My first valve build for fifty years! Vox AC15 (1960 version) - Sound Clips!

[DLPublic]

Posted by: sluckey
« on: August 05, 2016, 07:13:31 am

This tube is prone to microphonic ringing. There are silicon rings that can be placed on the tube to act as dampers. Using grommets to shock mount the socket may also help. Many times you just have to get another tube.

I knew the EF86 was prone to microphonics and have already used rubber washers (cut from silicone vacuum piping I had to hand) to mount the base.  Strangely, having prodded a few wires around the EF86 base and in particular lifted the screen grid wire clear of the others, I fired the amp up again today and this time no high pitched oscillation.     I had also slightly rotated the speaker cabinet so as not to direct the sound directly towards the amp chassis (which was still sitting on the table top).  Initially thought this may have been the reason for no oscillation, but even when directed back at the chassis it did not oscillate.  Also I believe the hum has reduced as it is hardly audible when the brilliance switch inserts the 220pF capacitor.  I watched a video demo of a AC15 hand wired this morning and that had slight hum and hiss, so I do not feel so bad about it.

A simple fix that I used is a J12A switching jack. Just wire the switch terminal to the sleeve terminal. This will provide a ground to enable the oscillator when no footswitch is plugged in.

Wired an ON/OFF switch in lieu of footswitch and the Vib/Trem worked although experiencing some motor-boating at certain settings of the depth/Speed controls which limits the useful range.  This could be caused by having fitted an ECC83 instead of ECC82, so will hold off troubleshooting that until I get the correct valve installed.

Put a 5.1M resistor across the switch. 1M will probably work also.

I have just ordered the additional silva mica capacitors to extend the brilliance options (as per your mod) so willl add the resistor when I do the mod.

So all in all I am very pleased with the result and the fact that it appears to be mainly working without too many problems.
Dave

[sluckey]

I have just ordered the additional silva mica capacitors to extend the brilliance options (as per your mod) so willl add the resistor when I do the mod.

If you use the switch I specified you will not need any resistors.

[DLPublic]

[Posted by: sluckey « on: August 05, 2016, 08:04:51 pm »
If you use the switch I specified you will not need any resistors.

Just had another look at your mods document and notice you specify a make before break switch.
Mine is break before make.   .

Will try the resistor fix first, then consider changing out the switch to MBB.
Dave

[sluckey]

You will need several 5.1M resistors if you don't use a MBB switch. Like this...

     http://sluckeyamps.com/hammond/hammond_ao39.pdf

[DLPublic]

A small update...

I was a bit apprehensive about cutting the tolex along the string channels and even considered not doing it.
However, it turned out to be easier than I was expecting.

First I located the channel with the round end of a small steel ruler, which created a mark where I needed to cut.
Then taking extreme care, I cut along the string channel trying to keep the cut centred (as much as possible) along the channel.
The string was then tapped into the channel using a small block of wood and a rubber hammer.
I found that working around the cabinet one to two inches at a time produced the best result.
The front string join is hidden under one of the feet, whilst the ends of the back string are stapled under the control panel cutout.

Tolexed the two back panels and these are now fixed with gold coloured countersunk bolts/screws with cup washers to the cabinet.
Looks nice.

Also have received a make before break 2P6W rotary switch for the brightness control so now need to change that out and install the additional capacitors.  Hopefully this will prevent the audible click/pop when selecting brightness options.

An Harma Retro balanced ECC82 is on the way for the modulator stage.  Hopefully this will sort out the motor-boating issue with the Vib/Trem.

So the only thing left really is to install a small aluminium plate under the amp tray for the speaker and footswitch jack sockets and wire these up.  Oh one extra thing... I need to make the serial plate from a peice of thin aluminium and then print/apply a decal to it.

The end is nigh 
Dave

[DLPublic]

New MBB 2P6W rotary switch installed with all the 'brilliance' capacitors as per Sluckey's mod.
New (ECC82) valve fitted and it appears to have cured the motorboating issue.
Speaker and Footswitch jacks installed and wired up.
Et Voilá - Job Done!

Spent an hour or so playing my DIY strat through it.
My FX pedal board switched power supply introduces some noise which can be filtered out with the top-cut/brilliance controls and is also drowned out when playing.  However I may need to look for a linear PSU for my pedal board.

Final photos attached!
Dave

[pompeiisneaks]

Looks incredible! Nice job.

 

~Phil

[DLPublic]

My DIY Hank B. Marvin kit 
Dave

[sluckey]

Very, very nice!

[NO_H2O]

Wow. That is sweet. I am going to go throw rocks at my AC15 project now. Very nice work.

[DLPublic]

Here is a sound clip.

Recording conditions...
1. An SM57 microphone situated at an angle approximately 4 inches from the AC15 speaker.
2. The microphone was plugged into an 'AudioBuddy' pre-amp which then was connected to the microphone input of a laptop running Sonar X3.
3. This was a single take, i.e. no editing, with a UB Hank backing track and yes I am a bit rusty!!!
4. I have panned the guitar 75% left and the backing track 75% right so you can alter the relative balance of the two components, i.e. pan left to hear more of the guitar.
5. My HBM stratocaster was connected to channel one (the EF86 channel) via a Zoom g2.1Nu loaded with the appropriate EFTP patch created by Charlie Hall.
6. Channel volume is approximately at twelve o' clock with the top-cut approximately 9 o' clock to reduce some of the noise from my multi-FX pedal.
7. There is no post-processing, e.g. compression, gating, eq, et-al., in Sonar just the faders set as per above.  So what you hear is what is coming from the amp.

https://app.box.com/s/dk4kgsxd0upwj7pbmx4n9emnfdlcmnz7

Please bear in mind this recording was intended to reflect the sound of the amp and not the quality of my playing   

Dave

[sluckey]

Please bear in mind this recording was intended to reflect the sound of the amp

I like the sound but there is so much FX that I have no idea how the amp actually sounds.

[DLPublic]

Posted by: sluckey
« on: August 14, 2016, 10:00:20 am
I like the sound but there is so much FX that I have no idea how the amp actually sounds.

Point taken.  Will attempt to a clip of do some basic chords, etc. without any effects, using various amp settings tomorrow.
Dave

[DLPublic]

Here are some more clips without any effects of my AC15 at various amp channels/settings.

I decided to record a simple clip onto my Boss RC-3 looper which is then played through the amp using various settings.
The clip is of course the Animals' intro to the House of the Rising Sun (HOTRS), which back in the sixties, every self-respecting pop guitarist would learn.  .  I haven't listened to or played it since so apologies for any rustiness.

The setup remains a Shure SM57 mic angled in front of the speaker cone (about 6 inches away) which is connected to a laptop microphone input via an AudioBuddy pre-amp using Sonar X3 to record each track.  The only post processing I did was to normalise each track to -3dB max so tonal differences would be more noticable.

The file name conventions are...
CH1   ... using Channel 1 (the EF86) - high gain input
CH2   ... using Channel II (Vib/Trem) - high gain input
V10   ... Volume at 10 o' clock  (all clock positions are as viewed from the back)
V3     ... Volume at 3 o' clock
NOTC ... Top Cut turned fully anti-clockwise
TC3   ...  Top Cut turned to 3 o' clock position (to remove the hiss)
BR1   ...  Brilliance on position 1 (i.e. no capacitor)
BR6   ...  Brilliance on position 6 (220pF capacitor)  - these two positions represent the two tonal extremes
NoVIBTREM ... Vib/Trem Depth control turned fully anti-clockwise
VIB    ...  Vib/Trem switch in Vibrato position  (Depth control around 9 o' clock)
TREM ...  Vib/Trem switch in Tremolo position (Depth control around 9 o' clock)

Hope that is clear. So here are the clips...
https://app.box.com/s/erl7uf3im2n3tkuvoghatfqlesnzgtcv

Would be very interested to hear how my amp sounds compared to others based on the Vox AC15.
Dave