[jjss49]

Some time back, I bought, for $350, a lovely older AVA Dac, called the FET VALVE TOPP Dac... it runs 2 pcs 12AX7 tubes in its output stage, and from my use, it will only read a 44.1k digital input - any higher frequency bit rate fed to it is not read. 

Pics of the DAC below...  my understanding is that is is a NOS R2R DAC (presumably, back then, they were all R2R, as delta sigma DAC processing was not commercialized yet...)

The sound of this unit, with its pair of Mullard 12AX7's, is absolutely lovely.  Dimensional, warm, coherent top to bottom, great big and deep image with good specificity.  Listening to it, I became curious about what DAC chipset it runs... opening it up, I see a pair of chips inside labelled ' P9712AD  DM74LS08N' - for the DAC chip geeks out there, what DAC chip is this?  Made by whom?  I am just curious to know.  What is the timeframe of this DAC... late 80's early 90's?

[rlee8394]

That’s not a DAC chip, but a quad 2-input AND logic gate. That TOPP-DAC is a Delta-Sigma unit, not R2R. Can’t remember the DAC chipset, maybe a Philips unit.
-Ron

[jjss49]

Ron - thanks for your input and knowledge - here are the other chips inside the unit... the big one is the input receiver i think ...  then there are several that are connected to heat sinks...

[rkeir]

I still use an AVA “Insight” DAC from 2008. I think this was the last model AVA used the Philips chip. If I recall correctly, back when your FET VALVE TOPP DAC was in production, FVA was not a fan of 1 bit d/a converters. I seem to recall a lengthy piece he wrote on the subject in The Sensible Sound magazine. So I think rlee probably is correct that your unit has a Philips chip.

[jjss49]

interesting... my online research found a european 'blue book' type source with a very complete listing of AVA gear going way back

it lists this FET VALVE TOPP DAC dates back to 1997

[rkeir]

I’m not sure if I understand what you are driving at but your serial number is your production date - 1998.

[rlee8394]

Yes the CS8412 is the input receiver from Crystal Semiconductor. The other three pin chips mounted on heatsink are linear voltage regulators, 5 volt and 12 volt devices.

-Ron

[jjss49]

so odd ron - i cannot find a DAC chip in here!!!    

rk - no point... i wasn't sure what the vintage of this DAC was... did not know the serial # has date of production info in it on AVA gear... that is good to know. 

i am curious to know if this dac has a bitstream or r2r chip doing the conversion... doesn't change how great it sounds, would just satisfy my curiosity

thx for your help

[avahifi]

The Philips X4 oversampling chip is on the botom side of the circuit  board.

Caution, don’t plug or unplug the RCA digital cable while the DAC is turned in.  We have seen that kill early versions of the the big Crystal input chip. If that happens, we still havea very few replacements,

Frank

[jjss49]

thanks frank! 

happy sunday...

the philips chip you reference ... do you recall if it is a bitstream or R2R type of D to A converter?

in researching philips d/a chips of that era, i am seeing TDA 154x or 153x numbered chips, which i believe are all R2R... would love to know which one is in this one, appreciate your indulging my curiosity

your point on not plugging/unplugging digital coax in whilst the unit is on is now noted - thank you!

[avahifi]

This series of our DACs used the Philips TDA1541A chips. Great for CD playback, not so good for hi res computer sound files.

Frank

[jjss49]

Many thanks Frank.  I am slowly collecting more and more of your gear... it is all so well designed and sounds wonderful.

I also bought a newer FET Valve Hybrid DAC w/ 6922's and Wolfson bitstream DAC chip... very interesting to compare the sound of two DACs you built, some 15 years apart!

That and a great Synergy 300 amp which now drives my ProAc speakers thru a Don Sachs tube linestage...  heavenly music.

[dB Cooper]

I still use an AVA “Insight” DAC from 2008. I think this was the last model AVA used the Philips chip. If I recall correctly, back when your FET VALVE TOPP DAC was in production, FVA was not a fan of 1 bit d/a converters. I seem to recall a lengthy piece he wrote on the subject in The Sensible Sound magazine. So I think rlee probably is correct that your unit has a Philips chip.

I remember the article, which used to be on the AVA website amongst the Audio Basics issues.

[jjss49]

i have been searching for that old article
i remember the sensible sound, have some back issues from way back then
no luck finding frank's article so far though