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Old 4th February 2012, 01:32 AM   #31
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Default Abletec ALC0240-2300

Here’s my experience with the Abletec ALC0240-2300 module.

This device is marketed as a “plug and play” two channel power amplifier complete with power supply, and it should be a simple matter for the end user to connect up the mains power, input connectors and speaker connectors and start using the amp.

Unfortunately, due to (amongst other things) the deficient instructions provided by Abletec, end users who configure the amp in single-ended mode in accordance with the published Abletec “block diagram” and connect it to unbalanced sources will end up with severe hum in both channels.

The reason for this is that Abletec’s block diagram for single-ended operation with unbalanced sources depicts the + and – inputs of both channels without any ground connections.

In order to prevent or minimise hum, it is necessary to either ground the – input of each channel to a ground pin on the amp (or to the star earth point if the amp is grounded to the chassis), or use shielded two core cable with only the shield grounded at both the preamplifier and the amp.

Sadly, none of this information can be found in any of the documents published by Abletec, and it seems that Abletec just assumes that the end user will know these things. As many hobbyists have only limited technical literacy, Abletec should provide that information, together with clear and unambiguous connection diagrams.

Which raises the next issue I have with Abletec. It is not clear from the Abletec block diagram whether the ground symbols on the block diagram depict internal grounds on the amp PCB or ground connections which need to be made by the end user. For example, Pins 3, 8 and 9 are internally connected on the PCB and it is necessary to make a physical ground connection only if you want to ground the amp to the chassis. All internal PCB grounds should be marked as such in the Abletec block diagram, and external ground connections clearly identified.

Finally, there is the curious absence in Abletec’s specifications for the amp of its input impedance.

In order to avoid pumping of the power supply rails, Abletec has the left channel of the amp connected in non-inverting mode and the right channel in inverting mode.

I measured the input impedance of each channel of the amp (with 8 ohm loads) when configured in single-ended mode in accordance with the Abletec block diagram, with the following results:

Left Channel
Frequency Input Impedance
10Hz 12.44kΩ
1kHz 11.9kΩ
10kHz 8.775kΩ
20kHz 4.74kΩ

Right Channel
Frequency Input Impedance
10Hz 3.75kΩ
1kHz 3.8kΩ
10kHz 3.06kΩ
20kHz 2.3kΩ

There is a marked asymmetry between the input impedances of the two channels, with an unusually low input impedance in the right channel. When the amp is used with a typical vacuum tube preamplifier with capacitor-coupled output, the result will be audible channel imbalance, premature LF roll-off in the right channel and increased distortion (particularly if the preamp does not use a cathode-follower output).

When auditioned in such circumstances, a negative perception of the performance of the Abletec amp will be the likely result.
Abletec should have disclosed the input impedance characteristics of the amp, as this is essential information for the end user.

There are, however, two cures for this problem.

The simplest is to discard the “anti-rail pumping” setup and wire the amp for unbalanced sources as shown in the attached image. Note that this only works with preamps that are compatible with 10k loads. If hum continues to be a problem, just use shielded two-core cable.

The other, more complex, alternative is a construct a high quality two channel unity gain buffer and interpose it between the input sockets and the input pins of the amp. This method permits the “anti-rail pumping” setup to be used without disadvantage.

I opted for the “simplest” cure and found that the amp performs very well indeed when connected to my home-built vacuum tube preamp (which uses 6DJ8 cathode-followers with both sections of each output tube connected in parallel).
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File Type: jpg alc0240-2300-Mod.jpg (228.4 KB, 1407 views)
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Old 24th February 2012, 11:33 AM   #32
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Default SMD opamp choice Abletec ALC0180-2300

I did replace the original MC33078 opamp (SMD) on my Abletec ALC0180-2300 board. I did change it for the OPA2604 (SMD). I have some experience with different opamps and the OPA2604 (SMD) is a safe and good choice.
The LM4562 and equiv. are not-my-cup-of-tea.

If you have the tools and experience do change the opamp, to my opinion the sound improved a lot.

Wim.
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Old 28th February 2012, 12:06 PM   #33
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Default opamp change

Again prove that I little invenstment (and effort) a product can sound so much better. The OPA2604 is a perfect choice for this module. My Keith Jarrett Trio 'Live at the Blue Note' CD box is again up-to-the-level-I-can-live-with level.
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Old 9th March 2012, 10:42 AM   #34
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Default Abletec based IRS20955 based amplifier

Just wanted to point that the Abletec modules are using International Rectifer's IRS20955 / IRS20957 based Class D IC.

They use a dedicated IC which is not available to the DIY market, which allows them to use the IC in an optimum way. The Abletec modules are a self-oscillating design.
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Old 11th April 2012, 03:45 PM   #35
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Default ALC0180-2300 Mains Rectifiers

I have two ALC0180-2300s of which I'm making changes to one so I can compare it with the other. Eventually these will be a pair of bridges for the final amp but I'm using them singly while experimenting.

I've ordered a set of OPA2604s as Wim suggests; however, before inserting those, I have a mod which I always find worthwhile before any signal component changes - namely the mains cable to oxygen free copper and the replacement of the cheap rectifiers with Schottky devices.

The idea is to avoid introducing RF noise at the mains input due to the reversing voltage switch-off spikes in the rectifiers. Schottky rectifiers are fine for simple transformer/rectifier/capacitor supplies as the reverse voltage is usually not too high for them. When it comes to switch-mode supplies, there is a little more to it.

The ALC0180s have four secondary diode rectifiers type ES3B with a fast 20nsec recovery time. Added to this, there is a RC snubber across each one. Clearly the designer was considering RF interference from these. However, other than cost, what I can't understand is why the mains input voltage rectifier is a 'Bog-Standard' GBL06 bridge type with no snubbers.

The GBL06 has no figures specified for its switch off time and can thus be assumed to not have that parameter optimised for low RF emission.

Mains voltage (230v in the UK) is far too much for a Schottky rectifier so I've searched out a fast, soft recovery type to use - namely Fairchild's FFPF04S60STU (Farnell 188-5724). Of course 4 of these TO-220F packaged devices are needed to be squeezed in where the bridge was but it is possible with care.

The result: The original was good, clear and revealing but slightly shouty and up front. The modified version sounds more relaxed and analogue-like.

Give it a try and post your impressions of the mod. (And don't touch anything with a mains voltage on it!).

Andy

'Bridge' rectifier picture attached.
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File Type: jpg Bridge(ish) Rectifier.jpg (123.1 KB, 1150 views)
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Old 25th May 2012, 09:49 AM   #36
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Default Changing MC33078 to OPA2604 on ALC0180-2300

Quote:
Originally Posted by wimdehaan View Post
I did replace the original MC33078 opamp (SMD) on my Abletec ALC0180-2300 board. I did change it for the OPA2604 (SMD). I have some experience with different opamps and the OPA2604 (SMD) is a safe and good choice.
The LM4562 and equiv. are not-my-cup-of-tea.

If you have the tools and experience do change the opamp, to my opinion the sound improved a lot.

Wim.
Following on from my posting on 11th April 2012, I've now changed the MC33078 op-amps on one of my two ALC0180s to OPA2604 as suggested by Wim.

Using an acoustic recording with plenty of space around the instruments (track 6, Crooked Still, Shaken by a Low Sound), I've tried again and again to hear any difference between the ALC0180s with the MC33078 and OPA2604.

Listening for any kind of detail or spacing of instruments or anything else, I can't honestly say I can hear any difference between the op-amps.

Having changed the high-voltage rectifier diodes first, the op-amps might have sounded different had I not done this; however, I'm not going to take them out!

Conclusion? I'll stick to upgrading the rectifiers first.

I'd be glad to hear of others' similar experiences.

Andy
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Old 27th December 2012, 02:56 PM   #37
bkdc is offline bkdc  United States
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The simplest answer is to use balanced inputs. The next best answer would be a transformer.
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Old 15th January 2013, 04:07 PM   #38
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Sorry to bump this thread, but does anyone know if there is any documentation available asides from the datasheet on the abletec website.

I am a noob to diy, i bought a few boards from profusion, i have 3x alc1000 and 6x alc0300. Trying to figure some things out but i am noob.
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Old 15th January 2013, 06:53 PM   #39
DaDude is offline DaDude  Norway
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Default Some info...

ALC1000

Mains connector
Pin 1= AC_N (Neutral)
Pin2= AC_L (Live)
Pin3= PE (protective Earth same as earth. Not needed).

Be careful pressing the contact.

PCB has contacts on the backside as well....
If you wish to connect balanced (with XLR) then Input+ to pin9 (IN+) at CON1 and signal- to pin10 (IN-) at CON1 and finally the signal to signal GND to pin8 (GND) at CON1. If you do single ended connect signal to pin9 and gnd to pin10+pin8.


ALC0300

Mains connectors
CON2= AC_L (Live)
CON3= AC_N (Neutral)
(No earth)

Balanced signal (with XLR) to input skal connect your signal+ to pin9 (IN+) at CON1 and signal- to pin10 (IN-) at CON1 and finally your signal GND to pin8 (GND) at CON1. If you do single ended connect signal to pin9 and gnd to pin10+pin8.

Hope this helps.

I did get better documentation by contacting Abletec directly, but can unforunately not find it at the moment.

Svein
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Old 22nd January 2013, 04:15 AM   #40
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does someone know how to connect a power led to this?

anyone know of some easy to integrate triggering circuitry?
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