Found an old SI 5066

Panelhead · « **on:** 5 Mar 2005, 06:26 pm »

I matched up a couple of 5066 for dc offset and was starting on making a amp using one for each channel.
Disassembling one it only had the four screws holding the case together. The two in the battery compartment were not there.
Further looking shows a date of 7-3-2003 on the board. The input cabling is a lower quality than the newer versions.
But most disturbing, there are no clamping diodes on the outputs. I am not sure if they help or hurt the sonics, but Tripath says they have to be there.
I never listened to this one, it was picked up on ebay as part of the Soundpax system. But the soldering seems to be of lower quality.
This shows me how to look at the case and tell the earlier T amps from the newer, more refined model. If the two screws are not in the battery compartment, it is the older version.
I think all the ones being sold as part of the Soundpax system are the older version, buyer beware.

George
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BillyM · « **Reply #1 on:** 5 Mar 2005, 07:36 pm »

Mine, with the older version board, had the two screws in the bottom of the battery component. ...had a date of 7/03 as well...

Clamping diodes are definately not there.

...from what I've gathered (keep in mind I dont have one to test, nor have I read any specific specs on the clamp's on the later SI's) these may limit the outgoing voltage to make clipping less pronounced. ...imagine an audio-ignorant user hooking a portable CD player and SI (both volume maxed) up to a set of their flat-panel speakers.

Other than circut protection, do the clamping diodes have any effect on the sound of the SI? I believe some diodes have a certain ammount of capacitance

--BillyM

doggie · « **Reply #2 on:** 5 Mar 2005, 09:40 pm »

Thanks for starting this thread. I was just about to ask the same question. I was recently looking over the photos of the SI boards from George's choke mods and noted how different they looked from my own. I have opened 4 units over the space of about three months. None looked like those photos. None had the black diodes that show so well here next to the chokes:

I just received three "new" units directly from SI and they were all of the "older" style. In fact now I understand why Vinnie mentioned adding clamping diodes because the Tripath spec calls for them but it seems as if some SI boards do not come with them. Can these diodes be added across the output/speaker terminals or do they need to be at the chip pins as the Tripath schematic shows?

I have some 3amp 100vPIV fast recovery diodes. Would these work or is there a better kind. If so what would you use? One other noob question: does the stripped marking on the diode go towards the speaker terminal(s) or the power ground(negative)? For that matter, the schematic seems to show one channel with the diodes "grounded" to pin 35 and the other to pin 20 but it seems that both pin 35 and 20 are then connected to power ground. Is that right? If so can all of these diode leads be connected to a shared point and then to battery negative?

Hope I am not screwing this up to much. My soldering iron is safely holstered a waiting informed comment

Thanks,

Paul

Panelhead · « **Reply #3 on:** 6 Mar 2005, 03:51 am »

If a lot of th SI boards do not have them, it is not a big deal. The first two I opened had them, assumed all did.
Not having them should improve sonics. There is capacitance, maybe not linear.
The diodes are marked just like all others, the current flows from pos to neg. The band is the neg side. So they hook up reversed polarity, the band goes to the ouput side and the other goes to ground.
They make lots of sm schottky diodes. The ones in the picture are most likely SMC size. A 3 amp 20 volt would be plenty. I have used these in disc players, should be great.
The Tripath sheet shows them right at the pins. The four on my SI boards are not right at the chip.
BTW, there are two more on the topside of the board. There is a total of four on each.
Since I have two without doides I may go ahead and try modding them. But still have an order for two more from PCMall. If they will show up this month as expected it can wait.
The quality of the wire for the signal is much better on the boards with diodes. Since I do not use the pot, they are clippped off on the input and the output of the pot is connected to the RCA's. I may try removing that whole connector and just putting better wire in. That cheezy grey ribbon cable in these is has no place in a unit with this kind of potential. It belongs in a 20.00 amplifier.

George