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Purifi VTV Amplifier (Eval-1)

jbo3320

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Hello guys!

This is my first post since joining the forum.

I was oblivious of the criticism before I purchased my amplifier and making recommended fixes to improve the quality and safety of the product as I am living in Korea and it's hard to make the return.

I'm going to follow the instructions on @Rick Sykora's guide on the VTV Amplifier first.

I'm wondering if there are more stuff that I should be concerned about.

Also, I have a main concern about switching the R17 resistor on the Eval-1 board as to change the gain setup.

I'll be pairing the Amplifier with a Topping D90LE with preamp mode enabled. I've heard that the DAC can provide max 5V RMS.

I'll be powering up a KEF R3's and probably going to listen around 70dB max 80dB since I live in an apartment and the speakers will be mainly used on the weekends and after work at night.

Is using the no buffer (bypass configuration) on the Eval-1 going to be enough to achieve the volume I want?

Otherwise what should I change the R17 resistor to? (I'm thinking around 6dB of the Front-end gain so around 6.6 kOhms ) ~20dB total including the purifi modules.

I appreciate all help!

Thanks,

Ben
 

NTK

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  • The gain without the buffer is 13 dB = 4.47x.
  • With the Topping D90LE outputting 5 Vrms, the maximum output voltage to the KEF R3 will be 22.3 Vrms ( = 62 W @ 8 ohm load )
  • 22.3 Vrms is 18 dB ( =20 log10(22.3/2.83) ) over the standard voltage used to rate loudspeaker sensitivity.
  • Therefore, for the R3 with sensitivity = 86 dB/2.83Vrms, your setup will produce max (peak) SPL of 104 dB (@ 1 m in free space).
  • With 2 speakers, the total SPL will increase by ~ 3dB to 107 dB.
I think it is fully adequate for normal listening level in a normal sized room.
 

staticV3

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@jbo3320 the D90LE will only output 4.2Vrms out of the box. If you want the full 5.2Vrms, then you have to go into the settings and change the maximum output level:
Screenshot 2022-10-07 at 20.00.57.png
 

Rick Sykora

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Welcome to ASR!

Looks as though you have got some helpful advice already. @NTK did a nice job of walking through the calc. Bear in mind the distance is 1m and may be different than your normal listening distance...

I do not have a Topping D90. My SMSL M200 supposedly puts out 4.2V for the XLRs and have had no issues with keeping my (Buckeye) Purifi gain at HIGH. This is also with an Echo link in the chain as well. I listen at about 3m with speakers of comparable sensitivity to the R3s. I would avoid modding the EVAL-1 gain resistors unless you find a clear need AND you are very comfortable with SMT soldering. :)
 
OP
J

jbo3320

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  • The gain without the buffer is 13 dB = 4.47x.
  • With the Topping D90LE outputting 5 Vrms, the maximum output voltage to the KEF R3 will be 22.3 Vrms ( = 62 W @ 8 ohm load )
  • 22.3 Vrms is 18 dB ( =20 log10(22.3/2.83) ) over the standard voltage used to rate loudspeaker sensitivity.
  • Therefore, for the R3 with sensitivity = 86 dB/2.83Vrms, your setup will produce max (peak) SPL of 104 dB (@ 1 m in free space).
  • With 2 speakers, the total SPL will increase by ~ 3dB to 107 dB.
I think it is fully adequate for normal listening level in a normal sized room.
Thank you for the thorough calculations!
 

Holmz

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  • The gain without the buffer is 13 dB = 4.47x.
  • With the Topping D90LE outputting 5 Vrms, the maximum output voltage to the KEF R3 will be 22.3 Vrms ( = 62 W @ 8 ohm load )
  • 22.3 Vrms is 18 dB ( =20 log10(22.3/2.83) ) over the standard voltage used to rate loudspeaker sensitivity.
  • Therefore, for the R3 with sensitivity = 86 dB/2.83Vrms, your setup will produce max (peak) SPL of 104 dB (@ 1 m in free space).
  • With 2 speakers, the total SPL will increase by ~ 3dB to 107 dB.
I think it is fully adequate for normal listening level in a normal sized room.

If we knock that back for classical having a crest factor of ~18 we get to an RMS of 90dB with the 107dB peaks.
And for 12dB crest factor, typical of rock, we get an RMS of 95dB with the 107dB peaks.

I agree with your conclusion it should be enough, providing that 90dB SPL is considered enough.
And with a sub, then some extra low end can make it more in dB(C) land, than dB(A).

If the OP is using a low output source (i.e. 1v) then an extra 10-13dB of gain may be needed somewhere.
I would not dick around with the 5.2 versus 4.2v as that is a fraction of a dB.
Better might be adding a few dB more gain in the amp if need be later on.

One can always want more, but not really need more.
 
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jbo3320

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If we knock that back for classical having a crest factor of ~18 we get to an RMS of 90dB with the 107dB peaks.
And for 12dB crest factor, typical of rock, we get an RMS of 95dB with the 107dB peaks.

I agree with your conclusion it should be enough, providing that 90dB SPL is considered enough.
And with a sub, then some extra low end can make it more in dB(C) land, than dB(A).

If the OP is using a low output source (i.e. 1v) then an extra 10-13dB of gain may be needed somewhere.
I would not dick around with the 5.2 versus 4.2v as that is a fraction of a dB.
Better might be adding a few dB more gain in the amp if need be later on.

One can always want more, but not really need more.
I'm just worried that I won't have much volume control resolution if I use the current buffer stage which has 14dB ending up with 27 total dB.

On Amir's review, he said that he reached the maximum output at as low as 1.5V.

Also I haven't got a subwoofer yet but have been considering one.

Does it make a huge difference? I have a rather small room and will be using the speakers in near field region.

I live in an apartment right now and I'm worried about the resonance and transfer of the acoustic energy to other floors.

If you think it's viable what do you suggest I'd get under a $1000 budget?

Do I need to set up some kind of acoustic damper?

Are you saying I shouldn't run the D90LE at 5V configuration as opposed to the 4V?
 

staticV3

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That's the menu you can pop up by holding the select button and then powering on right?
yea
I would avoid modding the EVAL-1 gain resistors unless you find a clear need AND you are very comfortable with SMT soldering. :)
from what I understand, bypassing the buffer can be done by just setting some jumpers. No soldering required
I would not dick around with the 5.2 versus 4.2v as that is a fraction of a dB.
+1.73dB actually (4.3 vs 5.25 for the D90SE)
I'm just worried that I won't have much volume control resolution if I use the current buffer stage which has 14dB ending up with 27 total dB.
With 4Ω load, the 1ET400A clips at around 260W (=32.25Vrms).
With the buffer enabled you will reach that point with 32.25*10^(-27.5/20)= 1.36Vrms on the input.
With the buffer bypassed you will clip the output with 32.25*10^(-12.75/20)= 7.43Vrms on the input.

With the D90LE in 5V mode, you will only be able to drive the EVAL1 to a perceived 80% of its max output power, though from what you've told us, you're not seeking peak SPL values anyway.
Are you saying I shouldn't run the D90LE at 5V configuration as opposed to the 4V?
5V out of the D90LE and low gain on the EVAL1 will give you the least amount of noise out of the Amp.
 

Holmz

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I'm just worried that I won't have much volume control resolution if I use the current buffer stage which has 14dB ending up with 27 total dB.

On Amir's review, he said that he reached the maximum output at as low as 1.5V.

Also I haven't got a subwoofer yet but have been considering one.

Does it make a huge difference? I have a rather small room and will be using the speakers in near field region.

I live in an apartment right now and I'm worried about the resonance and transfer of the acoustic energy to other floors.

If you think it's viable what do you suggest I'd get under a $1000 budget?

Do I need to set up some kind of acoustic damper?

Are you saying I shouldn't run the D90LE at 5V configuration as opposed to the 4V?

5v/4v =1.25:1 which is 1.5 in power, which is maybe ~2dB.

Are those buffer cards replaceable for a touch higher gain?
(In the near field you don.t need it)
 
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jbo3320

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5v/4v =1.25:1 which is 1.5 in power, which is maybe ~2dB.

Are those buffer cards replaceable for a touch higher gain?
(In the near field you don.t need it)
It's configured so that you can choose between the 13 dB and 27 dB. If you want something in between I have to replace the resistor
 
OP
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jbo3320

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yea

from what I understand, bypassing the buffer can be done by just setting some jumpers. No soldering required

+1.73dB actually (4.3 vs 5.25 for the D90SE)

With 4Ω load, the 1ET400A clips at around 260W (=32.25Vrms).
With the buffer enabled you will reach that point with 32.25*10^(-27.5/20)= 1.36Vrms on the input.
With the buffer bypassed you will clip the output with 32.25*10^(-12.75/20)= 7.43Vrms on the input.

With the D90LE in 5V mode, you will only be able to drive the EVAL1 to a perceived 80% of its max output power, though from what you've told us, you're not seeking peak SPL values anyway.

5V out of the D90LE and low gain on the EVAL1 will give you the least amount of noise out of the Amp.
Yes! That is correct.

I was worried about the gain being too small to output a good listening level but by your calculations, it seems like it'll be more than enough :)
 
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