fill35U

Thinking about it, you might want to put a 33R 1W metal film resistor in series with the +15V trigger from the "acting master" module. Before it gets to the circuit where the module triggers itself! That'll limit fault current in case of serious problem, and hopefully blow open if the fault continues for more than a few seconds. At 20mA per module (including the "acting master"), it shouldn't amount to more than a 4V drop. I'd expect that 11V would still be sufficient, and that signalling each module wouldn't take more than 20mA. Obviously, you want to try this scheme on just the "new master" alone first, to see if it can turn itself on. Then add modules one at a time, monitoring the +15V trigger for consistent but not excessive droop. You could also pull down that +15V trigger with various resistances (or use a variable power supply) to find out what minimum voltage is acceptable to turn the slaves on and keep them on.

The schematics we have aren't the easiest to read, at least with my software. And it looks to me like they're incomplete in regards to the details of how the slave modules are different and how they link together. However, based on what I can make out, and from photos of the interior: I *guess* that you could run her with no master module, or with a slave substituted for the master, if you could generate the "power on" signal to send to the slaves. I'm pretty sure that signal is generated in the master, and sent to all the slaves at the same time via the grey ribbon cable at the front of the amp boards. That same signal is what makes the "power on" (green) LED light, and is sent to the LED board by gray ribbon cable. The LED board gets a 3-conductor ribbon, since it needs to show "standby" status as well(LED lights red). But the ribbon from the master to all the slaves is 2-conductor. I think that 2-conductor cable carries +15V on Pin 1 of the connector (outside pin), and in "power on" it makes Pin 2(middle pin) go to 0V, lighting the LED and telling the slaves to turn on. BTW "turn on" may just involve input muting and output relays, the amp sections probably stay idling warm in "standby". Each slave module should generate its own regulated +15V supply as the master does. So it should be easy to pick one slave module and make it act like a master: tie the +15V from the regulator to Pin 1, and tie Pin 2 to ground. If you're lucky, they used the same boards for masters and slaves, just populated them accordingly, so you'll have lots of free pads or jumper points to play with. That's my best guess! It would be nice to have a working amp to examine to know for sure. Good luck!

It truly was a masterpiece collection! Thanks again to Mark for making it happen!

Yes, they're just at the signal input off the RCA's. 100k for the -35, without actually looking at my -55 and based on the rest of the schematic I'd guess the same.

If those pots are a relocation of/addition to the RP2 pots on the amp boards, then they affect the output impedance of the amp. You could change the power seen by the speaker in much the same way by using rheostats(hefty ones!) at the output. But when you get into that territory of low damping factor, interaction with the speaker impedance can cause the "voice" of the system to change... kind of the point of the whole "TFM" circuit. A long time ago, when she was almost brand new, I added a volume pot to the *input* of my first TFM-45 (profile pic). Crude but effective, it's been very useful over the years.

HARRIS LABS INLINE ATTENUATORS Also sold through Parts-Express. Might make the quiet passages just a tiny bit more or less noisy. With great power...

FWIW, during the Stereophile review of the Thiel CS3.6 back in '93 ( HERE ), they managed to blow apart a midrange driver. Even more interesting is that Thiel had already provided a spare midrange with the speakers... Thiel certainly did innovative stuff! I can't seem to find much info on that midrange driver. Did it have a special name? I think the hollow cone design is really cool- any cross-sectional views? Why was it abandoned and never copied?

Thanks, Jim! No need for apologies- just a sanity check. Makes sense to me now. There's a lot more to it than the "numbers game" of a speaker's nominal impedance or an amp's wattage rating...

Sorry, if I'm still confused! I'm with you all the way up to this point Lighter load from a resistance viewpoint.. Working harder because of increased current demand into a less resistive load.. Increasing the resistance of the load makes (the typical voltage source) amp work less hard. I think you're saying the more reactive the load, the less its overall impedance is due to resistance? And that highly reactive loads, especially low impedance, can be very difficult for an amp? I'd certainly agree with that. But everything is frequency dependent, including how much the amp cares.

The Carver Pro amps have a wide range of power ratings and topologies. Just because it's "pro" doesn't mean it's "better" (or "worse"). Professionals have to choose the right tools for the job, too. The salient difference is that most of the Pro amps have a clipping eliminator, usually switchable. While definitely neither a panacea nor without drawbacks, it can help. But in home use, you should be able to see the TFM-42's clipping indicator LED's and hear the effects of clipping, and reduce the volume before things get too bad. If you're playing that loud and long, power compression comes into play- and that can help you or hurt you, depending on what you do next...

Servicing is better sooner than later! At this age they all need some kind of TLC. The TFM-42 I'm working on now ran pretty good at first glance, but on recapping I found two caps that had dried out so bad that they might as well have not even been there: a VAS decoupling cap and the -11.4V supply filter. Half of the rest of the small caps were merely in poor shape, par for the course... Jim, I don't understand when you say a lower impedance speaker presents a lighter load to the amp, or how a lighter load makes the amp work harder?

FWIW, conventional wisdom is to always keep your receiver switched to the highest speaker impedance setting. A page explaining the whole mess is HERE . There are *lots* of reasons why a replacement driver might behave and sound differently from the originals. Rod mentioned sensitivity, a huge factor. But on the basis of nominal impedance alone, a 4 or 8 ohm driver will interact with the speaker's passive crossover differently than the factory 6 ohm did. You might end up with a huge dip or peak around the crossover frequency, or the crossover point shifted so far down that the woofer's resonant impedance peaks affect response. I'd suggest waiting to either find direct replacements, or to research what would be acceptable substitutes. Not much point in putting in the effort to fix them if they're not going to sound their best, right? Good luck!

Saw "Suicide Squad" on Sunday, heard the song, had to put it in the CD player!

For Barry (and as a followup to Dom's "Hot Rats" post!):

Welcome to theCarversite, Boomer! Looking forward to seeing pics of your gear. If you hang around here for long, you'll probably be adding more!

Good point about auditioning classic speakers, Kev! But like anything vintage, their performance may be compromised by age. And if you don't take the time and effort to restore them, or have the experience to judge them, you won't know if you're hearing them in their full glory. But I guess if you come across something you really like as-is, you can still enjoy the music!

Cool fix on the dustcaps- and I always thought that stuff was for taping primates together! If they sound this good now, imagine how great they'll be when you get the SDA working! Pics?