News:

Forum upgrade to SMF 2.1.2, still working on re-theming.

Main Menu
Welcome to Solid State Guitar Amp Forum | DIY Guitar Amplifiers. Please login or sign up.

May 16, 2022, 08:11:14 AM

Login with username, password and session length

Recent Posts

 

Recent posts

#1
Amplifier Discussion / Re: Fender eighty five - how t...
Last post by joecool85 - May 09, 2022, 10:12:03 AM
Quote from: phatt on May 07, 2022, 06:37:30 PMYes open back delivers a more spatial sound hence fuller effect especially in small spaces but can present weird sonic issues in larger venues.
You may notice that a lot of big pro gigs tend to use closed back cabinets.

A player friend noticed this weird effect at an old wooden school gig where his open back rig was giving him a crossover of out of phase in the position he was limited to in the building. It can mess with your brain and the sonic result can be off putting.

That does not happen as much with a closed back cabinet.
Although it can still effect a closed back cab it is not as bad.
Venues with big Glass windows can have really bad reflections.
Phil.

I never really thought about it as I don't typically play out, but just at home.  That makes a lot of sense though.
#2
Amplifier Discussion / Re: Fender eighty five - how t...
Last post by phatt - May 07, 2022, 06:37:30 PM
Quote from: joecool85 on May 05, 2022, 03:08:51 PM
Quote from: phatt on May 04, 2022, 08:26:15 PMFor me personally I tend to like Sealed Cabinets for single speaker combos.

Phil.

I was just talking about this with a co-worker.  I believe combos should be open-back, the way God intended.  Just kidding, though I am an open-back believer.
Yes open back delivers a more spatial sound hence fuller effect especially in small spaces but can present weird sonic issues in larger venues.
You may notice that a lot of big pro gigs tend to use closed back cabinets.

A player friend noticed this weird effect at an old wooden school gig where his open back rig was giving him a crossover of out of phase in the position he was limited to in the building. It can mess with your brain and the sonic result can be off putting.

That does not happen as much with a closed back cabinet.
Although it can still effect a closed back cab it is not as bad.
Venues with big Glass windows can have really bad reflections.
Phil.
#3
Amplifier Discussion / Re: Correcting Headphone Jack ...
Last post by SemiConductive - May 06, 2022, 10:34:21 PM
Quote from: Enzo on May 05, 2022, 09:14:38 PMYou have three LEDs - plus power indicator -  A, B, and P?  I'd wager channel A, channel B, and Peak.
I'd check the IC for function

Quote from: g1 on May 06, 2022, 12:19:43 PMIs there a jack for PEQ footswitch?  I think you may be able to turn it off and on so you can use it like a lead boost etc.

Ah, g1, I think you nailed it.

I thought the footswitch was a simple  A/B channel switcher. It's just a TR type jack. But after digging into the schematic and the service manual, I see the footswitch controls the A/B channel switching, the P-EQ, and the Effects loop (S models only).

So they multi-plexed the three functions onto a two wire footswitch. All the extra circuitry is supporting the switching functions. And the reason the LED never goes off is that I don't have absolute switching on the control panel. I can set levels to 0 effect, but I can't actually "shut it off" - which can be done with the foot switch.
#4
Amplifier Discussion / Re: Correcting Headphone Jack ...
Last post by g1 - May 06, 2022, 12:19:43 PM
Is there a jack for PEQ footswitch?  I think you may be able to turn it off and on so you can use it like a lead boost etc.
#5
Amplifier Discussion / Re: Correcting Headphone Jack ...
Last post by Enzo - May 05, 2022, 09:14:38 PM
You have three LEDs - plus power indicator -  A, B, and P?  I'd wager channel A, channel B, and Peak.


I'd check the IC for function
#6
Amplifier Discussion / Re: Fender eighty five - how t...
Last post by SemiConductive - May 05, 2022, 08:57:04 PM
Quote from: nooneknows on May 02, 2022, 04:37:39 AMBTW, any hint about the speaker too? Any experience with different cones?

I am partial to Jensen C12R and C12K (I had them in my old Peavey Classic 30 and they were both delicious compared to the original mounted, with a preference for the C12K) but I don't know how they sound compared to the one installed in the Eighty Five, which I suppose it could be an Eminence, rebranded.



Hemp cone speakers tend to be much less bright.

I put in an Eminence hemp into a Frontman amp and it killed the excess treble. Didn't fix the tone stack but it did tame the treble.  For your 12" application, the Cannabis Rex is the hemp option.
#7
Amplifier Discussion / Re: Correcting Headphone Jack ...
Last post by SemiConductive - May 05, 2022, 08:07:48 PM
Back on topic, I have another question on this amp. (This might be answered by a user manual, but there are none that I can find. Service, yes, user, no). 

Anyway... there's an LED on the Parametric EQ section (Level, Frequency, Q are the control pots). There's an LED on the front panel in this section. In the circuit that LED103 / LED P on the right side.

It appears to be controlled by IC 103 1/4 and/or a feed labelled "P" from TR109's emitter, above, in the Parametric EQ section.

In practice, it doesn't ever seem to be off, in any user control setting. Would that be a surprise? Does the circuit suggest it would be off in some particular state? Seems like a lot of circuitry to use if they only wanted to send it a "light me" voltage full time.
#8
Amplifier Discussion / Re: Correcting Headphone Jack ...
Last post by SemiConductive - May 05, 2022, 07:22:33 PM
Quote from: g1 on May 05, 2022, 03:00:11 PM
Quote from: SemiConductive on May 04, 2022, 03:58:20 PMWhat's the function of IC111 i.e. what fault is it protecting against?
It senses DC at the output and kicks out the relay to protect the speaker.  It's also supposed to be able to prevent over-current but I'm not sure if that function is being used.  (see datasheet attached)

I see, thanks. Makes sense to keep it in place then. I could obviously still have an issue even with the speakers disconnected. Better to have it .

--
Taking my own thread off topic for a moment.. Just for curiosity to expand my electrical/electronic knowledge while we're here: what sort of current are we looking at for this speaker that's getting 50 watts at 8 ohms? 

If I use this formula, is it correct or am I missing other factors of audio and A/C signals?:

ohms = watts / ampsĀ²
8 ohms = 50 / ampsĀ²
2.5 = amps

And does that mean this is valid?:
volts = amps * ohms
volts = 2.5 * 8
volts = 20
#9
Amplifier Discussion / Re: Fender eighty five - how t...
Last post by joecool85 - May 05, 2022, 03:08:51 PM
Quote from: phatt on May 04, 2022, 08:26:15 PMFor me personally I tend to like Sealed Cabinets for single speaker combos.

Phil.

I was just talking about this with a co-worker.  I believe combos should be open-back, the way God intended.  Just kidding, though I am an open-back believer.
#10
Amplifier Discussion / Re: Correcting Headphone Jack ...
Last post by g1 - May 05, 2022, 03:00:11 PM
Quote from: SemiConductive on May 04, 2022, 03:58:20 PMWhat's the function of IC111 i.e. what fault is it protecting against?
It senses DC at the output and kicks out the relay to protect the speaker.  It's also supposed to be able to prevent over-current but I'm not sure if that function is being used.  (see datasheet attached)

Quote from: SemiConductive on May 04, 2022, 09:26:37 PMSlightly OT: For you guys who can't read the schematic I posted... did you click on the graphic once you got there to zoom it? Inquiring minds want to know (so I can plan better next time if needed).
My computer is old and my eyes are too. :)  The picture of the schematic only offered me one level of zoom and it still was too small for me.  Probably the zoom function was not working right with my old browser.