[dBel84]

I have not compared the SOHA II to any amp directly and as incredulous as this may seem , the Bijou is still bare on a breadboard and with the kids about, it gets very little use. I don't recall feeling that the Bijou lacked bass, in fact everytime I do listen to the Bijou, I wonder why it is still on a breadboard

..dB

 

[dBel84]

Quote:

Originally Posted by Cankin /img/forum/go_quote.gif Any estimates of the cost of the kit or PCB board?

PCB's have yet to be made but you can work on the ballpark of about $15, while parts costs will depend how boutique you build the amp - base cost with chassis, connectors etc is $150 odd.

I think you could build this amp comfortably below $200, and this includes high spec components..dB

 

[dBel84]

I don't like Grado's. There I said it. The only Grado's I have heard that I liked were the RS1's and generally use my pair (the lowly SR60s) as a test phone to make sure the amp makes sound and doesn't fry the drivers. sad admission but true.

Well I had been doing a lot of fiddling and was using the grados while doing so and it actually made me stop and think that they just might be half "listenable". After a little more listening, I think this amp has real synergy with Grado's - wouldn't have thought it were possible for me to actually enjoy using them but there you go.

I also ended up completely dismantling the bread board to case it up , here is a "in-progress" pic:

and seeing as I was going to be sans amp ( all others are out and about at the moment) I decided to finish wiring up the original proto which I am not sure what to call , so perhaps for the moment "The amp that won't be" . It's a real pity the servo was unstable as it really is an elegant design and also has an amazing sound.

A few pics of it too:

Front:

Back:

Top off:

Dark shot:

and I did start the process of casing up the Bijou, so hopefully one day I will be able listen to each of them..dB

 

[Ferrari]

Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif ... and I did start the process of casing up the Bijou, so hopefully one day I will be able listen to each of them..dB

It reminds me that I still have to finish the case work for mine too. Free time is something very scarce for me lately.

Btw, thanks for your first impression of the SOHA II.

 

[mwofsi]

Whilst this project comes towards a happy beginning, can I question the name?

I'm fond of the SOHA name, but is the SOHA II really an opamp hybrid amplifier?

Someone has mentioned this before.

Shouldn't it be an SDHA or Child Of SOHA?

 

[Ferrari]

Quote:

Originally Posted by mwofsi /img/forum/go_quote.gif Whilst this project comes towards a happy beginning, can I question the name? I'm fond of the SOHA name, but is the SOHA II really an opamp hybrid amplifier? Someone has mentioned this before. Shouldn't it be an SDHA or Child Of SOHA?

As you can see in the schematic posted by runeight in post #83, the SOHA II is NOT an OpAmp hybrid amplifier. SOHA II uses tubes as input/VAS stage while the output stage is discrete transistors based. The OpAmp is part of the DC servo circuit (to zero out the unwanted DC components) and is isolated from the audio path.

 

[mwofsi]

Quote:

Originally Posted by Ferrari /img/forum/go_quote.gif ........the SOHA II is NOT an OpAmp hybrid amplifier......

Thanks Ferrari, that is the point I was trying to make

Any thoughts about whether the name is appropriate?

 

[Ferrari]

It's a further development of the original SOHA with HUGE improvement.
So, why not SOHA II?

 

[mwofsi]

Sorry Ferrari, you posted at the same time as I edited.

The original SOHA name is an acronym(?) for "Simple Opamp Hybrid Amplifier",
which the SOHA II no longer is

 

[mwofsi]

Actually it appears that the original name stood for "Stoopid Opamp Headphone Amp" from the original article!

The title of that Headwize project page has it as "A Simple Tube/Opamp Hybrid Amplifier"

Kind of stepping all over my own point here

It's still a two stage amp with no global feedback and is a development of the original. No longer Opamp based though.

 

[Beefy]

Quote:

Originally Posted by mwofsi /img/forum/go_quote.gif No longer Opamp based though.

Does it really matter?

 

[mwofsi]

Does it really matter in the big scheme of things?

No.

Can Runeight call his amps anything he wants to?

Yes.

I'm just asking though before it's all finalised.

 

[mwofsi]

Whilst I'm being controversial:

By the way just noticed that there is feedback, separating this even further from the first published SOHA

The use of dual tubes on the input is also quite a change.

Is it necessary to use a matched pair of tubes?

I take it that it's just not possible to use two tubes in series (ie one half of the first tube combines with one half of the second for each channel), opening the possibility of non-matched or two different front-end tubes? I think that is answered in this post http://www.head-fi.org/forums/f6/soh...ml#post4412207
but I'm not sure?

.

 

[dBel84]

The naming of this amplifier was no easy matter and although several names were bandied about, SOHA II Super Single Ended Hybrid Amplifier was what it has become and the name is here to stay. The SSEHA part is easy enough , the SOHA II part is historical and if you are even vaguely aware of the history, you will understand that this is runeight reclaiming his design. The principles remain the same, the means of achieving the goal have changed.

As for the tubes, the design theory has been well explained in an earlier post. They do not need to be tightly matched but if they are significantly different, the plates will not bias equally. You can use any number of tubes with a similar pin configuration to the 12AU7 , either 6.3V heaters or 12.6V - there really are quite a few tubes you can choose from..dB

 

[regal]

I guess I really disagree with the comment that the Bijou lacks bass, but there really isn't any OTL tube (non-hybrid) that performs great with something like Grado's. This new Hybrid should be just the ticket for Grado's and the like.