Blown Fuse in Amp Problem (newbie)

[electrokinesia]

That's really interesting Mark, I never would have thought of that! The amp is actually 100W/channel though: 30W is the amount of power that I was told would need to be applied to the cutter head in order to get a loud enough record.

Even though I don't have a test tone record yet, I think I managed to establish some kind of reference level because my HP400 has been precisely calibrated. I set the HP400 to +10 and got a 1kHz sine test tone to -6dB which should be +4dB/0 VU. I am aware I could be completely screwed up here, as I'm not sure if +4dB is the same as +4dBu. From what I understand it isn't a dBm reading as the measurement was not across an impedance of 600 ohms. It was a start anyway haha.

So I tried some test cuts. Progressively bumped up the volume and adjusted the EQ, and in less than an hour I was cutting a track that was comparable in volume and EQ to records in our genre.

What surprised me is how good it sounds already. I'm using old lacquers to get started. I didn't even have my heat light, home made vacuum pump or stylus heating coil hooked up yet, and as far as I can tell there's no audible noise in the cuts!! I have a 3 degree drag angle on the cutter head... seems to work!

It's been a while now I've been researching, gathering equipment, assembling and adjusting, so to listen back to that cut and hear it sounding GOOD for the first time is an extremely rewarding experience! I'm sure there will be more difficulties ahead, but for now I'm just going to enjoy that it's worked out as well as it has so far.

Mike

[gold]

Even though I don't have a test tone record yet, I think I managed to establish some kind of reference level because my HP400 has been precisely calibrated. I set the HP400 to +10 and got a 1kHz sine test tone to -6dB which should be +4dB/0 VU. I am aware I could be completely screwed up here, as I'm not sure if +4dB is the same as +4dBu. From what I understand it isn't a dBm reading as the measurement was not across an impedance of 600 ohms. It was a start anyway haha.

You haven't calibrated to a reference level because your phono playback has not been calibrated. The first step is to calibrate playback to the reference level. Then match the record level to the playback level. You know you are in the ball park which may be close enough for you.

If you started with an oscillator or other sound source and calibrated the way stated above it is correct. dB are relative units. They are only useful to look at the relationship between two signals. For the unit to be meaningful it has to be tied to a reference level.

dBm is a power measurement reference level because current will be generated across a 600 ohm load. dBu is a voltage measurement. It assumes a bridging load with no influence on level. In a modern recording setup they are used somewhat interchangeably but dBu is a more correct unit in a voltage transfer system like all modern equipment is. This is all theoretical and not particularly important to your situation. But since the concept of reference levels came up you should have this rolling around in the back of your head.

If you are happy with the cuts you could just chug along as is. I think it's a good idea to know some theory.

[mossboss]

All is well that ends well Than!
Good to see all the input
The guy is up and running
Fine tuning comes along as one keeps at it that's for sure
Electro! As Paul is suggesting if you happy chug along
You'd be surprised how much more tricking up you will do as time goes by
Keep Rocking
Cheers

[Serif]

...I'm not sure if +4dB is the same as +4dBu. From what I understand it isn't a dBm reading as the measurement was not across an impedance of 600 ohms. It was a start anyway haha.

dBm is referenced to 1 milliwatt - whence the "m." (1/1000 Watt). This is usually also referencing a 50 Ohm load in radio scenarios. However, it usually references 600 Ohms in telephony and audio. However, there is no official reference impedance for dBm in any scenario. It has to be stated or be understood in context.

dBu is referenced to 0.775 Volts. This is the voltage drop across 600 ohms that results in 1 mW of power. It is used for any load, even though it was derived from a 600 Ohm network standard.

0 VU can be calibrated to any voltage. My meters are often set to where 0 VU = 1.55 Volts. On the D/A and A/D, I have -14 dBFSD = 0 dBu (i.e., 0.775 Volts), but have 0 VU = -8 dBFSD. This lets the meters stay in the sweet spot, without pegging, when responding to already-premastered program. Recovery is usually down to -4 dBVU.

So I tried some test cuts. Progressively bumped up the volume and adjusted the EQ, and in less than an hour I was cutting a track that was comparable in volume and EQ to records in our genre.
...I didn't even have my heat light, home made vacuum pump or stylus heating coil hooked up yet, and as far as I can tell there's no audible noise in the cuts!!...

American tepid wax? (;

Hey, if it works, it works!

Did you use a paint brush to remove the swarf as it was being cut away?

It's been a while now I've been researching, gathering equipment, assembling and adjusting, so to listen back to that cut and hear it sounding GOOD for the first time is an extremely rewarding experience! I'm sure there will be more difficulties ahead, but for now I'm just going to enjoy that it's worked out as well as it has so far.

Mike

Thanks for the report,
- Chuck Spindle

[Serif]

Thanks for the groovy echo...

"What did you think of the shot put event?"

"At foist, I didn't like it."



- Trip Elkhut

[electrokinesia]

Ok, that clears up some questions I had about dB. Looking forward to getting that test tone record. I'm all for theory: I'd prefer to have competent knowledge. My current state of ignorance on so many of these issues is due to me being so new at this. It's my intention to learn as much as I can.

American tepid wax? The ones I'm using are labeled "audiodisc recording blank, New York USA" from Audiodevices Inc. I got them cheap on Ebay a couple years ago. They look to be rather old, hard to say, maybe 35-50 years old?? They're working great so far, but I'm looking forward to trying some new lacquers as well.

As for the swarf, yeah I brushed it towards the center and it wrapped itself around the center pins, which made for easy removal. I couldn't resist lighting the swarf on fire since I've heard so much about it's flamability Of course I didn't have a large amount so it wasn't that impressive, but I think that was a the thickest plume of smoke I've ever seen! haha

Thanks for the support and encouragement mossboss and everyone!

Mike

[Serif]

Ok, that clears up some questions I had about dB. Looking forward to getting that test tone record. I'm all for theory: I'd prefer to have competent knowledge. My current state of ignorance on so many of these issues is due to me being so new at this. It's my intention to learn as much as I can.

You will be able to work with others and you will be able to dial in the ideal performance of your rig when you work with, or at least around, the numbers. My lathe's "advance" computing inputs are designed to work with +4 dBm (as they call it in the manual) nominal levels, but there's enough gain for them to work on levels calibrated around +0 dBm. Fortunately, audioland 0 dBm is the same voltage as 0 dBu (0.775 v RMS). Radioland 0 dBm, however, would be 0.223606... v RMS, yes?

American tepid wax?

You know...

http://en.wikipedia.org/wiki/American_Hot_Wax

(Complete with breathtaking performance by consummate thespian, Jayson Leno.)

As for the swarf, yeah I brushed it towards the center and it wrapped itself around the center pins, which made for easy removal.

I think we're in Bob's your uncle, territory, mate. Keep the machine clean and oiled. As Mossy indicated, you'll soon be modifying things, left and right, like McGruber and "nailing" all manner of mechanical/electrical troubles.


- Doug Intuit

[mossboss]

Bobs Your uncle! Thats an Australianism Is it not? Mmmmm Cheers

[subkontrabob]

Cool, I wasn't aware that I have nephews

happy cutting!