agedhorse

21 hours ago, BlueMoon said:

I have a Crown xls power amp with selectable input sensitivity. I regularly use it with my Avalon U5 preamp. Sounds great.

Adjustable input sensitivity isn't going to matter with the Avalon, it's MOL is +30dBu which will drive every power amp I have ever seen with loads of headroom to spare.

For that console, mic level will probably be more appropriate.

18 hours ago, LukeFRC said:

I measured the Tecamp cab I had and stuck all the measurements into whatever that cab modelling software is - let’s just say I liked my puma amp but would buy a different make cab next time

Do you have the TS parameters for the drivers used in the cabinet, or did you assume that they were stock drivers (which they likely are not, even if they look like it)

First, I am assuming that you man ShuttleMax 9.2 since there was not a 6.2 model in the Shuttlemax series. If it's a Shuttle 6.2, let me know and I will get you a copy of the correct manual.

It depends on what you are trying to do. Line level is fine IF the console that you will be feeding is capable of handling line level (most pro consoles will have no problem), but if not you can switch to mic level (which is about 20dB lower)

The controls only affect the DI when switched to post-eq mode.

I have attached a copy of the owner's manual, there is all the info you need about how the DI section works.

ShuttleMax 9.2 Owners manual.pdf

That's a pretty early build, before they started using ICEpower modules.

You are probably going to have to find somebody qualified to reverse-engineer the power supply to determine what's really needed to be reliable. So far, you have succeeded in discovering a couple of ways it doesn't work...

Does anybody know how many of these amps might have been built? This may explain why there are no spare parts available.

On 01/11/2022 at 00:42, Phil Starr said:

I wondered what you'd offer here. I can't imagine you would design anything but systems. You aren't working at the bottom end of the market and there is some quality engineering going on. I guess each new range starts with a design spec and a blank sheet of paper. Everything in a new range of products is going to work well together but do you retrospectively check a new amp will work well with all the old speakers and vice-versa? That would work for a manufacturer with a 'house sound' but limit some innovations.

 

It would be interesting to expand upon this. If all manufacturers are conscientious and competent then buying a whole rig from one range would make a lot of sense. If they are consistent in their house sound then buying an amp from one range and mixing it with a speaker from an older range would still cut down the variables they would have to deal with. There would be advantages to both customer and producer in brand loyalty.

 

People will still mix and match, I guess it's the difference between cooking from a recipe where someone professional has blended the ingredients to produce a consistent and reliable result and trying different ingredients each time in search of the unobtainable best with the risk of something awful.

 

Your detailed thoughts would be really interesting.

I have designed all kinds of products over my career, mostly pro audio and bass products, but some acoustic and electric guitar products too. This includes both high end touring electronics/speakers as well as lower end electronics/speakers (including for some popular brands/models).

I first look at the requirements, both performance and cost, and then look to see what components are already on the market that I might be able to use or easily adapt into the enclosure that the product will need. I will also look at my historical designs to see if I have already designed a driver that might be suitable. I really don't like reinventing the wheel, especially at the higher end where the transducer engineers have spent a fair amount of time and money on. That said, I probably put more energy into the lesser models because I NEED to squeeze out the most performance possible for the least cost. This is true in all product lines actually.

I find it more challenging to get the maximum performance out of the minimum cost, that's what separates the experienced engineers from the onanists. In the middle, giving up a dB or two of performance may not matter as much but at the low end every dB counts, and may be the difference in a viable product and one that's not. At the very high end, there's a LOT more effort placed on pattern control, the evenness of the response at the edge of the pattern, distortion, power compression (thermal and electromagnetic), and also structural since the cabinets may end up over your heads.

Yup, insignificant heating issues.

9 hours ago, Matt P said:

@Downunderwonder your maths looks right to me (although it is nearly 20 years since my thermodynamics lectures at uni)

 

the TC Electronic combo that is shown above might have a side mounted vent/fan but it also has an air gap all round the head in that enclosure so there is some ventilation for the amp (and i'm not going to mention the actual rating of that particular amp being much lower than the quoted value)

 

I think this little 250w head is going to get rather warm and possibly shut down (assuming it has a thermal cut-out)

As there is an insulating layer of wood between the amp casing and the outside world it will be difficult to keep track of how hot the amp itself is getting. 

 

Matt

Yes, the air gap will reduce the enclosure heating effects somewhat which is why I keep mentioning worst case.

My calculations show that with 25 degrees C ambient, a 31cm x 31cm x 31cm wood box with nominal 12mm thickness, the final temperature after "forever" (called the asymptotic limit) will be 33 degrees C with an 8 degrees C total temperature rise. This is about what I would expect worst case, pretty much trivial.

Here's one handy enclosure calculator, there are several. These sorts of formulas are also used in the heating and air conditioning industry too, the walls will have a thermal resistance, and if playing in the sun there will also be heat gain due to radiation.

https://www.powerstream.com/temperature-rise-in-an-electronics-enclosure.htm

3 hours ago, Downunderwonder said:

Please explain. Ime micro amps all get nicely warm to hot enough to be properly glad it's got a fan.

 

My gut instinct is the inside of a 112 is claustrophobic enough that it would get extra warm in there with that amount of heat being shed continuously and the main heat loss being out through the walls of the cabinet.

There's not much heat involved, the average dissipation is less than 50 watts worst case.

1 hour ago, Downunderwonder said:

Either I am missing something or you don't have any appreciation of the thermodynamics at play here.

 

All amps sink heat into the air one way or another. Heat from transistors goes to finned heat sinks or direct to air. The air may be fan assisted or just convection.

 

In this case it is the air inside of the cabinet, with no ventilation! Thus the air gradually gets warmer and warmer with each pass through the amp. All of the aml heatsinks and fans in the world don't change the heat transport to the outside air.

 

Agedhorse seems to be saying the cab exterior surface can radiate enough heat that the air inside won't ever get uncomfortably hot?

 

I think if I ran a hairdryer inside a cabinet it would take quite a long time for the surface to get a little bit warm by which time it would be hell hot in there and likely blow up the hairdryer first. Quid pro quo a cabinet is a good thermal insulator.

 

Down at the other end of the curve the amp heats much less than a hairdryer so conceivably it could warm up the cab just enough that it radiated the same amount but I still reckon that it get would too warm inside for the good of the amp.

 

So all in all it's a bit of  mystery.

 

Added to that I don't understand you not wanting to do the first test with the amp sideways, feeling for a warm draught out of the top port, with a chance to decide discretion is the better plan.

Not going to be a problem at <50 watts of dissipation, it would take DAYS to raise the temperature 10 degrees C above ambient.

The amount of heat in the speaker being discussed is insignificant in the big picture

I only have a couple of saddle mounting systems left for those amps.

Yes, be VERY careful when "home brewing" any hardware for an amp, I have seen too long screws ruin an amp beyond economical repair (aside from being dangerous).

On 04/11/2022 at 15:03, mario_buoninfante said:

I see what you are saying @Baloney Balderdash, but just to be clear, I'm not trying to get rid of the amp. I would simply like to find a neutral amp (to pair with a cabinet) that doesn't affect my bass+preamp+pedals sound, if that makes sense.
At least on paper, I just find redundant going through 2 preamps (pedal and amp preamp). Not because you won't get a good sound, thousands of people do, but because I'd like to have 1 sound, whether or not I'm using the amplifier.

Hope that makes sense.

Yes, it makes perfect sense IMO.

11 hours ago, Hooch said:

If you aim at using a separate power-amp, mains preamps are the way to go imo. A preamp pedal won't be juicy enough in most case, whatever power-amp it sees. Totally relies on power-amp input sensitivity of course, but even with what i *think* are good ones in this field (Acoustic Image Focus SA), had thinner and much noisier results than with mains preamps - with the noticeable exception of the Grace Alix, whose output is on par with preamp pedals.

My experience and testing suggests that it's very dependent on the preamp and preamp pedal. There are a good number of pedals that have no issues driving power amps to rated output, the real issue is a shortage of specifications that provide the definitive answer. 

For example the TwoNotes revolt preamp's MOL is +11dBu (from their specs) and it operates from a standard 12V DC power supply.

3 hours ago, Phil Starr said:

Now this is where it gets interesting, to me at least. Let's have a look at one of the classic bass speakers used in a lot of mid-priced cabs, the Eminence 12A-2 and beside it what happens to the bass response when you put it in a 50litre box. You can see the speaker has a natural peak of about 4db in the 1-4kHz region and almost 3db of bass boost just above 100hz when you put it in a portable sized cab. Once again you have a smiley faced loudness contour, the auditory version of a high salt, high sugar snack. It's almost the same response as the ELF just slightly less exaggerated. Obviously if you mix these two they are going to add their irregularities to make a super sweet, super salty mix. Only palatable to a few maybe. Can you tame it with the tone controls? Well that depends, you have that 400Hz mid control but it of course is only centred there. Turn it up and it will boost the 120hz as well as at 1kHz where the eminence is starting to peak. Turn down the treble? Well the Eminence is starting to fall off the side of a cliff at this point so cutting a few db at 2kHz is going to cut the highest frequencies right out of your sound. If your sound is Jamerson of course that won't. worry you. (Brilliantly Jamerson is in the spell check)

 

So now we are back to art. No-one is going to sit down with all these graphs and use them to set their tone controls. By the time you've factored in the bass, pups, strings, fx and room acoustics it is just too complex but it is easy to see why some marriages just break down. Marrying the slightly bright old school sound of the ELF with the slightly bright old school sound of one of the bass world's best loved speakers isn't going to let you maneuver very much and you might miss those mids when you are playing with your over loud band. 

 

Designers certainly sit down with these graphs when developing amps and speakers. They really aren’t intended for end users, especially because of the misunderstanding of the correlation between the graphs and how this translates to end results.

18 hours ago, NancyJohnson said:

I try to read some of the more technical posts here and it's like I just go word blind; I'm not saying this data isn't useful in some capacity to some people, but by and large surely, given the amount of Poweramps and stomps out there, a lot of this is no use to anyone?

 

As previously posted, I ran (several) rack set ups for 30+ years.  Not once have I suffered from anything not working or under performing.  Not once did I refer to the manual of any unit to read up on input sensitivity (or anything). The only thing I didn't do 'properly' was to always have the poweramp outputting at 100% and controlling the output volume off the pedals/rack kit.  

 

Maybe I was just lucky.  

If you can’t understand the specs, than you either need to have somebody help you, by lucky or buy products designed to work together.

It’s no different than taking gigs where you need to sight read, if you can’t do it, don’t take the gig and don’t criticize those who do. 

9 hours ago, Tech21NYC said:

When I spoke to one of the techs at Crown he said the specs on power amps make sense when using them for the proper application. They measure the wattage with a 1kHz sine wave for comparative purposes. In a pro-audio application they calculate how much power they need in relation to the amount of speakers they need to power. A rule of thumb is that if you are powering speakers with a 500 watt rating you will need a 1000 watt amplifier. This will give you the proper amount of power and headroom to handle peaks. The sound tech that we hire for our band told me with class D amps he likes to have 3 times the power needed. 

 

The problem that players trying to use these amps for a musical instrument application encounter is that they are trying to use a product that was not designed for that application and don't understand how the amps operate. Pro-audio power amps are expecting the output of a mixer. A 32 channel mixer can output over +22 dBu which is why they have a higher input threshold than a typical guitar or bass amp. The gains on those amps are really used to attenuate the input so the mixer's high output doesn't clip the input to the power amp.

 

You don't want any SS amp especially a Class D amp operating on the verge of clipping. Here is more info from Crown regarding amp power.  

Since I spent much of my career in the pro audio industry, there are a lot of misconceptions going around.

First, it’s acceptable to power an amp at 2x the RMS rating of a speaker provided there’s is minimal clipping or OD/distortion components in the signal. As soon as distortion is added, no matter where in the signal path, this recommendation changes and the power handling of the speaker and amp (in RMS metrics) should be pretty similar, and for heavier distortion, and heavy compression, the speakers should be capable of greater power handling than the amp provides (by ~50% if you follow the guidelines of some driver manufacturers including JBL).

This also assumes that a proper HPF is also used.

Crown’s recommendation is being taken out of context when quoted for bass guitar amplification.

10 hours ago, Waddycall said:

 What’s not helping me is the mix of specs and a lack of understanding of their correlation.

My QSC amp has a rated input sensitivy at full output into 8 ohms of 1.15 Vrms (+3.4 dbu).

the microbass 3 has a nominal output level of 0dbv. 

Consumer line level is -10dbv so it’s clearly higher output than that.

Pro line level is +4dbu. 

A bit of playing around with an online calculator puts 0dbv at 1 Vrms (+2.21 dbu).

im concluding from this that the microbass won’t get my power amp to full output but it should get it fairly close.

does that seem right?

Nominal output level doesn't tell you all that much, what's more important is the maximum rated output level of the preamp. Generally, it needs to be about 6dB greater than the rated sensitivity of the amp to be sure you have sufficient drive capability to drive the amp into limiting (most pro audio power amps have internal limiting, and you want to be sure you can drive into this rather than clip the output of the preamp).

Also, all numbers need to be expressed as volts rms.

17 hours ago, mario_buoninfante said:

that's fair. I did see some official videos (in Italian though) on YT where the presenter was saying one could even go straight into that with their bass.
I think it's the gain stage they have in place that allows that.

Maybe, but this is the reason for published specs... to be able to answer these kinds of questions without guessing.

Since the Carbines are fan cooled, the orientation is not important PROVIDED the vents are not blocked.

22 hours ago, mario_buoninfante said:

I start thinking that the GR Bass Pure Amp might just be the ideal solution for this, since they also have a gain stage in case the preamp doesn't provide enough signal.

Maybe, but there's no input sensitivity spec anywhere in their documentation so there's no concrete way to know for sure without trying it (or asking the manufacturer what the input sensitivity is for rated output).

In general, pro audio power amps are +4 to +8dBu rated sensitivity with the level controls fully up. Generally you will want 6dB of drive headroom to avoid overdriving the preamp while approaching the clip or limit point of the power amp.

Some power amps also have exhibit lower sensitivity when driving unbalanced inputs, and many preamps have 6dB lower maximum output level when driving from unbalanced (or unbalancing via adapters) outputs. 
 

These are all things that need to be tested/verified to determine compatibility. It’s not always easy with the limited specs that are often provided.

Read the answers you got from me (and others) on talkbass where you posted the same question.

11 hours ago, Chienmortbb said:

@Phil Starris right, the greatest  care was taken to ensure the integrity of the Amps under test. It has to be remembered that some high powered amps, especially those not using bridging techniques, are capable of over 250v peak-to-peak between the speaker terminals.

 

It is also worth asking the question as to whether you need to use the power amp output to measure the frequency response of an instrument amp. 
 

The figures I got at the preamp output was so close to the response at the speaker terminals that it makes no sense checking the sharp end. 
 

It seems that, excepting @agedhorse’s patent, most designers content themselves with the preamp section and that sets the sound of the integrated amplifier. 

 
Incideny I would love to try one of @agedhorsedesigns and might just start saving up for one. 
 

 

I would suggest that in general, testing at the preamp out is much safer, and likely to get results that are plenty close enough.

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