DIY Sony VFET pt 1

[ClaudeG]

Ah, sorry, now I believe I get it - confused because my parts still haven't arrived but looking at pictures and from your comments I do understand the trim pots are not already mounted on the OS boards with the other parts Papa mounted, hence up to us to adjust the 20V.

Correct?

 

[Soundhappy]

Yes correct 🙂 Have a nice evening

 

[ClaudeG]

Thanks, I believe I need a good night... and to get the parts physically to see and feel all that rather than just read about it LOL

Good night too!

Claude

 

[juanitox]

In the meantime, I'm very curious how the Silmics IIs will work out. I understand you did not like them, Juanitox, but could you tell us why?

just a matter of good taste 😀

 

[MEPER]

Does the VFET follower have less than x1 voltage gain since the gain is only 10 dB while M2X has 14 dB of gain. Both have x5 "magnetic voltage gain" from Edcor even that M2X has Edcor wired as auto-transformer?

 

[Zen Mod]

Edcor 600:15K :

normal use ( galvanic isolation between pri and sec -) gain 5V/V = 13.98db

autoformer use - gain is (1+5)V/V=6V/V=15.56db

not counting losses

 

[MEPER]

Thank you!
So x6 vs x5 in front end and then some losses.
VFET must have a bit more losses than M2X to make of for the 10 dB vs 14 dB gain.

I was thinking of using my M2X amps to drive the bas speakers and use VFET to drive mid and tweeter. But then there is a little bit of gain difference.

Maybe "blasphemous" to use M2X for that purpose.
I assume that below 180 Hz class A does not make much sense?

 

[drjbf1]

NP and Mr MR have previously pointed out that as followers the Sony parts have negative gain. In the article NP says "it has significant voltage loss as a follower". I haven't read anywhere what the loss is, but in some LTspice sims I did, 1 volt IN got me about .6 volt OUT. Not sure if that is an accurate figure in this case though....that seems a bit high compared to the measured overall gain compared the transformer gain in this amp.

 

[Zen Mod]

Nature of the Beast

fire up LTSpice and you'll clearly see resistive nature of part, that's one of the reasons why you have that silly triodish character

 

[kbergsson]

@Meper, I have been thinking in similar terms, The VFET (once I get the time to build it) on my JBL075/Altec 1505B/299 horns (passive filter on JBL tweeter and run 1505B/299 down to ca. 500Hz), M2 or Sissy on the Altec 828/515C (down to somewhere between 120-60hz. Need to find a good solution there) and then a big class D on my two JBL2242H in soon to be modified Altec 620 cabinet clones. Ample opportunities for failure but also potential for a spectacular result. 🙂
Today I'm using passive filters on the Altecs VOTs and no bass support. Sounds great with FW amps. But why not try to reach for more 🙂

 

[Zen Mod]

I was always thinking about simplest possible arrangement, I mean only that one being simple enough to not disturb my laziness :

say that I have OB with Tannoy 15" up (xovered full range, no high pass on bass section) and Beyma 15" as bass helper

say that I'm driving Tannoy with nice 10W amp

then F4, fed from previous amp output, driving bass helper

manipulation of F4 level easy

in the end, I'm driving all that with nice 10W amp, being lazy to haul F4 to even try

 

[kbergsson]

ZM you are not greedy enough 🙂
I had for several years Lowthers in Mau IV horns, passive pre and a PSE 2A3. That was simple and good up to a limit, perfect records got perfect sound, less than perfect records.... bleeding ears.

 

[MEPER]

I am fine-tuning speaker placement and listening position after I re-organized the listening room. So I need to get this into place with M2X amps before I switch to VFET. I have these RCA splitters and the crossovers are prepared for bi-wire / bi-amp. Now I only bi-wire. But tempting to try out how bi-amp would work. M2X is better to drive low impedance than VFET (I assume) and the 15" woofers has a dip to about 4 ohm (else impedance curve is nice around 6 ohm). The preamp in use in the moment is SSII and this amp should have no problems driving both amps as SSII is made for driving headphones.

 

[Dennis Hui]

Wow. That is one serious crossover!

Perhaps I missed it, but how will you adjust for the difference in gain
between the M2x and vfet amps?

Cheers,
Dennis

 

[thompsontechs]

What Dennis said, there is some series coin in those parts.

 

[kbergsson]

Nice system @Meper

 

[MEPER]

Thank you!
Yes, the filter is the 1. grade version of Troels Gravesen OBL-15 speaker crossover. The two filters are maybe like $1000......or so in components.

I will try first without any adjustments and listen how it sounds.
To adjust levels I could maybe insert a passive preamp between preamp and M2X. I have a 24 stepped 10k Goldpoint attenuator in my passive pre. A simple voltage divider could maybe also do it......?

Another wilder suggestion......I have two SSII preamps. The preamps has high input impedance so I could just use two of them so my Bluesound Node 2i (with upgraded PSU 🙂 ) could drive both SSII.....but not easy to adjust levels when it is a pot instead of a stepped attenuator where I could just count "clicks".

 

[rayma]

I am fine-tuning speaker placement and listening position after I re-organized the listening room.

Move that coffee table out of the way, the sound will be better. Try it.

 

[MEPER]

I can try......then I miss a place for the red wine.....or coffee....

There are some "music" in the table as I got it 2nd hand and the owners was the parents of a member (the vocalist) of a famous "former" Danish rockband "Big Fat Snake".....

 

[rayma]

I had a beautiful coffee table of a similar size, and it ruined the sound due to reflections from the top.
Listen and then move it, or at least cover it with a wool rug etc. for testing. You can instead have a
table on one side of the listening chair/couch.