

 

The discussions of overkill usually involved C103, the main power reservoir cap. I am absolutely convinced that the 1000uF specified there on the schematic is inadequate. Some of us have used caps as large as... 16000uF? there (I've got 12000uF in one of mine) to good effect, but I'm pretty sure everyone agrees this is overkill. 4700uF is probably a relatively safe and sane size that will sound good. (The most immediately noticeable benefit to increasing C103 above the "recommended" 1000uF is, erm, 'significantly improved low-frequency response', i.e. the bass goes from fairly weak and flabby to... not. biggrin.gif ) It should be noted that the cheap (in every sense of the word...) Bravo/Indeed 6DJ8 headamps that were all the rage a year or so ago used a (very very cheap) 6800uF cap here, while otherwise following the rest of the schematic as published, more or less (no input caps), and I'm pretty confident that their having done so is one of the reasons those little amps sound so good and were so popular, however briefly.

 

[quote]There are notes on the BOM that r103/203 and r107/207 should be replaced with some thing of better quality since they are in the audio path but I don't know what to look for.

[/quote]

 

I used some quasi-exotic resistors from Digi-Key, alleged to be identical to some pricey European boutique brand, but at a fraction of the cost. Alas, it's been almost two years, and I can no longer immediately remember either brand name. frown.gif

 

They're green in color, but that's about all I know. Maybe someone else knows which ones I'm talking about.

 

(God, this new post-editor-for-dribbling-idiots is annoying. If some moderator with the patience to understand this abomination wants to fix the formatting of this post... have at it, and more power to you. And to think, I'd forgotten why I rarely post here anymore...)

post #287 of 490

Here is mine still in casing up progress..just waiting to get me out of the couch biggrin.gif does anyone tried the Indeed amp with our amp?

 

which sound nicer?

 

 

p1280799a.jpg

post #288 of 490

I am committed now! I ordered the PCB, 2SK117s and an NOS Russian 6N23P from eBay today. I am hoping that I didn't get the wrong tube but from my research I think they are direct equivalents. I realized that it might take up to 30 days for the tube to get here so I might wind up getting something else anyway... and I will start rolling tubes.
 

Quote:
Originally Posted by Nemo de Monet View Post
And to think, I'd forgotten why I rarely post here anymore...)


Well I'm really glad you did. I was actually just starting to wonder if the smaller input caps were going to be a problem since I hadn't found any picture with people using them.

 

I followed James' advice and picked out some carbon composite resistors for r103/203 and r107/207 for a few cents more I figured why not. 

 

I am trying to get my Mouser order finished up. I have switched c101/201 to 1000uf Panasonic FCs I read that these sound pretty good and there are a bunch in stock so that's a plus even though it breaks my all Nichicon scheme. On that note does the quality of c103 effect the sound or is it simply the capacitance  that is helping out the bass?

 

I am going to sub the 2SK310s out for IRF510s because they are more readily available. 

 

Now I just need to pick out the panel mount stuff. Any advice on a pot that is also a switch?

 

PS. sorry about my stream of consciences posts. I get to typing out a reply and think of about 10 other things I want to say.

post #289 of 490
Thread Starter 

I suspect that the "quality" of C103 (i.e. low ESR) has a certain effect, but no amount of "quality" will compensate, as far as I can tell, for too-low capacitance.

 

Can't help you on a switched pot, as I never use 'em. As far as I'm concerned, the fact that the amp runs (by default) on 24VDC, and those illuminated vandal-proof pushbutton switches run on 24VDC, is a beautifully synergistic pairing just waiting to happen, like steamed rice and Japanese curry. biggrin.gif

 

GT20V: I have one of the "Bravo" amps, which were identical to the Indeed, except for the engraving. I've discussed the commercial amp at the links below:

 

http://www.slugsite.com/archives/1289

 

and

 

http://www.slugsite.com/archives/1357

 

The short version is that the DIY "Super Simple" is superior in just about every way. The main differences - all shortcomings, IMO - in the Bravo/Indeed amp are:

 

1, no input coupling caps

2, unspectacular 25VDC output caps

3, very very unspectacular 25VDC C103 reservoir cap with little space for a quality replacement

4, IRF630s

5, no fuse

6, questionable heatsinking

 

With regards #6, I've had my Bravo amp running 24/7 for around ten months now, and it's failed to blow up, melt down, fall over, or sink into the swamp. I may just be lucky, however. smily_headphones1.gif

 

In terms of sound quality, I'd say the "Super Simple", if built with reasonable quality components and sensible component values, has lower noise, better bass response, a generally livelier and more enjoyable sound, and better bass response, and can be safely run at somewhat higher voltages. The Bravo isn't *bad*, per se; a lot of people really like it, after all. It's just hampered by some fairly ignorant and short-sighted cost-cutting measures which prevent it from living up to its full potential.

post #290 of 490

Alright I am still confused about about what pot I need and looking at the board isn't helping me much. All the pots I'm finding have 3 pins the board shows 6 holes. Well 5 because two of them share a trace, I am assuming this is just to reinforce the stability of a board mounted pot. I am also assuming that the rear most pot holes in the board are are a switch as I read that it is originally designed to take a board mounted pot/switch. 

 

I also am confused by all the different types of LEDs and their ratings. I understand that this amp will operate with out but I would like to use an orange one to light the tube. 

 

/noob

post #291 of 490

OK, well for the LED, pick your LED then use a calculator to figure the resistor value, like this one http://led.linear1.org/1led.wiz

About the pot, you need a stereo pot, it will have 2 gangs each with 3 terminals. The board is setup for a pot with a switch like this one but at 100k not 10k

post #292 of 490

Perfect thanks James! So the r106 is based off of what the value of r106, makes sense now I was thinking it was odd that there was only one for that position. Thanks for the advice on the pot too. When (if) I finish this amp will it be in no small part because of your help and everybody else in this thread.

 

Am I correct in thinking that the rear most holes/pin for the pot are for a switch mechanism?  


Edited by yellowjeep - 10/3/10 at 7:38pm
post #293 of 490

Yeelowjeep,

Yes you are correct. That is the switch. Mine came with alps pot that have the on-off switch built in. it occupy the whole 8pin.

post #294 of 490

Thanks GT20v! I guess its what I am looking for doesn't exist so I suppose I will mount a rocker switch on the back and call it a day. 

 

I used the link that James provided so my soft orange LED is a go. Just need to pick out a pot a switch and a power supply. I will worry about an enclosure after I know it works. Thanks again everybody.

post #295 of 490

Alright. Everything is ordered but the PS and PS jack I still have to figure out what I am going to do there.

 

This should be interesting.

post #296 of 490

emo,

 

Sorry I failed to read your reply earlier :P

 

Anyway thanks rot he summary of SSimple vs Indeed amp.....u just save me the money biggrin.gif

 

but...i have some question here..

 

1, no input coupling caps<<Isnt to be a better design not to have input caps? less stuff in signal path is better?

 

2, unspectacular 25VDC output caps<<< This can be change to a better one I guess?

 

3, very very unspectacular 25VDC C103 reservoir cap with little space for a quality replacement<<same as above unless space issue...

 

 

just to see the diff btw Ssimple n bravo/Indeed amp.

 

post #297 of 490
Thread Starter 

GT20V:

 

1. In theory, maybe. In reality, it's not quite that simple, as, among other things, DC offset can become an issue. As far as I can tell they were omitted to save space and money, not for any dubious sonic improvement.

 

2. You certainly can change the output caps (I've done so), but what were there were kind of laughable for an "audiophile" product. (Mine began leaking electrolyte within about six months.)

 

3. You're extremely constrained as far as what will fit here, in terms of voltage + lead spacing + overall diameter. If you want a reasonably quality low-ESR 35V cap here, you'll almost certainly have to drop down to 3600uF, which may or may not be... suboptimal. My biggest complaint here is really that they used a 25V part on a 24V rail, a very noobish no-no, IMO.

 

You certainly can replace all the elecrolytic caps, and the tube. Even the resistors in the signal path, if you're feeling really ambitious. At the end of the day you'd wind up with a cramped amp with a questionable layout, marginal heatsinking, no fuse, and no easy way to be mounted in an enclosure...

 

post #298 of 490

yeah agreed..done my research abt indeed amp...I conclude our amp is better!yeah!

 

 

 

post #299 of 490

I built this amp without board, p2p. Of course first upgrade, I made, was remove input cap (1 cap in signal path is better than 2). Then start scratching noise, wen turning pot, DC come from tube to pot.

I can't eliminate Dc offset from tube grid/pot with so low 24V power. Wen I connect 48V PS from Starving Student amp, DC on pot disappear.

 

So, in this schematic input cap is essential.

 

Nemo de Monet, can you check DC offset on your Bravo amp pot? Are schematic slightly different?

 

This Super Simple amp is not Sijosea amp copy, same principle , but different

post #300 of 490
Thread Starter 

The circuit, as far as I can tell (I haven't checked every resistor...), is identical, save for the lack of input caps, and the addition of a tiny tantalum cap on each channel between the drain of BG201/BG202 and ground. On mine they aren't marked. What purpose they serve, I'm not 100% sure. Given the cost-cutting involved in making the things, I figure they're there for a reason, though.

 

I'm not sure an actual accurate schematic was ever published for the Bravo or Indeed amps. On eBay, one of the two sellers, I forget which, was using Sijosae's old schematic, taken directly from HeadWize or wherever.

 

I'll try to pop the bottom off mine tonight and see what DC is present at the pot, if any.

New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › A Super-Simple 6DJ8 Headphone Amp