Allo Volt+ D Amplifier Review

[bigjacko]

It's pretty amazing that the included stepped attenuator at this price. And a good one apparently. Those can easily cost a much or more than this amp.

The step attenuator is very stiff to turn, I don't like it. Is step attenuator always hard to turn or there are better ones out there?

 

[restorer-john]

The step attenuator is very stiff to turn, I don't like it. Is step attenuator always hard to turn or there are better ones out there?

There are likely ways you can reduce the spring tension on the click-stop points in the attenuator. Back in the day, I used to bend the spring plate back a bit with ball bearing detent switches to give a "nicer" feel to the operation.

Many such switches can be modified to feel "nicer". Take out the postional detent altogether and pack the shaft/sleeve with 500,000- 1,000,000 wt silicone oil (used in R/C cars differentials). The contact points are usually so close together the wiper never ends up in no man's land.

 

[sir_frigorifero]

the knob is very cheap and crappy, it makes the attenuator very hard to turn.

i changed it with a bigger one, and while it's still stiff, now is easier to operate

 

[restorer-john]

the knob is very cheap and crappy...i changed it with a bigger one, and while it's still stiff, now is easier to operate

I don't know what to say without it coming across as rude, crude, or just plain bawdy.

 

[sir_frigorifero]

I don't know what to say without it coming across as rude, crude, or just plain bawdy.

i'm sorry but given that english is not my main language i'm having an hard time figuring what you're saying

 

[bigjacko]

There are likely ways you can reduce the spring tension on the click-stop points in the attenuator. Back in the day, I used to bend the spring plate back a bit with ball bearing detent switches to give a "nicer" feel to the operation.

Many such switches can be modified to feel "nicer". Take out the postional detent altogether and pack the shaft/sleeve with 500,000- 1,000,000 wt silicone oil (used in R/C cars differentials). The contact points are usually so close together the wiper never ends up in no man's land.

Thanks for the advice. I tried to open the step attenuator, but I could not open it because everything was soldered in one piece. How did you open your step attenuator?

 

[Doodski]

It's not a easy attenuator to modify. it has 2 screws and the rest is soldered.

 

[bigjacko]

It's not a easy attenuator to modify. it has 2 screws and the rest is soldered.

The screw had nut at the end that no tool could get it. I tried to unscrew for a long time and thought that was the way to "change" something, but I was wrong haha.

 

[thyristor]

Seems that there is a gain switch on the bottom.

And also AM bandwidth avoidance circuit.

 

[thewas]

Frequency response has a tiny bit of roll off at 20 kHz:

One short question, sorry if it has been answered already in similar amp reviews.

At which output impedances do you measure the frequency response, as it can vary significantly at high frequencies for Class-D implementations due to their output filters/inductivities like in below example:

 

[Biblob]

Is it possible to use this amp without volume pot and set the volume at a fixed value? If so, would it benefit the audio signal as well? It would definitely make it less prone to break/fail

 

[johan]

First , I would like to say a big thx you , to Amir , for the free work hs is putting into this great community.

The component you are discussing about is a ..."simple" common mode choke , used a lot on analog devices they are slowly disappearing as part of the "cost cutting drive".

Next (with blue pots) is a very smart design called a "capacitance multipler". It drops the DC voltage about 1.5V and it removes noise by up to 50db (0-20Khz) (PSRR) on your DC power. Yes you can use up to 31V on Volt+D

The output filter on Amp is NOT a datasheet copy(not TI design). We spent a lot of time finding optimal values and fine tuning the output filter, we have much , much more filtering the normal datasheet .

I think that one of the reason why people find Volt+D to sound good...is the noise reduction on the output filter. I am fully aware that it should not matter, and yet it is my opinion that it does. I have no hard data to explain it but this output goes direct to speakers. Very good speakers have zobel networks and such that remove the HF noise (attenuate it) but most speakers have substandard (or none at al ) filters and somehow some of the hi frequency finds the way to your ears. (again no hard data but its what I think and design to remove it)

Note that I do design using a AP machine but I do not get guided by only THD+N at 1Khz. I pay attention to other (measurable) data and try to attenuate.

 

[YSC]

Doesn’t expect this level of performance with a stepped attenuators as standard

 

[Doodski]

Is it possible to use this amp without volume pot and set the volume at a fixed value? If so, would it benefit the audio signal as well? It would definitely make it less prone to break/fail

Yes, fixed value resisters could be used instead of the volume pot attenuating resister(s). Dial up the volume you want and then measure the pot resistance at that setting. Order in resisters of said value and then solder them across the appropriate wires that lead to the attenuator assembly. You won't hear any difference, nada nothing. Otherwise just dial up a level and use any other volume control you have in the system if you have one.

 

[AudioSceptic]

the knob is very cheap and crappy, it makes the attenuator very hard to turn.

i changed it with a bigger one, and while it's still stiff, now is easier to operate

Double entendres aside, the bigger the knob, the easier it will be, as it's simply a matter of leverage. Twice the radius, half the effort.

 

[Tatteredmidnight]

What are the dimensions of this? They don’t seem to be listed on the manufacturer’s site, and I’ve been fooled by the panther twice now (he’s much bigger than I initially thought).

 

[sir_frigorifero]

Double entendres aside, the bigger the knob, the easier it will be, as it's simply a matter of leverage. Twice the radius, half the effort.

not only a matter of leverage because the attenuator positioning makes it tricky to operate since you have the upper and lower plate ledges and the metal support on the left, so you must have tiny hands to operate it from the front otherwise you have to grab rightside which can be uncomfortable.
a bigger knob can partly solve those issues.

What are the dimensions of this? They don’t seem to be listed on the manufacturer’s site, and I’ve been fooled by the panther twice now (he’s much bigger than I initially thought).

it is quite big compared to other class D amps. when i'll get home i can give you exact dimensions

 

[Tatteredmidnight]

not only a matter of leverage because the attenuator positioning makes it tricky to operate since you have the upper and lower plate ledges and the metal support on the left, so you must have tiny hands to operate it from the front otherwise you have to grab rightside which can be uncomfortable.
a bigger knob can partly solve those issues.

it is quite big compared to other class D amps. when i'll get home i can give you exact dimensions

Much appreciated. Also, you missed my double entendre, so 1:2 on that front lol.

 

[Tks]

The power supply is the largest challenge in amplifier design. Not only it gets expensive, but also it usually degrades performance a lot in the design. Magnetic interference, leakage current you name it. And well it's simply bypassed here. I am curious to see the performance with power supply from allo or some other power supply people would actually use.

I thought power supplies were something non botique conpanies simply pick off a shelf from OEM's?

@amirm

Hows the stepped attenuator feel (wish more companies would use this in desktop amps tbh). Also do you have a SINAD vs Power Level going?

 

[JohnBooty]

i'm sorry but given that english is not my main language i'm having an hard time figuring what you're saying

"Knob" is (primarily UK/Aussie) slang for one's male anatomy.