carver c1 preamp infrasonic filter

[robertcdt 16]

I find this filter confusing and not sure when to use it.

when playing vinyl find it to have some use if I forget to turn it off and play a cd I get distortion is there something wrong with my c1 or is that the way it works.

[wrf 4,923]

The infrasonic filter is designed to be used when playing vinyl. Some, if not all turntables will generate an extremely low frequency rumble.  The infrasonic filter will removed that rumble.

 

If your infrasonic filter is generating distortion, there is something wrong.  It could be a dirty switch or something else.  

 

All C-1s are getting old.  Switches and POTs get dirty over time.  Electrolytic capacitors degrade.  You should consider a refresh where all electrolytic caps get replaced and everything gets cleaned. If the problems with the infrasonic filter persist, a good tech can diagnose them following the refresh.  Until then, just leave the filter OFF.  It's really only useful with turntables that have large amounts of rumble. 

[Sk1Bum 11,388]

Hello robertcdt and welcome to thecarversite.com. Glad you found us.

 

If you've not found them yet, the owners and service manuals can be downloaded here:

 

https://thecarversite.com/manuals/mandir/Carver C-1 owner manual.pdf 

 

https://thecarversite.com/manuals/mandir/Carver C-1 Service Manual.pdf

 

You may find them useful. I certainly did. Well, the owner's manual anyway. I am in no way an electronics tech, and the service manual is mostly Greek to me.   Fortunately, there are many talented techs here that understand it well.

 

 

[robertcdt 16]

6 hours ago, wrf said:

The infrasonic filter is designed to be used when playing vinyl. Some, if not all turntables will generate an extremely low frequency rumble.  The infrasonic filter will removed that rumble.

 

If your infrasonic filter is generating distortion, there is something wrong.  It could be a dirty switch or something else.  

 

All C-1s are getting old.  Switches and POTs get dirty over time.  Electrolytic capacitors degrade.  You should consider a refresh where all electrolytic caps get replaced and everything gets cleaned. If the problems with the infrasonic filter persist, a good tech can diagnose them following the refresh.  Until then, just leave the filter OFF.  It's really only useful with turntables that have large amounts of rumble. 

 

[robertcdt 16]

Thanks for the advise. I have been leaving it off and that is working . I will give it a shot of contact cleaner hopefully that will help but I am never that lucky.

I would love to learn more about recapping. I am a dental tech and have been repairing lab equipment all my life  with some experience with replacing electronic components.

I think I will start with something smaller than the c1 I have a technics SL 1700 turntable its board is small and not so many parts.

Dose any one have a opinion about the kits on eBay c1 refurbish kit parts $38.00 parts and instructions $95.00 ?

[Receiver2000 4,001]

Wrlcome!!!

[Sk1Bum 11,388]

On 9/24/2025 at 5:10 PM, robertcdt said:

Dose any one have a opinion about the kits on eBay c1 refurbish kit parts $38.00 parts and instructions $95.00 ?

 

Several have reported counterfeit parts in some kits. I don't know if @Circuits & Concepts has a kit, but he would be the only one that I'd fully trust. Les is also a member here, highly respected, and runs a good business. 

 

Most of the techs here source out the parts from Mouser, Digikey, and Parts Express (I think).

 

[TimD 71]

I'd be more inclined to order from a known reputable source like Mouser. Not only are these no-name kits full of questioable parts, they are padded with uneeded stuff as well as overpriced.

[MattB 129]

On 9/24/2025 at 5:10 PM, robertcdt said:

Thanks for the advise. I have been leaving it off and that is working . I will give it a shot of contact cleaner hopefully that will help but I am never that lucky.

I would love to learn more about recapping. I am a dental tech and have been repairing lab equipment all my life  with some experience with replacing electronic components.

I think I will start with something smaller than the c1 I have a technics SL 1700 turntable its board is small and not so many parts.

Dose any one have a opinion about the kits on eBay c1 refurbish kit parts $38.00 parts and instructions $95.00 ?

Welcome!

Shortly before I found this site, I purchased a M1.5t rebuild kit from the same vendor.   while all of the parts inside were quality brands, the instructions were somewhat vague and there was no list of any oddities/ updates to the design.   i.e. "some versions of M1.5t had a 2.2uF cap in location C-xx, but later versions have a 10uF.  this kit is shipped with a 10uF"   so I had a small handful of capacitors left over and were missing others.  fortunately I had a few spares in my stash from other recent projects, but I did have to buy a couple non-polar caps from digikey and wait a week to get it.   There were also baggies of small signal PNP and NPN transistors and I couldn't read the part numbers.  they are not listed in the instructions other than being provided "just in case you need them".    that sounds wonderful!

 

While buying singles from a place like digikey can be cumbersome, I highly recommend doing the research and digging up the parts yourself so you know what you're getting.  also consider the "BillD mod" if you do decide to take on the C-1 yourself.  I haven't done it yet, but planning for it as a winter project.

Edited Thursday at 02:56 PM by MattB

[Nahash5150 10,681]

On 9/23/2025 at 8:07 PM, robertcdt said:

I find this filter confusing and not sure when to use it.

when playing vinyl find it to have some use if I forget to turn it off and play a cd I get distortion is there something wrong with my c1 or is that the way it works.

 

As others have said, that switch should be inaudible when activated or not. It rolls off frequencies lower than about 10Hz (these are so low we can't hear them, but the speakers can still respond to them) , which protects your speakers from 'rumble' generated from turn tables. However, if you use speakers which utilize sound ports for better bass response, it's a good idea to keep that filter active since vented cabinets tend to 'run away' from infrasonic signals which might be present in any media, and overextend the woofer, leading to damage.

 

 

 

8 hours ago, MattB said:

Shortly before I found this site, I purchased a M1.5t rebuild kit from the same vendor.   while all of the parts inside were quality brands, the instructions were somewhat vague and there was no list of any oddities/ updates to the design.   i.e. "some versions of M1.5t had a 2.2uF cap in location C-xx, but later versions have a 10uF.  this kit is shipped with a 10uF"   so I had a small handful of capacitors left over and were missing others.  fortunately I had a few spares in my stash from other recent projects, but I did have to buy a couple non-polar caps from digikey and wait a week to get it.   There were also baggies of small signal PNP and NPN transistors and I couldn't read the part numbers.  they are not listed in the instructions other than being provided "just in case you need them".    that sounds wonderful!

 

There are no less than 8 versions of the M-1.5(t) !!!

[Rob 5,974]

Welcome to the site. I have bought kits in the past and won’t do it again. There are many versions that have updated components. I prefer to do my own parts list for the components that are in my unit. You can also see how parts fit in their respective areas and tweak them to fit better if needed. 

[robertcdt 16]

On 10/2/2025 at 6:04 PM, Nahash5150 said:

 

As others have said, that switch should be inaudible when activated or not. It rolls off frequencies lower than about 10Hz (these are so low we can't hear them, but the speakers can still respond to them) , which protects your speakers from 'rumble' generated from turn tables. However, if you use speakers which utilize sound ports for better bass response, it's a good idea to keep that filter active since vented cabinets tend to 'run away' from infrasonic signals which might be present in any media, and overextend the woofer, leading to damage.

 

 

 

 

There are no less than 8 versions of the M-1.5(t) !!!

 

[robertcdt 16]

On 10/2/2025 at 9:54 AM, MattB said:

Welcome!

Shortly before I found this site, I purchased a M1.5t rebuild kit from the same vendor.   while all of the parts inside were quality brands, the instructions were somewhat vague and there was no list of any oddities/ updates to the design.   i.e. "some versions of M1.5t had a 2.2uF cap in location C-xx, but later versions have a 10uF.  this kit is shipped with a 10uF"   so I had a small handful of capacitors left over and were missing others.  fortunately I had a few spares in my stash from other recent projects, but I did have to buy a couple non-polar caps from digikey and wait a week to get it.   There were also baggies of small signal PNP and NPN transistors and I couldn't read the part numbers.  they are not listed in the instructions other than being provided "just in case you need them".    that sounds wonderful!

 

While buying singles from a place like digikey can be cumbersome, I highly recommend doing the research and digging up the parts yourself so you know what you're getting.  also consider the "BillD mod" if you do decide to take on the C-1 yourself.  I haven't done it yet, but planning for it as a winter project.

yes  you are correct 40 pages of general instruction with some good information but very vague when it came to working on the c1.

I did a recap on a Bose 901 series IV today it went very well only 12 capacitors. The kit came from affinity for artifacts his instruction are good for small

project. Plan on recapping a technics SL 1700  turntable next. amazon sells a desoldering iron for 35 dollars that works great if you need a reasonably priced one. plan on doing the c1 soon just trying to do these smaller project  first to get more experience first. Its all about the desoldering.    

 

[3M_Audio 2,020]

Good idea to practice on some smaller/simpler boards first. Just be aware that on the more modern boards, to save money manufacturers often went with very thin fiberglass as opposed to the glass epoxy boards in better quality older equipment. The fiberglass boards are much less forgiving of excess heat. I've restored a couple Technics consumer TTs and they all had fiberglass boards.

 

And on the infrasonic filter, I'll second what @wrf said. Just use that for turntable playback otherwise leave it off.

[robertcdt 16]

yes Glenn I am seeing that all boards are not equal. I did not  know about different materials thanks for that info. was working on a neato robot vac board and had a problem with burning the board  this was before I got a de soldering iron.

when de soldering I start with a little flux I like the fact it marks the joint that needs to be de soldered and hope it protect the board from over heating.  is there any thing else I can do to prevent over heating the board? Is the Carver C1 board a good board what is your opinion of it? 

Thanks

Robert

[3M_Audio 2,020]

10 minutes ago, robertcdt said:

yes Glenn I am seeing that all boards are not equal. I did not  know about different materials thanks for that info. was working on a neato robot vac board and had a problem with burning the board  this was before I got a de soldering iron.

when de soldering I start with a little flux I like the fact it marks the joint that needs to be de soldered and hope it protect the board from over heating.  is there any thing else I can do to prevent over heating the board? Is the Carver C1 board a good board what is your opinion of it? 

Thanks

Robert

All of the original C-series boards were good quality and take re-work pretty well. Do a YT/Internet search on the Japanese-made Hakko FR-301. It's a little money but if you are going to do an appreciable amount of this type of work, it's a very worthwhile investment. Quite a few of us here at TCS have these.