agedhorse

Yup, this was also suggested Saturday on your TalkBass thread asking for help on the same amp... post #19. You could at least have the courtesy of following up there with your resolution IMO.

On 11/07/2023 at 18:13, Downunderwonder said:

OP reckoned one of the originals had nasty noises, and some numbnut has put adhesive/sealant on it. Not toast?

Maybe not, no way to know without a little more troubleshooting.  The good news is that we do still have the newest PH 10" driver (8 ohms) in stock.

46 minutes ago, Downunderwonder said:

There's that, and then the chances of the other two going out on you must be pretty bad. You might get a good enough deal buying four and only be up for one lot of shipping. Could be worth it.

At this point, we don't know if any of the speakers are damaged yet. We do know that one is (very) incorrect. 

On 07/07/2023 at 13:52, ltank said:

I'm truly appreciative of your prompt responses! Currently, the cabinet isn't at my place, it's situated at our studio. But I'll swing by, give some of your ideas a try, and gather some more info so I can answer your questions better.

 

The original speaker placed above the new one has given out. I'm not sure what the tape is doing there, but I'll get back to you on that one.

 

That's a good point, I wish I had thought of it earlier. I currently don't own a multimeter, but I will acquire one soon and then share the findings with you here.
 

Fortunately I use a GK1001RB which is solid state and can take 4 and 8 ohms.

Sorry, I wasn’t feeling well for a couple of days and missed this.

First, a professional service technician that made that kind of mistake (substituting a 4 ohm driver for an 8 ohm driver in a 410 needs to hand in any credentials he may (or may not) have. That’s a bone-head error in judgement, just like choosing a BP-102 which is about the worst driver I can think of for that application. 
 

The original vendor for the earlier PH cabinets went out of business, the parts for those drivers are no longer available. The closest match to the drivers in your cabinet is the Legend CA-10 (8 ohm), and the drivers are wired series-parallel. Note that wiring so the polarities are correct is essential. If you need a diagram, message me and I will get it for you. 
 

This is why I always recommend verifying that the cabinet you are buying used is really what you think it is, I see folks get burned all the time. 

A piece of heavy carpet might help, but some of this is going to be caused by the acoustic coupling between the speaker’s acoustic output and the top diaphragm of the riser.

A high pass filter is one tool that may help, a parametric eq is another tool, turning down a bit might help too. 

3 hours ago, 3below said:

GX 5 from memory, I picked up a nearly new XLS 1502 for far less than the quoted repair cost. 

The GX-5 is an easy amp to repair for a qualified authorized service center.   They have also proven to be extremely reliable over the past ~20 years or so. I don't recall any of the ~100 GX series amps that I had installed ever failing, they were at least as reliable as the RMX amps, but in a smaller  (shallower) package.  That said, the reduced cost of manufacture of some new amps can make them less costly to purchase in some cases. 

Which model?

On 20/06/2023 at 08:34, 3below said:

 

This why I like some older kit, chosen wisely it can be easily self repaired in the event of problems unlike my QSC power amp that totalled itself (switched on at the time but not doing any amplifying!). 

Why wasn't it repairable? Any authorized QSC service center should be able to service this. It's certainly not a self-repair type device, but it was never intended to be a DIY service device with the technology involved.

How are the secondaries attached to the bridge rectifier?

Theres a lot of sloppy wiring and terminations showing in the picture.

With that wiring, I would be wary of intermittent short circuits that load down the secondary. 

12 hours ago, BigRedX said:

But surely the power stages of all non valve amps are designed to be as transparent as the price point allows?

 

The "sound" is mostly in the pre-amp section (and any short-comings due to cost-cutting).

Not necessarily, it depends on the designer's intent and ability.

2 hours ago, Hellzero said:

You still can rebias the output stage tubes to this specific load to avoid this, but nobody will do it, except some crazy techs. 😉

 

And yes I've seen some melted output transformers in my life, but way more blown speakers leading to this, both for mismatched impedance.

How would you propose to change the impedance matching by re-biasing? Bias does nothing to the high reflected impedance LxdV/dT effect.

6 hours ago, Chienmortbb said:

I should have read your post before posting myself. However it is only the cable and connection  point that passes  the current. The socket will only pass what is being drawn by appliances attached to it.

 

One other word of caution. Many Far Eastern imports come with IEC C14 (kettle) connectors but are fitted with 5A cable. That’s barely enough for an 800W amp.

 

 

Hold on a minute, 5A is plenty more than enough for an 800 watt amp (especially if it's SMPS/class D). 

If you were to do then math, with an 80% efficient amp (typical for a quality SMPS/class D), the IEC safety regulations calculate the input power as: (rated audio power x 1.2) x 0.125 duty cycle, so for an 800 watt amp this would be 120 watts mains input. Now if you wanted to use a higher duty cycle than the minimum (I typically use between 33% and 40% myself) to account for overdriving the power amp or high levels of compression, the calculation would be (800W x 1.2) x 0.40 = 384 watts input. Now divide by 230V and you get 1.67 amps which is EASILY handled by a 5A cordset (with the correct fuse for protecting the cord).

On 03/06/2023 at 00:36, BillyBass said:

@Bill Fitzmaurice & @Downunderwonder Electrician here.  In the UK, every circuit would be protected by a device ensuring automatic disconnection of supply, at the fuseboard.  This will be either a fuse, a miniature circuit breaker, an RCBO or an AFDD.  The reason we have fuses in plugs is due to a quirk of history.

 

The Germans bombed the crapp out of us in world war 2 and after it finished a lot of rebuilding was done.  Electricity for the masses was a relatively new thing anyway, here in north London, we didn't get a power station until the 1920s and initially, I assume, it would have been the more affluent and the middle classes that got an electricity supply.

 

The usual 20A circuit Bill mentions was, back then a 15A fused 'radial' circuit, using 2.5mm csa copper cable (actually the imperial equivalent of about 2.5mm).  Radial circuits are: fuse>socket>socket>socket etc, the 'radial' or round name comes from the cable having the line or live conductor going out to each socket and then a neutral coming back, but both conductors, along with an earthing conductor, are enclosed in the same cable.

 

To save money after the war the 'ring final circuit' was invented (fuse>socket>socket>socket>fuse).  This used the same sized cable but then looped back into the fusebox, so there are two cables coming from the fuse, the combined surface area would be about 5mm, which was enough to take 30amps.  It became a cheap way of doubling or tripling the capacity for very little extra copper.

 

The trouble with ring final circuits is that there are some inherent safety issues.  One such issue, the fact that there could be, potentially 30 amps (or 32amps with modern circuits) passing through sockets connected to leads and appliances that would be fried by 30/32 amps (single sockets in the UK are rated at 13A.  Double sockets are also rated at 13A but, anecdotally, can take up to 18-19A before they are put under serious strain).  

 

Consequently, plugs are fused.  Standard domestic plugs have a 13A fuse at most, though, 3A, 5A, 7A and 10A are common fuses that might also get used.  As @BigRedX correctly points out above, the fuse is there to protect the cable, so if a kettle lead can only take 10A, it should have a 10A fuse at most, not 13A.

 

Only three countries in the world have 'Ring final Circuits'.  The UK, Ireland and one country in the Middle East.  They save money at the expense of safety.

Well stated. 

20 hours ago, Hellzero said:

Much higher impedance loads, not putting an 8 Ohms cabinet on a 4 Ohms output transformer (OT) tap... 

Not necessarily, some tube amps are fairly sensitive to output stage loading. A 50% mismatch could result in double the L(dI/dT) voltage which can over time (or immediately) break down insulation in the output stage. 

6 hours ago, Hellzero said:

And you are right.

 

To keep it simple with (valve) amplifiers always use the amplifier's output (tap) matching the cabinet impedance, never use a lower impedance cabinet than the output impedance (tap) chosen on the amp, but you can use higher impedance cabinet than the impedance of the amplifier's output (tap), even if it can create some slight distorsion or slight out of phase sound, which you won't really notice and certainly not the audience.

 

Clearer?

No, some tube amps are particularly sensitive to a higher impedance load, because the reflected impedance to the tubes an primary of the OT can cause ringing and larger than expected voltage spikes which can damage OT’s, tubes and in some cases arcing between the pins of tubes.

On 01/06/2023 at 03:32, BassAdder60 said:

Ashdown are also I believe more pro A/B amps that can be easily repaired throughout its life, something they still stand by today.

Class D for them is in some cases a disposable amp should it seriously go wrong IE power module dies etc

 

However the other big brands are heading down that Class D road for very good reasons and that is the public want light weight gear now.

 

We are slightly off topic but the question about modding an ABM600 to 2.67 ohms  was purely out of interest if possible, it’s not. 
Mesa, Genzler, GK, Aguilar and more are offering amps to 2ohms or 2.67 ohms which today is fantastic for mixing 8 and 4 ohm cabs or running more combinations. 
 

The ABM600 is a superb amp and will remain with me for now sitting on my 4ohm Ampeg SVT212AV 600w cab. 

There are companies that have no problem supporting 15-20 year old class D amps as well, making them non-disposable. 
 

it depends on the company and not the technology used ime. 

The current in an electrical power circuit is generally considered to be continuous (there are a few exceptions, every region is slightly different) and the distances are much longer than what is being dealt with on a PCB or interconnection wiring.

50 amps of building power circuit would require at least 8 times the copper area as an audio circuit or internal power wiring for an audio device). This is because the audio circuits are designed around a minimum 12.5% duty cycle, and the voltage drop is based or wire cross-sectional area its length and the current in the wire. Power electrical current is based on 100% duty cycle (80% in the US for non-continuous loads). 

On 02/06/2023 at 01:45, bagsieblue said:

Nope, its a minimum load not a maximum load.

Actually, it depends very much on the amp. 
 

Tube amps reflect the speaker’s impedance back through the output transformer to the plate circuit. This output matching transformer maintains the voltage (and current) ratio so that the high impedance plates transfer the energy effectively to the low impedance load. 
 

When the load is mis-matched to the plates, the voltages can increase to unsafe levels, especially when the output stage is overdriven. This effect is generally worse when the load is higher than the impedance tap is set for.

some amps are more forgiving of mismatches than others, though the cost of being wrong can become awfully expensive. 

8 hours ago, itu said:

I think that...

 

Because people mix power (W) and loudness (dB), these kind of questions come up every now and then.

 

Wattage means how much energy a power amp can push to the load (a cab). If the load stays the same, doubling the power will increase loudness around 3 dB. This is pretty much the lowest difference you can hear: from 500 W to 1000 W the difference is up to 3 dB (if the load stays the same).

 

Power (wattage) consists of impedance (Z, meaning resistance, inductance, and capacitance; this is frequency dependent), voltage (V, volts), and current (A, amperes).

 

Volts and amperes can be easily calculated, as we already know both the impedance of a cab and the wattage of an amp. Let's say it's 400 W, and Z = 8 ohms.

 

I = U / R [A = V / Z]

and

P = U x I [W = V x A]

 

P = U x U / Z, or U x U = P x Z

400 W x 8 ohm = 3200 VV => U = 56.5 V

 

I = P / U => 400 W / 56.5 V = 7 A

Now is this clear? Here we have an 8 ohm cab, and an amp that pushes up to 7 amperes to that cab.

 

The next step is to understand, what happens, when impedance is halved (the equation assumes that the power amp is capable to push double wattage to that 4 ohm cab):

800 W x 4 ohm = 3200 VV => U = 56.5 V

BUT the big thing here is this:

Current has to double, as

I = P / U => 800 / 56.5 = 14 A (!)

That amount of current means far bigger components that can handle big currents = heat. It is not so uncommon that the amp is not able to cool itself down with such currents. In worst case the amp section may melt. When we go further down to lower impedances, 2 ohms equals 28 A, and 1 ohm equals 56 A!

 

A very rough wire diameter table would look like this:

7 A - 1 mm2, AWG 18 

14 A - 2.5 mm2, AWG 14

28 A - 6 mm2, AWG 10

56 A - 25 mm2, AWG 4 (components have to be enormous!)

 

You should understand this: it is far easier to increase voltage than reduce impedance. If the amp is not capable of pushing energy to a super low Z cab, 8 ohm cab may actually be the louder one!

Your wire size examples are for long runs of wire and based on a combination of voltage drop,  temperature rise and continuous duty cycle. They are generally accepted sizes based on installed building applications with common insulation types. 
 

Components and component interconnections are sized differently for each application. For example I work with 50A transistors that have leads roughly equivalent to 2.5mm dia wire. It’s because the leads are short and the parts are used in <50% duty cycle applications. 

13 hours ago, Sparky Mark said:

In the real world I'm not at all surprised that the ABM600 outperforms many amps with higher advertised outputs. The ABM600 is probably running with extremely low % THD at its rated output whereas many amps are now rated at relatively high %THD. When I owned an ABM600 it was much more powerful than my 800 watt head. I believe Ashdown when it states its peak power of 1200 watts whilst others might struggle to produce peak levels even 20% above their published continuous outputs. 

The peak power of ANY 600 watt rms amp IS 1200 watts. It’s just two ways of describing exactly the same thing. It’s just a math conversion between units. 

The Diesel is based on the tuning concepts in the TL cabinet, using the EVM-15L for the driver. The internal volume is pretty close to the stock EV recommendation (actually EV recommended a range of internal volumes, a range of porting versus internal volume and thus a range of tunings).

In that box, the EVM-15L is good for right about 200 watts RMS down to ~60Hz  and does so with very high sensitivity. 

These were calcs/plots that I did on the Diesel 115 w/ EVM-15L when designing the Subway speakers, in order to understand the legacy products and why they were as successful as they were. In this case, there was very little driver performance left on the table and because of the sensitivity (at the expense of power handling, it's only a 200 watt RMS driver regardless of the 400 watt numbers applied to the proline series), it will generally take about twice the power of most suggested "upgrade" drivers to achieve what this cabinet achieves with 200 watts.  unfortunately both the driver and the box are very heavy which was a non-starter for the new product line.

Most of the Mesa Diesel 115 cabinets were loaded with EVM-15L drivers. This was specifically for the mid voicing.

The EVM 15L/B drivers are good for about 200-250 watts RMS mechanically above 50Hz. The series 2 and proline drivers are mechanically the same, the only difference is a coating on the VC which helps bind the coil to the bobbin.
 

The pro line drivers have pretty much the same mechanical power handling as the series 2, the way they were rated changed some.

On 06/04/2023 at 12:43, Downunderwonder said:

I seem to recall something about blocking out half the shelf port at the same time.

Which also drops the mechanical power power handling on a driver with already limited power handling.

2 hours ago, fretmeister said:

@agedhorse Why does the manual say 8-32 ohms then?

 

That might cause people to spend money when they don't have to. (Unless Mesa are going to start making headphones!   )

Because the vast majority of players are concerned with the ability to drive the lower impedance phones, something many headphone amps can not do well. We will look at updating the manuals at the next revision cycle to change this to include higher impedance phones too. 
 

I had to design a headphone amp for another product (guitar related) recently and the big issue was to be sure the new headphone amp could drive low impedance phones because more and more are going this direction. Many modern digital devices have limited voltage swing therefore can’t drive high impedance phones to more than a low volume.