Replacing Plate Amp in G501

[ca1ore]

I've discovered, along the way, a huge drawback to Genesis speakers - namely, they sound so good that they're good for a lifetime; unfortunatey the amps don't last that long. Bought a spare for my G201system but never could find a spare for my G501s. Now I've finally blown the plate amp in the latter and though Gary has always been happy to help, age and obsolescence have conspired against me this time. I figure I have a number of options:

1. Give up on the speaker and sell for parts (con: hate to do this)
2. Mothball the woofer section and move my 4/8 sub into close proximity to take over the bass (con: sub contributes significantly where it is now)
3. Replace the plate amp with a DIY class D like the Bash 500 (con: will lose servo capability, plus no clue as to the impedence of the 3-driver bass section)
4. Use my spare G2000 amp to power the G01 (con: is this even possible; don't want to roach the spare)
5. Try to get the plate amp repaired; (con: not sure most technicians will be able to make heads-or-tails of the amp; is Rick Cullen still around?)

At this point I am leaning towards #3. Any opinions or, even better direct similar experience?

Thx!

Simon

 

[DonH50]

Check eBay/Craig's list for an amp or replacement speaker with working amp?

If you are good at DIY, and Gary can help with a schematic (saving much time and effort tracing out the loop), you could probably roll your own feedback circuit for the servo.

Getting a tech to look at the amp might also be worthwhile, but what to do depends heavily on what blew out. Equivalent power transistors may be hard to find, for example.

These are always tough situations...

 

[mep]

I would lean towards #5. A good tech should be able to fix the amp.

 

[garylkoh]

I would lean towards #5. A good tech should be able to fix the amp.

Problem is that even a good tech would not be able to get some of the parts because some of the ICs have been obsolete for over 10 years already.

Rick Cullen is still around - in Wyred for Sound - but he didn't make the Class D amps.

The impedance of the 3-driver bass array is about 1.3ohms. Class D is ideal.

 

[garylkoh]

Check eBay/Craig's list for an amp or replacement speaker with working amp?

If you are good at DIY, and Gary can help with a schematic (saving much time and effort tracing out the loop), you could probably roll your own feedback circuit for the servo.

Getting a tech to look at the amp might also be worthwhile, but what to do depends heavily on what blew out. Equivalent power transistors may be hard to find, for example.

These are always tough situations...

We don't have the schematics as these were designs from the previous company. The power MOSFETs are hardest to find and first to blow up, second is the HIP4080 Class D bridge driver. That usually blows up taking the power transistors with it.

 

[ca1ore]

Well, I removed the plate amp from the back of the speaker and examined it by eye. There does appear to be a blown fuse on the top circuit board (pigtail fuse in position F1) - could it be that simple? Any idea as to what fuse type would have been used? I just cannot tell for sure - looks like a 10A 125v fast-blo mini glass type - does that make sense?

Also, if the bass array is 1.3 ohms, does that mean it would not be drivable from a traditional amp (seems very low impedence)? How about from something run-of-the-mill like a BASH500 plate amp? Sorry for the ignorant questions.

 

[DonH50]

Gary -- I was afraid it was gonna' be something like that. Power transistors, esp HV, and controllers seem to have relatively short lives... What is the feedback sensor for the servo? Second voice coil, accelerometer, or something else?

ca1ore -- That seems reasonable; fuses generally have markings on them (often on the end caps) you could look up if it doesn't just say e.g. 10A 125V. It may not be a fast blow; Gary might know, or you could look at the fuse in the other speaker. You'd have to make sure whatever replacement amp you get is stable down to 1 ohms. As Gary said, these days a class D amp would be a great choice.

 

[garylkoh]

Feedback sensor is an accelerometer.

I'm pretty sure that it's a 10A 250V slow blow fuse. It protects the power transistors - so that if the controller fails, it doesn't take out the power transistors. So, looks like that's the problem. If you can find a HIP4080AIB, you might be able to fix it. Problem is that will be a 20 year old IC, and even if NOS are not reliable.

 

[garylkoh]

The BASH 500W might work...... might!

 

[ca1ore]

Feedback sensor is an accelerometer.

I'm pretty sure that it's a 10A 250V slow blow fuse. It protects the power transistors - so that if the controller fails, it doesn't take out the power transistors. So, looks like that's the problem. If you can find a HIP4080AIB, you might be able to fix it. Problem is that will be a 20 year old IC, and even if NOS are not reliable.

Replaced the fuse and indeed amp does not work. Clearly something failed and took out the fuse. I'm not going to fuss with trying to fix it - have neither the time nor, frankly, the technical knowledge. Local amp repair guy does not sound enthusiastic so looks like for now I will just 'ask' the proximally located 4/8 sub to take over bass duties.

Gary, perhaps you and I can chat about whether it would be technically or economically feasible for me to retrofit the 501 with one of your newer plate amps; versus experimenting with something like the BASH500 (not sure what your cryptic 'might' really means ).

 

[garylkoh]

OK, Simon. Give me a call again after I've had the chance to de-stress from CES. This is only the first day.

 

[ca1ore]

Hi Gary:

Thanks for your willingness to engage in these conversations - particularly for speakers that pre-dated you in the company.

I may have an opportunity to acquire a pair of Genesis V speakers. I assume it would be tricky to try to employ the external amp to drive my broken 501, but do you have a view on the performance of the V versus the 501 (I have seen comments that the V was actully better than the 501, not sure, never heard one)? And whether I would just be taking on a whole different set of problems with the older, flat amp?

Thx!

Simon

 

[garylkoh]

Hi Gary:

Thanks for your willingness to engage in these conversations - particularly for speakers that pre-dated you in the company.

I may have an opportunity to acquire a pair of Genesis V speakers. I assume it would be tricky to try to employ the external amp to drive my broken 501, but do you have a view on the performance of the V versus the 501 (I have seen comments that the V was actully better than the 501, not sure, never heard one)? And whether I would just be taking on a whole different set of problems with the older, flat amp?

Thx!

Simon

You'll be taking on a whole new set of problems. I assume that the comment that the G-V was better than the G501 was due to it having 4 woofers and an external amp instead of 3 woofers and an internal amp.

However, the 3 woofers of the current G5.3 displace far more air than the old G-V because of nearly 100% longer excursion. Also, the external amp was an old Class B design, the new Class D has far better damping. The very long cables with the "flat" amp also makes the servo system less accurate. You'll have boomier and less accurate bass with the old amp. Also, you're replacing a 12 year old plate amp with a 17 year old amp?

 

[DonH50]

Would someone be willing to redesign his amp, or design a new one? It would take someone who could take an existing servo amp (e.g. Rythmik, Velodyne, etc.) and adjust the sensor and feedback circuits to work with the old. If just the output stage of the old amp is fried, could a new amp replace the ouput stage, leaving the servo circuit intact? I assume the loop might have to be tweaked to match the gain and bandwidth of the new amp...

This whole thing sounds like a mess...

 

[ca1ore]

This whole thing sounds like a mess...

I guess it's the challenge of pushing stuff beyond its 'useful life'. I must confess to not really liking speakers with integrated amplifiers because, even though the synergy can be optimized, my experience is that amps have a shorter lifetime than speakers do. So when an older amp goes, but the mechanical speaker remains fine, the thing becomes a big lump. I've kept an ear to the ground for spare parts to my 201s (have a few tweeters, a couple of 'brown' woofers and a spare servo amp) but never came across a spare plate amp for the 501, alas. It speaks to the the enduring quality of these things that, 12-15 years on, I've heard nothing that has prompted a replacement.

 

[ca1ore]

I assume that the comment that the G-V was better than the G501 was due to it having 4 woofers and an external amp instead of 3 woofers and an internal amp.

More that there was 'magic' in the dome midrange that was lost when the 500/501 went to a cone. Don't know if it's really true.

Also, you're replacing a 12 year old plate amp with a 17 year old amp?

Indeed, that did occur to me; though, in this case it would be replacing a non-functional 12 year old plate amp with a functional 17 year old one (for as long as it lasts, that is).

Just 'thinking out loud'.

 

[garylkoh]

More that there was 'magic' in the dome midrange that was lost when the 500/501 went to a cone. Don't know if it's really true.

When I had a thousand of the dome midranges made to support customers with the IM8300, G-III, G-V, etc. I did try them out. After listening to one, and then listening to the replacement, I'm not surprised that Arnie ran away from the dome midrange. It wasn't cheaper, and it was far from better.

Indeed, that did occur to me; though, in this case it would be replacing a non-functional 12 year old plate amp with a functional 17 year old one (for as long as it lasts, that is).

Just 'thinking out loud'.

The point is "as long as it lasts"......

 

[garylkoh]

Simon,

if you are still on board, it took a while, but I've redesigned the plate amp on the G5.3 to work with the older drivers and older speakers. Unfortunately, it's got to be 2013 prices, and not 1993 prices.....

 

[ca1ore]

I have been able to 'make do' with a S4/8 sub, but it would be nice to have the bass section of the 501 working again. I've been keeping an eye open for a used set of 501s but so far no joy (figured I could sell of the parts I didn't need), although I suppose those amps will be just as old as the one I blew. Wish I could find somebody local to at least look at the thing to ensure it is not just a simple cap replacement, but nobody seems willing to even look. Anyhow, let me know via PM or email what a 2013 priced amp would run me can you please? Then I can decide if I think it is worth it or not. Sure glad I have a spare amp for my 201s!!

 

[ca1ore]

Well, after almost 18 months of trying to not notice that my center channel has lousy bass, I finally decided to stop being a cheap ba$tard and just buy one of Gary's replacement plate amps. Bah, should have done this right from the start. True drop in and speaker sounds great again.