[runeight]

It actually could be related to choice of O/P devices. Slim possibility, but still there.

This is because the noise from the BJTs increases with idle current and temperature and the O/P devices are running at 100mA. Compared to the max current for these devices this is very small current, but there could be a small, but audible noise difference between different types of BJTs.

I guess I'd have to look at specs and do math to see if this could be real.

Maybe a better BJT whiz than I am could offer some thoughts on this.

 

[holland]

i've used some toshibas and bd137, it didn't affect anything. i've also swapped tubes around with no benefits.

 

[runeight]

Then we can discount the BJT noise issue.

Which leaves us with, most probably, either ground current issues or noise from some other components in the system such as the HV regulator.

 

[FallenAngel]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif ...such as the HV regulator.

Which you REALLY shouldn't touch, 100V through a finger sucks!

 

[runeight]

It does get your attention though doesn't it.

You, even the 100V in this, under the right circumstance, can be deadly. So, as always, I urge everyone to understand that you are working with HV and to use all the proper procedures.

So, how does your new SOHA II sound?

 

[holland]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif Which you REALLY shouldn't touch, 100V through a finger sucks!

LOL! Sorry for laughing at your expense, but it was a good laugh that I needed right about now.

 

[Jrossel]

Quote:

Originally Posted by bmwpowere36m3 /img/forum/go_quote.gif Bump for status on prod PCB's

SOHA II boards have arrived. If you are in the US, you can order the board through glassjaraudio.com International orders please PM (your email) or Email me directly.

 

[bmwpowere36m3]

Quote:

Originally Posted by Jrossel /img/forum/go_quote.gif SOHA II boards have arrived. If you are in the US, you can order the board through glassjaraudio.com International orders please PM (your email) or Email me directly.

Awesome, already ordered and can't wait to build

 

[Mikenet]

Tube selection question: what tubes would give me the lowest gain in the SOHA II?

 

[FallenAngel]

Quote:

Originally Posted by Mikenet /img/forum/go_quote.gif Tube selection question: what tubes would give me the lowest gain in the SOHA II?

Gain isn't very high, seriously. I'm using GE 5963 and GE 6680 (two builds), there's no problem with too much gain. In fact, I would say that the gain is pretty much perfect for me. I use the middle point of my POT (or Stepped Attenuator) which works perfectly.

 

[FallenAngel]

As promised, a few comments on SOHA+JISBOS vs SOHA2 (both with GE 6680 tubes).

I'm been listening to the SOHA+JISBOS at work for hours on end and the SOHA2 at home. Tonight I have them side by side, both fed off a simple diyMod (Sonicap Gen1 output) and listening using MarkL modded D5000 headphones. I chose these headphones because they're very detailed and the "brightest" I have to try to catch all the nuances and faults of my music. I listen to a lot of music from French R&B (Jenifer, Koxie, Kenza Farah) to Rap (WuTang, 2Pac, Immortal Technique, Eminem - non-radio stuff, that stuff sucks) to rock (Linkin Park, Korn, System of a Down) to pop/dance (Kelly Clarkson, No Doubt, and even threw on Britney Spears for good measure).

Both amps sound great and I really enjoy them both, but having them this close together and listening to the same song with both, the differences are clear.

As some of you you know, I've been dealing with some background noise issues on the SOHA2 prototypes (yes, it's actually on both and when I let the amps warm up for a good 30 minutes, the noise is almost non-existent but still just barely there - definitely not something I notice when listening to music, even through the quiet parts).

So on to sound comparison.

First off, I have to say the SOHA2 is a speed demon! The bass (where it's most noticeable) is sharp, hard-hitting and very precise. The SOHA+JISBOS is a little slower and "mellower".

Bass (continued): More prominent in SOHA2, just a very good quality punch or rumble (when the song has it) instead of what I hear in the SOHA+JOSBOS which is a more mellower drawn out bass line. Certain victory for SOHA2 for my music taste, and I love strong bass, I just don't want to be overwhelmed.

Mids : Again the mids on the SOHA2 come out to the front a little, more in-your-face than the SOHA+JISBOS. You might say that SOHA2 is more analytical in the mids and it's easiest for me to think of SOHA2 as a strong classical singer while the SOHA+JISBOS is a more of a sultry jazz voice. Depends on mood to which I would prefer at the time; I would usually go for SOHA2.

Highs : The highs seem more sweet in the SOHA+JISBOS. I would not say the SOHA2 is less detailed, it's not, but the top end does sound sharp (I am trying to avoid using the world "clear" because there is no muddying of the highs at all in the SOHA+JISBOS, the SOHA2 is just more "sharp", perhaps even leaning to shrill with some instruments).

Note separation: SOHA2, no question. I'm pretty much note-deaf and I hear the instruments with this amp, not just a generalization of which notes they produce. The only other amp I hear that with is the Beta22.

How everything works together : Both amps have their (as I learned only today) distinct sound signatures. I think both are really great amps and I am enjoying both; choosing one isn't something I would want to do.

I will not have a final answer to which is better/worse, nor will I write a "conclusion". I like both, I'm very likely to keep both and use both regularly.

I will leave this note though: for Sennheiser HD600 & HD650, the SOHA2 is a clear winner.

 

[Mikenet]

The gain doesn't seem to be excessive by any means, it's just that I listen at low levels, and hate fighting with the pot(pots have a lot of issues at the lower end of the range). My main amplifier is an output buffer with volume control--it has a gain of 1. The example tubes given on the SOHA II site show gains ranging from 8.7 to 13. It doesn't specify if these are power or voltage gains...most designers list voltage gains. In which case a voltage gain of ~10 would give me a power gain of ~20dB, which would cut my range by a factor of 4(since perceived volume doubles very roughly every 10dB). For most users this is perfect, for me it's just a little loud. If I could change tubes and reduce it somewhat, it'd be worth a shot for me I guess. Otherwise I can just try out one of the standard tubes.

I wanted to try out tube amplifiers, and it looks like I can't get extremely low gain without sacrificing the sound I'm looking to try out. I could add lots of negative feedback, but that would cancel the "magic" distortion. I could build a cathode follower buffer stage(it would be almost exactly the same topology as my unity gain solid state amplifier...a mosfet source follower), but that would be extremely low distortion, and again, the tube "magic" would be lost.

I was looking for low gain tubes to try out in the SOHA II(I'm on winter break...so it looked like a good project to try), as that might help. Otherwise it looks like I'm stuck throwing an attenuator on the input, or doing something crazy like throwing a voltage divider between the input stage and the buffer stage(I'd need to think about it for awhile to see if the voltage divider would even work here...but that would give me some "magic" distortion by driving the tubes hard, and then throwing out the extra level...but it would destroy the negative feedback).

 

[Mikenet]

Great review FallenAngel.

 

[wiatrob]

Thanks FA, for elucidating the subtle yet distinct differences between the low ends on both amps. I've just started listening to the II with Ortho's (per dB's suggestion) and will have a report soon...

Can't wait to start my second proto build (on the bench RSN), with Toshiba output devices and higher current support...

 

[runeight]

Quote:

Originally Posted by Mikenet /img/forum/go_quote.gif The gain doesn't seem to be excessive by any means, it's just that I listen at low levels, and hate fighting with the pot(pots have a lot of issues at the lower end of the range). My main amplifier is an output buffer with volume control--it has a gain of 1. The example tubes given on the SOHA II site show gains ranging from 8.7 to 13. It doesn't specify if these are power or voltage gains...most designers list voltage gains. In which case a voltage gain of ~10 would give me a power gain of ~20dB, which would cut my range by a factor of 4(since perceived volume doubles very roughly every 10dB). For most users this is perfect, for me it's just a little loud. If I could change tubes and reduce it somewhat, it'd be worth a shot for me I guess. Otherwise I can just try out one of the standard tubes. I wanted to try out tube amplifiers, and it looks like I can't get extremely low gain without sacrificing the sound I'm looking to try out. I could add lots of negative feedback, but that would cancel the "magic" distortion. I could build a cathode follower buffer stage(it would be almost exactly the same topology as my unity gain solid state amplifier...a mosfet source follower), but that would be extremely low distortion, and again, the tube "magic" would be lost. I was looking for low gain tubes to try out in the SOHA II(I'm on winter break...so it looked like a good project to try), as that might help. Otherwise it looks like I'm stuck throwing an attenuator on the input, or doing something crazy like throwing a voltage divider between the input stage and the buffer stage(I'd need to think about it for awhile to see if the voltage divider would even work here...but that would give me some "magic" distortion by driving the tubes hard, and then throwing out the extra level...but it would destroy the negative feedback).

Mikenet, the gains listed on the website are voltage gains as you suspected. MHO is that you could increase the NFB by a small amount with little affect on the SQ but a bigger effect on the gain. What gain do you want to have?

As you read on the website the NFB reduces the gain spread of the different tubes making it possible to roll quite a few different types of tubes with having to make gain adjustments.

Don't put a voltage divider between the tube and the buffer. That will simply ruin the HF performance of the tube stage.