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post #16 of 1669
Hi,

I've built the power supply part of my SOHA II today, and much to my surprise it gave out correct voltages when I finally dared to plug it in (wearing safety goggles and rubber gloves =).

I'll try to get started with the amp itself tomorrow… As for more BD139 alternatives, I seem to recall someone here using BD137s instead. Should these work without other changes to the BoM?
post #17 of 1669
Quote:
Originally Posted by Arkku View Post
As for more BD139 alternatives, I seem to recall someone here using BD137s instead. Should these work without other changes to the BoM?
That would be me, and yes.
post #18 of 1669
Quote:
Originally Posted by GeWa View Post
...I'll stick with the BD's than. I hate to desolder stuff...
I used transistor sockets everywhere. They are available at Digikey and Mouser, not sure about overseas. They work great not only for output transistors, but for the regs in the PSU as well. If you are using larger heatsinks, it's a downright PITA to replace any of those. Sockets there help a bit. I have all my TO-220 package ICs socketed on the SOHA II.

Swapping transistors in the socketed versions are easy as pie. Only problem is how to handle reverse pinouts. You can socket both sides if you like. I didn't as I want more airflow.
post #19 of 1669
Thread Starter 
Quote:
Originally Posted by Arkku View Post
Hi,

I've built the power supply part of my SOHA II today, and much to my surprise it gave out correct voltages when I finally dared to plug it in (wearing safety goggles and rubber gloves =).

I'll try to get started with the amp itself tomorrow… As for more BD139 alternatives, I seem to recall someone here using BD137s instead. Should these work without other changes to the BoM?
That's great Arkku. Take your time and follow the steps and, if all the components are in the right places, it should come up without any problems.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #20 of 1669
Has anyone figured out what kind of ventilation we need if we're using the 14551601? Is it possible to have no extra holes drilled?

Also, on a similar train of thought, will there be a group buy for pre-drilled cases along with the pcb group buy?
post #21 of 1669
I heard pabbi1's SHOAII and was really, really impressed. I think he was using 5863 or something like that. Just curious, what's the gain with this tube? I say that, because it was definitely over 10 and I'd like to set another amp to around this much gain, as it was perfect given my low output sources.
post #22 of 1669
Thread Starter 
This depends on the topology of the circuit as much as it does the tube. The raw gain (mu) of a 5963 (12au7) is about 17. In the SOHA II using a 5963 gives a gain of about 12 because a very small amount of NFB is applied to compress the wide spread of mu for all the possible tubes that can be rolled into a much narrower range. This is discussed on the website at Cavalli Audio.

So, YMWV according to the topology of the circuit and the tube used. There is no hard rule.

Edit: Ferrari's post below is correct on the mu which is 21 not 17.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #23 of 1669
Quote:
Originally Posted by luvdunhill View Post
I heard pabbi1's SHOAII and was really, really impressed. I think he was using 5863 or something like that. Just curious, what's the gain with this tube? I say that, because it was definitely over 10 and I'd like to set another amp to around this much gain, as it was perfect given my low output sources.
I think that you mean 5963 double triode (5863 ???). The voltage gain of this tube is 21x, however the effective gain of the SOHA II is lower. I have measured that once but can't remember the exact number. Effective gain depends on the tubes used in the front-end of the amp.



Edit: runeight was beaten me for a couple of minutes.
post #24 of 1669
Thread Starter 
Quote:
Originally Posted by rds View Post
Has anyone figured out what kind of ventilation we need if we're using the 14551601? Is it possible to have no extra holes drilled?

Also, on a similar train of thought, will there be a group buy for pre-drilled cases along with the pcb group buy?
rds, I am currently talking with Jeff about pre-fab'd front, rear, and top panels for the long Hammond enclosure. The amp needs lots of ventilation and will probably get too hot if just the tube holes are opened and nothing else. I have been thinking of a perforated sheet (50% open) that is the right thickness to slide into the case with the holes drilled for the tubes and the B+ adjustment. Still working on it.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #25 of 1669
Sounds good. My personal issue is that I will be building mine around Christmas, which might be too early to have those panels in hand. But I see someone has been kind enough to make dimensional pdf drawings - that's great for me. I can use a center punch, but I hate using rulers.
post #26 of 1669
Quote:
Originally Posted by rds View Post
But I see someone has been kind enough to make dimensional pdf drawings - that's great for me. I can use a center punch, but I hate using rulers.
I created a set of templates for the bottom - I think that Pabbi used them - they were pretty painstakingly laid out (I don't do CAD) by hand. Case drilling is pretty straightforward with a glued down template and a steady hand...

Is anyone (other than Ferrari, who has a much bigger case) using an unventilated top?
post #27 of 1669
I posted my build in the other thread in this forum. My build has vents on the corners. The tops themselves have no other slits or holes. It does get warm, but I don't feel it is too warm. I don't recall seeing any builds that have a fully closed system.
post #28 of 1669
Thread Starter 
Quote:
Originally Posted by rds View Post
Sounds good. My personal issue is that I will be building mine around Christmas, which might be too early to have those panels in hand. But I see someone has been kind enough to make dimensional pdf drawings - that's great for me. I can use a center punch, but I hate using rulers.
rds there are dimensioned drawings on the website in various places. They locate the holes on the front panel and the holes on the tube for clearing the tubes and the hole for the B+ adjustment.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #29 of 1669
Quote:
Originally Posted by wiatrob View Post
Is anyone (other than Ferrari, who has a much bigger case) using an unventilated top?
I originally built mine without a ventilated top, but it got extremely toasty, almost uncomfortable to touch. I ended up cutting a couple of ventilation slots in the top and it runs much cooler now.
post #30 of 1669
I am at this point too, I built a fan into mine which doesn't induce electrical noise but with open cans, I can hear it at the low levels I prefer when listening. I plan to cut a few vents into the top / sides of mine..dB
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