After Eighty - Small Ashdown Combo On Steroids

[Chienmortbb 393]

Firstly a warning: There are dangers in opening or building amplifiers. Unless they are battery powered, somewhere inside there are mains voltages that can KILL. Depending on your location these could be between 100V ac and 230V ac nominal. Only open an amplifier if you really know what you are doing. I  worked in Electronics until my retirement and was an IEng (Incorporated Engineer) Electronics, having studied to degree level. Despite that, I do  not know everything and have had to cram up on current safety requirements in order to make this amplifier safe. I have used commercial power modules form ICEPower that are built, and certified, to current standards around the world. DO NOT try to build amplifiers with low cost power supplies and/or amplifiers purchased from EBAY, Ali-Express, Bangood etc. Remember that you are connected to your amp when playing, don't save pennies, save your life.

Now on to the build.

 

The Trigger's Broom of Amps?

 

I have one of the original carpet covered After Eight combos. It is rated at 15W and has an 8" Sica 35 watt speaker that is showing signs of wear. The amp makes a strange noise after a deep notet is allowed to sustain. It is hard to fault find and I have decided to rip out the guts and rebuild it. This project is related to my other project to turn the Basschat BC112 into an active FRFR cabinet and much of this design will be used (or possibly discarded) for that design.

The existing unit is from the series that included the Perfect Ten and Five Fifteen and appears to have been codenamed the BakPac series. Eight Ten and Fifteen tells us the size of the speaker and the amp can have extra components added to increase the power output for the Ten and Fifteen inch variants. The powers abvailable from the amp is 15 watts, 30 watts and 65 watts respectively.

The controls are shown below including the new handle that I had already replaced. You can just make out the outline of the old handle in the picture.

 

 

Edited July 8 by Chienmortbb
Added safety warning

[Chienmortbb 393]

I found a label inside the box that seems appropriate to share.

Back on subject though:

Despite the  shape of the combo being a cube, the speaker cabinet is approx 29x29x14.5 cm. That is an internal dimension of approximately 12 litres. I want to put a new speaker in and  I have chosen the P-Audio E8-200*. This is an 8", 200 watt neodymium driver that suits this cabinet well. Hovever unlike the Sica speaker it replaces, it does not work best in a closed cabinet. *http://p-audio.co.uk/products/P-Audio_E8-200N_200W_8_Inch_Low_Frequency_Driver_with_2_Inch_Voice_Coil.php

 

 

 

 

As you can see the speaker sits centrally in the baffle and there is nowhere I can put a 75mm port on there. So the question is top, side or bottom? More on that later.

 

[nilebodgers 203]

Triangular corner ports?

[Chienmortbb 393]

The construction of the After Eight sees the amp  chassis mounted on the back of the cabinet. As you can see below, there is nowhere to put the port except below the amp and that is a very small space indeed.

Incidently, the white two way connector was put there by me, and in this photo, the loudspeaker leads are not connected. If you look closely at the printed circuit borad, you can see where the extra components for the bigger combos would go. You can also just see the small gap at the bottom between the chassis and the cabinet where air is allowed into the space below the chassis, aiding the natural convection cooling of the amp.

Edited May 25 by Chienmortbb

[Chienmortbb 393]

11 minutes ago, nilebodgers said:

Triangular corner ports?

I did think of that but adding them to an assembled cabinet is not easy, the calculations for them are not easy. As we are on the subject, one thought was to rebuild the cabinet in light weight ply but this is difficult with te lockdown and also more work than I was thinking of. However the carpet covering has to go and will be replaced by either a tough vynyl (tolexish) or TuffCab.

[stewblack 3,981]

I shall be an avid follower. 

[Maude 3,893]

Ooh this looks interesting. I need some inspiration to get an amp/cab project back on track. 

Looking forward to progress. 🙂

[tauzero 949]

What about side ports?

And as you've got a lot of unused power capacity in the speaker, are you going to get the components to take the amp to 65W?

[Chienmortbb 393]

Of course the dreaded lockdown is slowing down the supply of parts I have ordered. Some from the UK and some from the far east. Sadly the stuff from the far east seems to have stalled somewhere around Thailand and DHL seem to be washing their hands of it. First class post here seesm to be takling a week or  more and my last UK order was delivered to the wrong address. As I am shielding I cannot collect it ( I know where it is). Never mind lots I can still do.

Edited May 25 by Chienmortbb

[Chienmortbb 393]

11 hours ago, tauzero said:

What about side ports?

And as you've got a lot of unused power capacity in the speaker, are you going to get the components to take the amp to 65W?

I think a side port is the way to go. I was thinking top port  as it might throw up some mids,  but then it would invite things to fall into the cabinet

As for uprating the amp, I have tha parts. However I think it needs an uprated transformer to get  65 Watts. Also there is a fault on the amp, the main reason I am reworking it. However I will be looking at that at some point in the build.

[songofthewind 632]

Is there room for a long slotted port in the front, below the baffle?

[Chienmortbb 393]

On 09/05/2020 at 11:10, songofthewind said:

Is there room for a long slotted port in the front, below the baffle?

Yes but it is a lot of work, less that the four cornered triangular port but having worked with Phil Starr and Stevie I have seen and heard the benefits of a single large round port. Remember that the only access to the inside of the cabinet is through the hole in the baffle. Of course I could remove the baffle with some difficulty and that would also allow me to move the  driver and also allow room for an HF driver. If I were to do that, I would prefer to start from scratch.

 

There is some good news today, some of the parts from Thailand have moved to Singapore. Not a great leap but although reported last night, it happened on Wednesday. So maybe they will arrive in the not too distant future.

Edited May 25 by Chienmortbb
spelliongs and adding infomation

[Chienmortbb 393]

After some investigation, it has to be a side port. as can be seen by the mock ups below, the port cannot co-exist with the top strap.

 

Go to the side though and there is just enough room for the port. I have just realiswed I did not put the lip of the port on the side view but it is only 5mm

 

Next step is to remove the carpet covering so I can cut the hole for the port.

[Greg Edwards69 34]

A further port thought. Is a bottom port viable, like on the barefaced one10, or is the power amp in the way?

https://barefacedbass.com/product-range/one10.htm

[Chienmortbb 393]

6 hours ago, Greg Edwards69 said:

A further port thought. Is a bottom port viable, like on the barefaced one10, or is the power amp in the way?

https://barefacedbass.com/product-range/one10.htm

I did think of that but as I understand it, unless the bottom is well clear of the floor ( much more than the amount Alex designed into the one10) the tuning will be affected. Now that can work for you, as it seems to on the one10, but I don't have the measurement gear to hand to check the tuning. So it has to be a side port.

Edited May 12 by Chienmortbb

[Chienmortbb 393]

The carpet (why do the call it that, it's felt) has come off but it was a b*gg*r,  took three hours and it looks a mess.

Tomorrow, weather permiting I will get the sander out, clean it up and cur the porthole (no cruising or Jane MacDonald jokes please).

The box is made from a sort of heavy chipboard, denser than we usually get and the baffle is MDF. I almost wish I had started from scratch and made a new cab from light weight ply.

Edited May 14 by Chienmortbb

[Chienmortbb 393]

Well I got the sander out and thought I had not done very well. It was hard and there is still a lot of adhesive and carpet residue on the sides but it is much better than the picture above. The covering is not due untill next week so I think I will test wrap that with the cabinet as it now is to see how it will look. However I suspect, like paint, it will show all the lumps and bumps.

My original thought was to keep this cabinet. It is supposed to be a low cost build made  largely ftom existing components and materials. It is very heavy though and a ply cabinet would be much lighter. Thinking cap on.

On to the electronic design for a while.

Edited May 14 by Chienmortbb

[Pea Turgh 716]

I love a “pimp my amp” - there should be more!

Maybe a nice new cabinet would give you the opportunity to place a port in a more preferable location?

[Chienmortbb 393]

Don't tempt me Pete. Right the good news is that some of the parts reached Heathrow this morning. The others are still somewhere between Singapore and Poole even though they were ordered two days earlier. Anyhow I will not peer too intently into the oral cavity of a equine present.

The chassis is now stripped (although the transformer is still fitted). The boards are laid out on the chassis as can be seen in the picture.

On second thoughts I will move the bridge adaptor to the centre and rotate the ICEPower module so thate the airflow from the fan blows ditrectly past the whole of the power supply/amp module.

 

 

Edited May 14 by Chienmortbb

[Mottlefeeder 110]

Have you checked that your preamp will not be affected by the fan EMF if you have a common supply. I put a fan on a 12 v battery powered system and found the preamp became unusable. I now have to use a pedal preamp fed from its own battery.

David

[Chienmortbb 393]

On 14/05/2020 at 19:58, Mottlefeeder said:

Have you checked that your preamp will not be affected by the fan EMF if you have a common supply. I put a fan on a 12 v battery powered system and found the preamp became unusable. I now have to use a pedal preamp fed from its own battery.

David

I have not tested it. My current plan is to run the fan only as the temperature rises  and I was going to power the fan from the unregulated auxilliary supply (+25V) while the preamp is powered by the regulated =/-15V. This wsas because |I was worried about exactly what you describe.

I am still investigating as I cannot find the information I need in the ice power literature, I might have to run the amp while heating it with a hairdryer to test the thermal performance. More later.

[Mottlefeeder 110]

Another couple of options would be to use a 230V ac fan, or a 12 v fan on a capacitive divider and bridge rectifier as here (shudder)

David

[Chienmortbb 393]

Thanks for the suggestion. I would rather keep 230V out of the way as muct as possible.The fan I am using has come from a piece of audio equipment so I am hopping it will be OK. I will be checking the disturbance on the supplies  soon. 

[Chienmortbb 393]

I have made some progress although other, more boring projects, neede my attention. The chassis was stripped of everything except the IEC mains input socket/fuseholder and the on/off switch. The best part of modifying an existing amp is that most of the holes are cut. ON the other amp project the worst  part was cutting the holes for the mains switch. In the picture below you can see the switch/fuse holder and IEC input socket. The transformer was attached on the right hand side. You can still see one of the mounting bolts. You xcan also see the bodge I had to do as the mounting spacer for the preamp ended up in one of the ventilation slots. Four washers and some superglue created a solid fixing.

The smears are from the heatsink compound that thermally coup[led the original heatsing to the chassis. it gets everywhere but can be cleaned up with thinners or white spirit.

 

[Si600 2,173]

4 hours ago, Chienmortbb said:

The smears are from the heatsink compound that thermally coup[led the original heatsing to the chassis. it gets everywhere but can be cleaned up with thinners or white spirit.

Brake cleaner works as well. We use it at work to clean PC processors and the heatsink.