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Thread: Restoring an old Crown IC-150 preamp - caps and IC's

  1. #11
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    Dave:
    You need to think about the LFR Volume pot mate if your serious that is.....The Linear pot required is usually 10x the original value depending on the taper. You see Linear pots are far superior accracy loike to Loggies in audio.

  2. #12
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    I had designs on a DACT attenuator at 500K, which is probably overkill in the extreme for one of these, but who knows...

    By the way, to any out there with downers on IC's in general, I ought to remind you that mixing desks of the 70's onwards were full of them! Each channel has gain, tone and panning and the line stages in each one were often IC based I believe, many even using the old LM301 as used in the IC-150.

    By the way, I remember reading of Stan's concerns regarding the IC Op-Amps in his DAC's having such high output which then had to be attenuated. the Crown used this output (up to 10V) specifically to recommend driving as much signal level down the interconnects as possible (removing many cable "differences" as a result methinks) and then adjusting the gain at the power amp (oh alright, another bloody potentiometer or resistor leg). The intention was to keep overall system noise as low as possible. probably irrelevant today to a degree, but the instruction manuals were incredible in the depth gone into technical and semi-technical info for the owners of their gear back then. Mind you, since this preamp in original form wasn't much cop at low output volume levels, it was probably just as well
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  3. #13
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    Quote Originally Posted by DSJR View Post
    The IC's originally supplied were LM301's, judged dreadful by today's standards (and even when the thing was new it seems). Whats in there is summat like 3532's. Works well if the preamp is run nearly flat out, but noise and distortion, together with a overly-crisp sound, develops at low volume levels. I have some 833N's I could drop straight in, the OPA604's seem popular and I'm tempted by the LME49710N, although this may be too "wide open" for the design.[/IMG]
    The Burr Brown's will all have the house sound, laid back and a bit loose in the bass area. The OPA27GP is a good all round contender. The LME49710N is low noise and is more on the neutral side. The AD843 has plenty of vigour and more gain than the stock chips. The AD797 is a superb chip if the loading is low enough and would be my first pick, it has slightly more gain but sounds magnificent but can oscillate if the circuit doesn't suit. It may be a case of trial and error to get the sound you like.
    Phillip.

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  4. #14
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    Thanks.. In some LM301 implentations, I note a small value cap was taken from pin 1 to pin 8. In the IC150, pins 5 and 8 aren't connected.. it would appear the descendant IC-150A, which used was successfully updated with LM49710N with no mods apart from regs added to the power suply (I'm not that keen on going that far ). I don't want to turn the thing into a slush-box, but neither do I want to risk oscillation or return to the famous "cut-glass" sonics this unit was renowned? for when used incorrectly (according to Crown).

    http://www.diyaudio.com/forums/solid...50a-pooge.html

    In the IC-150A, a few of the cap values were "modernised" and the phono stage completely re-worked (for the better?????). I don't know how far different the rest is - the basic bits outside the IC's are very simple apart from the tone, panorama-balance and loudness bits... This later model used LF356H IC's - early FET type?
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  5. #15
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    Quote Originally Posted by DSJR View Post

    I ought to remind you that mixing desks of the 70's onwards were full of them!
    I used to own a loverly Studiomaster 16-4 Mixing desk with beautiful massive VU's. was such a giant desk for it's actual spec..I later bought the posh Mix down gold , Phil Collins used to own one.. that was great but i missed the analogue meters of the old
    Last edited by Rare Bird; 23-11-2011 at 00:16.

  6. #16
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    So come on Andr'e, you seem to be a man of hidden depths to me... Did you do recording and mixing as a job, or in your spare time?????
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  7. #17
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    Quote Originally Posted by DSJR View Post
    So come on Andr'e, you seem to be a man of hidden depths to me... Did you do recording and mixing as a job, or in your spare time?????
    I did 2 years in total studio Engineering courses. I had my own studio in the spare room crammed packed solid with vintage Anologue Synths, mixers, multitrackers etc. never persued it as a job tho.The courses were handy regarding MIDI which was a pretty new thing back then before that i was relying on Control Voltage (Volts Per Octave, Herts Per Volt), Gate (Volts & Short trigger) to get everything to communicate with each other..However their was a wonderful sync unit by Garfield Electronics that was a godsend for many things
    Last edited by Rare Bird; 23-11-2011 at 00:16.

  8. #18
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    Love those mini DC300A stylee knobs
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  9. #19
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    Quote Originally Posted by Reid Malenfant View Post
    As for the 25uf NP there may well be some Nichicon caps that will do the trick, i think they are the MUSE range & these are non polarised, this one should do the trick

    Hope that helps... By the way, good idea to increase the reservoir caps to 1000uf from 250uf
    Thanks for the donor post, as it's been very helpful. The donor preamp for parts has arrived, the volume pot has been swapped over and I've put on four Panasonic 1uF caps where I inavertantly ripped out the tants, which were the later and supposedly reliable type. They were cheap enough and easily replaced if necessary.

    Actually, this preamp, despite having everything against it, sounds very clean and not at all grainy or harsh. Detail retrieval is fine as well, despite the balance and panorama pots in the circuit at all times..

    The 25uF caps aren't available any more, but I noticed that the later models (SL2) use 22uF 50V NP cap value as you suggested and all of them have a 560 ohm following to the output. If you take all the tone control gubbins out, it's actually a very simple circuit I think.

    You know, I was chatting to Dave W at the weekend about vintage vs. new kit. I really think that maybe some low cost gear has dramatically improved (but with nasty casework), but the best standards in amps and speakers were already there in the 70's (good sources apart from FM tuners were good due to accident as much as anything else IMO). This preamp in stripped "pure" form could be done for very little money now (and exists as a line buffer in many CD players and DAC's I reckon) but in todays prices I shudder to think how much it could cost - ARC money certainly...
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