Noise at idle

[travisc]

Shawn,

these are the specs, it appears the amp is ac- coupled in, and dc servo out.

any thoughts would be appreciated

SPECIFICATIONS

Minimum Performance, IHF standards<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Power

2 channels, continuous W/ch:

8 ohms 4ohms 2 ohms 1 ohm

(audio band) 400 650 800 1200

(rated distortion) (26 dBW) (28 dBW) (29 dBW) (31 dBW)

(short-term,

Limited by fusing)

4 channels, continuous W/ch:

8 ohms 4 ohms 2 ohms 1 ohm 100 200 325 400

(20 dBW) (23 dBW) (25 dBW) (26 dBW)

Current capability 100 A peak into 0.1 ohm with the IHF

Dynamic-headroom signal; 20 A continuous

Dynamic headroom (IHF) 1.5dB (e.g, 1200 watts into 2 ohms)

Distortion (all types) 0.05% or less, to rated output

Slew rate 200 V/us (100 V/us in 4-channel configuration)

Sensitivity 1 V for rated output

Bandwidth -3 dB points @ 3 Hz and 160 kHz

Frequency response 20 Hz 20 kHz + 0.075 dB, load-invariant

Noise 96 dBA below 1 W,

116 dBA below rated 8-ohm power 4-channel,

119 dBA below rated 8-ohm power 2-channel.

Seperation 90 dB @ 1 kHz, 70 dB @ 20 kHz

Damping Greater than 100 @ 20 kHz,

1,000 @ 2 kHz, 2,000 @ 200Hz

Limiting None. (Circuit thermally protects itself when

output devices exceed their safe operating area.)

Input impedance 48.5 k-ohms in parallel with 200 pF

Fuses(3 sets) 2 for ac mains; 1 each for speakers (user decides value of

these fuses, which lie inside feedback loop to prevent

degradation of the sound); also for internal power supply

(not user accessible).

Circuit topology Complimentary throughout amp, input to output.

Highest-quality film capacitors used throughout.

8 x 250 W high-speed bipolar devices/ch (total of 32);

2 x 3200 VA toroidal transformers w/ 2 taps each

(1.6 KVA/ch); sperate rectifiers for each channel,

Filtered w/ 2 x 22,000 uF caps per channel (=0.18 F).

+55 V power supply rails, each channel. Gain = 29 dB.

+5 mV offset; no inductor at output.

Dimensions 19w x 7h x 24.5d (483 x 178 x 622 mm)

Weight 84 lbs (38 kg)

[LarryC]

Sensitivity 1 V for rated output

Only 1 V for 400 - 600 watts out is too high a sensitivity for K-horns. At that rated output, 3 to 4 V sensitivity would probably be much more satisfactory.

I can't find a sensitivity figure for the SE OTL on the Transcendent web site, but it does say that "Gain is set at 9 dB. This is perfect for high efficiency speakers when driven from an active preamp or high level source."

[travisc]

Thanks Larry

Coytee's DBX amp and mine are more similiar than not. They are configurable for 2, 3, or 4 channel op. Would it be better to run them in 4ch/100w for more sensitive speakers? What are some of the ill effects IYO of running high eff speakers with these amps. mine is dead quiet at idle but does have its quarks as stated above.

[LarryC]

Thanks Larry

Coytee's DBX amp and mine are more similiar than not. They are configurable for 2, 3, or 4 channel op. Would it be better to run them in 4ch/100w for more sensitive speakers? What are some of the ill effects IYO of running high eff speakers with these amps. mine is dead quiet at idle but does have its quarks as stated above.

Your question is above my pay grade unfortunately -- do the db figures you posted above represent the amp's gain? If so, a 6-db difference (at 8 ohms) between 400 and 100 watts would certainly be noticeable, in my experience, although it would be much more noticeable if the noise level were close to threshold than if it's pretty loud to begin with. However, 20 db amp gain is not outlandish, so that might do the trick.

Here is Transcendent's take on amp gain and sensitivity: http://www.transcendentsound.com/amp_input_sensitivity_and_gain.htm. He claims that horn speakers with efficiencies over 100 db "can get by with" only 20 to 30 db combined preamp-amp gain, which seems a little biased toward his products. The Peach plus the BX at 20 db appear to combine to 40 db, which probably shouldn't be that bad. I had about 43 db combined gain with an earlier amp and preamp, and thought it acceptable (barely). I now have about 20-25 db combined, and find the background very quiet.

I've run K-horns with up to 200 watts and now have 100, so I don't think there is much to worry about provided you don't zap them with something in your system (I once blew a woofer with a 25-watt amp). My main concern with such high power would be the quality of the "first watt." However, the noise we're discussing can really interfere with music. The blacker background from low-noise electronics will show up in greater clarity and the music standing out more all the way around. I suspect that's part of the secret of the SE OTL.

Larry

[sfogg]

Larry,

"Only 1 V for 400 - 600 watts out is too high a sensitivity for

K-horns. At that rated output, 3 to 4 V sensitivity would probably

be much more satisfactory."

Agreed... and this is *exactly* what he can end up with by turning down the input level controls on the DBX.

The input level adjustments let him lower the input sensitivity.

Shawn

[LarryC]

Agreed... and this is *exactly* what he can end up with by turning down the input level controls on the DBX.

The input level adjustments let him lower the input sensitivity.

Shawn

Hell's bells, that's simple enough. I missed that he had level controls. Go for it!

[DRBILL]

Does the Peach have diodes in the power supply? If it does, you may need to install RF snubbers. When diodes cut off they radiate a blaze of harmonics that can be picked up on associated gear as a faint hiss or whine.

Try hanging 680pf 500v ceramic caps across the diodes.

DRBILL

[Coytee]

Thank you (everyone).

Been snooping around and think I just might buy one of those MC-2102's. I LOVE the way they look. When I talked to McIntosh today on phone, he told me the input sensativity on it is about 2.5 volts. Given what Mark presumes above about the OTL's being 2.5 (I don't know if accurate or not), if that is the same, then it suggests to me that the 2102 might be as quiet as the OTL's.

Will know more shortly about the 2102. If I disappear forever, you may presume I got it and the wife had issues. lol

[:$]

[sfogg]

" When I talked to McIntosh today on phone, he told me the input sensativity on it is about 2.5 volts. Given what Mark presumes above about the OTL's being 2.5 (I don't know if accurate or not), if that is the same, then it suggests to me that the 2102 might be as quiet as the OTL's."

Nope, 2.5v alone tells you nothing.

Is that 2.5v for 1w of output? 10w? 20w? Full power?

Without knowing that you can't compare that to the SE-OTL. *IF* the SE-OTL is 2.5v for full output remember it is putting out a little over a watt at full power. If the McIntosh is 2.5v for full output that means it is going to be putting out about 100w at the same input level that the SE-OTL is putting out 1w. IOW... the noise will be more of a problem on the Mac then it would be on the SE-OTL.

Shawn

[LarryC]

Does the Mac have level controls, and wouldn't those let you lower the sensitivity if needed? 2.5 v. for 100 watts out is about what I have, and it's reasonably quiet for me.

[Coytee]

Looked at 2102 on McIntosh's site today. Doesn't look as though it has ANY input knobs. All it says on their site is

Sensitivity:

2.5 volts unbalanced inputs

5.0 volt balanced input

Life was so much easier before I discovered how nice tubes can sound lol

[]