I just got this nice preamp. Not sure why so many have hate for them, but whatever, their loss. I put it in the tape monitor loop from ye olde marantz 4220, which has been my main amp for the past 18 years or so. I can’t hear anything different when it’s in the loop, Other than a little scratchiness on the tone pots (to be expected). I’m sure the phono sections could use an update, it’s got a fair bit of noise when all the way up, and we’ll see how nice it sounds. All in all, I’m not sad for the purchase. I needed something to drive the HK citation 24 that I’ve been working on, so that I can eventually get to building my take on the IDS-25 speakers, and this fits the bill for now.
So the thing I’m wondering about this at the moment, is where to find the brackets to rack mount it. I have a couple of old relay racks, one currently serving as the stereo cabinet, and would like to mount it properly in there. I can make my own brackets from aluminum angle stock, but it’s not 100% clear to me how they would get mounted to the preamp cabinet. There are two holes in the panel extrusion that look like they could be tapped, but currently there’s no threads in there. Seems odd that the front of this would have a gap like that, but it’s all factory as far as I can tell.
Anyone have one of these they can take a picture of how the brackets mount.
So the thing I’m wondering about this at the moment, is where to find the brackets to rack mount it. I have a couple of old relay racks, one currently serving as the stereo cabinet, and would like to mount it properly in there. I can make my own brackets from aluminum angle stock, but it’s not 100% clear to me how they would get mounted to the preamp cabinet. There are two holes in the panel extrusion that look like they could be tapped, but currently there’s no threads in there. Seems odd that the front of this would have a gap like that, but it’s all factory as far as I can tell.
Anyone have one of these they can take a picture of how the brackets mount.
Its a great chassis for a whole new preamp, the original circuit (both phono and line stage) are really dated and don’t sound very good.
The Crown manual has the rack mounting info on page 10. It uses the two sheet metal screw holes
in each side of the extrusion, each hole being next to one corner of the cabinet.
https://www.crownaudio.com/en/product_documents/ic-150a-owners-manual-ic-150aownersmanual-pdf
in each side of the extrusion, each hole being next to one corner of the cabinet.
https://www.crownaudio.com/en/product_documents/ic-150a-owners-manual-ic-150aownersmanual-pdf
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Thanks Rayma! I should have rtfm! 😉.
I Will go find a copy, since I need to crack it open and order electrolytic capacitors for power supply, and maybe a few other things.
I’ve heard crown are good about selling people parts, even for old equipment like this, so maybe they have the rack brackets still available for reasonable money? If not, I have all the tools to make my own.
I Will go find a copy, since I need to crack it open and order electrolytic capacitors for power supply, and maybe a few other things.
I’ve heard crown are good about selling people parts, even for old equipment like this, so maybe they have the rack brackets still available for reasonable money? If not, I have all the tools to make my own.
Any rack mount ears that you have on hand should be usable, with holes drilled in the right places.
Use thick enough material so it can take the weight. They do list the Crown part # in the manual.
Use thick enough material so it can take the weight. They do list the Crown part # in the manual.
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Hahahaha! lololololol!
I knew somebody was going to have to pipe up like this 😉
I find it laughable that people slag on these preamps. the circuit is about as close to a passive preamp as you can get, which seems to be all the rage these days. And the tone controls have a defeat setting, so you basically have a stepped attenuator and a few resistors in the signal path, aside from a single opamp per channel. And if the opamp is bothersome, there are plenty of “upgrades” to drop in. If it had a fancy name on it, people would be eating it up. But that’s fine, I like being able to buy nice stuff for cheap. I’ve got a beater McIntosh preamp on its way to restore, and I’m sure the design of its circuits is entirely more dated, and even totally restored may not sound as clean as this “monstrosity” from crown. I’m slightly regretting having bought the McIntosh, as I really didn’t need anymore projects at the moment, but the price was right. (I’ve seen ones that had caught on fire sell for more 25 years ago). And I really miss looking at the very satisfying blue glow of the 1960’s McIntosh gear, since having to leave my old Mc amp behind in a move, something that will never happen again!
You’ve also gotta love seeing the old stereophile review of the crown DC300, talking a bout how it was the best things they’d ever heard, and now people contort themselves in to a pretzel to hear flaws in them that simply aren’t there, unless the amp is failing and needs repair. I just picked up a pair of 200wpc crown PA amps that are basically the same circuit for $100 ea.
Keep hating! I’m always glad to get great gear for so cheap! To me, it’s all about the speakers and the room. If you can hear your amp, something is wrong with it. I’m positive that some speakers probably sound better with some power amps due to various compatibility issues and the ability of a given amp to drive a particular speak load properly, but that’s got little to do with the preamp which is driving the amp. Phono stages are another thing entirely...
Other than making sure there is an appropriate safety capacitor setup for this, I may just leave the rest alone if it all looks good. Part of me is in favor of replacing. Old electrolytic caps on principle, but they’re not causing any hum, and if not leaking, they may get left alone.
That's a very nice manual. Ah, the olden days...
Looks like they are using the LM301A fully decompensated, which is why the gain might be fairly high at 20.8 dB (that's about 4.3 dB more than usual). Given the part's rather modest noise performance, they wisely included an output attenuator.
It is this one that I would want to modify. Total attenuation stock comes out to 10 dB (resistor values: 604 ohms output series plus 1.3k to 887 ohms parallel, giving a load of about 2.8 kOhms, in parallel with 11k feedback, so about 2.2k. Now you might argue that this is mostly going to be used when output levels are low anyway, but still, this seems noticeably heavier than with most any load you would attach - high-frequency distortion is likely to degrade (old opamps rarely make good load drivers), and channel separation might suffer as well. In these modern days it is not unusual for people to long for 12 dB attenuators with regular 16.5 dB preamp stages just to get their volume pots into a sane operating range, so here we would want about 4 dB more.
So I would suggest
R160/260 887R --> 715R (or 681R)
R161/261 1.3k --> 3.32k (or 3.3k)
(metal film 1% 1/4 W)
This would give an attenuation of 16.2 dB (remaining gain: +4.6 dB) with an output resistance of 605 ohms, while total opamp load is up to 4.64k || 11k = 3.26k. Still lower than I'd like tbh, but less severe for sure.
In terms of upgrade options for the ancient LM301, OPA132 seems a fairly good one. NE5534 may need some extra circuit changes (the value for the 10M feedback resistors R133/233 would have to be lowered to 2-3 megs or so, and a bypass cap across the supply rails definitely would not hurt) but has potential for even better performance.
Looks like they are using the LM301A fully decompensated, which is why the gain might be fairly high at 20.8 dB (that's about 4.3 dB more than usual). Given the part's rather modest noise performance, they wisely included an output attenuator.
It is this one that I would want to modify. Total attenuation stock comes out to 10 dB (resistor values: 604 ohms output series plus 1.3k to 887 ohms parallel, giving a load of about 2.8 kOhms, in parallel with 11k feedback, so about 2.2k. Now you might argue that this is mostly going to be used when output levels are low anyway, but still, this seems noticeably heavier than with most any load you would attach - high-frequency distortion is likely to degrade (old opamps rarely make good load drivers), and channel separation might suffer as well. In these modern days it is not unusual for people to long for 12 dB attenuators with regular 16.5 dB preamp stages just to get their volume pots into a sane operating range, so here we would want about 4 dB more.
So I would suggest
R160/260 887R --> 715R (or 681R)
R161/261 1.3k --> 3.32k (or 3.3k)
(metal film 1% 1/4 W)
This would give an attenuation of 16.2 dB (remaining gain: +4.6 dB) with an output resistance of 605 ohms, while total opamp load is up to 4.64k || 11k = 3.26k. Still lower than I'd like tbh, but less severe for sure.
In terms of upgrade options for the ancient LM301, OPA132 seems a fairly good one. NE5534 may need some extra circuit changes (the value for the 10M feedback resistors R133/233 would have to be lowered to 2-3 megs or so, and a bypass cap across the supply rails definitely would not hurt) but has potential for even better performance.
The manual is something else. I wrote to them asking about parts, but since Harman took over, they don’t seem to have anything anymore, which is unfortunate. Nice folks, and very quick response to my query, though! Fortunately since there are no parts to be had, the manual makes clear dimensions, etc for the mounting brackets, and lists proper screw size and pitch.
Thanks for the upgrade suggestions, I’ll definitely have a closer look in the coming weeks. I also ended up with a McIntosh C24 that needs a little love, and will probably start on that first, since the crown seems to be problem free aside from noisy tone controls, which should be remedied with conductive grease on the shafts of the pots to ensure they are making a solid ground connection.
It’s interesting regarding the overall noise from this preamp, they suggest in the manual to run it with the volume knob on the high side, and cut back the gain on your power amp for the lowest noise levels.
Thanks for the upgrade suggestions, I’ll definitely have a closer look in the coming weeks. I also ended up with a McIntosh C24 that needs a little love, and will probably start on that first, since the crown seems to be problem free aside from noisy tone controls, which should be remedied with conductive grease on the shafts of the pots to ensure they are making a solid ground connection.
It’s interesting regarding the overall noise from this preamp, they suggest in the manual to run it with the volume knob on the high side, and cut back the gain on your power amp for the lowest noise levels.
You’re living in the past defending a 50 year old very early solid state design that wasn’t very good, buying cheap junk doesn’t make it good. Its a good chassis, put any Pass preamp in it and listen. But you need something better than a DC 300 to hear it.