Rod Elliotts Project 97.....

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reever

reever

Member
Joined 2005
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
 
M

mauropenasa

R.I.P.
Joined 2005
webalice.it/mauro.penasa/index.html
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
 
Bikeman

Bikeman

Member
Joined 2003
Hi Reever.
I used the P97 and P3a together as an integrated amp.

See:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=49786

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
 
reever

reever

Member
Joined 2005
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
 
M

mauropenasa

R.I.P.
Joined 2005
webalice.it/mauro.penasa/index.html
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
 
Bikeman

Bikeman

Member
Joined 2003
Well, I could turn it higher, just didn't need to as 1/3 was plenty loud enough! :D

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. :hot:

Let us know how it goes.

Mark
 
P

paulb

Member
Joined 2001
reever said:
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.
Click to expand...
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.
 
reever

reever

Member
Joined 2005
Thanks guys, all of this information is exactly what I'm looking for. At this point, I'm probably gonna hand wire this thing. I don't know if that is good or not, but I need to see if it works! My 3875's function EXACTLY as expected, and they are hand wired also.
My 2134's should be in today and I could get started with this. I'm doing everything here at work during my lunch hour, so nothing gets done very fast. Can't do anything at home at this point, too much work being done at home, and wife wants house stuff completed before hobby stuff...


-reever
 
C

carlosfm

Banned
Joined 2003
Bikeman said:
Hi Reever.
I used the P97 and P3a together as an integrated amp.

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.
Click to expand...

Forget the OPA2134 on that PCB.:bawling:
It will sound much better if you care for make a decent PSU bypass on each op-amp.
 
taj

taj

diyAudio Member
Joined 2005
project 88

I'm currently building Rod's project 88 pre-amp. No tone controls [don't need no stinkin eq], and it's designed for 2134's. I should be finished it shortly and can let you know my impression, but I still need a couple of elusive components and a nice case to mount it in.

I'm also building his Linkwitz Transform and PSU circuits for use with the same preamp. I suspect I'll also use his relay mute circuit, remote control circuit, and maybe even build one of his amps one day [just for the fun of it -- literally], but I have a pair of Bryston 4Bs :mischiev: here and a Dynaco for the tweets, so I'm fairly well amplified already.

..Todd
 
reever

reever

Member
Joined 2005
Taj, why no "stinkin' eq"?

I guess I'm ignorant to this. It seems that most here just use a volume control. By using 1 or 2 volume controls is this the correct way to balance out your speakers??
Other than possibly introducing noise into the amps why not add some type of control to the "end product"?

Maybe I'm missing the "minimalist approach" to what is trying to be done here. Personnally, I like to turn some dials, maybe thats what I am used to doing, I don't know for sure.....
Oh yeah, still reading this forum before building the preamp

:D
-reever
 
D

dotneck335

Member
Joined 2012
perlave said:
Regards, I am an electronics student who has to do the elliott preamplifier, project 97, could someone please pass me the position of the components , the PCB to design it in layout ?. Thank you
Click to expand...
Huh? You'll get the layout when you buy the board from Rod. It's an excellent design---I used it to upgrade my ancient Dynaco preamp and it's GREAT!!
If you're asking anyone here to steal Rod's layout instead of buying it (it's only $24!), forget you!!
 
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