Presto K8 fuzz, distortion and high frequency tone issue!

[elyr]

Hi All!
I'm new here, just got a Presto K8, tubes in great shape but Ill replace the caps in the next week.
I'm using Apollo 12" dubs and a ruby stylus, with some success! Right now I am just testing with some prerecorded music from my computer into the radio input of the Presto.

There are some issues to be resolved though. I get a fair amount of distortion, and some pretty audible noise when the music starts playing.
Worse though is about 3 minutes into cutting 78s, a high frequency tone is introduced to the recording. Anyone have this problem before?
Will replacing the caps help to resolve issues like this?

Thanks! Any advice is appreciated

[Gus]

I think it's an impedance problem
between computer's output and Presto's radio input (don't forget it's a 70 years old amp)
did you use inverse riaa equalization curve?
maybe someone else with the same lathe can help you.

but first read here

http://lathetrolls.com/lathetrolls/forum/viewtopic.php?f=1&t=146&p=578&hilit=impedance+radio+input&sid=c5b6ecf8de5ee74f22f058aa3521dc61#p578

[elyr]

The article posted above says that the radio input is about the right impedance for a modern audio signal coming from an aux output, so I don't think impedance is the problem.
And the bizarre tone I get after 3 minutes of cutting? I'm not sure what that would be!

I'll replace the caps and see if there are remaining issues.

[Gus]

Before start to change amp caps

read this post

http://lathetrolls.com/viewtopic.php?f=1&t=4377&p=26852&hilit=distortion+on+piano&sid=eec26aab79038ee544f324b406f1024f#p26852

and search for similar problem on this great forum.
Some of these questions have answered in the past.

[Steve E.]

You are cutting 78s, right? so 3 minutes in is approaching the end of the cutting area when cutting Out -> In.

Expensive test, but: Try cutting a silent groove. That is, a groove without electricity hooked into the head.

I'm going to guess that you will still get this high-pitched sound. Which is to say, as the friction increases nearer to the center of the record, the stylus is whistling as it cuts the lacquer.

Are you using fresh acetates or old ones?

Remember that 78s were typically cut with styli with a much rounder tip. You are putting more stress on the tip than they typically did back then. How deep are the grooves that you are cutting? Can you tell?

Make sure as well that the whistling is not being produced by your playback stylus damaging the soft groove. What kind of playback stylus are you using, and at how many grams of force?

[elyr]

You are cutting 78s, right? so 3 minutes in is approaching the end of the cutting area when cutting Out -> In.

...as the friction increases nearer to the center of the record, the stylus is whistling as it cuts the lacquer.

Are you using fresh acetates or old ones?

Remember that 78s were typically cut with styli with a much rounder tip. You are putting more stress on the tip than they typically did back then. How deep are the grooves that you are cutting? Can you tell?

I'm working without a microscope, so I'm not sure how deep my grooves are. I am using Apollo dubs and a Ruby stylus bought in November, so that shouldn't be the problem. Will reducing the weight on the cutting head reduce the friction without affecting the fidelity?

Also, are there any sonic indicators that my cutting stylus is damaged?

[Steve E.]

if the first three minutes of your cuts sound good, I doubt the stylus is damaged.

OK, I'm looking at pix of a k8. Trying to remind myself of what they are all about... (see below...)

So the arm swivels. It may be that it is mistracking more as it gets towards the middle.

Hey, anyone with a K8 care to pitch in. KrisD? Where's that Alex Steyermark when you need him?

Do try a test with a silent groove. If it happens, then we know it's a physical/mechanical problem, not an electrical one.


http://imgur.com/XtPva.jpg

http://imgur.com/2wjoW.jpg

http://imgur.com/UDBu1.jpg

[elyr]

Looking at the Presto head above, I see that mine doesn't have an advance ball. Could that cause the head to be exerting extra weight on the stylus, and possibly causing the whistle? Does anyone know where to get an advance ball and who installs them?

[Steve E.]

Prestos rarely do. I think that is more of a Westrex thing.

[Jccc]

Has anybody modified the K8 amp to make the output volume louder? Like change the output transformer or change the pre amp tubes?

[Jccc]

Nevermind that last post i made! I found out why the 5c head was not cutting loud enough. i opened up the cutting head and realized the rubber damping material had dried up and hardened. Also the rubber that goes around the cutting stylus had hardened up as well causing the stylus to not move around.
I replaced it and did a test cut and the head cuts nice and loud! I did not even recap the amplifier or replace the tubes!

I cant believe how loud this machine cuts.

[Techie]

Great news! What did you use as a replacement for the damping material?

[Jccc]

Hello i used this "self fusing silicone tape" i picked up over at dixieline lumber.
I used that for the little rubber part that was used for holding the stylus in place as it hardened up over the years.
I also noticed that part where you insert the stylus was really stiff so i loosened it up when i added the silicone tape there.

I did not change the big yellowish damping thing inside as it was still pretty flexible. I might have to change it later on down the road as i messed it up while i was trying to get it off to get to the inside.

[Stevie342000]

I had a 5C head and cutting arm, sold the Presto 5C now with a bit of regret.

Mine was earlier than the one pictured as it was just plain metal but had a clear plastic type damper which I assumed was Presto Flex it did not look like rubber.

It would be in my humble opinion that once the Presto 1-D came out the first with Presto Flex damping they used that material for all the heads after.

My guess as that head and arm is later then it would use Presto Flex. Do we have any pictures of the different types of damping material used on the Presto heads? Should they be in the Lathe trolls Wiki for all to reference. It's easier than searching all the threads for all the information. We should be using the Wiki much more effectively, so that the information that all newbies or not need is there for peeps to digest and then post any questions with problems they face.

I now have a Presto 1-D which has been rewound for 15 ohm and has had a full service. Is there a lifetime limit on Presto Flex?

It's a fairly early plastic damping material, does anyone know what it is made of? What's the modern equivalent and where would you purchase it from? If my research is right the 1-C came out about the same time as the 6N cutting lathe circa 1940.

The Presto 1-D came out in 1947 and became the de facto Presto standard head, the damping material allowed for a greater frequency response. Many many lacquers were cut on a Presto 1-D head especially at the independent labels such as Sun Records.

[Jccc]

Yes i believe that big yellowish piece inside of the 5c head is also Presto flex material. Inside of mine it is still flexible so i did not replace it. I will probally do it down the future though.

I remember reading on here that you can replace the presto flex with "Sorbothane rubber"

If someone on the board knows of a better material and where to purchase it that would be great!

[Stevie342000]

The 5C I had had the same clear yellowing plastic material for the damping.

Sorbothane sounds like a good option to me. Where do you get that from? Mine is ok but perhaps we should post the results on the Lathe Trolls Wiki for future reference.

[BrotherJack]

Hey Jccc,

Newbie here with the same K-8....I'm having the same issue of heavy fuzz and distortion.
You don't happen to have a photo of what parts "hardened up" on you do you? I see the large "yellowish" material once you open up the cutter head, but not certain where the other parts you mentioned are.

Any help is much appreciated!

thx!