Amp Tech Thread / Ask a tech Q

[VOLVO)))]

That's too baby ass IMO. Metaldave, if you need parts lemme know, i got the hookup

[liquidsmoke]

(as some of you already know) I'm running a mini SS class D 350 watt bass head for guitar into 6 speakers(2 eight ohm cabs, each cab rated at 300 watts). Guitar is in B and I use a ton of distortion from a pedal. At high volume levels with more low end dialed in than I normally use weird stuff happens. The volume will kind of pulse down and back up repeatedly when I let heavy power chords drone. Is this the speakers failing or not being able to properly reproduce the low end? Fortunately I don't need that much low end in my tone so I have it dialed back enough to avoid said pulsing but I would like to understand what I'm hearing when I do have the low end cranked more. Oh yeah, the 2x12 has Eminence Swamp Thangs and the 4x12 has unknown blank 75 watt speakers.

[justinhedrick]

(as some of you already know) I'm running a mini SS class D 350 watt bass head for guitar into 6 speakers(2 eight ohm cabs, each cab rated at 300 watts). Guitar is in B and I use a ton of distortion from a pedal. At high volume levels with more low end dialed in than I normally use weird stuff happens. The volume will kind of pulse down and back up repeatedly when I let heavy power chords drone. Is this the speakers failing or not being able to properly reproduce the low end? Fortunately I don't need that much low end in my tone so I have it dialed back enough to avoid said pulsing but I would like to understand what I'm hearing when I do have the low end cranked more. Oh yeah, the 2x12 has Eminence Swamp Thangs and the 4x12 has unknown blank 75 watt speakers.

liquid, I am not sure why, but it seems like you have the most problems of anyone with your setup. How loud are you running this thing?

are you sure the speakers are in phase?

[moose23]

My knowledge of such things is limited/none but it sounds like the description of blocking distortion described here:

http://www.aikenamps.com/BlockingDistortion.html

[dunwichamps]

im not sure that would be blocking distortion Moose since he is running a SS amp its much less prone to that problem but it could happen. I would think its more like a speaker issue

[liquidsmoke]

The pulsing phenomenon only happens when I turn the bass up more than usual. I run very loud but not as loud as for example some folks who use two 100+ watt tube heads into a full stack.

Finally got my matching 2x12 the other day and after that is a bit broken in I'll crank the bass up at high volume again and see how it handles. It definitely could have been a phasing issue with the different cabs I was using before.

This is just me being curious as we have a bass player and I try not to compete too much on the low end of the spectrum. That bass knob is fun to crank sometimes though. I know they vary but for B tuning so far I think bass amps are the bees knees into guitar speakers, for guitar.

[RacerX]

A bass amp doesn't play nice with a guitar cabinet when you crank the bass control?

No way.

[liquidsmoke]

A bass amp doesn't play nice with a guitar cabinet when you crank the bass control?

No way.

I have it dialed back enough to avoid said pulsing but I would like to understand what I'm hearing when I do have the low end cranked more

The pulsing phenomenon only happens when I turn the bass up more than usual.

...This is just me being curious as we have a bass player and I try not to compete too much on the low end of the spectrum.

[hayseed]

 I have a noisy Thunderverb 50 all of a sudden! Its making a very annoying buzzing sound that gets louder when i get near it. It was not like this last week when i used it. I did transport it fro one practice spot to another but it wasnt dropped or bumped. My troubleshooting has been this:
1. Swapped out all of the cables to see if i had a bad one- done and good
2. took my pedal board out of the line and went direct guitar to amp- done and good
3. changed wall outlets to see if i had some dirty power happening- done and good
4. changed guitars to see if it was a pickup- done and good

Any ideas what it could be? I am no tech, but i like to have an idea of what I'm getting into when I take it to one! Thanks

[RacerX]

I have a noisy Thunderverb 50 all of a sudden! Its making a very annoying buzzing sound that gets louder when i get near it. It was not like this last week when i used it. I did transport it fro one practice spot to another but it wasnt dropped or bumped. My troubleshooting has been this:
1. Swapped out all of the cables to see if i had a bad one- done and good
2. took my pedal board out of the line and went direct guitar to amp- done and good
3. changed wall outlets to see if i had some dirty power happening- done and good
4. changed guitars to see if it was a pickup- done and good

Any ideas what it could be? I am no tech, but i like to have an idea of what I'm getting into when I take it to one! Thanks

Caps.

[VOLVO)))]

Those amps are fickle and shitty, could be a number of things. Have you gotten shocked yet?

[hayseed]

No shocks yet. Just a hum when I'm at a distance and a loud buzz when I get close.

[hayseed]

I have a noisy Thunderverb 50 all of a sudden! Its making a very annoying buzzing sound that gets louder when i get near it. It was not like this last week when i used it. I did transport it fro one practice spot to another but it wasnt dropped or bumped. My troubleshooting has been this:
1. Swapped out all of the cables to see if i had a bad one- done and good
2. took my pedal board out of the line and went direct guitar to amp- done and good
3. changed wall outlets to see if i had some dirty power happening- done and good
4. changed guitars to see if it was a pickup- done and good

Any ideas what it could be? I am no tech, but i like to have an idea of what I'm getting into when I take it to one! Thanks

I opened it up today and did the pencil test with the tubes. V1 (far right, channel a&b, ECC83 ) was noisy as was the position above it (fx loop, 12AT7) though not as bad. I switched tubes between v1 and v3(far left) and it helped with the buzz a little bit but v1 was still microphonic when i tapped it. Could that be a tube socket gone bad?

thanks

[VOLVO)))]

Just swap out all the preamp tubes, sockets can't go microphonic.

[hayseed]

Thanks. I will order a new set today. There is a tube for the reverb and fx loop(ecc81). Should I include change those as well? Not sure how much those positions affect the rest- I don't use the fx loop anyway.

[thestone]

Have an orange rockerverb 100 that just died on me the other day.  Was playing at about half volume, and suddenly it went quiet.  No crackle or any other bad sign, just stopped making noise completely.  Tried different cab and cables to no avail.  Power seems to be present in amp i think.. didnt really spend too much time on it, just plugged into different amp and moved on.  Any ideas, or common things to look for?  And yes i know everyone says these are cheap pieces of junk.

[VOLVO)))]

Phase inverter and screen grids are the first thing to check. Take all the shields off the preamp tubes and make sure they are all firing. I just did this with the same piece of ass amp.

[sinofmalice]

Hey ya'll,

I just picked up a Sunn 200S (late 60s). It's got 2 speaker inputs -- one is labeled "16 ohms" and the other is "External Speaker 8 ohms." So my understanding of my basic cabinet options for this amp are as follows:

1. Obviously, a 16 ohm cab into the 16 ohm input;

2. An 8 ohm cab into the "External Speaker" input. I'm under the impression that it's okay to use the "external speaker" input by itself with this amp. Please correct me if I'm wrong. I know with some amps you are not supposed to do this;

3. Two 16 ohm cabinets (1 in each input). My understanding is that plugging into the 8 ohm "external speaker" input switches BOTH inputs to 8 ohms. So, 2 16s = 8ohm load.

Do I have this right?! Also, I am planning on using this for guitar. If anyone is familiar with this amp and can offer tips/suggestions, please do! Thanks for reading.

[VOLVO)))]

Neg, you can daisy chain two 16s to the 8 ohm tap, but not use both taps at once. There's no weirdo switching, it's the 16 ohm tap from the tranny to one jack, and the 8 to the other.

[sinofmalice]

Shit okay gotcha. So then I'm assuming it's still okay to use the 8 ohm "external" jack by itself with an 8 ohm cab? Just want to be absolutely sure. Still learning about all this stuff...

[VOLVO)))]

yesh! perfectly fine!

[sinofmalice]

Awesome. Thanks for the help, man.

[RAGER]

During my move the square pilot jewel somehow popped off my Super Bass (68-69).  Any of you techey types knows if there is a difference other than the price between the assembly form Mojotone and the one from AES.  They both say genuine Marshall old style.

[VOLVO)))]

Are there any dimensions on the websites? I can't seem to find any.

[RAGER]

0.44" Length x 0.44" Width x 0.27" Depth-AES

Dimensions: 7/16 x 7/16" x 1/4" Deep-Mojotone