[sdiy] Coolaudio VCAs: V2162 noisier than V2164?

[Stewart Pye]

It might be worth asking THAT. Their applications engineers are very 
helpful, which is a good reason to buy their chips and not Cool Audio's...

Regards,
Stewart.



On 12/24/2015 9:28 AM, Mattias Rickardsson wrote:
> On 22 December 2015 at 11:56, Stewart Pye <stewpye at optusnet.com.au> wrote:
>> I haven't used the 2162, but I'm sure (at least with the THAT part) it will
>> live up to the data sheet.
>> It appears that the 2162 (in single ended mode) is capable of 20dB more gain
>> and 20dB less attenuation than the 2164, which could result in more noise.
>> Also, read the THAT 2162 datasheet carefully, especially noise
>> considerations on page 8.
> Those considerations should be cool, but one thing that I've *not*
> done like the datasheet is the input resistor of 20k. Since I used a
> soundcard directly as the test tone generator, with a signal of just a
> couple of volts, I put 2k5 as input resistance and recalculated the
> voltage values to give me the same input currents as in the datasheet.
>
> I found the clip level where I expected it, so the signal calculations
> should be alright - but does it matter that I've changed the input
> resistor? Does the 2162 input behave differently (noise-wise) if it
> feels a lower impedance there?
>
> (Btw also the output resistor has been lowered for the same reason,
> but that is situated in the op-amp feedback path beyond a virtual
> earth summing node, so I guess it can't affect things.)
>
>> This may have the info you need:
>> http://www.thatcorp.com/THAT_Alternatives_to_SSM2164.shtml
> Interestingly, that page says
> "For best noise performance with the 2162, we recommend 20 kΩ for the
> input resistor (Rin) and for the output (Rout) resistor in the
> current-to-voltage converter."
> This could either mean just that you should avoid higher resistances
> as they give a lower signal current and worse noise due to lower
> dynamic range, *or* they could mean that the input resistor actually
> affects the behaviour of the VCA. I'm not sure! Are you? :-)
>
> /mr
>
>
>
>> On 12/22/2015 8:04 PM, Mattias Rickardsson wrote:
>>> Hi Chris,
>>>
>>> I'm using a MOTU UltraLite Mk3 Hybrid sound card and Arta software on a
>>> PC.
>>> The 2164 and 2162 have I/V converters built from a NE5532 low-noise
>>> op-amp.
>>>
>>> I've tried to eliminate all sources of stupidity (except myself) and
>>> compared different ways of disconnecting & comparing the sources of
>>> noise. With the 2164, the generator (MOTU) is noisier than the VCA,
>>> which is noisier than the op-amp, which is noisier than the analyzer
>>> (MOTU). With the 2162, the VCA is noisier than both the generator, the
>>> op-amp and the analyzer. I've also tried to eliminate all noise on the
>>> CV signal and tried to avoid HF oscillations.
>>>
>>> Is the 2162 used by anybody or in any product out there?
>>>
>>> /mr
>>>
>>>
>>>
>>> On 21 December 2015 at 17:40, Chris Juried <cjuried at yahoo.com> wrote:
>>>> Hi Mattias,
>>>>
>>>> What instrument(s) are you using for you SNR measurements?
>>>>
>>>> Sincerely,
>>>>
>>>> Chris Juried
>>>> Audio Engineering Society (AES) Member
>>>> InfoComm-Recognized AV Technologist
>>>> http://www.JuriedEngineering.com (Juried Engineering, LLC.)
>>>> http://www.TubeEquipment.com (Tube Equipment Corporation)
>>>> http://www.HistoryOfRecording.com (History of Recording)
>>>>
>>>>
>>>>
>>>> ________________________________
>>>> From: Mattias Rickardsson <mr at analogue.org>
>>>> To: synthdiy diy <synth-diy at dropmix.xs4all.nl>
>>>> Sent: Monday, December 21, 2015 10:21 AM
>>>> Subject: [sdiy] Coolaudio VCAs: V2162 noisier than V2164?
>>>>
>>>> Hi there VCA lovers,
>>>>
>>>> I've done some measurements of SNR & THD of the 2164 and 2162 VCA ICs
>>>> from Coolaudio, and I'm very surprised with the noise results I'm
>>>> getting. With the 2162 I cannot reach a SNR over 95 dB before
>>>> clipping, at any gain. With the 2164 at gain=1 I reach 120 dB SNR.
>>>> That's a huge difference!
>>>>
>>>> When trimmed properly the 2162 does have slightly better THD, but the
>>>> noise seems to always be there in the background. I hope my
>>>> measurements are correct... the "-97 dBV" noise spec in the V2164
>>>> datasheet seems a bit odd to me compared to the "-94 dBu" in the V2164
>>>> dataheet - or I've misunderstood them.
>>>>
>>>> Has anyone else tried the 2162 (either from THAT or from Coolaudio)
>>>> and compared it to the 2164 or other VCAs?
>>>>
>>>> /mr