[makasin]

Hey all, would a SOHA sound better than my current Creek OBH-11?
Also, will it have enough juice to power low-impedence phones like the sr225s?

What is a CSS? and what is a JFET? Why are there so many choices when building this amp? Do they have different sonic qualities?

 

[mrdon]

I can't answer all of your questions, but the SOHA sounds really, really good. I highly recommend it. It will power both Senn's and grados with no problem provided one uses the correct output resistor after the opamp.

 

[tomb]

Quote:

Originally Posted by makasin /img/forum/go_quote.gif Hey all, would a SOHA sound better than my current Creek OBH-11? Also, will it have enough juice to power low-impedence phones like the sr225s? What is a CSS? and what is a JFET? Why are there so many choices when building this amp? Do they have different sonic qualities?

There are many DIY amps that will sound better than the Creek OBH-11. I don't have one, but a little research into the circuit description indicates that the Creek amps use a dual-rail, virtual ground, opamp/opamp-buffer topology, with an improved power supply. That sounds similar to an improved CMoy such as Apheared's A47. IMHO, a PIMETA probably offers a vast improvement, and other DIY-Solid State amps simply get magnitudes better from there.

Tube amps such as the SOHA are a different animal than the Creek or DIY SS amps. They combine prodigous amounts of power, resulting in a richness and smoothness - with slightly less detail (typically) - that contrasts well with SS amps. The problem with tubes is that most use amazingly high voltages - 200, 300, even 500V. These are lethal voltages, so the DIYer's that build such amps are special and few.

However, there are a couple of tube amp hybrids that use voltages similar to SS amps.

Of those, the Millett Hybrid may be the most famous DIY tube headphone amp. It combines old automobile radio tubes (12V!) with solid state buffers - either an IC or custom SS. It has a wide following and there are a couple of revised designs that are imminent. IMHO, the Millett (and other tube amps) provide a richness and a certain mellowing of highs that combine very well with Grado's. The power will never be lacking - that is inherent in the power needs of the tube heaters. More info than you'd ever want on the Millett is at DIYForums.org.

The SOHA is relatively new foray into tube/hybrid designs. There is a detailed article in the Headwize Library for the p2p version. Digi01 has also sold many PCB versions through a couple of Group Buys already, and offers single sales through a website address. This info is available in the SOHA Build thread on the DIY section of Headwize. Early reports are that the SOHA has a huge amount of power, much more than even the Millett (from Vixr).

The SOHA is based on the 12AU7 tube, one of the most popular tubes in existence. It exists in huge numbers and variants as NOS tubes, and there are several new production offerings, too. The SOHA designers dedigned an ingeneous combination of boosted and regulated voltages to combine a +or-12VDC opamp with approximately 60-70V to the tube - good shocking potential, but not lethal.

As to your specific question - tubes are best operated with a constant current on their anode/cathode supply, allowing voltage to vary with the signal. There are many different ways to do this in the circuit. The easiest and simplest is with a CCS (Constant Current Supply) diode. The diode will only permit a certain, set current flow regardless of voltage conditions. The problem with this is that most all-in-one CCS's are only available at Mouser (a mystery). Because of this, the SOHA designers designed several CCS's to allow for worldwide availability. The JFET is a type of transistor combination to provide the same CCS capability for those DIYer's overseas that don't have good access to Mouser. IMHO, the sonic qualities of different CCS's are pretty much in the measurements. If you can get the Mouser parts, fine. If not, I think you would be hard-pressed to hear any difference.

Mrdon's reference to the correct output resistors pertains to the low impedance of headphones such as Grado's. They typically need much less GAIN (voltage amplification) than higher-impedance headphones such as Sennheiser's - perhaps something less than 5, or even 2 or 1. However, a tube is essentially a voltage amplification device. The standard gain from the 12AU7 in the SOHA is 14-18. This means the entire volume range you could stand to hear might be in the first quarter turn of the volume control - without correction. The output resistors in the SOHA provide this correction.

In either event, there will be NO lack of power ... none, nada, ... etc.

 

[makasin]

ok thanks a lot for the awesome responses!

So I think im gonna try to build one of these bad boys. Its gonna be my first serious DIY project (made an interconnect, but thats easy stuff), so im probably gonna screw up pretty bad. Whaat is the easiest way to build one of these? Should I order a pair of v3 PCBs from digi01's site and go from there?
Where is a good place to find all the parts I need?
I guess ill have to figure that myself, but i checked mouser and they are currently out of stock with a couple of the required parts.

 

[makasin]

What is the difference between 140-HTRL16V47 and 140-HTRL16V47-RC?
One is RoHS compiant and the other is not. Does it matter which one I use?
Is one better than the other?

This is a general question regarding all the ones that dont have an "-RC" ending. Does it matter if i use the RC version?
EDIT:
Ok so here is my Mouser order, note the 2 back-ordered products.
I searched around digikey and couldnt find the product, anywhere else I should look? It says itll take 10 weeks and i cant wait that long. I basically copied the BOM list on this thread: http://headwize.com/ubb/showpage.php...=6328&fpage=36
Is that all I need or am i missing something?
And as far as enclosures go, will I have to drill all the holes myself? Where do I find the enclosures anyway?

270-2.2K-RC 10 10 Ships Immediately 0.110 1.100

270-560-RC 10 10 Ships Immediately 0.110 1.100

270-11K-RC 10 10 Ships Immediately 0.110 1.100

270-1.3K-RC 10 10 Ships Immediately 0.110 1.100

270-1.0M-RC 10 10 Ships Immediately 0.110 1.100

270-300-RC 10 10 Ships Immediately 0.110 1.100

270-150-RC 10 10 Ships Immediately 0.110 1.100

652-3306K-1-202 2 2 Ships Immediately 0.560 1.120

140-HTRL100V100 4 4 Ships Immediately 0.420 1.680

140-HTRL35V470 3 3 Ships Immediately 0.300 0.900

140-HTRL16V47-RC 3 3 Ships Immediately 0.070 0.210

140-HTRL16V1000-TB 2 2 Ships Immediately 0.250 0.500

{[1429-1104 2 2 Back Ordered 0.440 0.880]}

689-LND150N3-G 2 2 Ships Immediately 0.550 1.100

270-360-RC 10 10 Ships Immediately 0.110 1.100

270-1K-RC 10 10 Ships Immediately 0.110 1.100

821-DB102G 4 4 Ships Immediately 0.330 1.320

512-MC79L12ACP 2 2 Ships Immediately 0.340 0.680

512-LM337T 2 2 Ships Immediately 0.500 1.000

567-273-AB 2 2 Ships Immediately 0.380 0.760

351-3310-RC 1 1 Ships Immediately 1.500 1.500

271-560-RC 1 1 Ships Immediately 0.090 0.090

78-1N4148 4 4 Ships Immediately 0.030 0.120

512-1N4002 2 2 Ships Immediately 0.060 0.120

313-1240-100K 1 1 Ships Immediately 2.840 2.840

575-393308 1 1 Ships Immediately 0.730 0.730

161-3502 1 1 Ships Immediately 1.290 1.290

161-1052 1 1 Ships Immediately 0.820 0.820

161-1053 1 1 Ships Immediately 0.820 0.820

504-AGC-1/4 1 1 Ships Immediately 1.080 1.080

504-S82022 1 1 Ships Immediately 1.960 1.960

553-FP30-400 1 1 Ships Immediately 13.990 13.990

595-OPA2134PA 2 2 Ships Immediately 2.630 5.260

 

[makasin]

can i just get any cap that is 0.1uF, 100V, 85C, etc?
or does it have to be polypropylene film?

is the voltage rating the discharge voltage or the maximum voltage?

The only stuff I need now are:
LM78L12ACZ IC VOLT REG 12V 100MA TO-92
and the capacitor (C2, C14)
Also I need an enclosure for it all.

 

[rreynol]

Quote:

Originally Posted by makasin /img/forum/go_quote.gif can i just get any cap that is 0.1uF, 100V, 85C, etc? or does it have to be polypropylene film? is the voltage rating the discharge voltage or the maximum voltage? The only stuff I need now are: LM78L12ACZ IC VOLT REG 12V 100MA TO-92 and the capacitor (C2, C14) Also I need an enclosure for it all.

Since it sits in the signal path, it would benefit you to get a good quality cap (i.e. not just 'any' cap)

 

[makasin]

ya but does the voltage rating matter?

 

[Blind Tree Frog]

it needs to be rated high enough to handle the voltage going through it.

 

[FallenAngel]

Quote:

Originally Posted by Blind Tree Frog /img/forum/go_quote.gif it needs to be rated high enough to handle the voltage going through it.

Oh yah, very descriptive. Most, if not all, high quality film caps are rated at very high voltages (100V, 250V, etc), much more than enough that you don't need to worry about it. I used Mundorf MCap ZN's from PartsConnexion. They're definitely a bit pricy, but since they will be the only cap in the signal path of the SOHA, $14 for a pair is not THAT bad and I think is worth it. PartsConnexion has a very good selection high quality film caps so you can easily pick and choose. For a much less expensive alternative, you can always use Panasonic Orange Drops, they'll only cost you a couple of bucks and should sound nice.

 

[makasin]

ok, well i actually found a place that sells the xicon one that was listed in the BOM. Is that one decent enough quality? Will i notice much of a difference between the one i got and the ones you mentioned?
Hopefully not because I have already spent around 100 bucks without shipping.

Anyways, so I finally have all the parts i need ordered. This is exactly what I got:
Quote:

Part # Mouser Catalog # Change to R9 270-2.2K-RC R3, R13 270-560 270-560-RC R11 270-11K 270-11K-RC R10 270-1.3K-RC R5, R15 270-1.0M-RC (regular CCS) 270-100K-RC (mu follower) R2, R12 270-300 270-300-RC R6, R16 270-150-RC R4, R14 652-3306K-1-202 C7, C8, C11140-HTRL16V47 C3, C4, C5, C6140-HTRL100V100 C9, C10, C12140-HTRL35V470 C1, C13 140-HTRL16V1000-TB C2, C14 1429-1104 689-LND150N3-G R8, R18 270-360 270-360-RC R7, R17270-1K-RC BR1, BR2821-DB102G VR1 512-LM78L12ACZ DigiKey LM78L12ACZ-ND VR2 512-MC79L12ACP VR3 512-LM337T 567-273-AB Power LED351-3310 351-3310-RC 271-560-RC D1, D2, D5, D6 78-1N4148 D3, D4 512-1N4002 R1 313-1240-100K 575-393308 J3 161-3502 J1 161-1052 J2 161-1053 Fuse 504-AGC-1/4 Fuse Holder504-S82022 DigiKey U1, U2 OPA2134PA-ND T1 TE70053-ND Antique Electronic Supply V1 T-12AU7-JJ V1 P-ST9-511

All I need now is an enclosure. Any recommendations on a decent cheap enclosure that isnt hard to work with? What kind of tools would I need in order to make an enclosure. I just need something that would be reasonably safe to transport on a plane as I am going back to school after winter break. Also, for the PCB version, the one thing im pretty confused about is grounding issues. On HeadWize, sbers77 said "YOU HAVE TO GROUND THE CENTER TAP CONNECTION." What does that mean? Also, will i have to splice the wire to get 2 rails of 12V? Basically, I am really confused about the whole transformer wiring setup (and realize this is probably the most dangerous area to be confused about haha)

 

[FallenAngel]

Quote:

Originally Posted by makasin /img/forum/go_quote.gif All I need now is an enclosure. Any recommendations on a decent cheap enclosure that isnt hard to work with? What kind of tools would I need in order to make an enclosure. I just need something that would be reasonably safe to transport on a plane as I am going back to school after winter break. Also, for the PCB version, the one thing im pretty confused about is grounding issues. On HeadWize, sbers77 said "YOU HAVE TO GROUND THE CENTER TAP CONNECTION." What does that mean? Also, will i have to splice the wire to get 2 rails of 12V? Basically, I am really confused about the whole transformer wiring setup (and realize this is probably the most dangerous area to be confused about haha)

Enclosure wise, I'm using Hammond 1455N2202. It's pretty big and has lots of room. It is aluminum and you'll need to drill a serious hole though it for the tube.

About the center tap, I'm thinking he was refering to the 2 wires connected together on the transformer.
This question, along with the split rails question is SERIOUSLY making me uncomfortable. If you're building Digi's board, you will not need to worry about the 12V rails, for a custom version, you will simply run 2 wires from the 12V and -12V regulator outputs.

Please do take care with this project as it deals with a little higher voltages vs solid state and 60V through your ass WILL hurt. Also, remember you're working with 120V AC from the wall when you're attaching it to the transformer so make sure all those connections are sealed off from you with SOMETHING (electrical tape if you must) and DON'T under any circumstances stick your finger into the circuit board while it's on! Although it seems like a dumb thing to do, but people reason with "I just need to move the board so I can take a voltage reading on this component" or "I need to adjust the Plate Voltage so I'll move the unprotected tube socket with my hand" and stuff like that.

 

[makasin]

so i dont really have to worry about any specific grounding or splitting of the wires? I just attach the wires to where they are required on the PCB and thats it? So will I need to invest in a dremel or something to get the enclosure made?

Could I theoretically make an enclosure out of thick-ish cardboard or go to home depot and get some wood? Or is it recommended to use metal for grounding/heat dissipation purposes?

And can I use the panasonic 100f flux capacitor? (stupid joke)

 

[sbyers77]

Quote:

Originally Posted by makasin /img/forum/go_quote.gif Also, for the PCB version, the one thing im pretty confused about is grounding issues. On HeadWize, sbers77 said "YOU HAVE TO GROUND THE CENTER TAP CONNECTION." What does that mean? Also, will i have to splice the wire to get 2 rails of 12V? Basically, I am really confused about the whole transformer wiring setup (and realize this is probably the most dangerous area to be confused about haha)

The transformer I used was the Amveco 62053 (Digikey P/N: TE62053-ND). It has 8 wires, 4 coming in, 4 going out, and depending how you wire the transformer you get different voltage configurations, take a look at the datasheet.

I wired the primaries for 115VAC being I am in North America. Following the datasheet, this means wiring the red and yellow wires together and the black and violet wires together. AC Line voltage is connected across the red/yellow and black/violet connectors.

Next, I connected the secondaries in series. Again, by the datasheet, "the red and brown wires are connected together... take the output across the green and blue wires." So I do as the datasheet says and get 30VAC across the blue and green wires. When I tried to turn on my amp I got really strange readings and nothing worked. Turned out the problem was I didn't connect the red/brown wires of the transformer to the ground pads of the PCB. After I did that it fired up perfectly. This is what I meant by "you have to ground the center tap connection."

A picture is worth a thousand words... take a look, it's still uncased.

 

[Yen]

Quote:

Originally Posted by makasin /img/forum/go_quote.gif Could I theoretically make an enclosure out of thick-ish cardboard or go to home depot and get some wood? Or is it recommended to use metal for grounding/heat dissipation purposes?

Yes, you could enclose it in any enclosure that most suits your aesthetic, usability and safety preferences. Thus, you can use any that protects the user from touching the transformer, PCB and connectors (especially the ac-inlet).

I went for cheapest solution (5 bucks), and bought a wooden key locker from a local ratshack-type of shop. It was just big enough to accomodate the board and the transformer. Examples in my sig.

Even though the transformer and boards are almost touching each other, there is absolutely no hum, nothing. As you can see from my pics, I havent connected casing ground or the center tap thingie and it works fine. So dont bother yourself with it and connect the transformer to its place, and remember to ground pot, input and output connectors to their spot.

As casing tools, I have a 10 buck battery drill, 3-10mm drill bits and a knife (main tool of mine

). It depends fully on your cases' material, your skills and experience and how nice you would like your case to become. I have mainly used wood and plastic, which are easy to work with basic tools. Metallic (aluminum) cases are nicer, but they might not be most forgiving because it is hard to correct the mistakes you have made to the surface. However, they are IHMO in most cases most beautiful enclosures. With a dremel, you can make precise holes easier and generally makes your enclosing life easier, but it is not a mandatory tool.

Additionally, like FallenAngel said, I would really emphasize and recomment you to protect any connections from and to the transformer and AC-inlet. I have used protected abico-connectors. Although the amp's voltages are lethalsafe, it hurts (I have tested with our 230V from the wall

)

I have used mine for 100 hrs and I have loved every minute of it! It is magnificent piece of engineering, especially for the price. Just remember to unplug your headphones before turning it on and off.

I am considering the muting delay (epsilon12) by amb from headwize, but it will cost almost as much as this amp!