Could my speaker be the problem?

[jomaco]

Hi guys

I made my amp perhaps a little buzzy but I can live with that, sounds great except for one thing... when playing anything involving the bottom two strings it just sounds really fuzzy (muddy? not sure of the correct term) and I just know it's not right - it especially does this at higher volumes. When playing the top strings it sounds lovely then I hit for e.g. an A5 or anything like that and it just goes (if i could type sound) "bleuurgh" and is not clear, the notes are not defined or seperated from one another and it's as though I've picked a weird setting on a fuzz factory or something. At higher volumes if I play the bottom four strings in a chord it's just really not quite right.

I've checked everything - valves, connections, grounding and I've even replaced every component on the circuit board with new ones. Perhaps the main thing is that I've sent it off to be checked and it has been sent back working. When i tried it with my speaker it sounded the same as before and so the only thing I can think of is that the speaker just does not like the amp.

I'm using a Peavey Sheffield 1200 that I think was taken from a Peavey 5150 or 6505 cab. I'm considering buying a G12H because from what I've heard that supposed to work nicely with an 18watter - so my thoughts were if it doesn't work with that it's never going to work.

So can anyone help? Has anyone experienced this problem before? Could it be the speaker?

Thanks very much. Hope you can help

Jon

[krx]

I don't have any experience with those speakers, but what you described sounds like a classic case of speaker "fart." Have any friends whose cabs you could play through to check?

If your cab is open-backed, you might also try putting the back right up against a wall and see if that reduces the farting. This would point to the speaker as the culprit and not something else.

[Deadwood]

Well obviously you don't have any other speakers to try or you would have by now, Peavey Schmeavey, get a real speaker regardless of whether it is the speaker farting out, there's not much can go wrong with a simple amp like the 18 watter but just try to play it through something else to put your mind at ease, if a tech's looked at it n says it's fine then it must be the speaker, or the tech. You'll still need a good speaker in the end though. As you say, G12H would do nicely.

[zaphod_phil]

Also what kind of amp is it exactly, and what kind of cab is the PV speaker in? The problem you describe could well be a problem either with the amp's power supply section, it's valves, or indeed the speaker.

[guitarmike2107]

Also what kind of sound are you going for… some have found the bass in the 18 to be not what they are after or maybe the bass just needs a bit more attenuation than a normal 18 watter.
Mike

[jomaco]

Hi guys thanks for your replies

Phil: The tubes have been swapped around for new ones etc. and although I built the amp i'm not experienced enough to find faults but I believe the power supply and everything in the amp in general were checked and are working as they should be.

As for the bass. If I understand where you are coming from correctly. It isn't a case of the bass not being the sound im going for, it's more of a fault so that to anyone's ears the sound that i'm hearing would not be right.

Based on what's been said I think I will try get hold of another speaker and hope for the best. In any case as mentioned I could do with a nice speaker to play it through when i eventually get it working anyway

Thanks

Jon.

[Archer]

I currently have the same problem and I think it is the speaker. Apparently, the Celestion G12H works great with the 18w, especially for classic rock

[reubster]

From your description, it certainly could be the speaker.
If it is, based on the fact that you hear the problem on bass notes, it could be voice coil/airgap problem.

You can usually check this by removing the speaker and with the magnet down, carefully push the cone.
If there is a problem you will feel some scratching rather than a smooth excursion. It can be really subtle [which is why bass notes tend to bring it out]
This is usually due to foreign material in the air gap [eg iron filings, gunk etc] or a condition where the voice coil was overheated and the windings have come loose due to glue melting.
FWIW, I had an older Peavey speaker [Blackwidow] and the magnet was detachable from the airgap [three hex screws].
I was able to clean out the airgap and get it working fine,
The bottom line is for an 18 watter, it would never sound as good as a G12H.

[jomaco]

Hey

I bought a G12H, sounds nice on the high strings but I seem to have the same problem. Any ideas?

Thanks again

Jon

[nyazzip]

sounds like it could be a parasitic oscillation too....i have a little PP DIY amp that produces weird harmonic "parasite" notes on lower registers....sounds a bit like one of those Hendrix octividers or even an octave pedal, except the parasite tones are not actual octaves....i think OPT mismatch or incorrect coupling caps can cause this phenomenon but i don't know. just something to keep in the back of your mind

[zaphod_phil]

sounds like it could be a parasitic oscillation too....

Yes, that could indeed be the problem. Why I mentioned the power supply, is that a dodgy filter capacitor could also cause that type of problem. Or even just a bad solder joint somewhere. And we still don't know what variety of 18W it is. I would also recommend measuring voltages on all the valve pins to see if anything looks off.

[jomaco]

It's a PP18 from ampmaker so I guess it's a LiteIIb. OK, I guess I will try measure the voltages again and check all the solder connections. I have checked them before to no avail but we shall see...

Jon

[jomaco]

Hi

I've checked all the solder joints and they seem ok. Are the filter caps the 3 large ones and if so how would I go about checking if they work - I do have another set of three but how can I tell which ones are working and which aren't?

Also i'm yet to to re-check the valve pin voltages but will do soon.

Thanks!

Jon

[zaphod_phil]

It might also be a good idea to post some gut shots for the collective to look at, and see if they can spot anything.

[jomaco]

Hi

First - sorry about this being in the cabinet and speaker section as I have now found that the speaker isn't the problem as thought earlier in the post.

I checked the voltages. They seem slightly higher than those suggested in the DL section but I don't think they we're for the Lite IIb so i'm not sure if they apply. Generally they did not seem all that different apart from V2 which seems way out. Perhaps these mean more to someone with more experience?

Hope i've done this right. Here goes...

Voltage reading from pin to ground:

V1:
1: 164.4V
2: 0
3: 1.2V
4: 11.55V
5: 11.55V
6: 165.2V
7: 0
8: 1.212V
9: 11.5V

V2
1: 209.5
2: 9.75V
3: 12.55V
4: 11.45V
5: 11.45V
6: 215.6V
7: 9.75V
8: 12.56V
9: 11.5V

ings I took about 4 months ago for V2 were as follows

1. 230.5V
2. 57.5V
3. 83.5V
6. 237.5V
7. 59.4V
8. 83.2V
9. 11.36V

As you can see they are very different. The thing is though, as I recall I had the same problem then as I do now...

V3
1: -
2: 0.075
3: 11.47V
4: 11.47V
5: 11.63V
6: -
7: 352.0V
8: -
9: 330.02V

V4
1: -
2: 0.088V
3: 11.65V
4: 11.65V
5: 11.55V
6: -
7: 352.6V
8: -
9: 332.3V

As suggested I have uploaded photos of the amp wiring etc. to this album:
http://www.rumsu.com/jomaco/My+album/pic/19260

If someone could take a look I would be very grateful for any help given as it's starting to get quite frustrating having not got anywhere for a number of months prior to completion of all the wiring. Everything I try just doesn't seem to get me any further and in my lack of experience it's hard to know what will work and what won't. Hope you can help

Thanks again

Jon

[stevesuk]

With the type of valve/tube bases you have used, it is always a good idea to 'flare' the pins away from the centre. It makes it easier to solder and keeps the conductors apart.
You have a lot of solder on the valve base pins and this can hide dry joints.
You have also left an excessive amount of bare lead to each termination. If this has been repeated under the board it is possible that this could be shorting to another conductor or ground.
The circuit layout looks fine, the wiring layout dress and soldering would be something to revisit.
I have attached a similar gut shot, notice how the pins on the bases are flared and the wiring lays flat to the chassis.
Steve UK
www.valvepower.co.uk

[krx]

I'll second everything Steve said and add a little more about your soldering technique, which looks pretty dodgy (but will get better with practice!):

* Make sure you make a good mechanical connection first before soldering. Crimp the wire around the lug, don't just stick it through the hole. Solder is to ensure a good electrical connection and provide some mechanical support. Think about joining two pieces of wood. A butt joint is very weak but a dovetail joint is very strong. The glue reinforces the connection, but the strength doesn't come from the glue.

* Check out some videos on good soldering technique. Your solder joints do not look good (ragged, probably a lot of "cold" joints). I suspect you may be melting the solder on the iron rather than on the joint. Use the iron (with a little solder as a conductor) to heat the joint then apply solder to the joint. Remove the iron and let cool. Don't let the wire move while it cools (a good mechanical connection should prevent that). You should get a smooth, shiny (unless you're using lead-free solder) surface, not a ragged or dull one.

* I see that your grid stoppers are floating up in the air connected to some wires. What happens if they move and short to the chassis, each other, etc.? You need to put a terminal strip or something there to provide mechanical support.

* Make sure you are using a decent soldering iron. I like the Weller 40W adjustable unit for amp building. Anything of similar power that's adjustable should work fine.

* Buy a bag of cheap resistors and some perfboard, terminal strips, or turret strips and practice soldering (and desoldering).