Recent trashing of the VTA ST-70

[Marvel]

On 4/18/2022 at 4:42 PM, captainbeefheart said:

On 4/18/2022 at 4:30 PM, John Warren said:

The PC board layout was done by newbie.  

 

 

I concur, poor layout for more than one reason.

I sort of agree, but this was designed to pretty much be a drop in replacement for the original board, so connections to the board were made to follow the original placement of wiring.

 

On 4/18/2022 at 4:42 PM, captainbeefheart said:

 

Pin 8 looks tied to a transistor, which I am sure is also tied to pin 3. Is that a TO-92 package? I am curious what the tail circuit looks like with just one transistor, I typically need at least two get a high enough AC impedance to be worth it. A TO-220 package would indicate a 10M45S type current source package which will give decent results but it doesn't look like that package to me.

 

He added a CCS (constant current source) to his original design, which was released in 1989. I've got the previous version without the CCS circuit. Roy Mottram designed the upgrade boards, Bob Latino came along later. Was the Latino one reviewed built as a kit or by Latino? The paperwork with my board says it has a factor of 10 improvement in THD and IMD measurements. IF that is true, something isn't right on the one tested on ASR. As I wrote above, Bob Latino is no longer working with Roy (as of May 1).

[captainbeefheart]

6 hours ago, Marvel said:

I sort of agree, but this was designed to pretty much be a drop in replacement for the original board, so connections to the board were made to follow the original placement of wiring.

 

 

He added a CCS (constant current source) to his original design, which was released in 1989. I've got the previous version without the CCS circuit. Roy Mottram designed the upgrade boards, Bob Latino came along later. Was the Latino one reviewed built as a kit or by Latino? The paperwork with my board says it has a factor of 10 improvement in THD and IMD measurements. IF that is true, something isn't right on the one tested on ASR. As I wrote above, Bob Latino is no longer working with Roy (as of May 1).

 

I agree they wanted to keep the same connections but I also think there could have been a happy middle ground where you keep the same ins/outs yet arrange the components with a little more care instead of how they do it. The way they do it has a clean look with the resistors all lined up in rows but it's not optimal.

 

As for the new design with all triodes and the LTP, the results is why I said it has worse performance yet they claim better performance, you may be correct in that there was something wrong with the amp Amir tested because for what they have to work with they should easily get much better numbers without much effort. I like the addition of the CCS on the tail of the LTP but they chose a pretty poor component as I showed with the graph because their impedance above 10kHz drops like rock, you want a constant impedance over the entire audible frequency range at the very least.

 

With the same amount of tubes, 3 12AU7's they could have used one bottle for a cascode which will behave just like a pentode but with less noise and then DC couple to a shared bottle where one triode per channel is the split load phase inverter. This would the closest to the original and still improve upon it with less noise. The VTA is essentially a Mullard circuit with a triode first stage instead of a pentode but with worse performance. If we are trying to keep the original sonics then the cascode - split load would be the best option. If you want to change it completely then either do the Mullard circuit right or better, just use two dual triodes per channel and do a Williamson circuit which IMHO is a really great circuit.

 

Does anyone have a VTA 70 version in the New England area? I can take some measurements to see if they align with Amirs then we know the one Amir tested wasn't broken. It sort of makes sense something was wrong because you would  have to put forth some effort to get that high distortion at only 10 watts with this topology, something is way off balance here. 

[John Warren]

On 5/1/2022 at 9:03 AM, Marvel said:

I sort of agree, but this was designed to pretty much be a drop in replacement for the original board, so connections to the board were made to follow the original placement of wiring.

That has virtually no impact to the layout.

[Marvel]

1 hour ago, John Warren said:

That has virtually no impact to the layout.

I will certainly agree with that. Especially after seeing your boards.

[Idontknow]

In the end, I would never trust anything Amir has to say regarding listening impressions. He doesn’t understand the importance of matching gear and if he does, he obviously doesn’t practice it. 

[jjptkd]

34 minutes ago, Idontknow said:

In the end, I would never trust anything Amir has to say regarding listening impressions. He doesn’t understand the importance of matching gear and if he does, he obviously doesn’t practice it. 

I never heard of Amir or ASR before the Carver 275 review but the way they handled that whole situation burned me on them. The people there were lining up taking kicks at the old Bob Carver I found it all very distasteful, ended up getting banned for being a "troll" simply for calling them out on their childish antics oh well no love lost here screw 'em I say. 

[Idontknow]

You did fine. I banned myself from ASR so you’re not alone. They’re cult like and all they do is base everything on measurements. You can’t know how something will sound because Amir measures it. That stuff is for real factory professional technicians. Amir is not a professional tech. Have you seen how many items they’ve measured. Nearly a thousand components. No one in their right mind could properly evaluate that much gear in a life time. They just measure it and that’s it. Amir doesn’t even like tubes because they measure bad. Hello!

[a9050lx]

I have a VTA driver board bought 1.5 yrs ago in order to rebuild an old rusty st70. I used the 12AU7 version, as I have a hundred of them laying around in some iteration. Very listenable amp.My wife initially bought the amp at a yard sale for 10 bucks or so with all original output tubes (proud of her, I wasn't even with her!). It sat for 20 yrs or so until I rebuilt it, Just felt I had to do something constructive with it, painted the chassis hammertone bronze. rewired of course.Really not an unpleasant sounding amp by any means.No idea if it distorts unpleasantly at 10 watts or so,as with LaScala's 10 watts will drive you out of the room. I think as a push-pull amp it sounds just fine.

[Idontknow]

That’s good to hear. After hearing the ST35 though, I’ve really been enjoying the ST35’s.

 

 

[MeloManiac]

4 hours ago, Idontknow said:

That’s good to hear. After hearing the ST35 though, I’ve really been enjoying the ST35’s.

 

 

It will be interesting to see how the premium tubes evolve over time, compared to the standard ones. Do you have more info about the tubes? Brand, nos?

Most of the new 'branded' EL84 tubes are all made in the same production facility in Ching Chang, and you pay premium price for the name they print on the glass, and the colorful packaging. 

They are all mediocre quality compared to 1950s/1960s NOS tubes. 

[a9050lx]

Don't think I ever heard a bad 6bq5/EL-84 amp.I have an old Fisher console amp I borrowed the outputs from and built  two Simple push pull Tubelab amps,one with Fisher outputs and one with  Olson integrated amp output transformers.The Fisher Output transformer triode amp is very engaging.

[Marvel]

On 6/30/2022 at 3:34 PM, MeloManiac said:

Most of the new 'branded' EL84 tubes are all made in the same production facility in Ching Chang, and you pay premium price for the name they print on the glass, and the colorful packaging. 

 

Made me laugh out loud...🤣