I learnt something..

[JayDC]

So if you take an 18ohm 200w Resistor and wire it parallel with a 15ohm cutter head, the total ohms would come out to 8.18, and I'd have more head room in my amp to cut the high's..

[Jccc]

How do you do this? Do you just take two resistors from Radioshack and solder it to the wires coming from the cutter head before they go into the speaker output of the amp?

[markrob]

Hi Jay,

That will not do what you want. Yes, connecting the resistor in parallel will lower the total resistance seen by the amp to 8 ohms, but you will end up throwing away power into the external resistor, not into the head. A bad idea! You have 4 viable choices here.

1. If using a solid state amp, spec in an amp rated 2X the power (into 8 ohms) that you need to drive the head. Most amps aren't rated at 16 ohms, you you have to take into account that the actual power produced will be half of the rating.

2. Use an external transformer, sized correctly, to match the 16 ohm head to the amp. If the amp is rated for 4 ohm use, then you would likely get the best bang by matching 4 ohms - 16 ohms. This could get expensive as you would need a large hunk of iron to work at high power levels.

3. Use a tube based amp that has an output transformer with taps that match your head. Most will have this option.

4. Re-wind the head to better match today's solid state amps.

Mark

[JayDC]

yeah, I figured I'd get a new amp for the extra oomph.. My buddy told me last night attaching a dummy load to everything would drop the ohms, after reading a little in my electronics book it seemed to work out mathematically.

How much power would i lose? less then what I'm doing now? I don't think I need much more power, just a little more because my amp is tapped out (all the way up). I want it to run at lets say 3/4 full volume, cut at the same loudness i am currently cutting at, but yield a little more high end in the cut. When I make the adjustments to get more high end, I run out of amp volume, and I'm cutting -2 or -3 db less then before.

[subkontrabob]

as markrob pointed out, a properly spec'd transformer would be the way to go.

check out chapter 9.7 of volume two (about AC) from this marvellous series of free electronics ebooks: http://www.allaboutcircuits.com/

I don't remember any of the specifics (my brain is like swiss cheese ), but it's all there!

[JayDC]

I found a good cheap power amp, that is rated for 16ohms @ 160watts bridged mono,the pyle ppa300. Kinna a no name brand, and probably not the best, but its within reach for me atm. I think it would give me the correct amount of power, since the 1-D manual states it needs 1.2watts x 10 (120watts @ 15ohms) to cut high fidelity, and notes that an oversized amp is good for classical music.

[markrob]

Hi Jay,

That looks like a winner! Not very expensive either. Should be plenty for the head. Will give you over 20 db of headroom over 1.2 Watts. You'll probably run into the limits of the head in terms of distortion well before that.

Mark

[JayDC]

we'll see, this presto head surprises me daily. It so far has surpassed every stigma that was bestowed upon it. it cuts higher levels then i was told it would, it has a higher frequency range then even the manual states.

It is not the tools we use which make us good, but rather how we employ them.

[JayDC]

How do you do this? Do you just take two resistors from Radioshack and solder it to the wires coming from the cutter head before they go into the speaker output of the amp?

as stated earlier that it wont work, i figure i'll explain wat i was saying better..


wiring the resistor in parallel means to bridge the circuit, or to connect one end of the resistor to the positive of the circuit, and the other end to the negative.

wiring a series would mean to wire the resistor on the negative.

I think what your describing is called series parallel. I'm not sure, thats the next chapter of my electronics book..

[JayDC]

in case presto people are following this..


I also found a high grade tube amp that will handle a 16ohm load at about 160 watts with 4 kt120 tubes.. says the designer of the amp..

It's rated at 125 watts using 4 kt88 tubes..




VTA M-125 tube amplifier KIT

This is a 125 watt monoblock amp IN KIT FORM that uses four output tubes in a parallel push pull output circuit.
The amp is built on a 10 inch by 12 inch 16 gauge brushed stainless steel chassis and uses a modified VTA Mark III driver circuit.
The recommended tube complement is 4 X KT88, 6550, KT90, KT100 or KT120 output tubes, 2 X 12BH7 (recommended) or 12AU7 driver tubes,
and a Weber WZ68 Copper cap solid state rectifier.
NOTE - A tube set is not included with this amp KIT.
On the front face is an on/off switch and three bias test pins.
One test pin is used in biasing the two left output tubes and one test pin is used in biasing the two right output tubes.
The bottom center test pin is a ground pin. The rear face contains one RCA input jack, a fuse holder,
an IEC AC connector, and a pair of output binding posts.
The output binding posts may be set up for 4, 8 or 16 ohm speakers.
The amp has a switch which allows operation in pentode/ultralinear mode (125 watts) or triode mode (65 watts).
The triode/ultralinear switch may be used while the amp is running.

Power output (4 X KT88) 125 watts from 17 Hz to 32 KHz at less than 1% THD in ultralinear - 65 watts in triode
Power output (2 X KT88) 65 watts from 17 Hz to 34 KHz at less than 1% THD in ultralinear - 35 watts in triode
IMD .................................. <38> 95 dB below 125 watt output
The M-125 does not invert phase
Dimensions - 10.0" wide X 12.0" deep X 7.10" high
Weight (each) - 34 pounds > shipping weight 38 pounds


http://www.tubes4hifi.com/bob.htm#M125

[JayDC]

oops..