Ohms, Amps, Caps, and premature hair loss.

VBB

Active Member
Haha, hey all. I need a basic tutorial that I can't seem to grasp from all my reading.

First of all, my two multi-meters don't go low enough to test caps. What should I look for and even recommendations on which tool to buy, or where?

Next, I have 3 sets of speakers that are labeled 8ohms, but when I test them (at the terminals not connected to anything ) they are testing in the high 4s or low 5s. Would this result from bad caps, or resistors? Or bad components? I can test when I get the right meter.

NOW, for the biggie, I like old receivers instead of seperates. Something about the 3 ring circus appeal of a beautiful receiver brings back my childhood. So I'd like to use my receivers but run speakers with 4 ohm loads or high power demands. I'd like to add an amp, preferably tube, or warm tube like amp, to run with my receiver as a pre-amp. I've read that this adds too much noise.

Is there a way to add an amp and use what I have?

Any brand or model recommended for 75 to 150 watts per channel?

Do those tube buffers really add tube warmth?

So, I'm assuming a receiver that has an A,B,A&B selection for speakers, can handle running two pair of 8 ohm speakers at the see time? Does the receiver combine them to run a 4 ohm load, or does it keep them as separate 8 ohm loads?

Any help is greatly appreciated.

Equipment I'm trying to mix-n-match
Receivers :
Luxman R-1030
Sherwood 7210
HK 930
Onkyo Integra tx-108

Speakers:
Dynaco a25 quad stack
Advent NLA quad stack
ADS L300, L520, L690
Looking at a pair of Maggie mg3a, and Dahlquist dq10 or dq20
 
Cap meter question.
Buy a cap meter.
If you need to test small value caps make sure your meter goes that low

Speaker "ohm" readings.
Speakers rated at 8 ohms. The term is an AC impedance either across a certain frequency range. Your meter is testing DC resistance.
To go slightly further. The actual value of the speaker( impedance) will change depending on the frequency of the signal.being applied.

If your receiver has pre out , amp in jumpers , that's the best place to pick up a preamp signal for an external power amp.
I never used a tube buffer so I can't comment.
100w or more (Good quality) tube amp can run some serious coin (though I'm not sure you need that much. (As you go down this path, there are side paths you can wander off to as well (efficient speakers for instance).

A lot of broad conversation can ensue as it's not a clearly defined path with what you're suggesting .

Lastly if you're going prematurely bald, blame your mother.
 
Multiply the dc resistance times 1.25 to get approximate impedance.
To check value, leakage and Q of capacitors you'll need a LCR meter.
A or B speakers not A plus B just to be on the safe side.
 
All good advice above. You can't add an amp 'as a preamp', they are two different things. Your receiver has a preamp built in, and if it has pre-out/main-in jacks (as noted above) you can use Y connectors to send the preamp signal to another amp/receiver with main-in jacks AND back into the first receiver's main-in.

'Line level' is the voltage output by source components - tuner, CD player, etc. It's the lowest voltage of all, except for the signal direct from a turntable, which is so low it needs an extra preamp stage, which is why you can't plug anything else into a Phono jack. Preamp level is a slightly higher voltage than Line. And finally power output can be as much as 70 volts at max output. These levels should generally not be mixed - for example you wouldn't feed a pre-out signal into an AUX input, it requires a line level source.

You can daisy-chain receivers using the Tape Out jacks to Tape In (or AUX etc.). Then run a second set of speakers off the second receiver. But you have to control the volume of each from its respective receiver because the Tape Out level is at a constant volume. However, the preamp signal is controlled by the volume control so if you split the pre-out and go to two amps, both will be controlled by the source volume control.

Another way you can use more than one pair of speakers and not overload the amp/receiver is to get an impedance-controlled speaker selector box. You can play as many pairs as you can plug in, and the box will present a constant 8 ohm load to the amp. You will not be able to play them as loud as hooking them up in parallel to the amp, but you also won't set your amp on fire.

All that said, most people in the audio hobby get to a point in their journey where they either have only one pair of speakers they really like that does everything well, or they have several depending upon mood or music program, and they listen to only one pair at a time. If you're searching for the promised land, just remember more is not always better. The cost of two pairs of OK speakers could also buy you one pair of really good ones. But the important thing is to have fun, so do it however you like.
 
Yep, it's mom's fault. Her dad was bald.

I really never considered running two pair of speakers at once until reading all the comments about the double stacks of Original Large Advents. I guess I got caught up in the 'if one pair is good, two pair has to be better' thinking. That, and mixing and matching components like a mad scientist!

Thank you all for the great info and taking time to respond!
 
The advantage to stacking speakers like Advents is that you get more sound for a given speaker excursion. This improves power handling, particularly at high listening levels.

The disadvantage is that the tweeters (especially) will have overlapping sound waves, which will cancel each other out at certain frequencies. Those frequencies will loose like dropouts on a frequency response graph, like teeth on a comb. Hence the term comb filtering. That effect may or may not bother you.

Stacked 8-ohm speakers present a 4-ohm load, if they are wired in parallel. At a given voltage (excursion), the lower impedance will draw twice the current. So, the amp has to be able to deliver twice the current for a given voltage. If it can’t, you’ll have to turn it down to avoid clipping, and then you lose the advantage of getting higher listening levels.

Amplifier inputs are nominally at line level, but in practice they handle higher voltages, and in practice preamps amplify line levels to higher levels. You can feed an amp from line-level sources. But using tape outs for a second amp won’t work unless the amp has a volume control—tape outs are not affected by the volume control on the preamp. You want “pre-amp outs”, as others have mentioned.

Some amps with A and B speaker puts combine them in parallel. Combining two stacked sets (like your stacked Advents plus your stacked Dynacos) will present a 2-ohm load (nominally). Not many smaller receiver amps supply enough current for 4-ohm loads, let alone 2-ohm loads. But many power amps will do that, and most will feed 4-ohm loads happily.

I use an amp rated at 185 wpc into 4 ohms for stacked Advents, and I can achieve reference (=realistic) loudness for acoustic jazz, orchestral and wind music. Amplified rock is loud enough, but it’s hard to simulate standing in front of an Altec A7 stage speaker without standing in front of an Altec A7. The amp gets warm, but it’s designed to handle it.

Rick “everything is a trade off” Denney
 
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Thanks Rick! Good tip about the amp having a volume control. I hadn't thought that far through the chain and was considering some without it (incase I don't connect through a pre-amp out).

The stacked (or front/back) Dynacos are for a separate system in the basement, so they won't play with the Advent. 4 ohm load would be the minimum.
 
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