After Eighty - Small Ashdown Combo On Steroids

[Passinwind]

4 hours ago, Chienmortbb said:

I have looked at HYPEX before but found them just as hard to get information as ICEPower. I contatcted them and they pointed me to their DIY site.Sadly that only has separate power amplifiers and the beauty of the ICEPower and OEM Hypex modules is the intergrated mains and auxilliary power supplies.

I see the separate supplies as potentially a big plus actually. Not easier to deal with though, of course. My cost would be substantially higher though, and I already have too many amps!

[Chienmortbb]

16 hours ago, Passinwind said:

I see the separate supplies as potentially a big plus actually. Not easier to deal with though, of course. My cost would be substantially higher though, and I already have too many amps!

Separate supplies do offer more flexibility i layout i agree but thwe overal size of two modules is likley to be bigger espescially when the extra real estate for monting is considered. Of course the Hypex topology should be superiior.

[Chienmortbb]

Well the beauty of DIY is that you learn as you go. You might say you learn by your mistakes and anyone reading this thread will know that I am learning lots. From trying to use a vinyl sheet cabinet covering rather than Tuffcab to not fusing the auxiliary supplies from the ICEPower module.

In the case of the speaker cabinet tuning I have also made a mistake. A casual glance at the excursion graphs showed significant extra excursion around 40 Hz. This is roughly the fundamental of the E string on a four string bass tuned EADG.

I tuned the cabinet too high and tried to use a commercial 75 mm (3”) tuning port, rather than designing the cabinet for optimum performance and then sourcing the best port for the job.

It appears that standard 68mm rainwater downpipe would have been better and I will be trying that later. As the hole for the existing port is approximately 80 mm there will have to be some cabinet reworking. That is the part that hurts the most as the cabinet looked really good and I’m going to have to work really hard to get it anywhere near that good again.

Revisiting the cabinet modelling, I have also decided to incorporate a High Pass Filter to further tame the response and ultra low frequencies.

Implementing the High Pass Filter will require another small board so more metalwork to add to moving the power module. The question the is, do I go the whole way and replace the tatty strip board power regulator board? That means more metal work. Hey ho!

Edited July 15, 2020 by Chienmortbb

[Passinwind]

What specs do you need for the regulator John?

And BTW, I share your pain when it comes to metalwork. Literally, my fingers are a mess right now from hand filling a power switch opening in 1/8" aluminium two days ago

[Chienmortbb]

7 minutes ago, Passinwind said:

What specs do you need for the regulator John?

And BTW, I share your pain when it comes to metalwork. Literally, my fingers are a mess right now from hand filling a power switch opening in 1/8" aluminium two days ago

The current ones are just good old 7x15s and with through a full range 8" PA speaker the noise is barely perceptable, with both volunes at full and ears to the tweeter. The current ones are fine but they are not too pleasing on the eye, and take up a lot of room. I have a bunch of LM317/337 PCBs that I could put in but I am not sure how well they perform. The specs are +/-15V at 200mA.I could probably get away with 100mA but as I seem to be using that as a test bed, I need a little in hand.

Edited July 15, 2020 by Chienmortbb

[Passinwind]

2 hours ago, Chienmortbb said:

The current ones are just good old 7x15s and with through a full range 8" PA speaker the noise is barely perceptable, with both volunes at full and ears to the tweeter. The current ones are fine but they are not too pleasing on the eye, and take up a lot of room. I have a bunch of LM317/337 PCBs that I could put in but I am not sure how well they perform. The specs are +/-15V at 200mA.I could probably get away with 100mA but as I seem to be using that as a test bed, I need a little in hand.

There's always that one more thing, isn't there? 😎

[Chienmortbb]

At least one Charlie, 

Well I have moved the power module and the Speakon and I can just fit the fan if I decide to do so but it is really tight, I suspect a 60mm fan 10mm thick would be ideal but initially I will hope that conventional cooling works. 
 

[Chienmortbb]

I also tried the new port inside the old port, sealed with copious amounts of dense foam draught excluder. 
 

Actually I did cut it to 180mm (about 7”). It is better but still not as good as I hoped. I am going to add an HPF (High Pass Filter) and once  free to do so, take it to Guru @stevie for a blessing. 

[Chienmortbb]

No pictures today but I got the XLR from Sommer  today. It has gold pins and matches the gold writing on the back panel. Tomorrow I will paint over the legend that is no longer needed. It is masked, sanded and ready for spaying. 
 

Some more silly pictures.  I had no black screws so while the spray can was out......,

lyou can see that the new paint is blacker than the old but mainly because it has the look of just sprayed gloss. I could go over the whole panel with some clear coat to even that out but it’s the back and it looks OK. The eagle  eyed among you will notice the the screws are shifted down a little but I am happy with the result.

So next question. Do I need to have the output ground referenced. I was going to fit a ground lift switch but wonder whether to just hardwire it, either with, or without a ground?

Edited July 17, 2020 by Chienmortbb

[Chienmortbb]

Incidently the thin pencil line above the serial number label is where the wooden back of the cabinet comes to. It will be removed before the unit is reassembled.

So on to the headphone output. Traditionaly this has been  a potted version of the output sent to the speaker (see ESP's take on this) but as we are using a bridged amp, we cannot use that method. So I will be using a headphone amplifier based on the original CMOY head phone amp, click here to see the original design. . It uses a dual opamp and the PCB is very small.

There will be some changes to the circuit  especially the opmp. I wil be using the JRE4556 which has twice the current capacity of the OPA2134. More on components later.

Here is the pcb. It is about 20mm x 50mm (3/4" x 2").

 

Edited July 20, 2020 by Chienmortbb

[Mottlefeeder]

On 17/07/2020 at 15:14, Chienmortbb said:

No pictures today but I got the XLR from Sommer  today... ... Do I need to have the output ground referenced. I was going to fit a ground lift switch but wonder whether to just hardwire it, either with, or without a ground?

 

 

Rod Elliott recommends a connection to ground via a 10 ohm resistor bypassed with a 0.1 mfd capacitor. Covers most situations and doesn't not need a switch

David

[nilebodgers]

On 18/07/2020 at 14:27, Chienmortbb said:

Incidently the thin pencil line above the serial number label is where the wooden back of the cabinet comes to. It will be removed before the unit is reassembled.

So on to the headphone output. Traditionaly this has been  a potted version of the output sent to the speaker (see ESP's take on this) but as we are using a bridged amp, we cannot use that method. So I will be using a headphone amplifier based on the original CMOY head phone amp, click here to see the original design. . It uses a dual opamp and the PCB is very small.

There will be some changes to the circuit  though, more on that later.

Here is the pcb. It is about 20mm x 50mm (3/4" x 2").

 

Be interesting to know how you get on with that headphone amp design, the opa134 doesn’t really have the capability to drive low impedance phones (32 ohms and below) to high levels.

[nilebodgers]

11 hours ago, Mottlefeeder said:

Rod Elliott recommends a connection to ground via a 10 ohm resistor bypassed with a 0.1 mfd capacitor. Covers most situations and doesn't not need a switch

David

A further take on that is to have a pair of back-to-back power diodes (1N400x or similar) in parallel with the resistor and cap. They only conduct if there is a higher ground potential difference and then present a low impedance path. I have seen this  in some di box designs and it works well. The resistor is usually a higher value though, in the range 47 to 100 ohms usually.

[Chienmortbb]

3 hours ago, nilebodgers said:

Be interesting to know how you get on with that headphone amp design, the opa134 doesn’t really have the capability to drive low impedance phones (32 ohms and below) to high levels.

 

3 hours ago, nilebodgers said:

Be interesting to know how you get on with that headphone amp design, the opa134 doesn’t really have the capability to drive low impedance phones (32 ohms and below) to high levels.

I should’ve said that although I’m by using that basic circuit, I will be using the JRE4556 Opamp, capable of twice the current of the OPA2134. I published the original CMoy circuit as a reference. Some really good info on the circuit is at https://nwavguy.blogspot.com/2011/05/cmoy-ebay-headphone-amp.html

[nilebodgers]

36 minutes ago, Chienmortbb said:

 

I should’ve said that although I’m by using that basic circuit, I will be using the JRE4556 Opamp, capable of twice the current of the OPA2134. I published the original CMoy circuit as a reference. Some really good info on the circuit is at https://nwavguy.blogspot.com/2011/05/cmoy-ebay-headphone-amp.html

Good link, I liked that article. The same author has another good article on audio op-amps.

[Chienmortbb]

Sadly there has been no progress since my last post. I have been clearing our the garage, so I can use it as a workshop and then roof needed fixing, As it is due to rain tomorrow the temporary repairs will go on after dinner tonight but I hope to get someghing done this weekend.

[Chienmortbb]

Progress is slow as I am repairing my garage/workshop roof at the moment, However I have taken  the port out and I am not convinced it was properly sealed. Anyway the plan is to experiment. I will cut up a few squares of plywood about 11cm x 11cm (approx 4.5 inches square) that can cover the existing hole.  The I can use them to either close the hole (sealed cab) or try different ports. It will be screwed down with plenty of rubber seal to ensure it is air tight. More plus pictures to follow. 

Edited July 30, 2020 by Chienmortbb

[Chienmortbb]

The first new port is almost finished. I will check that it is totally sealed before I test it. I have routed the back of the wood and epoxied it in. I was not convinced that it was sealed so I used some PVA around the pipe.In smoothing the wood and excess glue, I got a slight flare so that may of may not help. 
 

I also have two other pieces of wood, one to test the sealed performance and another if needed for a different diameter port. 

[stevie]

John dropped his cab offwith me a couple of days ago, and I ran a set of measurements on it this morning. It all looks really good.

First, the impedance curve. It doesn't reveal any problems and shows a tuning frequency of about 61Hz. I also did a nearfield low frequency measurement, which is more accurate, and that says tuning is at 58Hz. For a very small cab like this, that's fine.

 

Edited August 13, 2020 by stevie

[stevie]

Here's the response at low frequencies. -10dB down at 50Hz is quite respectable for this size of box. I've been using the same driver in a larger cab for practice at home for the past few years, and I know it will go lower in a larger cab.

Nevertheless, it sounded good on audition, with a lean but tight bottom end that should be easy to fatten up with a touch of eq. Much better that than bloat and boom.

[stevie]

Finally, the on-axis frequency response curve. It's quite sensitive for an 8" driver - about 94-95dB - and extends up to about 3kHz. There's an ugly dip at 1.5kHz which requires further investigation. It's either a driver fault or it's being induced by the cabinet. I suspect the latter.

[stevie]

To troubleshoot the dip, I measured the cab at 30 degrees off axis. If the dip is caused by reflections from the cabinet sides, the effect will be reduced. The fact that the driver is dead centre in a square baffle will make matters worse.

The dip has indeed disappeared on the off-axis measurement, which proves that the cabinet is the source of the problem. This is not something I would worry about personally, as it's very likely to be inaudible.

Edited August 13, 2020 by stevie

[stevie]

Overall, a very nice little cab. I compared it with a fairly expensive 12" commercial cab (which shall be nameless) and it sounded much better to my ears, although rather on the lean side. To its credit, it made the 12" cab sound bloated.

I think this will surprise people when John's amp is fitted.

[stewblack]

3 hours ago, stevie said:

think this will surprise people when John's amp is fitted.

Looking forward to seeing /hearing this if it makes it to the SWBB 

[Chienmortbb]

Thanks Stevie, now to finish the amp.