What exactly do quality speakers improve?

[airwarrior]

Hey guys,

I just finished a JTM-45 build, and it sounds really good for the most part. I can't get much sustain at all out of it though even when cranked. There is also almost no feedback except for the low rumbly kind like the low E vibrating.

I'm playing it through an MG cab, because it was dirt cheap. Would upgraded speakers improve this at all?

[shane88]

yes

[airwarrior]

Ok, so dumping the shit speakers in the MG cab would improve the sustain? Really noticeably, or only if you're an audiophile noticeably?

Also, are there any good quality, cheap speakers? Or rather, cheaper speakers? I was looking at Celestion 30s, but they're awfully expensive. Are there comparable ones out there for cheaper?

[epluribus]

Originally Posted by airwarrior

Hey guys,

I just finished a JTM-45 build, and it sounds really good for the most part. I can't get much sustain at all out of it though even when cranked. There is also almost no feedback except for the low rumbly kind like the low E vibrating.

I'm playing it through an MG cab, because it was dirt cheap. Would upgraded speakers improve this at all?

Easy diagnostic: Take it to GC and plug it into another cab.

Got a good solid guitar signal? Hadda ask.

After all that...Presuming your voltages all check out, particularly Vp and bias voltage, the tubes should saturate and compress pretty well regardless of the speaker. IIRC, JTM45's ran pretty clean, but they'd break up quite nicely at about 7 on the knob. A bad resistor somewhere in the signal path might be eating up your signal causing the amp to run too clean. Ditto a drifted cap. Check the pots too while you're at it. Somethin' ain't happening somewhere.

As for the impact of speakers...efficiency would indeed make a difference to your gain structure. Saturation-wise, mainly it will impact available power from your power supply, or more accurately, how it gets used in the amp.

Beyond that, they can contribute to dirt if the speakers themselves tend to physically distort early. That can impact compression and sustain within the circuit for a strange variety of reasons, but the audible impact will be fairly minimal--not enough to account for what you've described here I wouldn't think.

As for new speakers at great prices, be sure to check out Weber. Really nice stuff.

Anyhoo, try the borrowed cab thing first, and plz keep us posted.

--Ray

[90wreck]

Originally Posted by epluribus

Easy diagnostic: Take it to GC and plug it into another cab.

Got a good solid guitar signal? Hadda ask.

After all that...Presuming your voltages all check out, particularly Vp and bias voltage, the tubes should saturate and compress pretty well regardless of the speaker. IIRC, JTM45's ran pretty clean, but they'd break up quite nicely at about 7 on the knob. A bad resistor somewhere in the signal path might be eating up your signal causing the amp to run too clean. Ditto a drifted cap. Check the pots too while you're at it. Somethin' ain't happening somewhere.

As for the impact of speakers...efficiency would indeed make a difference to your gain structure. Saturation-wise, mainly it will impact available power from your power supply, or more accurately, how it gets used in the amp.

Beyond that, they can contribute to dirt if the speakers themselves tend to physically distort early. That can impact compression and sustain within the circuit for a strange variety of reasons, but the audible impact will be fairly minimal--not enough to account for what you've described here I wouldn't think.

As for new speakers at great prices, be sure to check out Weber. Really nice stuff.

Anyhoo, try the borrowed cab thing first, and plz keep us posted.

--Ray

Wow....Right on!

[epluribus]

Originally Posted by 90wreck

Wow....Right on!

Whoa, I was right about something! This is goin' on the fridge! Hon-eeeeee...

--Ray

Gonna make the teenagers read this right after she does.

[Julia343]

JTM 45 + Avatar Closed-back Contemporary or Vintage 212 (or 412) with G12M Greenbacks and a THD Hot Plate FTW. One of the best gear combos available without breaking the bank.

[airwarrior]

I'll try it through a better cab. The thing is, is that it sounds great, and they're doesn't seem to be a problem with the amp itself. I just don't get the long never ending feedback rich sustain that I would like to have. Or would that be a problem with the head, and not the cabinet?

[908SSP]

Could be both. My recently finished Offset clone sustains like crazy. I play it on 9.5 with my attenuator at a respectable volume.

[epluribus]

Originally Posted by airwarrior

I'll try it through a better cab. The thing is, is that it sounds great, and they're doesn't seem to be a problem with the amp itself. I just don't get the long never ending feedback rich sustain that I would like to have. Or would that be a problem with the head, and not the cabinet?

Yeah, that sounds to me like a head "problem." Actually, if the head sounds good to you, it may be working fine but just needs a custom tweak to make it play the way you want. It's also possible that your power transformer is a bit too capable and isn't letting the circuit saturate--what they call a stiff power supply. But that's a pricey "fix," sooo...

To tune for sustain in my book means getting at least one gain stage somewhere to compress, and that means more dirt and saturation at that point. To do that I just experiment with the amp as-voiced.

One easy thing you can do is grab yourself a 25/25 cap and try bypassing Rk at various gain stages to see if that's enough to "poosh et over the cliff, eh." (Nigel) Or more accurately for a Marshall circuit, would that be smaller (brighter) uF? Can't remember.

Anyhoo, another really simple approach is to increase Rp someplace, as in swapping the typical 100K plate resistor for a 250K or something like that.

Anyhoo, either one will give you a gain boost wherever you do it, meaning that the modified stage will saturate and compress more as well as (More or less. 'Nuther subject.) all the following ones.

Where to put the mod? Since you built this I'm presuming you know your way around the inside of an amp. (If not, plz STOP. Deadly volts, bigtime.)

My personal solution is pretty simple. I just crimp an alligator clip to both ends of the cap or resistor I want to splice in and clip it into various locations. Then I fire up the amp and audition the sound to see if I like it. Even easier if you use perfboard (see Figure 1, below) and cermet pots for the resistance auditions--then you can twist 'em till they're just so and then weld in the permanet variety when you get 'er singin'.

In any event, if you like the sound you're really close already, so your tweak should be gentle and subtle--it won't take much.

Keep us posted.

--Ray

*********

An Ixampul uv Subtal and Eligunt Brane Surgeyury with th a-foarmintioned PerfBoard...

(Oh yeah...Figger 1.)



! A Kalamazoo Model II with four switchable cascading gain stages, a relocatable tone stack, and several switchable R/C values throughout.

To construct an audio oscillator, start by building an amplifier.

--
__________

Earplugs anyone?

[epluribus]

ps...You might also just stick a comp in front of the amp if you like 'er the way she is. Wicked results with my Univox 1221 clean machine.