Glockenklang Soul

[gbono]

Working on a very early version of this bass amp. The amp will shut down on power up (doesn't blow the fuse). I noticed that the wires from the PTprimary connected to the IEC mains socket (neutral connection) show a slight heat discoloring. The later version of this amp has a PTC thermistor wired into the primary side of the PT. I hope this PT isn't fried - it looks like an expensive toroid. Anyone work on this product before?

[J M Fahey]

Hi gbono.
What do you mean by shutdown?
The amp turns on, then self turns off?
Turns on but no sound?
Please elaborate.
If you have the schematic, or a link to it, post it.
Maybe it has some DC protection triggering or a thermal switch.
As you know, it's not a very common amp.
We are not talking Peavey or Fender here.
A couple pictures would help.

[gbono]

The schematic is in pdf format and it's 2 KB over the limit to post??

Power up means press the power button with the amplifier plugged into 120VAC. Unit doesn't blow fuses it activated a relay in the power supplt circuit and shuts down. There is no sound and oh the fans briefly come on briefly too and then shut off. Pictures below.

Good method for testing the toroid would be appreciated.


http://i284.photobucket.com/albums/ll33/bonosurf/DSCF050211.jpg
http://i284.photobucket.com/albums/ll33/bonosurf/DSCF050111.jpg

[gbono]

Schematics here:

http://i284.photobucket.com/albums/ll33/bonosurf/soul2.gif
http://i284.photobucket.com/albums/ll33/bonosurf/soul1.gif

[teemuk]

Unfortunately, your schematics do not include the power supply. There are also other parts missing.

If I'm correct, the small circuit part drawn on top of the output stage, however, depicts a soft start circuit: When powering up, the initial current is limited by a series power resistor. When the RC time delay powered by the 16VAC windings has charged enough, the relay bypasses the power resistor, letting full current flow.

So, relay clicking shortly after powering on is supposed to happen.


I can't see any fan driver circuitry portrayed and the schematic showing the protection logics is missing some parts. Sorry to say, without the actual unit in front of me, the schematic is a mess leaving a lot to guessing. Even the momentary operatyion of the fan can be usual. I have a feeling it is supposed to go on only when the amp is driven hard.

Check the usual suspects: DC in output or blown output transformers. These will usually trigger all kinds of muting and protection circuits.

Power transformers are usually pretty sturdy and do not fail too quick. If it's overheating and turning some thermistor on this should be easy to verify. If it had an internal thermal fuse tripped nothing would no longer operate. Chance is, the PT is ok.

[gbono]

Yes the schematic is a pig's breakfast - Glockenklang doesn't appear to have any other documentation?? Thanks for pointing out the relay operation - though I'm wondering if the TRIAC could be damaged?? I checked all the output devices with a DVM and I didn't see anything unusual there - though testing active devices this way always leaves me feeling doubtful.

I'm wondering why I see 120VAC on the AC input to the discrete bridge rectifiers for the +-30 V supply ?? Since we are on the secondary of the PT shouldn't this be a much lower voltage? Remember that I'm seeing this condition after the amp "shuts down".

[teemuk]

As far as I know, the Triac is a sort of last resort protection against considerable amount of DC voltage in the output; if such condition is detected, The triac will short the output and likely take down the power transistors, which however cost way less than a burned loudspeaker.

The 120VAC on the secondary side doesn't sound right. Can you simply  test the power transformer with all secondary loads disconnected? It would give rough estimation if the secondary voltages are within proper range.

[J M Fahey]

I also was puzzled by

Unfortunately, your schematics do not include the power supply.

so I looked all over it with a *very* open mind ......... and found it.
They say that the best way to hide something is in plain sight.
The PSU is there, only it's not drawn as a functional block but spread all over the place, every part of it close to what it feeds.
Above and below the speakon jacks, you have the main rectifiers: D18 toD21, main filters: C63 to C66.
The +/-15V preamp supply is above the input jacks, including its regulators U6 and U7 (7815/7915).
There are another two "low voltage supplies" which are not so.
They provide extra +5 and -5V *on top* of existing power rails which must already be around +/-70V, to fully drive output Mos Fets.
That's why they apparently they are fed by over 100VAC, in fact they have their own floating secondaries.
The whole amp design and construction strike me as *very* Korean, looks like if made by the same subcontractor that builds Hartkes for Samson, or an ex-partner.

[gbono]

JM, Thanks for finding the main supply on the schematic - I noticed the other supplies but couldn't figure out where the higher voltage supply was located. So where is the center tap located for the transformer? Was I reading the voltage incorectly and should have been measuring from the CT - that would give a reading of around 60VAC.

I guess I'll have to unsolder all these transformer connections and measure each "tap" from the PT to see what's going on?

Do you think this amp is a "boot-strapped" design where you run the low voltage (5V) supply for idle and low power and then bring in the larger supply to drive peak voltage? Class G??

A new transformer is going to coat 200 euro - I assume this amplifier is worth that cost?

THX

George

[J M Fahey]

Hi gbono.
I assume your transformer is fine.
Don't unsolder it because it's a mess.
If with everything connected we are in trouble, imagine with a lot of secondaries in the air, and no indication of colors in the schematic.
I think that the amplifier isn't smoking (let's try to keep it that way), the crowbar triac isn't triggered, or, as Teemu says, it would be blowing transistors and main fuse.
I think it's muted by one contact of Rel3A or Rel10K (it carries both labels) grounding the node ¿R10?-T163-C7 which is the power amp input.
Why? don't know yet, probably senses something wrong.
Measure + and - B on output transistors tabs, and DC voltage on the output rail, the common point of all those 1r ceramic resistore .
Check that you have continuity out rail->pin +1 on speakon, that pin -1 is effectively grounded and with *the other end* of a speakon speaker cable.
You might have something as simple as a bad connector (Juan the eternal optimist)
I think about light problems because your main fuse does not blow, the triac does not trigger, and nothing smokes or burns.
*Of course* they did not use 10k/100uF/9V Diac to trigger it, they *had*   to design something fancier , which will fail if it becomes unpowered. :loco
Oh well !!

[teemuk]

Do you think this amp is a "boot-strapped" design where you run the low voltage (5V) supply for idle and low power and then bring in the larger supply to drive peak voltage? Class G?

No bootstrapping, no Class-G.

There are just low voltage, low current power supplies wired in series with the high voltage power supply. In the schematic, the circuit is depicted directly above and below the PA's bias multiplier and current limiter section.

In MOSFET output amplifiers it's a rather common setup to power the voltage amplifier stage from a higher voltage supply than the output stage. Compared to transistors MOSFETs will introduce higher voltage losses, driving the output with higher voltage than the output's supply rails will compensate.

[gbono]

Okay when I measure the voltage on several of the low voltage supplies I get very low readings - 1.95VAC, .5VAC, etc. Remember that the amplifier is just sitting there with no power LED lite on the front panel - there is 120VAC on the primary side of the PT and 120VAC on the larger (60V) supply and the readings above on the smaller (15V) supplies.

Two things to consider - on the later version of this design they put a PTC thermistor on the PT - just a mistake in the earlier design or was the PT getting into trouble in the field? This amplifier definetly has seen some heating of the neutral connection on the primary side of the PT. Not sure what caused this and have asked the ownere if he had a problem with utility power in his area - it does happen here in Northern California - the local utility has equpiment problems and the neutral goes away and you get 240V or some such on the mains. Though I would assume that this type of damage to the PT would be blowing fuses. :grr

I'll check the supply rail voltage on the output devices. Yup, this amp just isn't happy with some fault that's going on. I would "assume" that the red front panel fault LED would stay on if the amplifier had a problem with the relay REL-KX or some other light problem as you say.

[gbono]

bumping this back up....

Still happening - On power up the amp will briefly light the red fault LED and then shut down except the fans come on at low rpm?

I checked out the transformer (torroid) and all secondary winding/voltages are correct - out of circuit. When I re-solder the secondaries back on the PCB and power up the amp I do not see correct voltages at the +-15v and +-5 supplies. I'm assuming that the issue is with the pre-amp and PA driver sections of the amp.

Checked limiter transistors Q5/6 and they appear to be okay.

JM's comments regarding the relays: REL3A/B are interesting but I'm not sure how they are disabling the low voltage supplies?