Toshiba 3950 - under the hood - John Swenson - Digital Drive

Digital Drive

Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it.

Toshiba 3950 - under the hood

Ok, so I had to take it apart! Inside are two pc boards and the transport. One board is the power supply, very cheap looking switcher. The other is the signal board, THIS looks quite expensive. Its a small board with only a few chips on it, but very fine lines, power and ground planes and a LOT of 47uf electrolytics (I think they got a sale on these).
There is one big chip in the middle with a gazilion pins (fine pitch guad flat pack) which presumably is the main DSP chip. There is a transport control chip, a video dac, the audio dac and the dual opamp, thats about it.
The DAC drives 2 47uf electrolytics that go to the dual opamp that drives 2 more 47uf caps, then there are the infamous muting transistors and a simple low pass filter.
From a sound point its important to note that there is no seperate digital filter chip. This is very important. NONE of the available digital filter chips have implemented the digital filter correctly. Wadia and Theta (and a few others) have realized this, but they have all chosen to implement the filter as a program on processors, a VERY inefficient way to do it. The net result is that they still haven't implemented it correctly, to do it right takes a LOT of computing power which even multiple processors don't have. It turns out that it IS posible to make a custom chip that does implement a digital filter correctly but to my knowledge nobody has done this for CD playback.
The interesting thing here is that Toshiba has a large custom DSP chip to handle the video processing, my guess is that they put the audio digital filter on there as well. With modern chip processes a correctly implemented filter would only take up a tiny portion of a large custom chip. From an economic stand point it makes sense, one less chip to buy, put on the board and inventory. I know that Toshiba has some very good DSP engineers, I would presume that they would actually implement the filter correctly given that they were already doing a custom DSP chip for the digital stuff. The upshot is that I think this cheap little player actually does the digital filter RIGHT!
I hooked a scope up to the output of the DAC and sure enough it looks like the above is correct. I did not see ANY ringing on transients, every other CD output I've checked has the telltale pre and post ringing which is the sign of the incorrect digital filter. The output was VERY smooth without the high frequency crud normally found on cheap CD DACs. and this was before the filter! I was very impressed.
In addition the power supply noise was very low, I expected a fair amount of digital crud on the power supply, there was a little but it was a lot lower than I expected. (I was on the 2 mv setting on the scope and the trace was barely thickened, it comes out to less than 1mv of noise on the power supply, WAY good for a digital circuit) I don't know how they did it, probably due to the power and ground planes on the board.

The disk was spinning much faster than 1X so I presume that a FIFOed architectureis used, which means the clock can go directly to the DAC chip which should lead to very low jitter and with the low noise on the power supply will result in a design very immune to transport issues, ie you can get good sound even with a cheap transport.
Given all the above its no surprise the 3950 sounds as good as it does. The weak point of course is the output stage. Get rid of the elctrolytics, use a GOOD output circuit and beef up the power supply to the DAC and output and this will be a real contender. There is plenty of room to implement a small power supply and output board.
I think you can tell I was really impressed with this player! If someone had told me the above details, I would have presumed it to be at least $500, yet its in a $70 player, amazing! And that isn't even touching on the video!
The above says NOTHING about the qulity of the transport. These things might last for a year and then die. I've heard some people have had them die after a short time. I think THATS what you get for cheap, the electronics seems to be way above its price.
John S.

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Topic - Toshiba 3950 - under the hood - John Swenson 22:44:56 02/27/04 (11)

Re: Toshiba 3950 - under the hood - jimmyjames 17:28:50 02/29/04 (0)

Dose the 3950 upsample it dose not say it nowhere on the - Ben Mc 15:03:00 02/29/04 (0)

Best Buy has the Toshiba 3950 for $60 ON SALE from $80 starting Sun. Feb. 28. - bilbobaggins 11:04:31 02/28/04 (0)

Thanks for this - dvb 07:57:20 02/28/04 (0)

Have any you guys look inside the Phip 727 I am going to git a 3950 today - Ben Mc 06:59:03 02/28/04 (1)

Re: Have any you guys look inside the Phip 727 I am going to git a 3950 today - Bare 20:37:24 02/28/04 (0)

welcome to the dark side - rosconey 03:11:39 02/28/04 (0)

Re: Toshiba 3950 - under the hood - Max 00:06:09 02/28/04 (0)

Well..................... - Alex Peychev 23:00:08 02/27/04 (2)

Which of the low-priced CDP's makes the best tranbsport? - IanS 10:37:15 03/01/04 (0)

Re the Pioneer - PabloP 08:35:31 02/28/04 (0)

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