Carver C-1, stumped

Hello all,
I recently acquired a Carver C-1 preamp and a M-200t power amplifier, but to achieve normal-low listening volume levels using speakers, I have to turn the knob to the 12:00 position, which on my Marantz using the same Carver M-200t driven by the 2270's preamp is deafening (I blew out an HD66- foam everywhere). On the C-1 by itself using headphones, the volume control seems to behave normally. What gives? Is the pot designed that way or is the c-1 toast?

Thanks,
MW

I use a C-1 also, and it is similar. Although running the Yamaha, it doesn't take to much twist on the dial.

Mute switch? I had a C-1 for a great many years and I don't think I got close to the 12:00 position on the volume knob. Ever.

The gain on the C-1 can be reduced by 3,6,9,12, or 21db by replacing resistors R258, R358, R259, and R359. This info is from a Carver service bulletin dated 7/12/88.
It reads as follows: "To be used as needed to lower the noise floor. To compensate for highly efficient speakers, so that the volume control is used in the optimum tracking area.
Example: volume control is set to '9 o'clock' at max listening volume, the 21db reduction will change volume control to '2 o'clock'for same volume.
Note: This reduction will be at main output 1 only, main 2 will remain the same high level volume."

So try main 2 output. If it is louder, more than likely the previous owner changed the gain on main 1 and forgot to mention it. I lowered the gain on my C-1 by 12db and now I get moderate volume at the "10 o'clock" setting and ear splitting levels at the
"3 o'clock" setting.

My brother can explain the benefits of this procedure better than I can. Hopefully he will chime in.

Hi Mageworlder,

M1.5tman is correct. Try "MAIN OUT 2".

According to a service bulletin put out by Carver in 1988 there were numerous complaints about non-linear tracking and preamp noise(hiss) at lower volume knob setting, say below the 8:00 position. For example: my C-1 would lose volume on the left channel before the right channel when trying to listen to it at very low volume levels, say late at night when everyone was sleeping and I didn't want to disturb them. At the other extreme, It would play at unbelievably loud levels at ~10:00 on the volume control. I would guess that it would max my amp out at ~12:00 volume setting.

In order to correct the problem it was necessary to lower the gain of "MAIN OUT 1" (which is programmable) in order to get away from the non-linear portion of the volume control and also to operate the preamp away from its noise floor. This would also allow the end user to get the best possible signal to noise ratio at normal or optimal listening levels.

This programming feature would in essence allow the C-1 to be "tweaked" to better match the input sensitivity of the owners amplifier and speaker combination. Again, with my NAD 2200PE amp having an input sensitivty of only 700mV (for rated output) matched with a pair of HPM-100's (92.5db @1watt in), I was able to program my C-1 down by 21db. Now I can set the volume control at about 10:00 for "just starting to get loud" listening levels and I'm out of the non-linear range of the volume control and getting the best signal to noise figure as possible from the unit.

Plus, there is one bonus to doing this that I really like. I don't have to worry about the kids cranking the volume knob so high that they drive the amp into clipping and frying my speakers. If I need the extra volume, which I probably won't because it's plenty loud for me as is, I can switch to "MAIN OUT 2".

I apologize if this explanation was long, but I hope it helped.

Paul

Thanks for the responses.
What are the default vaules of the resistors? I noticed that using the C-1 as a pre for my Carver M-200t, it starts clipping when I go a bit past the 12:00 position without even putting out much volume. Driving the same amp, my Marantz 2270's pre can get a LOT louder before clipping. Would this amp be worth even fixing or should I get another pre? Which ones would you recommend as a match to my Carver power amp?

I tried using the MAIN OUT 2 but no cigar. Same levels, same clipping.
Thanks,
MW

Have you tried a different set of inputs. I'm curious to know if it has the same problem on AUX 1, Aux 2, Tuner and Tape Monitor 1 and 2. There are alot of switches on this unit. Have you tried all the switches to see if there is any difference playing with the switches while the music is playing? Make sure that the tone and holography switches are in the OFF (out) position. This will eliminate those circuits from the loop. Also switch off the Infrasonic Filter on the rear of the unit. If that filter circuit is bad it may cause the problem you are having.

Paul

Thanks, Paul. I knew you would be able to help better than I. :thmbsp:

Thanks for your help so far, guys.

I did check all other inputs except for the phono (don't have my own) with two different CD players and a tuner with the same results. I flipped all the switches and experimented with the Infrasonic filter, same results. I have no idea what is driving the preamp to clip and I am thinking about taking it to a tech over spring break. However, I did attach images of a couple of suspicious resistors located on the underside of the pcb that appear to be added on, but I'm not sure if they were a tweak done in the factory or by the previous owner (an electrical engineer). He had mentioned that he stopped using the combo after he moved into an apartment because it was too loud, and suggested that I do a resistor mod. Maybe he himself had done it 15 years ago (albeit in an odd spot) and forgot about it. Do your C-1s have these resistors? the manual also mentions some sort of relay, but I didn't find any normal mechanical relays as seen in ordinary audio gear in there. It doesn't 'click' when you turn it on either. The whole thing is somewhat disappointing as these are my first separates and they sound very good using the holographic imaging with headphones; I notice things in songs that I hadn't noticed before.

Thanks for your time,
MW

Those backside resistors look damned suspicious. Do you have a schematic to see if they are in the signal path for all inputs? These were likely added on by a "well minded" tech and are hopefully your cuprits.

mageworlder said:

Thanks for your help so far, guys.

I did check all other inputs except for the phono (don't have my own) with two different CD players and a tuner with the same results. I flipped all the switches and experimented with the Infrasonic filter, same results. I have no idea what is driving the preamp to clip and I am thinking about taking it to a tech over spring break. However, I did attach images of a couple of suspicious resistors located on the underside of the pcb that appear to be added on, but I'm not sure if they were a tweak done in the factory or by the previous owner (an electrical engineer). He had mentioned that he stopped using the combo after he moved into an apartment because it was too loud, and suggested that I do a resistor mod. Maybe he himself had done it 15 years ago (albeit in an odd spot) and forgot about it. Do your C-1s have these resistors? the manual also mentions some sort of relay, but I didn't find any normal mechanical relays as seen in ordinary audio gear in there. It doesn't 'click' when you turn it on either. The whole thing is somewhat disappointing as these are my first separates and they sound very good using the holographic imaging with headphones; I notice things in songs that I hadn't noticed before.

Thanks for your time,
MW

Click to expand...

The reisistors appear to be in the PHONO 2 circuit. I have a low and a high serial number unit and neither has these resistors. It is possible to change the gain of Phono 1 and Phono 2. That is possibly what the resistors are for.

As far as the relay, there is no mechanical relay. The muting at TURN ON and TURN OFF is accomplished via an electronic clamping circuit. According to the owners manual It provides a 3-5 second delay of the MAIN outputs and Headphone at turn on and turn off. But upon experimenting with both units this morning, I've discovered that only the MAIN's are muted at TURN ON and TURN OFF. The headphones are not. So I suspect the owners manual is wrong in stating that the headphone output is also muted. I believe there may be a problem with the muting circuit in your unit. I would get a technician to look at it for you when you can.

If you really want to try it with your amp, The owners manual also states that the headphone output can be used to feed another amplifier. Of course, you'll need to get the proper adapter to do this. I haven't tried this myself. If you decide to try it, just make sure you turn the volume control all the way down before you turn the C-1 on or off.

Paul

Decided to use headphone amp

Thanks for checking your units out, Paul. Out of curiosity, what is the serial on your low-serial C-1? Mine is 0304 and came with a 'preliminary' manual that looks as if it came from a typewriter. Maybe the factory tweaked its original design, although the resistors still look suspicious. As I said earlier, I'm planning to drive out to the main Carver/Sunfire service station in Snohomish, WA (about 47 miles from where I live) on spring break or summer vacation to take it to a professional tech. For the interim, I decided to run it using the headphone jack. It actually sounds great, more detailed than my 2245 and 2270 receivers, and the sonic holography spatializer is pretty cool. It definitely sounds as if it's worth servicing to be able to use the main outputs. For the price I paid ($40 with an included M-200t poweramp) I couldn't go wrong.

Many more thanks for all you guys' time,
MW

Serial # 09127

Glad to hear the headphone tip works for you. :thmbsp: Hopefully running it like this won't cause any further problems internally.

I would definitely get it serviced. I like mine enough to have 2 of them. One is a backup.

It is a wonderful preamp and gives you a lot of flexibility with its numerous inputs and outputs.

These are easy units to work on. Plenty of space between components and neatly laid out. The muting circuit is relatively simple and if that is the problem, as I believe it is, it should be a cheap fix as far as parts. Labor, who knows.

Good luck and enjoy it. My brother and I both enjoy ours very much.

Paul