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Old 9th May 2005, 10:05 PM   #1
reever is offline reever  United States
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Default Rod Elliotts Project 97.....

Has anyone here used this?\\http://sound.westhost.com/project97.htm
Looks interesting, and I'm looking to substitute lt072 with LM833, 'cause I have about a million at my disposal.
Just a question for the Gurus out there.....

Oh yeah, I'm running a hand wired Brian GT 3875 with +/-28volts.
I tried the LM1036 but its just not working as expected...


-reever
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Old 10th May 2005, 01:28 AM   #2
rodolfo is offline rodolfo  Mexico
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a million wowwwwwww
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Old 10th May 2005, 02:28 AM   #3
reever is offline reever  United States
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Yeah, I know, as soon as I posted that I was sure someone would jump all over it

So no one has used this circuit? I am leaning towards an Integrated Amp and this looks like a decent way to go. Anyone with an opinion or a sugestion please chime in.....
Thanks
-reever
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Old 10th May 2005, 10:01 AM   #4
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From what see in the site, seems a well circuit built and the planner seems me reliable.
For the chips, the LM833 would work but you have problems of Voltage offset ( LM833= input BJT ). You suggestion to use or that original (TL072) that they have an audio quality better than what is believed ( have been second-hand by great marks as Quad and other ) or an other type but always with input to FET.

Ciao

Mauro
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Old 10th May 2005, 10:42 AM   #5
Bikeman is offline Bikeman  Australia
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Hi Reever.
I used the P97 and P3a together as an integrated amp.

See:

Finished first amp!

I found it has much more gain than I need, never had volume past 1/3.

I used BB 2134 opamps. Had a little overshoot on a scope. Maybe decoupling caps not enough for the high speed chips. TL072 will be no problem I'm thinking.
Had a tiny bit of hum, but that was just as likely being picked up by the output boards.
The only actual problem I had was that the pots are slightly set back on the board, which means using thick front plates is a problem. I had to cut a trench in my 5mm aluminium plate for PCB clearance.


Overall sounds great, nice and easy. Except for the PCB clearance issue.

Good luck!

Mark
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Old 10th May 2005, 11:40 AM   #6
paulb is offline paulb  Canada
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Should work fine with LM833.
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Old 10th May 2005, 12:08 PM   #7
reever is offline reever  United States
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Thanks for the responses. I have 2134's being sampled from TI, just waiting on the shipment. Should be here in a day or two.

Maupenas, is there going to be a major problem with the offset voltage, or is this something I can "tweak" to make use of the 833's? It sounds as if you think I shouldn't use them as a replacement for the TL072's. Obviously, I am new to this, and would defer to someone with more experience in choosing the "correct" replacement part.

Bikeman, with the issue of the volume not going past 1/3 range, could you change the value of the pot to accomodate this? It has been many years since "messin' " with circuits and the questions are floating around my head like a first year student!

Humbly,

-reever
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Old 10th May 2005, 12:43 PM   #8
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TL072 ( JFET input) has input offset characteristics distinct from LM833 (input BJT). Without goes into the technical worth, the JFETopamp am more "insensitive" than the BJTopamp to the value of the resistances that it polarize. The planner, when draws a net of equalization holds account of this parameters, and from it optimizes the values. In a lot of cases it may replace the two types, when ( as in this case ) there are the series capacitors to the signal that stop the Internal DC voltage. If however find this tensions in the circuit often are feels of the troubles when is commuted the INput signal or when are used the pot. I have seen that other have tried LM833 and other chips without problems. Suggestion to increase the value of the output capacitors ( 2, 2uF ) to at least 47uF if uses (at output ) a GC with Zin <22Kohm, and to lead even of the series capacitors to the Input signal of the PRE., to avoid problems of dc inputs.

Mauro
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Old 11th May 2005, 08:57 AM   #9
Bikeman is offline Bikeman  Australia
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Well, I could turn it higher, just didn't need to as 1/3 was plenty loud enough!

Somewhere on Rod's site (might be in the construction pages - have to buy a PCB) there is a table of values for resistance and gain. I guess you could just go for a lower gain. I just never got around to it...

There is one thing I changed. The power amp boards I used have an input capacitor to block DC, so I took out the two bipolar electrolytic output caps. Just replaced them with wire links. Don't try this unless there is a input cap on the power amp boards.

Let us know how it goes.

Mark
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Old 11th May 2005, 11:34 AM   #10
paulb is offline paulb  Canada
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Quote:
Originally posted by reever
Maupenas, is there going to be a major problem with the offset voltage, or is this something I can "tweak" to make use of the 833's? It sounds as if you think I shouldn't use them as a replacement for the TL072's. Obviously, I am new to this, and would defer to someone with more experience in choosing the "correct" replacement part.
There are output capacitors in the design, and they block any offset voltage.
I used 2134s in my version and did not have a problem. However, you might want to use sockets and power it up the first time with the cheaper TL072s. It took me a while to find the cold solder joints. It's a small board with tight component spacing.
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