agedhorse

I just suggest that you have some real experience. I see a fair amount of unrepairable damage caused by attempted repairs.

I did suggest a factory authorized service center as they will have the necessary access to resources and parts. I would have expected them to be fully supported and serviceable for much less then the cost of buying a new one. It's not an inexpensive amp is it? (I don't have a good grasp of European/UK prices of course)

Why not have your amp repaired. I would expect that a qualified MarkBass authorized service center would be able to get this taken care of for you.

I have not seen anything that specifically states that the + and - signals are fully isolated from pin

This is an essential requirement for use with ANY amp that contains bridged topology.

6 hours ago, Silky999 said:

Thanks chaps, I’ll stick to a single cable.

Agedhorse......are you the same person as the font of GB knowledge on another forum? If so I read your post about changing out the leds and your very reasonable service charges. This Streamliner has the intermittent led issue and you’re a few thousand miles away.  I am a bit of whiz with a soldering station. Any particular tips or advice for swapping the leds? I’ve sourced some 30 mA leds, got my liquid flux, deoxit, solder sucker etc. Is there  an easy way to tell the flow direction for the led so I don’t put them the wrong way around?

Yes. The direction is screen printed on the PCB. 
 

Use all safety precautions, the PCB does not need to be removed. It’s a double sided board with plated holes so be be gentle.

There is no difference as the Streamliner's speaker outputs are parallel wired from a single output.

I suggest a single cable, simpler and just as effective.

Thanks Al, tried to grab the correct page from my phone but obviously didn't get it quite right. Cheers.

2 hours ago, Beedster said:

Hope all’s OK for you Andy

Thanks. 

I have addressed some of this to the best of my ability in a TalkBass thread. Rather than rehash this here, please take a look at the thread:

https://www.talkbass.com/threads/official-mesa-boogie-subway-series-club.1181245/page-1144#post-24825163

5 hours ago, Geek99 said:

Your English is fine

Yes, it appears not to be a language misunderstanding, just showing his true personality. 

59 minutes ago, Hellzero said:

 

I'm always astonished to read these kind of comments that are simply insulting, but having seen your location, I fully understand your superiority complex, don't worry.

Sorry for derailing your thread @JapanAxe, but I really can't stand this stupid sectarianism.

Excuse me, nothing I said was insulting nor was it intended to be.

I deal with international customers every day, I am aware that many use translation software that may not translate as accurately as assumed (either to or from anybody’s native language)

I simply suggested that this might be an explanation for the miscommunication rather than assume that you were being intentionally disrespectful.

The US is a very large country with diverse politics. Many do not find what’s going on in our country acceptable in the slightest. To assume that I (or anybody you talk with from the US) finds it acceptable is a form of casting stereotypes and may very well be wrong.

Is this how the forum thinks of all US residents? If so, if he talks for everybody here, I find it very sad.

8 hours ago, JapanAxe said:

@agedhorse - to be fair, @Hellzero does mention a resistor for discharging caps.

He mentions a resistor in series with an LED, which means that the discharge rate would be very low and the discharge time very high UNLESS there is an ADDITIONAL resistor (~10 ohm, 10-25W) like I suggested earlier.

I suspect that the communication issues here may be due to different native languages. If so, none of this is going to be very helpful.

8 hours ago, Hellzero said:

Thanks @JapanAxe. I was about to answer and the LED is there so you can see that the capacitor is fully discharged.

In a tube amp, the tensions are the most important, so with a multimeter and a capacitance meter (or an ESR that can manage high capacitance values and tensions) you can repair any amp. You have to know two things : how the tension flows and how the signal flows.

That said if the amp is blowing fuses, I don't think a scope will be of any use... And if you use a scope, you'll need a signal generator too...

How are the voltage (tension) the most important? There are many important aspects to the signal path of an amp, and while the voltage is ONE part of this, there are many other important factors in identifying not only where the fault might be located, but also what the fault might be.

"Tension" (voltage) doesn't flow, it is a potential. CURRENT flows.

Perhaps there is a challenge here with language?

On 28/12/2020 at 01:35, Hellzero said:

I've been into tube design and repairs for decades. The scope is not a vital tool to my own opinion, but a shorting big wire made with two clip-on pliers (one red and one black for polarity plugging), a 5 Watts resistor and a LED is a real vital tool.

You know that tension may remain in the capacitors if not properly grounded when shut down, that's why shorting them before doing anything is really vital. And for those not knowing this, there's a negative tension in most tube amps (won't go into details) that you have to discharge from the capacitor(s) by putting the shorting wire (with a LED and resistor) the other way.

Never directly short a capacitor to discharge it. The currents can be high enough to damage the electrode lead-out bonds inside the cap. It's probably the quickest way to ruin a good high value cap. A 10-25 watt resistor with about 10 ohms is a good value, and you don't have to worry about residual voltages either.

Without a scope, you would need a mighty fine crystal ball to see what's happening in an amp. I haven't seen any effective crystal balls marketed towards the electronics service industry myself.

Glad you liked the manual. I wrote it along with a LOT of contribution and detailed editing by a couple of seriously seasoned TalkBass members, one who is a very technically inclined and one who is a journalist, both are solid players. The primary focus of the manual was to provide accurate, detailed information that is useful to players and form a player perspective. These guys started with the WD-800 manual and the response was so overwhelmingly positive that it was a no brainer to continue this way. 

Writing manuals is unbelievably time consuming, and these guys stepped up to the plate to make it clear and player friendly, especially when describing features that have not been implemented before. 

Here are links to the WD-800 and TT-800 manuals, they might help those who are interested better understand the amps to determine if they might be a good fit or not.

WD-800:   https://mesa-boogie.imgix.net/media/User Manuals/070556_Subway_WD800.pdf

TT-800:   https://mesa-boogie.imgix.net/media/User Manuals/Subway-TT800-web.pdf

34 minutes ago, Jack said:

Whilst I'm sure somebody will be along with a counterexample within 5 minutes of my post, I'm unaware of any class D amp for which the sound of the power amp is a selling point. As you've said, tube amps and vintage amps yeah, but I bet the sound from (for example) a GK Fusion's preamp out and speaker out are near enough the same, one's just bigger. 9 - 49.9V bigger, if you believe certain people in this thread. 😉

So yeah, why would you bother? People though, right? Can't trust 'em. 

Not necessarily true, in that some class D output stages have additional emulation and modeling circuitry as well as damping adjustments and symmetry control at the point the POWER amp begins to overdrive.

That said, taking a signal from the speaker output using a conventional direct box is not a safe application. There are ways to do this, but with specialized hardware only.

Just now, Beer of the Bass said:

Are there any times people would really want to use a speaker level DI from the output of a class-D amp (or other bridged topology)? I was aware of using a DI on the speaker output as an occasionally useful trick with vintage style valve amps where you might want the colouration, there's usually no built-in DI output and the amp output is via a transformer anyway.

So it's a useful caution, but also, I'm not sure what the motivation would be to do that with a bridged power amp. Though I'm sure people will have attempted it...

Yes, I deal with this sort of thing often enough that these warnings (including warnings in the newer owner's manuals) are entirely justified.

14 minutes ago, 0175westwood29 said:

honestly tho this thread is surely about using di boxes that are meant for this, ie something like the two notes, radial or palmer stuff so these issues arent a problem please tell me no one is considering putting a standard di box between the amp and speaker

 

That's EXACTLY what is being discussed, and what the OP's situation involved.

On 27/12/2020 at 12:02, warwickhunt said:

The actual signal levels are 'approx'.  

.015v - mic/inst

1.0v - line

12v - speaker

So the level out of an amps own DI is line level (about 1 volt) whereas the voltage from the speaker out is 12v (ish).  External DI boxes are generally used to boost from instrument level up to line level.  I've never associated a DI with lowering/attenuating the level from speaker levels; obviously they must but I'd be interested to know if that is true of all DI boxes.    

External DI's are almost never used to boost the signal level from instrument level to line level. In fact, since the numbers you posted above are incorrect, let's clarify what happens with a typical direct box. For bass guitar:

Mic levels are typically in the range of .01V to .1V

Instrument levels are typically in the range of .1V to 1V

Speaker levels are typically in the range of 10V to 50V

A typical DI drops instrument level signal down to mic level (approx. -20dB) and for a DI with a speaker level input, drops the level down to mic level (approx. -40dB). This is (often but not always) done by the use of an step-down audio transformer (in combination with an input pad in the case of a speaker level signal). The transformer also galvanically isolates the signal source from the destination.

One very important thing to make note of... in the case of any amplifier that is configured in bridge mode (either externally or as an internal topological design element which is how many class D power amps operate), taking the output from a speaker out is a bad idea because neither the + or - terminals of the speaker output are ground referenced. When connected to a DI, the pin 1 connection becomes tied with the speaker - and results in shorting 1/2 of the output bridge. Also, the resulting fault current (which can be as high as 30 amps on some newer amps) will flow through pin 1, through the snake and into the console's grounding system. Since this grounding system is not designed for high currents, catastrophic damage can result. If this is an expensive console, somebody is going to be unhappy.

On 23/12/2020 at 13:15, mytilini said:

Agree, but the entire reason I bought the BG250 was that it had no effects loops, no line outs, an inbuilt tuner, no extension cabinet i.e. all I wanted in just one box.  Having done a bit more reading, I'm almost certainly gonna get the D120 to allow post-fade export of the tone-shaped signal to both the desk and that power amp at the same time.  LIght, quick simple and it'll cost me less than £20 from Amazon to do this - I already have top-grade mic leads from when I used to do the P.A. for my old band too.  Am gonna skip the TR3M altogether.

The balanced output clips at +2dB peak (-1dBu RMS) maximum, not enough for driving a power amp to rated output in the real world. You will need +4dBu (minimum) plus at least 6dB of headroom to make up for losses relative to real world implementation. 

On 23/12/2020 at 10:10, BreadBin said:

Yes, class D is just a different type of power supply. Lighter and more efficient, but the subject of many debates especially with regard to heft 

No sir, class D has nothing whatsoever to do with  the power supply. It has to do with the topology of the power amp only.

On 23/12/2020 at 06:07, mytilini said:

Related question (if I may) to the many, many minds greater than mine!  I've a TC Electronic BG250-210 combo, with a pre/post switchable D.I. output built-in.  Normally, that feeds the FOH mixer only, with me using the combo's speakers as my onstage backline.  Big gig next year, in which I need much more on-stage volume (TWO drummers!).  I've no other preamp signal output or extension cab options within that combo.

My thought is to feed the combo's inbuilt D.I. output, as the single input to a Behringer Ultra-DI D120 active 1 in-to-2 out D.I. box.  Effectively, to use the tonal set-up from the BG250, to input into a power amp.  I plan to connect one channel of the D120 via an output mic lead into the mixer.  The other channel's output would link a mic lead into the parallel-mode input of a spare Cerwin-Vega! CV-2800 P.A. power amp that I have.  That power amp puts out 600W. continuous, per channel @ 8 Ohms.   I'm going to hook up two 8 Ohm bass guitar cabs, one per channel.  The cab's are:

1). a JBL 1x15" loaded with a 600W. continuous Eminence Kappa speaker.

2). an Ashdown 4x10", giving a total continuous power handling capacity of 600W.

Question please - is this feasible?  Will a D.I. box's output have sufficient sensitivity to "drive" the input of this typical stereo P.A. power amp, or would I need to insert some other form of preamp into the signal chain?

Thanks in advance for any advice or help you can give and may I wish you all as happy a Christmas as possible in the current circumstances! 

Except that the DI out will not be able to drive the amp to rated output unless it's full line level (ie. nominal +4dBu)

On 23/12/2020 at 05:07, Lfalex v1.1 said:

As previously stated, try bridging it.

I did it with a QSC PLX 1202 (so about 600w bridged into 8 Ohms, 1200 into 4 Ohms)

I (on occasion) used it with an old Trace 2x10 with 2x80w OEM Trace (Celestion) drivers. 

You'd think that 600Wrms into a cab rated at 160w would cook it, but it didn't. It got way too loud (in rehearsal) before there was any evidence of my pushing it too hard.

Does the amp have a high pass filter? I ran the QSCs one at 30Hz. Prevents power being wasted on trying to force the loudspeaker system to reproduce low frequencies it simply can't.

If you understood that this amp is NOT rated for a 4 ohm load in bridge mode, you wouldn't recommend something dangerous to the health of the amp. Bad advice.

With that amp, which I know  very well, you are much better off running dual mono.

19 hours ago, Phil Starr said:

This is correct and in all probability you will be safe.

'all probability' is a scientists answer of course. You will almost certainly be safe. The doubt comes because speakers and amps aren't rated in the same ways. Amps are essentially rated on how much electricity they can pour into your speakers. Speaker limits are measured by how much heat they can take before they burn out, a thermal limit. Heat and music aren't the same thing. the heat limits are measured with a continuous signal and the bass filtered. Music isn't continuous so the speaker has chances to cool down, that's why Barefaced and nearly everyone else give a music rating for their speakers twice the heat limit. They are assuming that most of us won't do anything stupid and most of the time won't blow our speakers.

The second factor is that the test for speakers filters bass and bass players sometimes boost bass. The reality though is that if you use the rule of thumb that 200W into a 200W speaker is OK you are going to have to do something really silly to damage your speaker.

Except that most bass speakers fail from exceeding their mechanical limits not their thermal limits. 

The mechanical limits of a speaker can be as low as 1/2 the thermal rating, and when you exceed the mechanical limits you cumulatively cause damage to the suspension components and reduce their lifespan. Also, mechanical power handling decreases as frequency falls below ~100Hz on most speakers.

Generally, when you match the amplifier power (in RMS metrics) with the speaker rating (in RMS metrics) you will be reasonably well matched. This is a rule of thumb that’s holds up pretty well in the real world IME.