Do I have too much gain?

sts9fan · « **on:** 4 Apr 2007, 01:09 pm »

So first I will admit to having EXTREMLY limited experience with different types of gear so if I am way off please let me know.
I wanted to see what all the fuss was about with tubes so I built a bottle head pre kit and really liked the sound it gave my system with my old paradigm speakers. The problem was that there was and is a huge hiss when it is added to the system. I also had this hiss with the eastern electric BBA I auditioned so I can say it is most likely not the bottlehead's fault. There is a slight hum/hiss from my speakers without the pre but it cannot be heard from my listening spot. My odyssey amp is said to have around 30+dB of gain which seems like a lot(is it?). Could the slight noise be my unmodded squeezebox being noisy? Do you think my amp as too much gain for my system? I don't listen very loud at all. Thanks for your help.

Bob Reynolds · « **Reply #1 on:** 4 Apr 2007, 03:59 pm »

I think 30+ dB of gain for an amp is on the high side, but aren't the Druid speakers supposed to be very efficient? I recently noticed this set of measurements of the Druid

http://www.soundstagemagazine.com/measurements/zucable_druid/

From 100Hz to 5KHz the response varies by 25dB, so could it be that the frequency of the hiss is falling at one of the peaks?

Just a thought.

miklorsmith · « **Reply #2 on:** 4 Apr 2007, 04:16 pm »

Good gravy, these graphs have long ago been debunked. The manufacturer specifies a floor gap for the Druids and these measurements were taken with the speakers hanging mid-air, not allowing the speakers to function as engineered. I assure you speaker FR has nothing to do with this problem.

That IS a lot of gain for a hi-eff setup but I doubt that's the problem. I've had numerous combinations with the Druids and Definitions but never that much noise. Tube equipment can be quite noisy but not knowing the piece I couldn't say how much self-noise it generates.

rollo · « **Reply #3 on:** 4 Apr 2007, 04:17 pm »

30db is a bit hot for an amp. Do you know the gain of your preamp? Could be just to hot a combo. IMO.
Just for curiosity how much gain does the matching Odyssey pre have? Synergy man.

rollo

WEEZ · « **Reply #4 on:** 4 Apr 2007, 04:57 pm »

sts9fan,

The short answer is 'yes'. For an easy to understand and well written piece on the subject, have a look at this:

www.transcendentsound.com/amp_input_sensitivity_and_gain.htm

WEEZ

sts9fan · « **Reply #5 on:** 4 Apr 2007, 05:03 pm »

I don't know the gain of any of the odyssey preamps unfortunately. I have used a 12dB in line attenuator with good results but maybe its in my head but it seemed to dull the highs. I think the Bottlehead pre has 13dB and the EE BBA had adjustable gain. The noise was only bad with the BBAs gain up.
Again could it be I have a noisy source that is being amplified?

konut · « **Reply #6 on:** 4 Apr 2007, 05:14 pm »

Both the BBA and Bottlehead are specified at between 85 to 95db signal to noise ratio. While these are fairly respectable numbers for tube equipment, no weighting, the way the specs are measured, is given. I suspect those numbers are 'best case scenarios' that do not reflect the way your Odyssey and SB are measured. Unless you're spending many times more $, for tube equipment, than what the BBA and Bottehead cost, your not going to get high s/n ratios AT THE FREQUENCY EXTREMES. The other thing to note is with the gain of the Odyssey you're probably not having to turn up the pre too much and, sometimes, the best s/n ratio is not realized untill you turn up the pre to a point where its working in its optimum operating range. So the tip about the attenuators is a good one, but it may not solve the problem if the inherent s/n ratio of the Bottlehead is just too low.
In the pro audio world this 'matching' of components is called gain staging. Its all about matching components so that they feed each other to work in their optimum operating range ie. where their s/n ratio is greatest and distortion is lowest.
If your source is a SB3, I seriously doubt if its the source of the noise, unless its broken.

sts9fan · « **Reply #7 on:** 4 Apr 2007, 05:26 pm »

So I would guess its safe to say that my amp alone has too much gain for my speakers.

Quote

www.transcendentsound.com/amp_input_sensitivity_and_gain.htm

Thanks for this link I wish it had the math included though. Very informative.

Anyone got a low gain tube amp they want to trade for a Khatargo Extreme? aa

konut · « **Reply #8 on:** 4 Apr 2007, 05:35 pm »

Why do you need a preamp? You might think about the Promitheus, or other, passive. Less is more.

sts9fan · « **Reply #9 on:** 4 Apr 2007, 05:38 pm »

Why do I need a pre? I don't and actually I am currently building a amp that only has 13dB of gain so I will be all set once I get it put together. Honestly I just want to F with some tubes.

Bob Reynolds · « **Reply #10 on:** 4 Apr 2007, 10:11 pm »

Quote from: miklorsmith on 4 Apr 2007, 04:16 pm

Good gravy, these graphs have long ago been debunked. The manufacturer specifies a floor gap for the Druids and these measurements were taken with the speakers hanging mid-air, not allowing the speakers to function as engineered. I assure you speaker FR has nothing to do with this problem.

That IS a lot of gain for a hi-eff setup but I doubt that's the problem. I've had numerous combinations with the Druids and Definitions but never that much noise. Tube equipment can be quite noisy but not knowing the piece I couldn't say how much self-noise it generates.

I agree completely that speaker response is not the cause of the noise, but to dismiss the notion that it could emphasize the problem is mistaken.

I'd be interested in reading any info on the theory behind the response of the Druids.

miklorsmith · « **Reply #11 on:** 4 Apr 2007, 10:20 pm »

The Druids aren't ported per se, but they have a proprietary ventilation scheme that depends on specific mechanical loading on the driver. Take that load away and the speaker does not perform as it should.

Imagine taking your favorite ported speaker, removing the port tube, then enlarging the hole 3 times bigger. Would the speaker sound as designed? Of course not. This is effectively what the NRC measurements did, despite specific instructions from Zu. Owners will verify that 1/4" difference in gap height makes a big difference in bass response and that direct placement on carpet guarantees subpar bass performance.

The "speaker response" doesn't look anything like the graphs. The Druids are actually a smooth sounding speaker. So, they don't emphasize any noise aside from the "normal" concerns with speakers exceeding 100 db efficiency.

konut · « **Reply #12 on:** 4 Apr 2007, 10:39 pm »

While I don't doubt anything presented regarding the sound of the Druids, I don't think its relevent to the problem of hiss, which after all, is what the thread is about, unless that off axis peak at 5khz is contributing to the perception of hiss.

bundee1 · « **Reply #13 on:** 5 Apr 2007, 02:35 am »

I think the squeezebox might have too much gain. I think it outputs 6v while most cd players output 2v.

samplesj · « **Reply #14 on:** 5 Apr 2007, 02:48 am »

Quote from: bundee1 on 5 Apr 2007, 02:35 am

I think the squeezebox might have too much gain. I think it outputs 6v while most cd players output 2v.

No, stock a squeezebox is pretty much a normal source now.

It will output 2v RMS. That is around 6v PP, but those are what pretty much everything is now.

JLM · « **Reply #15 on:** 5 Apr 2007, 03:48 am »

Yes, you have too much gain.

You have a very "hot" set up (high efficiency speakers plus high output amp), in other words that combo can get waaaay loud with very little input. Tubes are notorius for being noisy around either high efficiency speakers or high output amps. In fact the system would be highly susceptible to any kind of background noise.

Possible solutions:

1. Unless you want additional sources, I'd just feed the Squeeze Box directly into the amps as per above.

2. If you want tube sound, Single Power builds good low noise tube pre-amps. (Actually they're headphone amps that can be setup as pre-amps.)

3. You could try a passive pre-amp as per above. A good cheap one is the Channel Island Audio VPC-3 but it only allows for two inputs (which should be enough to go with the Squeeze Box). The Promitheus TVC is reasonably priced and has a very long and positive thread here at AC. However build/delivery time from Malaysia has been slow and some have experienced realibility issues due to shipping, loose pots, and broken connections. (Note that a transformer based volume control has lots of little wires that each must be soldered in place.)

dado5 · « **Reply #16 on:** 6 Apr 2007, 03:57 am »

Yep to much gain and it is in the wrong place in the chain - your system is not synergistic.

Your pre is generating the 'rush', the Odessey is amplifying every bit of it and the Druids are letting you know what's going on.

My recommendations in descending order (your taste and priorities will likely be different):

1. Ditch the amp. Too much gain and power for the Druids. Try a Bottlehead amp instead or a deliberately low gain tube amp like those made by SAS or Quicksilver. Almost any solid state amp (except a few Pass designs maybe) is going to have too much gain for your set up.

2. Ditch the pre and go passive. Electraprint Audio has an excellent passive pre solution that is cheap.

3. Ditch the speakers. Go with any number of lower efficiency models.

4. Get a bigger room and sit further away.

Steve Eddy · « **Reply #17 on:** 6 Apr 2007, 04:37 am »

Quote from: dado5 on 6 Apr 2007, 03:57 am

2. Ditch the pre and go passive. Electraprint Audio has an excellent passive pre solution that is cheap.

If you're talking about the PVA, it's a 1:8 step-up transformer which is about 18dB of voltage gain. The 2 volt output from his digital sources is already higher than the input sensitivity of most amplifiers so there's no need for that much voltage gain, which in the case of the PVA comes at the price of a rather punishingly low input impedance of about 150 ohms.

se

dado5 · « **Reply #18 on:** 6 Apr 2007, 07:19 am »

Quote from: Steve Eddy on 6 Apr 2007, 04:37 am

Quote from: dado5 on 6 Apr 2007, 03:57 am
2. Ditch the pre and go passive. Electraprint Audio has an excellent passive pre solution that is cheap.

If you're talking about the PVA, it's a 1:8 step-up transformer which is about 18dB of voltage gain. The 2 volt output from his digital sources is already higher than the input sensitivity of most amplifiers so there's no need for that much voltage gain, which in the case of the PVA comes at the price of a rather punishingly low input impedance of about 150 ohms.

se

Jack winds it to order in a number of ratios. It does require a low output impedance, but the spec is to 600 ohms.

sts9fan · « **Reply #19 on:** 6 Apr 2007, 12:08 pm »

Thanks guys!

The amp is going shortly once I get my Zen V9 built.