Replacing A1 Module With A2 Module
The original Goldmund Mimesis amplifiers (Mimesis 9.2, Mimesis 3, and Mimesis 6) had A1 modules, as are shown in the attached schematic. These amplifiers had a magical sound that we are all trying to replicate. Alex's PCB has been designed to use all original parts, including everything from the A1 module.
There has been some complaining that normally T6 (BC182B) transistor should have its C-B shorted and not E-B. In the A1 module, Goldmund has always shorted E-B. I don't know their reason for doing so, could be noise issues, etc. But that's how it's supposed to be if you're going to build a clone of the fantastic sounding original Goldmund Mimesis amplifier.
New Goldmund amplifiers have used the upgraded A2 modules and more recently have been using a brand new unpotted version of the A2 module. These modules use all new transistors, a different resistor, and have an added capacitor. Bellow is what you'll need to replace in order to upgrade the A1 module to A2 module. PLEASE READ CAREFULLY!!!!
1.) Replace T3 (BC546B), T4 (BC546B), T5 (BC182B), and T6 (BC182B) with MPSA42 transistors.
2.) On T6 (the now new MPSA42), short C-B instead of E-B. This can be easily accomplished without any modifications to the PCB. BC182B's leg pin out is CBE and MPSA42's leg pin out is EBC. Simply solder in the new transistor facing the same way.
3.) Bypass the 6V Zener diode with a 1u film capacitor. The capacitor can simply be soldered to the bottom of the PCB without any changes.
4.) Replace R11 (20K) resistor with a 10K resistor.
5.) Change the BIAS resistor R23 (330R) by soldering in parallel a 1K to 1K5 resistor. Goldmund's service manual gives a range here, so if you have used a 1K5 resistor and the MOSFETS are overheating, you'll have to go with the lower 1K resistor value.
This info is directly from Goldmund's service manual. After the changes, the amplifier should perform 100% correctly.
Now everyone can stop crying about the T6 transistor being improperly connected and use an A2 module where C-B is shorted instead of E-B.
The original Goldmund Mimesis amplifiers (Mimesis 9.2, Mimesis 3, and Mimesis 6) had A1 modules, as are shown in the attached schematic. These amplifiers had a magical sound that we are all trying to replicate. Alex's PCB has been designed to use all original parts, including everything from the A1 module.
There has been some complaining that normally T6 (BC182B) transistor should have its C-B shorted and not E-B. In the A1 module, Goldmund has always shorted E-B. I don't know their reason for doing so, could be noise issues, etc. But that's how it's supposed to be if you're going to build a clone of the fantastic sounding original Goldmund Mimesis amplifier.
New Goldmund amplifiers have used the upgraded A2 modules and more recently have been using a brand new unpotted version of the A2 module. These modules use all new transistors, a different resistor, and have an added capacitor. Bellow is what you'll need to replace in order to upgrade the A1 module to A2 module. PLEASE READ CAREFULLY!!!!
1.) Replace T3 (BC546B), T4 (BC546B), T5 (BC182B), and T6 (BC182B) with MPSA42 transistors.
2.) On T6 (the now new MPSA42), short C-B instead of E-B. This can be easily accomplished without any modifications to the PCB. BC182B's leg pin out is CBE and MPSA42's leg pin out is EBC. Simply solder in the new transistor facing the same way.
3.) Bypass the 6V Zener diode with a 1u film capacitor. The capacitor can simply be soldered to the bottom of the PCB without any changes.
4.) Replace R11 (20K) resistor with a 10K resistor.
5.) Change the BIAS resistor R23 (330R) by soldering in parallel a 1K to 1K5 resistor. Goldmund's service manual gives a range here, so if you have used a 1K5 resistor and the MOSFETS are overheating, you'll have to go with the lower 1K resistor value.
This info is directly from Goldmund's service manual. After the changes, the amplifier should perform 100% correctly.
Now everyone can stop crying about the T6 transistor being improperly connected and use an A2 module where C-B is shorted instead of E-B.
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"This should be very interesting for all potential builders of the Goldmund Mimesis 9.2 clone. This information is straight from the official Goldmund service manuals and schematics.
One of the obsolete (but still abundantly available) transistors that Goldmund Mimesis 9.2 uses is the Motorola BSS71/BSS74 (T11 and T12 in Alex's schematic, please see attachment). In addition, the Motorola MPSA93/MPSA43 (T7, T8, T9, and T10) are also obsolete. Wouldn't it be nice to change all of these transistors with the current production of MPSA92/MPSA42? This change is not only possible, but very easy to implement. No changes are necessary to the PCB board's layout, so potential builders can build it any way they choose.
Bellow, on the right is the original part and on the left is the new replacement part that needs to be substituted in order to make this change. Again, this is all as per Goldmund.
(NOTE: For the protection circuit, MPSA93/MPSA43 can be replaced with MPSA92/MPSA42 without any further changes.)
T7 (MPSA93) = MPSA92
T8 (MPSA93) = MPSA92
T9 (MPSA43) = MPSA42
T10 (MPSA43) = MPSA42
T11 (BSS71) = MPSA42
T12 (BSS74) = MPSA92
C8 (100uF) = 150uF
C11 (100uF) = 150uF
C1 (47pF) = 100pF
C3 (4.7pF) = 8.2pF
C5 (4.7pF) = 8.2pF
C6 (4.7pF) = Omitted
R10 (1K) = 1K5
R22 (30K) and R19 (30K) = Replace with a single 10K
R20 (270) = 330
That's it!"
Hi Nagys,
What about C7 (4.7p) capacitor? Should be omitted or not ?
Best regards
One of the obsolete (but still abundantly available) transistors that Goldmund Mimesis 9.2 uses is the Motorola BSS71/BSS74 (T11 and T12 in Alex's schematic, please see attachment). In addition, the Motorola MPSA93/MPSA43 (T7, T8, T9, and T10) are also obsolete. Wouldn't it be nice to change all of these transistors with the current production of MPSA92/MPSA42? This change is not only possible, but very easy to implement. No changes are necessary to the PCB board's layout, so potential builders can build it any way they choose.
Bellow, on the right is the original part and on the left is the new replacement part that needs to be substituted in order to make this change. Again, this is all as per Goldmund.
(NOTE: For the protection circuit, MPSA93/MPSA43 can be replaced with MPSA92/MPSA42 without any further changes.)
T7 (MPSA93) = MPSA92
T8 (MPSA93) = MPSA92
T9 (MPSA43) = MPSA42
T10 (MPSA43) = MPSA42
T11 (BSS71) = MPSA42
T12 (BSS74) = MPSA92
C8 (100uF) = 150uF
C11 (100uF) = 150uF
C1 (47pF) = 100pF
C3 (4.7pF) = 8.2pF
C5 (4.7pF) = 8.2pF
C6 (4.7pF) = Omitted
R10 (1K) = 1K5
R22 (30K) and R19 (30K) = Replace with a single 10K
R20 (270) = 330
That's it!"
Hi Nagys,
What about C7 (4.7p) capacitor? Should be omitted or not ?
Best regards
I am just confused what voltage is that? and the power in rms for this amp, my wish is to make my own car amp so will I need to make a power supply? the voltage is confused for me ........... 60volts ac plus +80 and -80volts??????? 3 kind of voltages! do I need t toroidal transformer?
Sounds like nuts :
It seems that I do not have a copy of the protection schematic. Can someone point to me where I can find it?
It seems that I do not have a copy of the protection schematic. Can someone point to me where I can find it?
Bigpanda - Here's the protection circuit's schematic:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Hi Nagys,
I thought I had seen a software drawn version of it in some post. Just want to try and see if anyone had it or remember where it was. If not, I will go thru the thread all the way and find it. That is a whole 100 pages.... And if I didn't remember it right, I may just waste my time.
BTW, did alex hand you the gerbers or the original sprint files? I think it is time I have to get them ready for the fab. house.
Since ferynov was mentioning the 10000uf cap. -- do you think you can get 30mm diameter caps with 10000uf? Because I doubt if I can in my place. It could be a problem for me. All I have used before are 35mmD.
I thought I had seen a software drawn version of it in some post. Just want to try and see if anyone had it or remember where it was. If not, I will go thru the thread all the way and find it. That is a whole 100 pages.... And if I didn't remember it right, I may just waste my time.
BTW, did alex hand you the gerbers or the original sprint files? I think it is time I have to get them ready for the fab. house.
Since ferynov was mentioning the 10000uf cap. -- do you think you can get 30mm diameter caps with 10000uf? Because I doubt if I can in my place. It could be a problem for me. All I have used before are 35mmD.
I have a search engine for a brain, and know how to write queries and look for Alex and protection. Hehehehe.... I knew about where to start looking too...
Thanks
Thanks
Bigpanda - Yes, 10,000uF capacitors are available in 30mm diameters. I think in this PCB a 35mm will fit also. Plus, the original schematic only calls for 4700uF capacitors, those and 6800uF capacitors can definitely be found with 30mm diameters.
Should I ask Alex to draw in 35mm?
He did not send me any files yet, he should probably send them directly to you. The circuit board is good to go, the only thing that I'm still waiting on is for Alex to change the positions of C33/C32 and C36/C35.
Should I ask Alex to draw in 35mm?
He did not send me any files yet, he should probably send them directly to you. The circuit board is good to go, the only thing that I'm still waiting on is for Alex to change the positions of C33/C32 and C36/C35.
Hello from a first time poster.
I've read through the entire main thread and am really interested in this project. However, I don't have any electronics experience and noticed the warnings about this being an expert build. I'm wondering if I could find someone in the UK to build this for me, because if it turns out as well as it should, I guess it will be pretty special.
I have a couple of questions. Has anyone thought about doing a group buy for all of the components, or would most people have much of what they need? I wouldn't know where to start with this.
And roughly what do you think the total cost of all the components will be on top of the PCB price.
Is shipping to the UK a possibility?
And finally, since each of these are discrete boards, would it be theoretically possible to build a 5 channel amp for home cinema?
Thanks
Steve
I've read through the entire main thread and am really interested in this project. However, I don't have any electronics experience and noticed the warnings about this being an expert build. I'm wondering if I could find someone in the UK to build this for me, because if it turns out as well as it should, I guess it will be pretty special.
I have a couple of questions. Has anyone thought about doing a group buy for all of the components, or would most people have much of what they need? I wouldn't know where to start with this.
And roughly what do you think the total cost of all the components will be on top of the PCB price.
Is shipping to the UK a possibility?
And finally, since each of these are discrete boards, would it be theoretically possible to build a 5 channel amp for home cinema?
Thanks
Steve
Nagys,
Do you think it is better if we have components' ID on the board rather than the value itself. If I have the sprint files, I can change into that. Let's leave alex out of this tedious work. Should take me less than a day's work to do it.
Do you think it is better if we have components' ID on the board rather than the value itself. If I have the sprint files, I can change into that. Let's leave alex out of this tedious work. Should take me less than a day's work to do it.
Bigpanda - I really have no preference one way, or the other. Go with whatever you think will be easier for most builders.
Alex has created his latest PCB which will now use TO3 MOSFETS. He has done an incredible board. Unless anyone objects, I strongly suggest that we go with the TO3 PCB. Metal can MOSFETS sound significantly better than plastic MOSFETS. These are readily available from nearly all electronics distributors including Newark and Farnell. Here's a list of some readily available equivalent MOSFETS to the Hitachi 2SK134/2SJ49:
Magnatec BUZ900/BUZ905
Magnatec BUZ901/BUZ906
Exicon ECF10N16/ECF10P16
Exicon ECF10N20/ECF10P20
Here's the latest beautiful PCB from Alex:
Alex has created his latest PCB which will now use TO3 MOSFETS. He has done an incredible board. Unless anyone objects, I strongly suggest that we go with the TO3 PCB. Metal can MOSFETS sound significantly better than plastic MOSFETS. These are readily available from nearly all electronics distributors including Newark and Farnell. Here's a list of some readily available equivalent MOSFETS to the Hitachi 2SK134/2SJ49:
Magnatec BUZ900/BUZ905
Magnatec BUZ901/BUZ906
Exicon ECF10N16/ECF10P16
Exicon ECF10N20/ECF10P20
Here's the latest beautiful PCB from Alex:
Attachments
Vetinry - Group buy for components is not a good idea because everyone will have a preference on what they want to use and which version of the amplifier to build. All the parts are readily available. Since you're in the UK, I would suggest Farnell as your primary source. Other popular electronic parts distributors are: Newark, Mouser, and Digi Key. The hardest part to find will be the 2N5565 jfets, but I've included plenty of links where builders can get them in this thread.
Yes, you can build a 5 channel amplifier.
As for total cost, it depends on the quality of components that you'll purchase. MOSFETS, transformers, heatsinks, chassis, and large capacitors will be the most expensive items. You'll probably be looking at roughly $700 for a stereo amplifier.
I'm sure Bigpanda will be able to ship the boards to the UK.
This is a fairly simple and straightforward kit. But as with anything of this nature, some experimentation could be required. Having basic electronic knowledge is definitely a plus. That shouldn't scare you away, learn as you go along, it will be fun.
Yes, you can build a 5 channel amplifier.
As for total cost, it depends on the quality of components that you'll purchase. MOSFETS, transformers, heatsinks, chassis, and large capacitors will be the most expensive items. You'll probably be looking at roughly $700 for a stereo amplifier.
I'm sure Bigpanda will be able to ship the boards to the UK.
This is a fairly simple and straightforward kit. But as with anything of this nature, some experimentation could be required. Having basic electronic knowledge is definitely a plus. That shouldn't scare you away, learn as you go along, it will be fun.
@vetinry
It should scare you away, and it is irresponsible of NagysAudio to encourage a beginner to embark on the outlay of so much cash on an unproven design. It won't be fun, it will be Hell. A heartbreaker.
I wouldn't recommend this project to a seasoned builder, and they haven't even got one aboard, or he'd be making the same recommendation to you that I'm making. Don't do it.
w
DX for begginners
@vetinry, try DX amps. Fully tested and approved for begginners. Then, some day, come back and try this one. By the way, DX Blame ST is easier to assemble, with parts truly readly available, and not that expensive at all! And, best of all, superbly sounding amp! Some guys have built 5 units for home theater as well. So...
Typical mentality of someone who doesn't want to learn anything new, progress, and advance. If everyone was scared of the unknown and didn't want to learn anything new, where would we be as a human race?
Vetinry read the entire thread and was inspired enough to show interest. I say good for him! He's at the very least interested in electronics and this could be a great and challenging project for him.
Vetinry go ahead and challenge yourself, make mistakes, fix mistakes, read about electrical circuits, ask for help on this forum or others if you get stuck, learn something new and interesting and your reward will be far greater than just a fantastic sounding amplifier 🙂
Vetinry read the entire thread and was inspired enough to show interest. I say good for him! He's at the very least interested in electronics and this could be a great and challenging project for him.
Vetinry go ahead and challenge yourself, make mistakes, fix mistakes, read about electrical circuits, ask for help on this forum or others if you get stuck, learn something new and interesting and your reward will be far greater than just a fantastic sounding amplifier 🙂