HeadWize: DIY Workshop > SOHA V3 builder's thread.

Message [#40] posted on: 10-14-2006 09:51 AM CST (US).

Joined: Sep. 22, 2006
Locale: Belgium
Total Posts: 113

It should look something like this. It measures 21 by 16mm. The OPA is offset from the center to get "the trick" done with pin 1 and 7. Any comments, suggestions,.......critisism

Regards

Attachment: C2158.jpg

vixr

Message [#41] posted on: 10-14-2006 10:00 AM CST (US).

Joined: Sep. 17, 2005
Locale: 29.55.16.62N 81.20.36.92W
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gewa, good catch... You are correct. I rushed the drawing because I did it at work. I have the datasheet for the BUF and the 2134 in front of me and you are right... Pin 2 of the 2134 is the correct pin for the Vo of the buf to connect to.

tomb

Message [#42] posted on: 10-14-2006 01:26 PM CST (US).

Joined: Mar. 1, 2006
Locale: Atlanta, GA
Total Posts: 704

OK - I messed up on my understanding of that one. Guess that's why I asked for a volunteer to do the diagram. <wink>

[Edited by tomb on 10-14-2006 at 01:28 PM.]

tomb

Message [#43] posted on: 10-14-2006 01:38 PM CST (US).

Joined: Mar. 1, 2006
Locale: Atlanta, GA
Total Posts: 704

Vixr,
That's a great review of the SOHA so far. I am surprised that the output resistors really have an effect on bass, rather than just muting the highs. I have 4 Milletts ready to case up right now, and I deleted the resistors on 3 of them with no ill effects. I left them on one because I want to fiddle with the Intersil's. Although, from what I hear, you only get to fiddle once and then they're gone (which is why I kept the resistors in there). Anyway, didn't notice any loss in bass from one to the other.

I did notice a loss in bass when trying to delete the output box caps. I had purchased some Nichicon Muse ES's which were supposed to be good for bass in coupling caps, but without the box caps, the bass completely disappeared. Weird. Well, this isn't about Milletts, so enough of that.

The specs would predict your experience with the volume on the SOHA - but I wonder if it's gain rather than power. On the other hand, with those good-looking Cerafines, it could be power. <evil grin>

My experience with the 627's has been that they meet all the hype, and then some. I was curious about an AD8620, too - that thing is in the same league with slightly more detail and highs, but tremendous bass. Current handling is about 35-40ma for both, I believe.

Thanks for the offer, but I've got a JJ tube waiting. It was one of those that got good reviews for the SOHA.

Again, thanks for the comments and the comparison.

dytln_02

Message [#44] posted on: 10-14-2006 03:48 PM CST (US).

Joined: Feb. 23, 2006
Locale: Solo, jateng,Indonesia
Total Posts: 171

can someone explain to me...
I have change Tube in Soha, with no input connected I don't hear any hum, but when Input connected I can hear hum.
move my hand above the tube, I Hear louder hum
When I touch chasis with my hand, there is no hum.
With other tube is ok. no hum at all with input connected or not.

Another thing..
I use bluetooth and sony Ericsson T68i phone, to connect through internet (Gprs Signal). When I Connect internet, I can hear noise from SOHA. With Szekerez I don't hear noise.
distance from SOHA and SE T68i, is about 1.5 meter.
how to fix this thing.

vixr

Message [#45] posted on: 10-14-2006 05:33 PM CST (US).

Joined: Sep. 17, 2005
Locale: 29.55.16.62N 81.20.36.92W
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tomb, I put the jumpers back in and I think it does sound better. I was playing with the resistors at about 1:30 this morning and I guess I was fatigued... I also found that the heatsink from rreynol's BOM gets really hot. I changed it with one I salvaged from a dead RADAR display and its not near as hot. I even tried putting two of the smaller ones back to back and still too hot IMHO. Anyway, on to the case!

rreynol

Member

Joined: Oct. 13, 2005
Locale: Melbourne, FL
Total Posts: 100

Message [#46] posted on: 10-14-2006 08:30 PM CST (US).

Which heatsink are you talking about from my BOM. The default one is just the same one as specified in the original HeadWize article (567-273-AB) and I'd imagine it does get quite hot. Its rated for 49 degree c @ 2W. I ended up using the 567-270AB which has a better thermal rating on paper (70 degree c @ 4W) and it still gets quite warm.

vixr

Message [#47] posted on: 10-15-2006 10:21 AM CST (US).

Joined: Sep. 17, 2005
Locale: 29.55.16.62N 81.20.36.92W
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Hey guys, I was wondering if ther is any way to verify exactly which tube I have? I bought it on ebay, it says on the box and silkscreened on the tube that it is a ECC82 by JJ electronic, made in Slovak Republic. Its brand new, but the 60v test point shows a steady 70 volt reading. I think its the wrong tube. It sounds good though. It was only 9 dollars, so it isn't tragic if its not the right tube. rreynol, I didn't mean to sound like I was slammin on your BOM. Every part I ordered from it was perfect. I was doing a FYI thing on the heatsink being too small. Could someone suggest a good source for the correct tube for the SOHA? Also, just for clarity, what exactly does the 2134 do in the SOHA? I've got mine about 90% cased up... Just need to lay out for the hole for the tube in the belly plate and the locking 1/4 phone jack, in the front panel. I have a hole saw kit at work, but I have to go thru the security desk to get in the building...(hassle) tomb, I wasn't trying to give you a tube, I was hoping you could check mine to see if it was the right one. You live so close, that snail mail is pretty effective. Anyway, bottom line? The SOHA is a very cool amp.

tomb

Message [#48] posted on: 10-15-2006 11:37 AM CST (US).

Joined: Mar. 1, 2006
Locale: Atlanta, GA
Total Posts: 704

Woo-boy! So many questions. I'll try, as long as you understand that some of these are my own guesses.

[Quoting vixr]
Hey guys, I was wondering if ther is any way to verify exactly which tube I have? I bought it on ebay, it says on the box and silkscreened on the tube that it is a ECC82 by JJ electronic, made in Slovak Republic.

That tells you it's an ECC82. As you say, it's new production. I bought one, and it's sold by many of the favorite outlets we used for the Millett tubes (among others):
thetubestore.com/teslaecc82.html
www.tubedepot.com/jj-ecc82.html
www.tube-shop.c...5&ProcessType=9

[Quote]
Its brand new, but the 60v test point shows a steady 70 volt reading. I think its the wrong tube. It sounds good though. It was only 9 dollars, so it isn't tragic if its not the right tube.

The 30VCT is boot strapped by those 100uF/100V capacitors. That's not an accurate method, I'd guess, and depends a lot on the peak-to-peak voltage of the xfmr at load, and on the accuracy of the caps. (It could be those Jackcon's, in other words.) However, as long as the voltage is at least 50V, I don't think there's a problem - simply because it depends on the xfmr capacity. It's kind of like an un-regulated, free-wheeling voltage boost (my understanding).

[Quote]
rreynol, I didn't mean to sound like I was slammin on your BOM. Every part I ordered from it was perfect. I was doing a FYI thing on the heatsink being too small. Could someone suggest a good source for the correct tube for the SOHA?

The options are as numerous as places that sell tubes. That's what makes the choice of the 12AU7 type tube so great - it may be one of the most widely used tubes in existence. There have been several posts with reviews, etc., of the different 12AU7 variants and their performance in the SOHA. As for an explanation of the variants, this link explains the history of the 12AU7 and is extremely helpful:

12AU7 Tube Types

I've bought 8 tubes for the SOHA so far - three new production (JJ is one) and 5 NOS. Only one is labeled as a 12AU7.

[Quote]
Also, just for clarity, what exactly does the 2134 do in the SOHA?

If I understand correctly, tubes work by leveraging high voltages at extremely low currents, perhaps microamps and less. This is why when you see tube speaker amplifiers (or much of any other tube circuit), there is a transformer feeding the speaker. That's because there's almost no current to drive it - only voltage. The transformer takes the super-high voltage output from the tubes and brings it down to a lower voltage with some useful current.

In the SOHA, the OPA2134 provides the current - that's why we're interested in getting more. <evil grin> Actually, the voltage may be high enough with that B+ supply (70V in your case), the opamp may be over-driven (30V capability in a 2134, I think). That's why Runeight-Mains_hum-Batman put the diodes around the opamp - to limit the voltage spikes. At any rate, driving Senns should be no problem. Grado's may want a little more than the 35-45ma they will get from the 2134. Again, my understanding - it may not be completely accurate.

Note - I'm not trying to be overly-critical. The whole idea of using the 12AU7 opens a new realm to those of us building DIY tube headphone amps (as noted above).

[Quote]
I've got mine about 90% cased up... Just need to lay out for the hole for the tube in the belly plate and the locking 1/4 phone jack, in the front panel. I have a hole saw kit at work, but I have to go thru the security desk to get in the building...(hassle)

Photos, please. <wink>

[Quote]
tomb, I wasn't trying to give you a tube, I was hoping you could check mine to see if it was the right one. You live so close, that snail mail is pretty effective.

Hopefully, some of those links explain the tube. I am sure you have the right one.

[Quote]
Anyway, bottom line? The SOHA is a very cool amp.

No doubt, the rest of us will agree. I have 4 boards and 4 more coming. I hope to get something great out of them at some point.

EDIT: 30VCT, not 15.

[Edited by tomb on 10-15-2006 at 01:06 PM.]

vixr

Message [#49] posted on: 10-15-2006 12:12 PM CST (US).

Joined: Sep. 17, 2005
Locale: 29.55.16.62N 81.20.36.92W
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thanks tomb, I never would have figured out the op amp thing (I was way off) the tube links at least show the exact same tube I have.(one less thing) I will post pics soon, my home camera is pitiful compared to the one at the office.

dcheming

Message [#50] posted on: 10-16-2006 02:21 AM CST (US).

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Is anyone here planning on building a balanced SOHA V3?

digi01

Message [#51] posted on: 10-16-2006 02:36 AM CST (US).

Joined: Dec. 3, 2002
Locale: BEIJING
Total Posts: 622

[Quoting dcheming]
Is anyone here planning on building a balanced SOHA V3?

I am interested <smile>

is it possable to build a 3 channel soha first?the ground channel can be made with a opamp or another soha channel.

heady

Message [#52] posted on: 10-16-2006 05:27 AM CST (US).

Joined: Jun. 15, 2004
Locale: Singapore
Total Posts: 106

Hi digi01, what is the status of the buffer boards you have promised us? Thanks.

cetoole

Message [#53] posted on: 10-16-2006 07:57 AM CST (US).

Joined: Sep. 14, 2005
Locale: Maryland, USA
Total Posts: 171

[Quoting digi01]
[Quoting dcheming]
Is anyone here planning on building a balanced SOHA V3?
I am interested
is it possable to build a 3 channel soha first?the ground channel can be made with a opamp or another soha channel.

Of course its possible, but I cant see possibly how using a third SOHA channel, as you cant very well run the 12AU7 in unity gain. It would be pretty easy to do using an opamp. You could use the real ground as the reference for the ground channel, insead of a rail splitter as is common on other 3 channel amplifiers. Also, with a balanced SOHA, which is definitly doable, you would want to be sure to match the tubes at least somewhat, as differences in the hot and cold channels could cause some interesting sounds.

dcheming

Message [#54] posted on: 10-16-2006 02:15 PM CST (US).

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I know this is the wrong thread to ask in, but I already posted in Marketplace a few days ago: are there enough boards left from the GB that I could get three?

I'd like to build a normal stereo SOHA to check out the sound before I do a balanced version. I'll start looking around for a pair of matched and balanced 12AU7's. <smile>

digi01

Message [#55] posted on: 10-16-2006 07:06 PM CST (US).

Joined: Dec. 3, 2002
Locale: BEIJING
Total Posts: 622

for balanced version,it is easy with DRV134,or balanced signal transformer.

digi01

Message [#56] posted on: 10-16-2006 07:13 PM CST (US).

Joined: Dec. 3, 2002
Locale: BEIJING
Total Posts: 622

[Quoting heady]
Hi digi01, what is the status of the buffer boards you have promised us? Thanks.

the buffer is available.I will write a paper of full infor at my website.

Zang

beeah

Member

Joined: May 17, 2006
Locale: Finger Lakes, NY
Total Posts: 31

Message [#57] posted on: 10-16-2006 08:59 PM CST (US).

Here's mine... Dig the high-end chassis. <sticking tongue out>

I've been listening to for many hours now, from PC & portable MP3 only so far. I have a Toshiba 3960 on the way for work, and my home CDP is quite happy staying where it is...

Anyhow, I'm hearing distortion in a certain band in the upper mids. I can easily reproduce it from any source, and I've ruled out each source as the culprit by plugging the phones directly into it. Plus, while I hate to admit it, it sounds better when I bypass the amp and plug the phones straight into the PC. The MP3 player sounds better (more dynamic, maybe) through the amp, though.

I've also tried 3 different tubes - GE 5963, RCA clear top 12AU7A and presently an Amperex ECC82 (my fave, BTW) - so the tube's not the issue either.

My guess (hope?) is that it's caps or resistors that simply need some breaking in, but I've used the Vishay/Dale resistors as well as Wima & Cerafine caps before without issue. I've never used the Nichicon KZs before.

Any suggestions? I have no problems dialing in the 40V bias points, and my filament voltage is 12.5V or so.

Thanks!
-Joe

[Edited by beeah on 10-16-2006 at 09:07 PM.]

Attachment: C2159.JPG,C2160.JPG,C2161.JPG

dBel84

Message [#58] posted on: 10-16-2006 10:59 PM CST (US).

Joined: May 5, 2006
Locale: Portland, OR
Total Posts: 425

I finally got the time to case up my SOHA. It is a converted data switch box which I thought would make a neat home for the SOHA, haven't quite decided on the final colour yet. I can now stick it into the home rig and see how it performs between the amp and source as well as giving me a headphone amp there too. ( I have a switch to select rca out or headphone jack out )

@Joe - you shouldn't have any distortion , this amp really does perform well. I know that I did get some distortion when I was swapping out opamps and tubes and it turned out to be a nasty opamp ? a start at least but there could be many other reasons for this too. ps - neat casework <partytime>

If anyone is interested, I will post my impressions of how it sounds as a "buffer" ?? with gain <smile> . I am going to let it run for some time before doing any critical sort of listening although I am hoping that the benefits will be immediately apparent in the system <big grin> ..dB

Attachment: C2162.jpg,C2163.jpg

GregVDS

Message [#59] posted on: 10-17-2006 09:15 AM CST (US).

Joined: Oct. 25, 2005
Locale: Bruxelles, Belgium
Total Posts: 251

Digi01,

Can you give us details about the buffer board you have, and how is it possible to have it?

Many thanks,

Gewa,

Your board looks very good and interesting. Do you plan to produce it? Also, where do you source BUF634 with 5 pins?

All the best,

GregVDS

[Edited by GregVDS on 10-17-2006 at 09:25 AM.]

tomb