Ricard:
The basic noise of the 725D is about the same as the 725 and quite low. The analyzer circuit is working well and swapping a few opamps here and there helped. Getting the 20 KHz filter working better is very important. Its between the input amp and the first notch filter, it responded to opamp upgrades as well.
The monitor output noise is very much in line with what it should be. The metering circuit however has a problem and I have not figured out yet where the key circuit is. Its post filters and post distortion analysis, probably in the meter amp itself. That it doesn't change when the meter response is switched suggests its in that circuit. The older unit does not have the response control circuit so I'm flying blind.
I think it would also benefit from a DC cal of the input amps but I need an extender board to do it.
The basic noise of the 725D is about the same as the 725 and quite low. The analyzer circuit is working well and swapping a few opamps here and there helped. Getting the 20 KHz filter working better is very important. Its between the input amp and the first notch filter, it responded to opamp upgrades as well.
The monitor output noise is very much in line with what it should be. The metering circuit however has a problem and I have not figured out yet where the key circuit is. Its post filters and post distortion analysis, probably in the meter amp itself. That it doesn't change when the meter response is switched suggests its in that circuit. The older unit does not have the response control circuit so I'm flying blind.
I think it would also benefit from a DC cal of the input amps but I need an extender board to do it.
I think it is on this pcb ---->
The first pcb on the left of the near center pcb gap. from front top view..... Or, follow the wire from the monitor output port to that pcb.
There is a group of pcb on the left and a gap and a larger group of pcb on the right. The first pcb of that larger, right, group of pcb.
??
-RM
The first pcb on the left of the near center pcb gap. from front top view..... Or, follow the wire from the monitor output port to that pcb.
There is a group of pcb on the left and a gap and a larger group of pcb on the right. The first pcb of that larger, right, group of pcb.
??
-RM
Analyzers for sale -
There are a couple of nice analyzers - for a very reasonable price - for sale on ebay at this time:
A gen/analyzer combo from shibasoku - model AM57A. .003% Full Scale and 0-120dB range. About $1500.
Also, a Panasonic VP7723A about the same price; .0005%/ 0-130db range.
-RNMarsh
There are a couple of nice analyzers - for a very reasonable price - for sale on ebay at this time:
A gen/analyzer combo from shibasoku - model AM57A. .003% Full Scale and 0-120dB range. About $1500.
Also, a Panasonic VP7723A about the same price; .0005%/ 0-130db range.
-RNMarsh
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All very tempting. Is that THD or THD+N. I probably need something that goes lower for what I'm doing. Have you been able to extend the range using DM or notch?
they each measure both. But its THD spec number.
I have not tried a notch with the Panasonic --- own one.... dont own the other. With the Panasonic - it is a copy of the ShibaSoku concept and will show on loop-thru test better than spec's minimum. A notch will drop that to nothing, I guess.
-RM
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That is their best model. the one I use a lot. Highly recommended.
0-130dB distortion range. With internal source: .0001% max.
THx-RNmarsh
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Could you pls. send me a copy of Shibasoku 725B manual.
thanks advance.
sky2city@163.com
Roger.(sky2city)
thanks advance.
sky2city@163.com
Roger.(sky2city)
Richard.
Fine to me.
I have one VP7722 for spare part on hand, and going to do some investigation on it , dig out why it has good performance, such as Noise Floor, 2H, 3H.....
up to now, I got one piece of schematics, Page 1~3 of the service manual, about the input OP-amp.
anybody have the scan copy of 7722, It's appreciated for you help.
-Roger
sky2city@163.com
Fine to me.
I have one VP7722 for spare part on hand, and going to do some investigation on it , dig out why it has good performance, such as Noise Floor, 2H, 3H.....
up to now, I got one piece of schematics, Page 1~3 of the service manual, about the input OP-amp.
anybody have the scan copy of 7722, It's appreciated for you help.
-Roger
sky2city@163.com
If this VP-7722 can't be fixed, it's will be used for my investigation, dig out why it have so good performance on Noise Floor and HD.
Hope it can help to someone who are interest in it.
-Roger.
The operation is similar on ShibaSoku and mfr is same for both. Can you read the opamp part number on a pcb? I did a quick look inside a few weeks ago and it looks like mostly discrete circuitry..... ShibaSoku uses discrete opamp topology at front end.... IC Opamps other places.
THx-RNMarsh
Richard,
You are right. I check it in detial, I found it's discrete circuitry, not a OP-amp, the symbol A1~A3 in VP-7722 SM, just a symbol, and stand for discrete circuitry. Pls. refer to my attached.
the key component is the TO-99 marked in yellow circle. I will check the part number later on, given that my Vp-7722 is placed in my other place.
thanks.
Roger.
You are right. I check it in detial, I found it's discrete circuitry, not a OP-amp, the symbol A1~A3 in VP-7722 SM, just a symbol, and stand for discrete circuitry. Pls. refer to my attached.
the key component is the TO-99 marked in yellow circle. I will check the part number later on, given that my Vp-7722 is placed in my other place.
thanks.
Roger.
