Amp Build Diary

[Chienmortbb]

Hopefully I can post some more pics later asI have completed the mains and speaker wiring.

One of the many things I have had confirmed since starting this project is that an Amos quoted power has little to do with its real world output.

I don't know about valve amps, but ever snce the first solid state amp, the output powers have been quoted into 4 ohms when most speakers are 8 ohms as standard.

So if we look at my old BLX130 Trace combo, it was 80 watts into the internal 8 ohm speaker, reaching its quoted 130 watts only when an extension cab of 8 ohms was connected, most combos with a speaker out are the same although some disconnect the internal speaker when the external can is connected.

One point worth making here is that you should never plug or unplug s speaker when the amp is switched on.

So my amp module on this build is the BoYoHo My1-251 rated at 260eatts into 8 ohms and 500 watts into 4 ohms. Sounds great but there is a caveat. This rating assumes music inputs where the average power is 1/8 the peak power. BoHoYo are not alone. ICEPower also use the 1/8 figure. The 250ASX2 is used in the Tonehammer 500 but without thermal help only outputs about 60 watts continuos. Aguilar uses two fans to cool the 250ASX2 but no extra heatsink. While this approach works, relying totally on two fans will eventually fail. As fans age they shift less and less air and will eventually not be able to keep
the amp cool and the amp will shut down. A heatsink is as efficient at year 25 as it was on the day it was installed.

So to enable the amp to be used at higher average powers we need to cool the amp and that either means fans or bigger heatsinks or both, I try to avoid using fans as they are often they are less reliable component and can be noisy. That is why I added the extra heatsink to my build.

[Chienmortbb]

Yesterday was Chemo day so I did not have time to upload the latest pics.

Attached is the latest pic of the build. I have wired the mains and the speaker connections. I have added a ferrite core around them mains input. It is the cream coloured blob. This adds little to the amp itself although it will filter some of the high frequencies present on the mains. However its main purpose is to stop interference being injected back into the mains.

You can also see the speaker cable attached to the upper left hand rail. The supplied cable was too short to reach the speakons so I used a "chocolate block" to connect the speakon cables. The reason for attaching the speaker cable by cable ties is to ensure that there's no excess pull on the connector on the PCB. The cable is quite stiff and the cable tie acts as strain relief.

On the right you can just see the fuse board mounted to the right hand side of the case. These protect the auxiliary supplies from the aim amps power supply from short circuits or failures of the pre amp power supplies. I just need to connect the wires to the fuses then I can test the main amp and pre amp power supplies.

Edited July 3, 2015 by Chienmortbb

[Chienmortbb]

I have started to assemble the preamp board, the one shown in all the pictures to date was the Rev 1.0 PCB that is going into my combo rebuild later.

The preamp has all the resistors and the IC sockets installed and I will be installing all the capacitors tomorrow. The capacitors are last because they are tallest.

Although there are three IC sockets, each IC has 2 operational amplifiers. So six gain stages but as the ICs are audiophile quality, and because Charlie (passinwind) tweeks over and over again for the best performance/noise figures going.

Passinwind has designed Valve preamps for at least one well known bassist and although the EQ borrows from that design, he uses this solid state design himself in both the integrated 500W amp and the small form factor 700W design pictured in an earlier post.

[Passinwind]

I can tell you're making real progress now by all the emails asking for clarification of my shockingly shoddy documentation. There are so many little details that I've just taken for granted, things I've changed eleven times then changed back, and so on. As you say, I have been using this design pretty happily for a couple of years now though, so hang in there.

My latest tangent is an onboard preamp based on a simplified version of that board in your last post. Just bass, mid, and treble controls, with mid frequency switchable to three frequency centers. It was a challenge to make it small enough to fit in my target bass, but it is done and I should be auditioning it in the next day or two.

[Chienmortbb]

Ironically the omissions make for a more satisfying build. I am studying the circuit diagram/schematic more closely than I would if documentation were 100% and learning more as I go.

The Pre amp board is now complete apart from the wiring. Some of the components are now mounted off board as the preamp was designed before the HPF/PEQ circuit and taking components off board allows us to configure the circuits to the best arrangement.

Below is the picture of the completed board. It still needs to be wired but I will leave that until the front panel is complete. As you can imagine I am taking more time and care over the front panel as it will be on show more than the back panel.

Edited July 14, 2015 by Chienmortbb

[Passinwind]

[quote name='Chienmortbb' timestamp='1436874748' post='2821527']
Ironically the omissions make for a more satisfying build. I am studying the circuit diagram/schematic more closely than I would if documentation were 100% and learning more as I go.

The Pre amp board is now complete apart from the wiring. Some of the components are now mounted off board as the preamp was designed before the HPF/PEQ circuit and taking components off board allows us to configure the circuits to the best arrangement.

Below is the picture of the completed board. It still needs to be wired but I will leave that until the front panel is complete. As you can imagine I am taking more time and care over the front panel as it will be on show more than the back panel.
[/quote]

Nice job. Are you using a pot for setting final stage gain where R24 would go?

And I also agonize a lot more about front panels than the back ones.

[Chienmortbb]

Now I would appreciate some suggestions. The system is very flexible. I can choose to switch various circuits in or out. So the questions I am going over are:

1. Should I have the HPF switchable? Pasdinwind dies but after using his amp for some months he leaves it on all the time.

2. Effects return can be configured as series or parallel. Most Amps are currently series but parallel allows some local control over the wet/dry signal mix. Oh and should those the switch and EFX return level control be on the front or back?

3. The Parametric EQ section gives me control of the mids from about 100Hz to. 2000Hz and of course this overlaps the fixed middle control. It is worth adding a switch to change the fixed mid frequency? It makes the amp more flexible but more complex.

4. Active/Passive switching and gain change. Passinwind has only active basses while I have currently only passive ones. At least one of my bases will be converted to active in the next few months with a variation of the two band MM preamp but I want to have the ability to have the two options. So two Jack sockets or one Jack plus an Active/Passive switch?

I would appreciate any comments based on experience.

[Chienmortbb]

[quote name='Passinwind' timestamp='1436882283' post='2821661']


Nice job. Are you using a pot for setting final stage gain where R24 would go?

And I also agonize a lot more about front panels than the back ones.
[/quote] You spotted the deliberate mistake.Actually I cannot find that value at the moment so I am going through my stash to find it.
I was not planning to have a pot but now you mention it it could be a good idea. One issue though is that using a pot cups put the gain close to 1. ( or -1 as th opamp is inverting) the plan is to use LM4562 as the output opamp and this works well at unity gain. Other similar opamp a such as NE5532 becomes unstable at unity gain so a pot would probably need a series resistor to ensure stable operation if other opamps are to be used.

Having said that I think I have just talked myself out of using anything but the LM4562.

Edited July 14, 2015 by Chienmortbb

[Passinwind]

[quote name='Chienmortbb' timestamp='1436883217' post='2821675']
You spotted the deliberate mistake.Actually I cannot find that value at the moment so I am going through my stash to find it.
[/quote]

That particular value was used because I have a stash of ultra low noise resistors found on eBay that happened to be 18.7K ohms. I bought 100, at something less than 5 cents apiece. There are many great deals out there on oddball values that get surplussed when a production run ends. I would leave that one in there and stick with the gain staging arrangement as-is in that spot. A pot would vary output impedance along with gain, which may or may not actually matter to you, probably more so if using an output transformer.

On my newer build I didn't bother with an HPF bypass. I used that position for an active/passive switch instead, making the front end impedance switchable from 18.7K to 330K. Doing it that way keeps the 330K resistor out of the circuit when not in use, cutting thermal noise a little. Little things add up though, and it could be that the switch wiring will be noisier than that resistor. This is stuff that's pretty specific to your build though.

The effects I use are mostly time domain ones, which a parallel config usually works a little better for IME. I also like to use the EFX return as a mixer, adding another bass preamp or even a vocal feed for quick and easy monitoring at rehearsals. Could be handy for piping in canned music as well. The way I have set the board up allows both series and parallel operation if you want maximum flexibility. Series loop normalling jacks are a notorious failure point though, FWIW.

Edited July 14, 2015 by Passinwind

[Chienmortbb]

I hAve finally completed fitting and soldering the Pre Amp PCB and the High Pass Fillter & Parametric Equaliser PCB. They are pictured now in place on the chassis.

Edited July 24, 2015 by Chienmortbb

[Chienmortbb]

Seems like two steps forward and one step back at the moment. I was doing a parts order and added some tiny 9mm pots from AlphaTaiwan. One was for the FX return level control. Unfortunately I did not read the spec carefully enough and I got a PCB mounted pot with a knurled shaft. It is not chassis mount.

So as I did not want a big knob on the back panel that was proud of the back of the case, I set about mounting the pot on some stripboard with the idea to mount it on pillars, it worked quite well as you can see in the pictures attached.

As I was tightening the slotted screws that held the stripboard and pot, the screwdriver slipped and gouged the back panel. I did a test spot of brush applied varnish and it seemed to work well but over a larger it looked terrible. So I disassembled the panel, rubbed it down then applied the last of the spray lacquer I had. Not great but just about passes muster.

[Passinwind]

[quote name='Chienmortbb' timestamp='1438988231' post='2839316']

As I was tightening the slotted screws that held the stripboard and pot, the screwdriver slipped and gouged the back panel. I did a test spot of brush applied varnish and it seemed to work well but over a larger it looked terrible. So I disassembled the panel, rubbed it down then applied the last of the spray lacquer I had. Not great but just about passes muster.
[/quote]

Your back panel looks a lot more finished than any of mine ever have! Hope you get to actually playing bass through this soon.

[Chienmortbb]

Tomorrow is my eye operation so another delay. However I powered up the amp and power supplies today all work well.

[Phil Starr]

Good luck tomorrow.

[Chienmortbb]

Thanks Phil. If it is OK with you I will send the amp to you when it is finished so you can tell
mewhat you think. With my eye and my wife's illness I will not be gigging for a while. It would be great to get some feedback especially as I decided on the power output based on your 1x12 cab design.

Don't hold you breath though it will be a month or more.

[Chienmortbb]

[attachment=199859:2015-09-01 19.33.48.jpg]Looking good?

[Passinwind]

Thumbs up!

[LukeFRC]

Get well soon man!

[BigRedX]

[quote name='Chienmortbb' timestamp='1436882291' post='2821662']
Now I would appreciate some suggestions. The system is very flexible. I can choose to switch various circuits in or out. So the questions I am going over are:

1. Should I have the HPF switchable? Pasdinwind dies but after using his amp for some months he leaves it on all the time.

2. Effects return can be configured as series or parallel. Most Amps are currently series but parallel allows some local control over the wet/dry signal mix. Oh and should those the switch and EFX return level control be on the front or back?

3. The Parametric EQ section gives me control of the mids from about 100Hz to. 2000Hz and of course this overlaps the fixed middle control. It is worth adding a switch to change the fixed mid frequency? It makes the amp more flexible but more complex.

4. Active/Passive switching and gain change. Passinwind has only active basses while I have currently only passive ones. At least one of my bases will be converted to active in the next few months with a variation of the two band MM preamp but I want to have the ability to have the two options. So two Jack sockets or one Jack plus an Active/Passive switch?

I would appreciate any comments based on experience.
[/quote]

I don't know much about the technicalities of amp design, but from an end user PoV:

2. Both are effective. Personally I couldn't consider an amp that only had a parallel effects loop but sometimes it is more appropriate. What I would like to see is a socket switching system that bypassed the whole loop if either the send or return cable was unplugged.

4. Active/passive is really just about having 2 preset gain levels, and in many cases is a bit of a misnomer since I own passive basses with a higher output than many active ones. I'd rather see two inputs each with their own gain control and clip light so that the amp can be set up for use with any two basses and the relative levels adjusted to suit your needs.

[Passinwind]

[quote name='BigRedX' timestamp='1441186521' post='2856682']

4. Active/passive is really just about having 2 preset gain levels, and in many cases is a bit of a misnomer since I own passive basses with a higher output than many active ones. I'd rather see two inputs each with their own gain control and clip light so that the amp can be set up for use with any two basses and the relative levels adjusted to suit your needs.[/quote]

My active/passive switching scheme is just about input impedance; it's up to the user to adjust the volume control, which is several stages deep into the circuit. To do preset volumes for two inputs is not difficult, it's just not within my own preferred set of tradeoffs. My hope is that since Chienmort actually uses and cares about passive basses, he will figure out whatever enhanced feature set works for that application. I've been learning a lot about that myself recently as I work through prototype onboard preamp designs, it is a pretty huge and interesting rabbit hole actually.

[Beer of the Bass]

Something I've wondered about active/passive inputs and impedance; I'm well aware of the benefits of a high impedance input for passive instruments, but is there any compromise in performance when plugging an active bass into a high impedance input, gain issues aside?

[Passinwind]

[quote name='Beer of the Bass' timestamp='1441210368' post='2856981']
Something I've wondered about active/passive inputs and impedance; I'm well aware of the benefits of a high impedance input for passive instruments, but is there any compromise in performance when plugging an active bass into a high impedance input, gain issues aside?[/quote]

Yes, for starters noise floor is at least theoretically a bit worse, but as always, that depends on nuances of circuit design, both for the active bass preamp and the input circuit it plugs into. A single 1 Meg resistor is actually noisier than the opamps I use in the front end, especially if it's an old school carbon comp one. Many passive pickups are perfectly happy with a substantially lower load than 1 Meg, so I prefer to design on a case by case basis. And of course, how much noise floor matters to you is highly dependent on your playing situations.

There are also certain stability issues that crop up more often in higher impedance circuits, which can necessitate band-aid solutions that may or may not bug some people. You can probably guess where I fall on this one. The beauty (and curse) of DIY building is that one can obsess over any little thing that others may often ignore perfectly blissfully.

[Chienmortbb]

After my eye op I have had trouble as my new lens is quite different to my other eye.That is due to be operated on next month. So no need e work has been done. I have been running the power amp on its own using my Korg AX3000B as a preamp.

Although the AX3000B has a reletively low output but the amp iseems to have so much in reserve. I was a little concerned earlier when the amp got a little warm. However I realised it was in the sun all day.

One thing I have confirmed is that the Powercon for the mains. That is the blue plug in the pictures. It locks really well and fils you with a confidence that the IEC does not.

You can also see the speaker cable (Orange) connected via the speakon/Jack combo connector. The Orange cable is 2 metres of 2 core mains cable. Over the distance from amp to cab there is no need for a monster cable.

[Passinwind]

[quote name='Chienmortbb' timestamp='1446402011' post='2899125']
After my eye op I have had trouble as my new lens is quite different to my other eye.That is due to be operated on next month. So no needed work has been done. I have been running the power amp on its own using my Korg AX3000B as a preamp.[/quote]

Here's hoping the second operation goes as well as the first one. My old eyes have really been put to the test recently as I've been hand soldering some surface mount prototype onboard preamp stuff:



My wife brought home a really nice magnifier light as an early Christmas gift, but it turned out that she had overpaid badly, so back it went. I'll just get the one I really wanted eventually, but for the moment I'm done with this particular tangent anyway. I managed to port the same EQ scheme used in the boards pictured upthread to a much more compact format that works fine on a single 9V battery, something I wasn't at all confident in my ability to do.

[Chienmortbb]

The second operas just as duccesful but other things have delayed the project. You may remember that I stated this thread when my wife was ill. She got progressively worse and I took on the role of full time carer. Sadly she died in June. I am still sorting out the many problems bereavement caused but I will be continuing the project soon.

Edited September 5, 2016 by Chienmortbb