Bass guitar amplifier knackered?

Question:

Hi groups, I have a couple of questions to ask about my Trace Elliot BLX-80 bass guitar amplifier, but I suspect the questions may also be general to all guitar amps. I’ve been having various reliability problems with the amp, which manifest in the form of a loud hum through the speaker and crackling and buzzing that normally settles down after an hour of usage. I hooked my ocilloscope up to the output (without the speaker connected) and found that the output was clipping at 3v peak-to-peak. This is with the input gain set at 3/10 and the output gain set at 4/10, i.e. pretty low. The two main output transistors also got extremely hot VERY quickly when playing, i.e. within seconds, again without the speaker being connected. In addition to this, they also made a buzzing noise when output was driven through them, the volume of the buzz in proportion to the peak-to-peak voltage on the output. My questions are: 1) Should the amp be clipping at such a low gain setting? 2) Should the output transistors be getting so hot and making a noise? 3) Is this expected behaviour if the speaker isn’t connected? 4) I have already replaced the large capacitors on the power supply. Perhaps the transistors ought to be replaced too? Many thanks in advance, Patrick — Reverse the two elements of my email address to get my *real* address!

Response:

- Hide quoted text — Show quoted text – > Hi groups, > I have a couple of questions to ask about my Trace Elliot BLX-80 bass > guitar amplifier, but I suspect the questions may also be general to > all guitar amps. > I’ve been having various reliability problems with the amp, which > manifest in the form of a loud hum through the speaker and crackling > and buzzing that normally settles down after an hour of usage. > I hooked my ocilloscope up to the output (without the speaker > connected) and found that the output was clipping at 3v peak-to-peak. > This is with the input gain set at 3/10 and the output gain set at 4/10, > i.e. > pretty low. > The two main output transistors also got extremely hot VERY quickly > when playing, i.e. within seconds, again without the speaker being > connected. In addition to this, they also made a buzzing noise when output > was > driven through them, the volume of the buzz in proportion to the > peak-to-peak voltage on the output. > My questions are: > 1) Should the amp be clipping at such a low gain setting? > 2) Should the output transistors be getting so hot and making a noise? > 3) Is this expected behaviour if the speaker isn’t connected? > 4) I have already replaced the large capacitors on the power supply. > Perhaps the transistors ought to be replaced too? > Many thanks in advance, > Patrick

Well AFAIK it seems pointless measuring clipping without a load, after all clipping doesn’t occur until the amp hits its max capability. If the output trannys are getting hot with no load then there is a basic problem. Could it be that you are out of your depth here ?? —

Response:

– Hide quoted text — Show quoted text -> Hi groups, > I have a couple of questions to ask about my Trace Elliot BLX-80 bass > guitar amplifier, but I suspect the questions may also be general to all > guitar amps. > I’ve been having various reliability problems with the amp, which manifest > in the form of a loud hum through the speaker and crackling and buzzing > that normally settles down after an hour of usage. > I hooked my ocilloscope up to the output (without the speaker connected) > and found that the output was clipping at 3v peak-to-peak. This is with > the input gain set at 3/10 and the output gain set at 4/10, i.e. pretty > low. > The two main output transistors also got extremely hot VERY quickly when > playing, i.e. within seconds, again without the speaker being connected. > In addition to this, they also made a buzzing noise when output was driven > through them, the volume of the buzz in proportion to the peak-to-peak > voltage on the output. > My questions are: > 1) Should the amp be clipping at such a low gain setting? > 2) Should the output transistors be getting so hot and making a noise? > 3) Is this expected behaviour if the speaker isn’t connected? > 4) I have already replaced the large capacitors on the power supply. > Perhaps the transistors ought to be replaced too? > Many thanks in advance, > Patrick > — > Reverse the two elements of my email address to get my *real* address!

The general theory is don’t run a transistor stage into a short, but ok to run it into an open, and vice versa for tube stages. I’ve never trusted this though, and I would not recommend running an output stage, particularly at high volume settings, into anything other than its designed load impedance, or thereabouts. It’s impossible to say whether the clipping figures that you’re seeing are valid or not, when you are not running the amp into a proper load. Just connect 8 ohms worth of power resistors across the output if you don’t want to do your tests with a speaker on it. Ten 100 ohm 5 watt resistors or similar in parallel, will do. As far as the transistors running very hot is concerned, I wouldn’t expect this to happen if they run cool with no drive, and the output stage otherwise works ok. Make sure that the mounting screws are tight, and if they use a mica washer / heat paste combination for mounting, rather than a ‘dry’ silicon rubber pad, make sure that the heatsink compound hasn’t dried out to powder. Also, you should check again with a proper load, as without one, the stage may be hooting under driven conditions, which will give rise to huge dissipation in the transistors, and rapid heating. It isn’t unusual to be able to hear output transistors rattling in sympathy with the drive, when they are not operating into a proper load. For the crackling and hum problems, check the soldering on the input sockets, then the simple R – ZD derived supplies for the front end opamps. It’s common for the R’s and the ZDs to go badly dry jointed due to the elevated temperatures that they run at as a normal condition. Arfa

Response:

- Hide quoted text — Show quoted text -> My questions are: > 1) Should the amp be clipping at such a low gain setting? > 2) Should the output transistors be getting so hot and making a noise? > 3) Is this expected behaviour if the speaker isn’t connected? > 4) I have already replaced the large capacitors on the power supply. > Perhaps the transistors ought to be replaced too? > Many thanks in advance, > Patrick > Well AFAIK it seems pointless measuring clipping without a load, after all > clipping doesn’t occur until the amp hits its max capability. > If the output trannys are getting hot with no load then there is a basic > problem. > Could it be that you are out of your depth here ??

Yes, probably am out of my depth here! I’ve only got a basic knowledge of electronics (and I mean basic), but am always happy to learn more. It seemed odd to me that the amp should clip at low levels when it doesn’t need to actually provide any power to drive anything. Just for interest, I put a small resistor (10 ohms) across the output, but the result was exactly the same. I’ll try replacing the transistors. I’m sure they won’t cost much. P — Reverse the two elements of my email address to get my *real* address!

Response:

- Hide quoted text — Show quoted text -> Hi groups, > I have a couple of questions to ask about my Trace Elliot BLX-80 bass > guitar amplifier, but I suspect the questions may also be general to all > guitar amps. > I’ve been having various reliability problems with the amp, which manifest > in the form of a loud hum through the speaker and crackling and buzzing > that normally settles down after an hour of usage. > I hooked my ocilloscope up to the output (without the speaker connected) > and found that the output was clipping at 3v peak-to-peak. This is with > the input gain set at 3/10 and the output gain set at 4/10, i.e. pretty > low. > The two main output transistors also got extremely hot VERY quickly when > playing, i.e. within seconds, again without the speaker being connected. > In addition to this, they also made a buzzing noise when output was driven > through them, the volume of the buzz in proportion to the peak-to-peak > voltage on the output. > My questions are: > 1) Should the amp be clipping at such a low gain setting? > 2) Should the output transistors be getting so hot and making a noise? > 3) Is this expected behaviour if the speaker isn’t connected? > 4) I have already replaced the large capacitors on the power supply. > Perhaps the transistors ought to be replaced too? > Many thanks in advance, > Patrick > — > Reverse the two elements of my email address to get my *real* address! > The general theory is don’t run a transistor stage into a short, but ok to > run it into an open, and vice versa for tube stages. I’ve never trusted this > though, and I would not recommend running an output stage, particularly at > high volume settings, into anything other than its designed load impedance, > or thereabouts. It’s impossible to say whether the clipping figures that > you’re seeing are valid or not, when you are not running the amp into a > proper load. Just connect 8 ohms worth of power resistors across the output > if you don’t want to do your tests with a speaker on it. Ten 100 ohm 5 watt > resistors or similar in parallel, will do. > As far as the transistors running very hot is concerned, I wouldn’t expect > this to happen if they run cool with no drive, and the output stage > otherwise works ok. Make sure that the mounting screws are tight, and if > they use a mica washer / heat paste combination for mounting, rather than a > ‘dry’ silicon rubber pad, make sure that the heatsink compound hasn’t dried > out to powder. Also, you should check again with a proper load, as without > one, the stage may be hooting under driven conditions, which will give rise > to huge dissipation in the transistors, and rapid heating. > It isn’t unusual to be able to hear output transistors rattling in sympathy > with the drive, when they are not operating into a proper load. > For the crackling and hum problems, check the soldering on the input > sockets, then the simple R – ZD derived supplies for the front end opamps. > It’s common for the R’s and the ZDs to go badly dry jointed due to the > elevated temperatures that they run at as a normal condition. > Arfa

Thanks for the detailed response Arfa! I posted an answer to Rheilly just now, the gist being that the same problem occurs with a 10 ohm load. The transisters still get super-hot very quickly even at low volumes. The transistors are dissapating the heat to the heatsink OK and I’ve checked that they are nice and tight. They appear to be mounted on a pad rather than with paste. Would it be a sensible next step to replace the transistors? Thanks, Patrick — Reverse the two elements of my email address to get my *real* address!

Response:

Possibly the bias has shifted, possibly caused by a faulty (leaky and, by your fault description, noisy) coupling capacitor. If a coupling capacitor becomes electrically leaky, its DC blocking function is compromised and it will affect the following stage. The only way to repair it is with experienced faultfinding. You could try heating each cap in turn with a soldering iron and see when the fault changes. You may also have weak smoothing capacitors in the power supply. Try scoping the DC across the caps, it should be clean when the amp is idle and only a small amount of ripple when active. If there’s a serious amount of activity across the smoothing caps, they are duds. In fact, test this first- it’s straightforward and could save you a lot of time. Dave

Response:

> I’ll try replacing the transistors. I’m sure they won’t cost much.

Famous last words! I can’t remember offhand which devices the BLX-80 uses, but some of the earlier Traces used a complementary pair of power MOSFETs which are virtually unobtainable now. I’d suspect the output devices too. Check the associated resistors while you’re at it. Mike Schway | [Picture your favorite quote here]

Response:

- Hide quoted text — Show quoted text – > Hi groups, > I have a couple of questions to ask about my Trace Elliot BLX-80 bass > guitar amplifier, but I suspect the questions may also be general to all > guitar amps. > I’ve been having various reliability problems with the amp, which > manifest in the form of a loud hum through the speaker and crackling and > buzzing that normally settles down after an hour of usage. > I hooked my ocilloscope up to the output (without the speaker connected) > and found that the output was clipping at 3v peak-to-peak. This is with > the input gain set at 3/10 and the output gain set at 4/10, i.e. pretty > low. > The two main output transistors also got extremely hot VERY quickly when > playing, i.e. within seconds, again without the speaker being connected. > In addition to this, they also made a buzzing noise when output was > driven through them, the volume of the buzz in proportion to the > peak-to-peak voltage on the output. > My questions are: > 1) Should the amp be clipping at such a low gain setting? > 2) Should the output transistors be getting so hot and making a noise? > 3) Is this expected behaviour if the speaker isn’t connected? > 4) I have already replaced the large capacitors on the power supply. > Perhaps the transistors ought to be replaced too? > Many thanks in advance, > Patrick

You really can’t measure the output of the amp without a load on it. As I understand your setup, the only load on the amp was the input of the scope. That scope input is probably in the megaohm range. That’s a lot different from a 4 ohm speaker box. The amp won’t behave normally without a normal load. -Raf — Misifus- Rafael Seibert blog: http://rafsrincon.blogspot.com/ Photos: http://www.flickr.com/photos/rafiii home: http://www.rafandsioux.com

Response:

– Hide quoted text — Show quoted text -> Hi groups, > I have a couple of questions to ask about my Trace Elliot BLX-80 bass > guitar amplifier, but I suspect the questions may also be general to all > guitar amps. > I’ve been having various reliability problems with the amp, which > manifest in the form of a loud hum through the speaker and crackling and > buzzing that normally settles down after an hour of usage. > I hooked my ocilloscope up to the output (without the speaker connected) > and found that the output was clipping at 3v peak-to-peak. This is with > the input gain set at 3/10 and the output gain set at 4/10, i.e. pretty low. > The two main output transistors also got extremely hot VERY quickly when > playing, i.e. within seconds, again without the speaker being connected. > In addition to this, they also made a buzzing noise when output was > driven through them, the volume of the buzz in proportion to the > peak-to-peak voltage on the output. > My questions are: > 1) Should the amp be clipping at such a low gain setting? > 2) Should the output transistors be getting so hot and making a noise? > 3) Is this expected behaviour if the speaker isn’t connected? > 4) I have already replaced the large capacitors on the power supply. > Perhaps the transistors ought to be replaced too? > Many thanks in advance, > Patrick > — > Reverse the two elements of my email address to get my *real* address!

I am a little confused, you say there is humming and crackling through the speaker, but then later you say without the speaker connected. Do you mean the transistors get hot even without the speaker connected? Is this an amp head, or a combo amp?

Response:

> My questions are: > 1) Should the amp be clipping at such a low gain setting? > 2) Should the output transistors be getting so hot and making a noise? > 3) Is this expected behaviour if the speaker isn’t connected? > 4) I have already replaced the large capacitors on the power supply. > Perhaps the transistors ought to be replaced too?

No x 3 geoff

Response:

I had a problem with the speaker humming and crackling. I’ve unhooked the speaker and substituted it with a 10ohm resistor (to save annoying the neighbours) and still experience the same problems. It’s a combo amp. — Reverse the two elements of my email address to get my *real* address!

Response:

- Hide quoted text — Show quoted text – > Hi groups, > I have a couple of questions to ask about my Trace Elliot BLX-80 bass > guitar amplifier, but I suspect the questions may also be general to all > guitar amps. > I’ve been having various reliability problems with the amp, which > manifest in the form of a loud hum through the speaker and crackling and > buzzing that normally settles down after an hour of usage. > I hooked my ocilloscope up to the output (without the speaker connected) > and found that the output was clipping at 3v peak-to-peak. This is with > the input gain set at 3/10 and the output gain set at 4/10, i.e. pretty > low. > The two main output transistors also got extremely hot VERY quickly when > playing, i.e. within seconds, again without the speaker being connected. > In addition to this, they also made a buzzing noise when output was > driven through them, the volume of the buzz in proportion to the > peak-to-peak voltage on the output. > My questions are: > 1) Should the amp be clipping at such a low gain setting? > 2) Should the output transistors be getting so hot and making a noise? > 3) Is this expected behaviour if the speaker isn’t connected? > 4) I have already replaced the large capacitors on the power supply. > Perhaps the transistors ought to be replaced too? > Many thanks in advance, > Patrick

I’m also trying to isolate the problem to the pre-amp or power amp stages. The two circuits are on separate boards. Unhooking them causes a large 50Hz signal and lots of noise from the power amp, so I guess I need to tie down the input to the power amp. Should I just place a resistor across the inputs? I would guess I’d want a large value – any suggestions for something suitable? P — Reverse the two elements of my email address to get my *real* address!

Response:

- Hide quoted text — Show quoted text -> I have a couple of questions to ask about my Trace Elliot BLX-80 bass > guitar amplifier, but I suspect the questions may also be general to all > guitar amps. > I’ve been having various reliability problems with the amp, which manifest > in the form of a loud hum through the speaker and crackling and buzzing > that normally settles down after an hour of usage. > I hooked my ocilloscope up to the output (without the speaker connected) > and found that the output was clipping at 3v peak-to-peak. This is with > the input gain set at 3/10 and the output gain set at 4/10, i.e. pretty > low. > The two main output transistors also got extremely hot VERY quickly when > playing, i.e. within seconds, again without the speaker being connected. > In addition to this, they also made a buzzing noise when output was driven > through them, the volume of the buzz in proportion to the peak-to-peak > voltage on the output. > My questions are: > 1) Should the amp be clipping at such a low gain setting? > 2) Should the output transistors be getting so hot and making a noise? > 3) Is this expected behaviour if the speaker isn’t connected? > 4) I have already replaced the large capacitors on the power supply. > Perhaps the transistors ought to be replaced too? > Many thanks in advance, > Patrick > — > Reverse the two elements of my email address to get my *real* address!

Hi, try this link http://www.gmaudio.co.uk/trace_index.html regards, Tony.

Response:

Hi , I’m no expert but I don’t think trannys are supposed to get hot as you describe without a load on them. I had an old Akai stereo amp displaying the symptoms you describe and it died. First one Channel , then the other. I would take it to a techie if I were you. Could save you money in the long run. HTH Andrew(lefty)

Response:

No, it should not clip at 3V p-p. Unless you have the preamp gain up and the master gain low. If the output transistors are getting hot, most likely there is a problem in the pre-driver and bias circuit that is causing them to draw too much current. Usually such a failure destroys the output devices and several others besides. The loud buzz you hear is probably due to DC voltage on the output to the speaker, overloading the power supply. This causes lots of power supply ripple, which is the buzz you hear. Frequently, it destroys the speaker. With direct coupled amps, a small failure near the input ripples down the chain and blows the rest of it. Set the scope for Direct Coupling and see if there is DC at the active speaker terminal with respect to ground. (I’m not assuming that either of the speaker terminals is grounded.) In order to repair it, you would most likely need to replace the output and driver transistors, then test (or replace) the rest of the power amp circuit components looking for open resistors, bias diodes, and bad predriver transistors or op amps. Without a schematic, "shotgunning" is the most effective approach. Even with the schematics, we often find ourselves rebuilding the entire amp. Neil Preston Preston Electronics LLC Pro audio repair

– Hide quoted text — Show quoted text -> Hi groups, > I have a couple of questions to ask about my Trace Elliot BLX-80 bass > guitar amplifier, but I suspect the questions may also be general to all > guitar amps. > I’ve been having various reliability problems with the amp, which > manifest in the form of a loud hum through the speaker and crackling and > buzzing that normally settles down after an hour of usage. > I hooked my ocilloscope up to the output (without the speaker connected) > and found that the output was clipping at 3v peak-to-peak. This is with > the input gain set at 3/10 and the output gain set at 4/10, i.e. pretty low. > The two main output transistors also got extremely hot VERY quickly when > playing, i.e. within seconds, again without the speaker being connected. > In addition to this, they also made a buzzing noise when output was > driven through them, the volume of the buzz in proportion to the > peak-to-peak voltage on the output. > My questions are: > 1) Should the amp be clipping at such a low gain setting? > 2) Should the output transistors be getting so hot and making a noise? > 3) Is this expected behaviour if the speaker isn’t connected? > 4) I have already replaced the large capacitors on the power supply. > Perhaps the transistors ought to be replaced too? > Many thanks in advance, > Patrick > — > Reverse the two elements of my email address to get my *real* address!

Response:

>Even with the schematics, we often find ourselves >rebuilding the entire amp.

Early Crate was horrid for that. Sunn ‘Beta’ amps..UGGGHHHH! I remember the (then) Sunn company sending me out tons of parts to fix this ONE guy’s Beta Lead. THEN, someone decided to send me a schematic. Guy who sent it also went into detail about which wires NEEDED (!!!) to be connected (weird wiring connectors..don’t ask) if I wanted to NOT blow up the driver/output stage. I fixed it, but it was a nite mare by the time I was done. In the end, Sunn payed me 3x what the amp was worth to end this po’guy’s problem. Young kid, who’s mom got involved. HOW do ya explain a Beta Lead to mommie? She just want’s Jr’s amp fixed, was cool about it in the end, I think the local Sunn Dealer gave them some cab or something..really, it was a joke because the design concept was so flocked. I finally had to cut all connectors and hardwire. The schematics were color wrong. Great amp when it worked, the Beta series. Sucked to fix the early ones. Later, the PCBs were much better. Get 1 of THOSE 2 mod.. JJT

Response:

- Hide quoted text — Show quoted text – > Hi groups, > I have a couple of questions to ask about my Trace Elliot BLX-80 bass > guitar amplifier, but I suspect the questions may also be general to all > guitar amps. > I’ve been having various reliability problems with the amp, which > manifest in the form of a loud hum through the speaker and crackling and > buzzing that normally settles down after an hour of usage. > I hooked my ocilloscope up to the output (without the speaker connected) > and found that the output was clipping at 3v peak-to-peak. This is with > the input gain set at 3/10 and the output gain set at 4/10, i.e. pretty > low. > The two main output transistors also got extremely hot VERY quickly when > playing, i.e. within seconds, again without the speaker being connected. > In addition to this, they also made a buzzing noise when output was > driven through them, the volume of the buzz in proportion to the > peak-to-peak voltage on the output. > My questions are: > 1) Should the amp be clipping at such a low gain setting? > 2) Should the output transistors be getting so hot and making a noise? > 3) Is this expected behaviour if the speaker isn’t connected? > 4) I have already replaced the large capacitors on the power supply. > Perhaps the transistors ought to be replaced too? > Many thanks in advance, > Patrick

The transistors are likely fine, I would consider replacing any other electrolytic capacitors though. A can of freeze spray should help you track down the temperature sensitive area, you can pick it up at Radio Shack or similar place or you can hold an air duster can upside down. Let the amp warm up until the hum gets better, then give small areas or specific components a quick shot.

Response:

1. No. 2. No 3. No. 4.Yes. A loud buzz on the output that tends to settle down after a while usually points to bad power supply capacitors which you have already replaced. So now you have to look at other things. If new output transistors don’t do it, (usually is the fix most of the time) then you’ll have to dig deeper and the fix gets harder. Note that alumium electrolytic capacitors of ANY size are always the usual suspects. They can open, short or just quit filtering which can cause trouble. But then any component can go bad. Even a simple cheap resistor can open up, and suddenly shift the bias on the output stage making problems like you describe.

Response:

this is an 80 watt amplifier if its an 8 ohm speaker you are looking for about 25 volts rms or about 35 volts peak (70 volts p-p) if it 4 ohms about 18 v rms, 25 V peak, 50 V p-p > The two main output transistors also got extremely hot VERY quickly > when playing, i.e. within seconds, again without the speaker being > connected.

either shorted output transistor or loss of bias voltage (or both) > In addition to this, they also made a buzzing noise when output was > driven through them, the volume of the buzz in proportion to the > peak-to-peak voltage on the output.

possible power supply in the preamp/eq stages… check for a blown regulator > My questions are: > 1) Should the amp be clipping at such a low gain setting?

check you scope probe… is it set on x1 or x10? > 2) Should the output transistors be getting so hot and making a noise?

no > 3) Is this expected behaviour if the speaker isn’t connected?

no, not getting hot > 4) I have already replaced the large capacitors on the power supply. > Perhaps the transistors ought to be replaced too? > Many thanks in advance, > Patrick

any DC on the output? what does the ripple look like on the DC rails? measure the DC of the plus an minus DC rails. what is it?

Response:

> 1) Should the amp be clipping at such a low gain setting?

I’m not techie minded, so can’t help you with the other points. But I used to have one, and I could comfortably run the gain on max without clipping, with passive and active basses. Greg

Response:

8 ohm speaker. – Hide quoted text — Show quoted text -> if it 4 ohms about 18 v rms, 25 V peak, 50 V p-p > The two main output transistors also got extremely hot VERY quickly > when playing, i.e. within seconds, again without the speaker being > connected. > either shorted output transistor or loss of bias voltage (or both) > In addition to this, they also made a buzzing noise when output was > driven through them, the volume of the buzz in proportion to the > peak-to-peak voltage on the output. > possible power supply in the preamp/eq stages… check for a blown regulator > My questions are: > 1) Should the amp be clipping at such a low gain setting? > check you scope probe… is it set on x1 or x10?

Definitely correct. This is with very low gain settings. – Hide quoted text — Show quoted text -> 2) Should the output transistors be getting so hot and making a noise? > no > 3) Is this expected behaviour if the speaker isn’t connected? > no, not getting hot > 4) I have already replaced the large capacitors on the power supply. > Perhaps the transistors ought to be replaced too? > Many thanks in advance, > Patrick > any DC on the output?

About 0.02V which I guess is insignificant. > what does the ripple look like on the DC rails? > measure the DC of the plus an minus DC rails. what is it?

I assume you mean the power supply into the pre-amp stage – this is 60V, no ripple at all. That’s between +ve and Gnd. — Reverse the two elements of my email address to get my *real* address!

Response:

Many thanks to everyone who has contributed to this thread so far – it’s a good learning experience for me as I’ve not attempted to repair anything electronic before to any kind of level beyond the blindingly obvious diagnoses. In summary, it seems likely so far that it’s a problem with bias and that some DC is creeping in somewhere it shouldn’t. I need to start assaulting components with hot and cold things to try and identify which of them is causing failure. I had a read of this article ( http://www.tnt-audio.com/clinica/bias_e.html ) which seems like a good starting point for understanding how to adjust bias on a regular audio amp. In particular, it discusses taking a measurement of the voltage across the emitter resistor and dividing by the resistor value to get the quiescent current flowing into the transistor. Another observation: When I turn the power off (no load connected), the output maintains a steady 1V and stays there for a minute or so, before very slowly floating back to zero. I guess this is the beefy caps discharging. With a load connected, this doesn’t happen since the residual charge would be soaked up by the speaker. Is this 1V normal? Should it be making it to the output? I’m guessing it’s quite normal but I don’t want to leave any clue un-examined! Thanks again, Patrick — Reverse the two elements of my email address to get my *real* address!

Response:

I know nothing but the following place has a forum:- http://www.duncanamps.com/ Hope it helps BB

Response:

> > I’ll try replacing the transistors. I’m sure they won’t cost much. > Famous last words! > I can’t remember offhand which devices the BLX-80 uses, but some of the > earlier Traces used a complementary pair of power MOSFETs which are > virtually unobtainable now.

You’re probably referring to the "BUZ" 900/905 mosfets… Here’s a link for you: http://www.britishaudioservice.com/shop_trace_transistors.shtml Whenever I’ve ordered from these guys, the service was very good. fwiw, bk

Response:

– Hide quoted text — Show quoted text -> > I’ll try replacing the transistors. I’m sure they won’t cost much. > Famous last words! > I can’t remember offhand which devices the BLX-80 uses, but some of the > earlier Traces used a complementary pair of power MOSFETs which are > virtually unobtainable now. > You’re probably referring to the "BUZ" 900/905 mosfets… > Here’s a link for you: > http://www.britishaudioservice.com/shop_trace_transistors.shtml > Whenever I’ve ordered from these guys, the > service was very good. > fwiw,

That’s it! Thanks, Bill. I’ll keep this for reference next time I need it. $18 a "pop"? sheesh….. At least there’s a source. –Mike Mike Schway | [Picture your favorite quote here]

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