I have a Rek o Kut wtih a Audax 8ohm head. My amp may be down because of the circuits. I still may fix it, but I was wondering if there is a reasonably priced amp that I could use for cutting, available, without going broke or frying my cutterhead?? Right now I would be going from my computer for sound...................
thanks in advance for any possible info.
Mike
Suggested cutting amp
Moderators: piaptk, tragwag, Steve E., Aussie0zborn
Re: Suggested cutting amp
Hi,
Since its 8 ohm, any modern amp with 50 watts or more of power would work fine. You'll have to add the RIAA or other EQ "in the box" as needed. Placing a fuse in line with the head will help protect against damage. Start with a 1/2A until you gain some experience with the head and know how much you can drive it. These heads are pretty rugged and distort well before you get into the danger zone as far as power level.
Mark
Since its 8 ohm, any modern amp with 50 watts or more of power would work fine. You'll have to add the RIAA or other EQ "in the box" as needed. Placing a fuse in line with the head will help protect against damage. Start with a 1/2A until you gain some experience with the head and know how much you can drive it. These heads are pretty rugged and distort well before you get into the danger zone as far as power level.
Mark
Re: Suggested cutting amp
thanks for getting back to me, most appreciated
-
tapesandtubes
- Posts: 55
- Joined: Tue Nov 17, 2015 11:12 am
- Location: Philadelphia, PA
- Contact:
Re: Suggested cutting amp
I'm in a similar situation with my Presto K8. Would the advice given above apply?
Presto K8 | 6N
Re: Suggested cutting amp
Hi,
It could. Measure the head's DC resistance. If it measures 16 ohms or less, you should be able to drive it with a modern solid state amp to get an idea if its working. You will need to add some EQ to compensate for the head response and account for the need for the standard RIAA curve used to cut records. You can do this with two separate EQ's (one to flatten the head and one with the RIAA) or combine them.
Mark
It could. Measure the head's DC resistance. If it measures 16 ohms or less, you should be able to drive it with a modern solid state amp to get an idea if its working. You will need to add some EQ to compensate for the head response and account for the need for the standard RIAA curve used to cut records. You can do this with two separate EQ's (one to flatten the head and one with the RIAA) or combine them.
Mark
Re: Suggested cutting amp
Hello,
I want to use this forum to throw my question because it is similar
Days ago I bought a FAIRCHILD cutter head and it gives 8 ohm. I plug it an amplifier output 100 watts with 4 ohm. Although in the head there is very good audio and it perfectly heard but..................the needle barely receives vibration, also does not make an audio groove. What can happen and I can do so that the needle has vibration?
Alfred
I want to use this forum to throw my question because it is similar
Days ago I bought a FAIRCHILD cutter head and it gives 8 ohm. I plug it an amplifier output 100 watts with 4 ohm. Although in the head there is very good audio and it perfectly heard but..................the needle barely receives vibration, also does not make an audio groove. What can happen and I can do so that the needle has vibration?
Alfred
Re: Suggested cutting amp
Hi Alfred,
Here we are again eh? Are you sure for certain that the Cutterheads DC Resistance is 8 Ohms when measured with an accurate Meter? Be sure to re-check the Range of your Test Meter and ensure there's no multiplier on the range selection that you're reading, as the specifications for the Fairchild that I posted in another thread for you, quite clearly state that this is a 500 Ohm Cutterhead which means you may need to drive it (Like I did with my Ugly Duckling Head) through a Audio Transformer. It could though have been re-wound for 8 Ohms Operation, in which case you may need to re-visit the Armature Gap Setting again. Hope this helps, Best Regards
Soulbear
Here we are again eh? Are you sure for certain that the Cutterheads DC Resistance is 8 Ohms when measured with an accurate Meter? Be sure to re-check the Range of your Test Meter and ensure there's no multiplier on the range selection that you're reading, as the specifications for the Fairchild that I posted in another thread for you, quite clearly state that this is a 500 Ohm Cutterhead which means you may need to drive it (Like I did with my Ugly Duckling Head) through a Audio Transformer. It could though have been re-wound for 8 Ohms Operation, in which case you may need to re-visit the Armature Gap Setting again. Hope this helps, Best Regards
SoulbearRe: Suggested cutting amp
Hi Alfred,
Talk about serendipititous, MRATX has just posted for sale, in the classified and tip off section, what you may possibly need, and all for the princely sum of $5 + postage. Remember that the impedance of the Fairchild is stated as 500 Ohms and this is calculated when powered with a highly variable Audio Frequency Alternating Current. The DC resistance may be much much less than this 500 Ohms. As an example, the DC Resistance of my Ugly Duckling mono head is actually 180 Ohms Soulbear
Talk about serendipititous, MRATX has just posted for sale, in the classified and tip off section, what you may possibly need, and all for the princely sum of $5 + postage. Remember that the impedance of the Fairchild is stated as 500 Ohms and this is calculated when powered with a highly variable Audio Frequency Alternating Current. The DC resistance may be much much less than this 500 Ohms. As an example, the DC Resistance of my Ugly Duckling mono head is actually 180 Ohms
SoulbearRe: Suggested cutting amp
Hey...Soulbear,
I am glad to find here again ¡¡¡¡
I remember your post of the 500 Ohms, but my simple digital test meter indicates 7.5 / 7.8 Ohms, no more ¡¡¡..
I will take a photo and I'll send you...If it is correct, what should I do?
Many thanks for your kindness and effort
Alfred
I am glad to find here again ¡¡¡¡
I remember your post of the 500 Ohms, but my simple digital test meter indicates 7.5 / 7.8 Ohms, no more ¡¡¡..
I will take a photo and I'll send you...If it is correct, what should I do?
Many thanks for your kindness and effort
Alfred
Re: Suggested cutting amp
Hi Alfred,
If the coil resistance is sound, it could indicate there may be mechanical issues to resolve. Remove completely the centering tube assembly from the base of the Cutterhead. Next CHECK that the Armature has the free gaps/space to vibrate and CHECK that it moves freely and is not binding or siezed-up on its pivoting point. If things up to here look good, there is only one thing more I can suggest, and that is check that the Tubular Rubber cushions which are used to centre the armature have not become hard and brittle over time, and that they are soft and springy enough to be compressed slightly by the action of the armature when you feed audio to the coil. If the Rubber Cushions have become hard and brittle, no matter how hard you drive the coil you'll not get the movement from the armature and this will result in very low cutting levels, and you'll also be unduly stressing the coil to the point of burning it out, so be very careful. Depending on your competence and confidence, stripping, cleaning, and rebuilding your Cutterhead will do no harm in any event. Other than these points I don't know what else to suggest. Best Regards Soulbear
If the coil resistance is sound, it could indicate there may be mechanical issues to resolve. Remove completely the centering tube assembly from the base of the Cutterhead. Next CHECK that the Armature has the free gaps/space to vibrate and CHECK that it moves freely and is not binding or siezed-up on its pivoting point. If things up to here look good, there is only one thing more I can suggest, and that is check that the Tubular Rubber cushions which are used to centre the armature have not become hard and brittle over time, and that they are soft and springy enough to be compressed slightly by the action of the armature when you feed audio to the coil. If the Rubber Cushions have become hard and brittle, no matter how hard you drive the coil you'll not get the movement from the armature and this will result in very low cutting levels, and you'll also be unduly stressing the coil to the point of burning it out, so be very careful. Depending on your competence and confidence, stripping, cleaning, and rebuilding your Cutterhead will do no harm in any event. Other than these points I don't know what else to suggest. Best Regards
SoulbearRe: Suggested cutting amp
Hi Alfred,
Silly me, I thought about and then forgot to mention it in the above, but the simple expedient of substituting a decent wattage 8 Ohm loudspeaker in place of the Cutterhead ensures that the amplifier is delivering the goods and thereby eliminates the amplifier/audio chain as a source of the problem. DOH!!! Soulbear
Silly me, I thought about and then forgot to mention it in the above, but the simple expedient of substituting a decent wattage 8 Ohm loudspeaker in place of the Cutterhead ensures that the amplifier is delivering the goods and thereby eliminates the amplifier/audio chain as a source of the problem. DOH!!!
SoulbearRe: Suggested cutting amp
Hello Soulbear,
I checked what you have told me and everything seems right. More
over It may be that I expressed in my first message an incorrect understanding...
The needle receives vibration, but I think not enough to make a good groove. How many watts would be need to receive the recording head to generate a movement of 2.5 inchs per second? That is what the manual you sent me is indicating and if I cannot get this movement never I will never get a correct groove. Really I am somewhat discouraged 
Also in your follow message I do not understand what you are telling me. When I plug the cutter head, loudspeaker are not connected. So that what you want me to suggest?
Thanks, Alfred
I checked what you have told me and everything seems right. More
over It may be that I expressed in my first message an incorrect understanding...
The needle receives vibration, but I think not enough to make a good groove. How many watts would be need to receive the recording head to generate a movement of 2.5 inchs per second? That is what the manual you sent me is indicating and if I cannot get this movement never I will never get a correct groove. Really I am somewhat discouraged Also in your follow message I do not understand what you are telling me. When I plug the cutter head, loudspeaker are not connected. So that what you want me to suggest?
Thanks, Alfred
Re: Suggested cutting amp
Hi Alfred,
If you use the Two wires which are delivering the Audio to, and driving the Cutterhead, and connect these Two wires instead to a Loudspeaker, If the Loudspeaker works OK, then you will have eliminated the Audio Signal Path as a potential source of the troubles you are experiencing, that is what I was saying in the earlier post. The Fairchild PDF states that 0.6Watts should be the amount of power required to drive the cutter .0004" amplitude @ 2.5inches velocity at 1000CPS or 1000Hz. To help you I've included these Tables that I'd previously uploaded for another Troll Using the above and the reading you gave for the CutterHead Resistance you can see that the voltage needed to drive your Cutter is (Root) 0.6W x 7.5 Ohms =Root 4.5 = 2.12Volts. Can you send a quick 1000Hz signal to the Head and establish that this is the voltage that the head is getting from your amplifier? If you haven't got it already you can use the signal generator in the free to download AUDACITY software which is useful for loads of other stuff too. If I've correctly understood the literature I've read, you must do this test in the shortest possible time as any cutter will get HOT rather quickly and risk burn-out if fed a single frequency for too long a time period. If you are seeing this voltage at the input terminals of the Cutterhead when doing this test, and all the previous things check out, then I think there's nothing much else I can suggest. Run the Test and and if needs be, post another request for help on the main Secrets of the Trolls Board, and I'm sure other more knowledgeable Trolls will be more than willing to help and to pass on their expertise. Hope this Helps Soulbear
If you use the Two wires which are delivering the Audio to, and driving the Cutterhead, and connect these Two wires instead to a Loudspeaker, If the Loudspeaker works OK, then you will have eliminated the Audio Signal Path as a potential source of the troubles you are experiencing, that is what I was saying in the earlier post. The Fairchild PDF states that 0.6Watts should be the amount of power required to drive the cutter .0004" amplitude @ 2.5inches velocity at 1000CPS or 1000Hz. To help you I've included these Tables that I'd previously uploaded for another Troll Using the above and the reading you gave for the CutterHead Resistance you can see that the voltage needed to drive your Cutter is (Root) 0.6W x 7.5 Ohms =Root 4.5 = 2.12Volts. Can you send a quick 1000Hz signal to the Head and establish that this is the voltage that the head is getting from your amplifier? If you haven't got it already you can use the signal generator in the free to download AUDACITY software which is useful for loads of other stuff too. If I've correctly understood the literature I've read, you must do this test in the shortest possible time as any cutter will get HOT rather quickly and risk burn-out if fed a single frequency for too long a time period. If you are seeing this voltage at the input terminals of the Cutterhead when doing this test, and all the previous things check out, then I think there's nothing much else I can suggest. Run the Test and and if needs be, post another request for help on the main Secrets of the Trolls Board, and I'm sure other more knowledgeable Trolls will be more than willing to help and to pass on their expertise. Hope this Helps
SoulbearYou do not have the required permissions to view the files attached to this post.
Re: Suggested cutting amp
Hello Soulbear,
I tested you said and I think the result is a disaster.
0 db = 4 ohms., and as power amplifier gain = 0 ohms. As for voltage simply do not detect my tester, before or since.......
But there are sound in the head if I send him audio signal. I enclose video and photo of de multimer test ...
If you can keep giving me advice,,,as always many thanks. If you can do not help me more, where I should leave my problems?
Alfred
I tested you said and I think the result is a disaster.
0 db = 4 ohms., and as power amplifier gain = 0 ohms. As for voltage simply do not detect my tester, before or since.......
But there are sound in the head if I send him audio signal. I enclose video and photo of de multimer test ...
If you can keep giving me advice,,,as always many thanks. If you can do not help me more, where I should leave my problems?
Alfred
You do not have the required permissions to view the files attached to this post.
Re: Suggested cutting amp
Attach video
You do not have the required permissions to view the files attached to this post.
Re: Suggested cutting amp
Hello Mark,markrob wrote:Hi,
Since its 8 ohm, any modern amp with 50 watts or more of power would work fine. You'll have to add the RIAA or other EQ "in the box" as needed. Placing a fuse in line with the head will help protect against damage. Start with a 1/2A until you gain some experience with the head and know how much you can drive it. These heads are pretty rugged and distort well before you get into the danger zone as far as power level.
Mark
I am Alfred. I do not know if you could help me. I have one FAIRCHILD cutter head. Although really it get audio and with very good quality, I do not understand why it does not get enough vibration to the needle so that it can get to make a good groove. Needle almost moves..... What I need, what I do wrong? .. It has 4 ohm resistance in my multitester.
Many thanks if you could give me some comments.
Alfred