Back in the 80's ETI published a class A preamplifier to match a class A (System A?) power amp. IIRC, these were designed by Stan Curtis. I had built this preamp plus the ETI 5000 MOSFET amplifier. The preamp suffered severe RF oscillations when the volume pot was reduced to 0. Only many years later was I able to cure the problem, by using my own wiring scheme. But, alas, my home was burgled shortly after, and the preamp was taken.
I'm looking for the preamp circuit/article. Can anyone help?
It was also published in Electronics Digest.
I'm looking for the preamp circuit/article. Can anyone help?
It was also published in Electronics Digest.
Hi Shaun,
I have the original ETI magazine at home.
Will scan and upload.
I built it, still have it but it hasn't run for many years.
It was my first foray into DIY, along with a JLH inspired tape recorder
and a parametric equalizer.
I was quite happy with the sound at the time....but what did i know then ???😉 .
I have the original ETI magazine at home.
Will scan and upload.
I built it, still have it but it hasn't run for many years.
It was my first foray into DIY, along with a JLH inspired tape recorder
and a parametric equalizer.
I was quite happy with the sound at the time....but what did i know then ???😉 .
sreten said:
Hi sreten
I've seen in the link only the part for the power amplifier. The first part of the preamplifier - for which interested Shaun - is not appears in this link. I've tried to find the project in the web, because also me i am interested about the part of preamplifier; there are two or three sites related to this project but the preamp it is ignored.
I had the original Electronics Digest (winter 1985/1986) issue and a photocopy of the full project. Unfortunatelly this moment i found only the copy.
As for the circuit of preamp, it is a nice and simple implementation with discrete devices. I've not constructed never this preamp, but i am thinking to build this with some improvements and mainly by replacing the transistors with modern and superb devices.
There is another one thread (started by PMA) about phono preamps that plays in the first page. I think we may join this thread with the other, but someone may post the schematics.
I have not the possibility to do this.
Fotios
and would also like to look at the schematic..even thinking to build one with more modern low noise devices
I can't seem to find a trace of CeeVee's PM to me. Not really sure what happened there; my memory's not what it used to be.
I also have the article (in the circuits digest or whatever) and built the pre-amp.
A friend also built one and I can confirm the oscillation as the volume control approaches zero. The cure (for me) IIRC was 6K8 resistors in series with the wipers of the pot.
There is an error in the pcb also which requires a track to be cut and a wire link to be added.
It does indeed sound superb by any standard, at least in MM version it does..... I seem to recall that when I built the MC input boards I was not that impressed.
If you fail to get the article from other sources then P.M me and I will dig it out and scan it.
A friend also built one and I can confirm the oscillation as the volume control approaches zero. The cure (for me) IIRC was 6K8 resistors in series with the wipers of the pot.
There is an error in the pcb also which requires a track to be cut and a wire link to be added.
It does indeed sound superb by any standard, at least in MM version it does..... I seem to recall that when I built the MC input boards I was not that impressed.
If you fail to get the article from other sources then P.M me and I will dig it out and scan it.
There is a variety of possibilities for the cause of the oscillation but it seems to be present in every example.....
I will wait a few days and see if the guy who said he had already sent off the articles does indeed come up trumps..... If not then remind me and I will send you the article.
I will wait a few days and see if the guy who said he had already sent off the articles does indeed come up trumps..... If not then remind me and I will send you the article.
I recall the article going on about having to following their wiring scheme religiously or you'd not get the promised results. My fix involved common-sense routing of the grounding arrangement, which is not the same as theirs.
I would dearly love a copy. I'm sending you a PM.
I would dearly love a copy. I'm sending you a PM.
Hi Shaun,
I'll send it again next week....I'm away from Lisbon on work, i'll do it as soon as i get back.
🙂
CV
CeeVee, I am a new member of diy Audio, I am also looking for the circuit diagram for this Pre-amp. It will be greatly appreciated if you can assist me. Greggie
tanowa101@gmail.com
tanowa101@gmail.com
Scans of Curtis Preamp ETI Magazine Article
Dear Greg and others,
Scans of the Curtis preamp article from ETI are available on the web. Try one of the following links:
http://www.diyaudio.com/forums/solid-state/167408-eti-system-pre-amp-stan-curtis-full-article.html
or:
http://www.stancurtis.com/Moth pics/ETI Curtis Pre-Amp article.pdf
In my "home library", I have the issue of ETI magazine containing the preamp article, but it is in the Dutch language, so I assume that photocopies are not very helpful. At the URLs listed above you can find English versions.
Recently, I have built a copy of this preamp and particularly the line stage sounds great. The MC input stage sounds quite good but is in my opinion not as outstanding as the line stage. I used the original PC board layouts but simplified the wiring scheme (the one shown in the magazine article seems not very straightforward). There is an error in the PCB layout of the RIAA correction stage (I have a scan of the later-published erratum in case you are interested). The line stage as published suffers from severe RF instability, particularly at low settings of the volume control, which can be completely cured by soldering a 7k3 resistor between the input pads on the board and the wiper of the volume control.
As input transistors for the MC stage, I used 2N3019s which turned out to have low noise and worked well. The proposed BC107s can be replaced by BC547s and the MPSA06/56 pairs by BC639/640s.
Hope this helps, if you want to know more just drop me a line.
Best regards,
Aren van Waarde (aka arensattic)
Dear Greg and others,
Scans of the Curtis preamp article from ETI are available on the web. Try one of the following links:
http://www.diyaudio.com/forums/solid-state/167408-eti-system-pre-amp-stan-curtis-full-article.html
or:
http://www.stancurtis.com/Moth pics/ETI Curtis Pre-Amp article.pdf
In my "home library", I have the issue of ETI magazine containing the preamp article, but it is in the Dutch language, so I assume that photocopies are not very helpful. At the URLs listed above you can find English versions.
Recently, I have built a copy of this preamp and particularly the line stage sounds great. The MC input stage sounds quite good but is in my opinion not as outstanding as the line stage. I used the original PC board layouts but simplified the wiring scheme (the one shown in the magazine article seems not very straightforward). There is an error in the PCB layout of the RIAA correction stage (I have a scan of the later-published erratum in case you are interested). The line stage as published suffers from severe RF instability, particularly at low settings of the volume control, which can be completely cured by soldering a 7k3 resistor between the input pads on the board and the wiper of the volume control.
As input transistors for the MC stage, I used 2N3019s which turned out to have low noise and worked well. The proposed BC107s can be replaced by BC547s and the MPSA06/56 pairs by BC639/640s.
Hope this helps, if you want to know more just drop me a line.
Best regards,
Aren van Waarde (aka arensattic)
Shaun, i have built the preamp many years back and am still using them. I experienced slight hum and oscillation, with the wiring and earthing, but, correct eathing solved the problems, albeit by trial and error and the modification of the volume and balance control section which also solved the oscillation problem. If you are still interested in re building the preamp, drop me a line and i will forward my mods.
Hi SUZTEK
I did eventually sort it out: Implemented the resistor mod, and then applied my own understanding of correct earthing en voila! it was sorted.
I'd like to see what you've done, though. Will drop you a pm with my email addy.
I did eventually sort it out: Implemented the resistor mod, and then applied my own understanding of correct earthing en voila! it was sorted.
I'd like to see what you've done, though. Will drop you a pm with my email addy.
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