65 amps...

[bruno]

Recently got a hold of new 65 amps ventura, which I'm enjoying. Obviously had to take a pick inside, since it's sort of a simplified soho.

I found out that 65 uses a lot of details to limit bass and most likely blocking distortion, right after the input there is a sort of high pass filter formed by a 0,1uf cap and a 1M resistor.

The cathode of the first ef86 stage also has a sort of treble boosting cap. Along with some other cool details, which give the amp a characteristic tone which some of you seem to have picked up from the youtube videos of the soho.

[PRR]

> a sort of high pass filter formed by a 0,1uf cap and a 1M resistor.

2Hz. Does not shave any bass. More likely a defense against pedals with DC leakage.

[John]

More likely a defense against pedals with DC leakage.

The .1 cap... would that be in series with the 33k grid stop going into V1, in parallel with it, or going to ground?

I run cheap pedals.

[bruno]

Yes that is true the 0.1uf wouldn't shave enough bass.

Right at the input you have a 1M resistor to ground, then the 0,1uf cap, then another 1M resistor to ground, and then the 33k grid stopper in series with the cap.

Across the input jack there is also what appears to be a very small blue component, which looks like a cap, but I haven't been able to understand how it's wired, or what it does.

[John]

Cool, thanks.

[bruno]

[seedlings]

Thanks for the pic!  Always nice to have a look inside for curiosity sake.

CHAD

[tubeswell]

More?

[HotBluePlates]

If the chassis wasn't being used at all as the amp's circuit ground, I'd think the blue component was a cap from the isolated jack ground to the chassis to shunt RF interference.

But, I think I see other places where there are chassis bolts used as grounding points. If that's the case, the theory above doesn't work. In other words, it relies on a circuit that keeps chassis ground (including the ground wire of the power cord) isolated from signal ground (all other grounds used by the amp/power supply circuitry).

[bruno]

I believe that's precisely what is happening, however there are indeed bolts being used as chassis ground.

[clyde]

What is the IC on the chassis? 

[Geezer]

What is the IC on the chassis? 

Power-scaling circuit

G

[Willabe]

Power-scaling circuit

But where's the control pot for it?     

The mosfet and pot should be close together for stability.


                     Brad

[Geezer]

Power-scaling circuit

But where's the control pot for it?     

The mosfet and pot should be close together for stability.


                     Brad

http://www.65amps.com/the-ventura.html#7

The "Master" is actually "Master Voltage" (VVR)

Don't know how they get away with the distance.........

[Willabe]

Don't know how they get away with the distance.........

Huh. I guess it's working for them?


                     Brad     

[TubeGeek]

I have had a few of 65's amps come across my bench.  

Here is a pic of the component in question on the input jack...looks like a cap to me.  I zoomed in on it and it looks like it connects to a piece of brass which probably connects to the chassis.

This is from an Empire.

[Willabe]

Now that amp looks like the VVR mosfet is pretty close to it's control pot?


                           Brad     

[PRR]

> a circuit that keeps chassis ground ...isolated from signal ground

You can float the input jack and have the main audio-signal ground at the other end of the amp. In that case it is often done to use a small cap to shunt any RF at the input jack to chassis rather than make it flow all the way through the amp's signal ground system.

[Quatro]

You can float the input jack and have the main audio-signal ground at the other end of the amp. In that case it is often done to use a small cap to shunt any RF at the input jack to chassis rather than make it flow all the way through the amp's signal ground system.

What's an optimal value to get the job done?

Thanks

[HotBluePlates]

Probably something on the order of 0.001uF to 0.01uF.

Remember, this is not going from hot to ground, but from the ground lugs of an isolated jack to the chassis.

[6bq5]

the .1uf on the input is to block dc that develops when you lower the power scaling to max.   if you don't have it there the guitar vol pot will get scratchy from the dc developed on the input.    usually happens if you scale to go below 60v or so on the plates.   65amps uses dana hall's vvr circuit.     rh

[HotBluePlates]

The cap I was talking about is not in series with the signal, like a blocking cap. It's shunting from a ground terminal to chassis ground.

[bruno]

I drawed a little bit of the preamp too. It's an interesting amp, but nothing overwhelming.

[proaudioguy]

If the chassis wasn't being used at all as the amp's circuit ground, I'd think the blue component was a cap from the isolated jack ground to the chassis to shunt RF interference.

But, I think I see other places where there are chassis bolts used as grounding points. If that's the case, the theory above doesn't work. In other words, it relies on a circuit that keeps chassis ground (including the ground wire of the power cord) isolated from signal ground (all other grounds used by the amp/power supply circuitry).

What you describe here (isolating signal and chassis ground) is the only correct way to handle audio equipment shielding and grounding. The manufacturers in my industry that have tied audio signal ground to chassis ground have what is known as the pin 1 problem.  What should be draining off to earth ends up in the audio circuit.  Google is your friend here.
http://pin1problem.com/
http://www.rane.com/note165.html

[HotBluePlates]

The saving grace is that while pro audio has a large number of interconnected pieces of gear and maybe miles of mic cabling run through the walls, most often we just have a guitar and amp.

[bnwitt]

Yek! Terminal strips.  I thought Leo and Mr. Marshall brought us out of the stone age.

[SLW]

I would like to see your drawing of the circuit.  It is always fun to see how things are done.

[fuzz]

nothing new about this ventura ?

[neon333]

Recently got a hold of new 65 amps ventura, which I'm enjoying. Obviously had to take a pick inside, since it's sort of a simplified soho.

So what is different between the Ventura and the SoHo? Never seen the inside of either.

[phsyconoodler]

Yek! Terminal strips.  I thought Leo and Mr. Marshall brought us out of the stone age.

Indeed. Seems he uses terminal strips so people have more difficulty reverse enginbeering his circuit.They are all plagerized anyway,but he has a couple of tricks here and there to make them sweet sounding and he likely wants to keep it to himself while he's riding the wave.
  They go for a pretty penny,for a mediocre wiring job.It's all about being in the right place at the right time like Dr. Z.Nothing special about either amp,just solid build and they sound good.
  Pretty much like most of the builders on this forum.

[darryl]

Yek! Terminal strips.  I thought Leo and Mr. Marshall brought us out of the stone age.

. . . but there are still some of us who prefer to remain in the tagstrip stone age. 

[bigsbybender]

They are all plagerized anyway,but he has a couple of tricks here and there to make them sweet sounding and he likely wants to keep it to himself while he's riding the wave.
  They go for a pretty penny,for a mediocre wiring job.It's all about being in the right place at the right time like Dr. Z.Nothing special about either amp,just solid build and they sound good.
  Pretty much like most of the builders on this forum.

I remember him posting a lot on another forum when early on when he started this company... He's just like one of us but he got lucky. I recall him being having good manners online and being helpful toward others.