Hi,
I can't wait to build this amplifier! 🙂
I have some questions so I'm asking for your kind help:
1) Is the BOM the one found on post 407? - http://www.diyaudio.com/forums/solid-state/245619-tgm8-amplifier-based-rod-elliot-p3a-41.html#post3977457
2) compensation caps - 100pF or 68pF?
3) The t.b.d. caps - do I have to test different values or just follow the values on the BOM?
4) What's the maximum diameter for the 4700uF filter caps on PCB? Does a 63V fits?
5) PSU - Is the filtering on the board enough or should I had an exterior bank of caps?
6) BD's transistores - are these the best or the KSA/SC are better?
7) Speaker protection - what's the minimum DC offset that triggers it?
8) Any thing else important I should be aware?
For now these are my questions.
Many thanks!
I can't wait to build this amplifier! 🙂
I have some questions so I'm asking for your kind help:
1) Is the BOM the one found on post 407? - http://www.diyaudio.com/forums/solid-state/245619-tgm8-amplifier-based-rod-elliot-p3a-41.html#post3977457
2) compensation caps - 100pF or 68pF?
3) The t.b.d. caps - do I have to test different values or just follow the values on the BOM?
4) What's the maximum diameter for the 4700uF filter caps on PCB? Does a 63V fits?
5) PSU - Is the filtering on the board enough or should I had an exterior bank of caps?
6) BD's transistores - are these the best or the KSA/SC are better?
7) Speaker protection - what's the minimum DC offset that triggers it?
8) Any thing else important I should be aware?
For now these are my questions.
Many thanks!
Is there a Mouser BOM? I mean, they don't have Stackpole resistors and so on. What would be an equivalente BOM?
I ask this because shipping charges from Mouser are less expensive and they have a method of shipping that I can pre-pay custom charges so the package passes to customs quickly and not stay there for a month.
As I never used or bought smd parts before I'm a bit lost...
I ask this because shipping charges from Mouser are less expensive and they have a method of shipping that I can pre-pay custom charges so the package passes to customs quickly and not stay there for a month.
As I never used or bought smd parts before I'm a bit lost...
Last edited:
Member
Joined 2009
Paid Member
I would expect you can get what you need from Mouser but I don't think anybody has posted a BOM for Mouser.
I used the Stackpole resistors because they had good specifications, were cheap and were available from my preferred supplier. I'm 100% sure that Mouser can offer you suitable resistors, there are many good manufacturers of surface mount resistors. Look at the specifications of the Stackpole resistors and see what Mouser carries that has similar specifications.
I used the Stackpole resistors because they had good specifications, were cheap and were available from my preferred supplier. I'm 100% sure that Mouser can offer you suitable resistors, there are many good manufacturers of surface mount resistors. Look at the specifications of the Stackpole resistors and see what Mouser carries that has similar specifications.
Member
Joined 2009
Paid Member
1) Is the BOM the one found on post 407? - Yes
2) compensation caps - 100pF or 68pF? - I used 100pF if I remember correctly - whatever it shows on the schematic in post 407 is what I used. But you might like to experiment with the values if you are experienced in such things.
3) The t.b.d. caps - do I have to test different values or just follow the values on the BOM? - just follow the values on the BOM. The schematic in post 407 shows the values too (unless my eyes are wrong?).
4) What's the maximum diameter for the 4700uF filter caps on PCB? Does a 63V fits? - if you look at the photos you'll see the caps are placed close to each other. So you need the same size as those in the BOM. You can find out what size that is by looking up the specs for the recommended parts in the BOM and then look for equivalent units in different voltages. You may have to accept a lower capacitance to get the size you want in a higher voltage - I don't think that is an issue, just buy a part from a reputable supplier for the right voltage. The parts I used are rated at 50V and up to 63V peak so they may be suitable for you too.
5) PSU - Is the filtering on the board enough or should I had an exterior bank of caps? - the filtering on the board is enough (I did put snubbers on the rectifier).
6) BD's transistores - are these the best or the KSA/SC are better? - I don't know, you could try whatever you have on hand providing they have sufficient voltage ratings. The BD's worked well for me.
7) Speaker protection - what's the minimum DC offset that triggers it? - I never measured it, but it's fairly low - in theory just what is needed to saturate a transistor (< 1V) but this increases as the frequency rises from d.c. so that a relatively large amplitude signal at subsonic frequencies could also trigger it.
8) Any thing else important I should be aware? - go slowly, solder all the small parts first. Look at the photos on this thread. Ask questions as you go. When you are ready to solder in the power devices first bolt them to a heatsink so that they are all flat and coplanar before you solder their leads to the pcb.
2) compensation caps - 100pF or 68pF? - I used 100pF if I remember correctly - whatever it shows on the schematic in post 407 is what I used. But you might like to experiment with the values if you are experienced in such things.
3) The t.b.d. caps - do I have to test different values or just follow the values on the BOM? - just follow the values on the BOM. The schematic in post 407 shows the values too (unless my eyes are wrong?).
4) What's the maximum diameter for the 4700uF filter caps on PCB? Does a 63V fits? - if you look at the photos you'll see the caps are placed close to each other. So you need the same size as those in the BOM. You can find out what size that is by looking up the specs for the recommended parts in the BOM and then look for equivalent units in different voltages. You may have to accept a lower capacitance to get the size you want in a higher voltage - I don't think that is an issue, just buy a part from a reputable supplier for the right voltage. The parts I used are rated at 50V and up to 63V peak so they may be suitable for you too.
5) PSU - Is the filtering on the board enough or should I had an exterior bank of caps? - the filtering on the board is enough (I did put snubbers on the rectifier).
6) BD's transistores - are these the best or the KSA/SC are better? - I don't know, you could try whatever you have on hand providing they have sufficient voltage ratings. The BD's worked well for me.
7) Speaker protection - what's the minimum DC offset that triggers it? - I never measured it, but it's fairly low - in theory just what is needed to saturate a transistor (< 1V) but this increases as the frequency rises from d.c. so that a relatively large amplitude signal at subsonic frequencies could also trigger it.
8) Any thing else important I should be aware? - go slowly, solder all the small parts first. Look at the photos on this thread. Ask questions as you go. When you are ready to solder in the power devices first bolt them to a heatsink so that they are all flat and coplanar before you solder their leads to the pcb.
Member
Joined 2009
Paid Member
No I haven't tried that. I expect there are a quite a few interesting combinations possible using this pcb. For example, you could have
BJT only
IRF only
BJT in Class AB and IRF in Class C (default)
BJT and IRF both in Class AB
Use two BJTs with no IRF
Use... well, you get the picture, you can try many things!
Member
Joined 2009
Paid Member
Two more questions:
What are the resistors that most influence sound quality? (My ideia is to buy 0.1% thin film for these and thick film for the rest).
Can I use 0.25W (easier to source and less expensive) instead of 0.5W?
Thanks.
What are the resistors that most influence sound quality? (My ideia is to buy 0.1% thin film for these and thick film for the rest).
Can I use 0.25W (easier to source and less expensive) instead of 0.5W?
Thanks.
Paulo, R1, R2 & R10 will have the biggest influence on sound quality. You can go 0.1% but more important IMHO is to chose ones with a low tempco. for thermal stability.
Edit, you should be able to get away with 250mW in most locations except where 1W or higher is specified. I suspect that R14 and R18 will need to be at higher. In the case of R18 you could get away with a 250mW if you dropped it to 33R or thereabouts. This is speculation on my part - I'd have to do the math, which is time consuming and uninspiring.
Edit, you should be able to get away with 250mW in most locations except where 1W or higher is specified. I suspect that R14 and R18 will need to be at higher. In the case of R18 you could get away with a 250mW if you dropped it to 33R or thereabouts. This is speculation on my part - I'd have to do the math, which is time consuming and uninspiring.
Last edited:
Member
Joined 2009
Paid Member
I'm not convinced that fancy resistors will be audible but in general, anything that is outside of the feedback loop can not be linearized by it and so requires extra care. This means R1, R2, R5, R8 and R10. For caps it will be C1, C2 and C3. And for semiconductors it is Q1, which forms the all too important feedback error amplifier.
Last edited:
Yeah I'm not into exotic resistors either. I used the Stackpole resistors that Bigun specified and they worked well.
thin film smd resistors use the same "metal film" that we all use as good quality through hole resistors.
thick film smd are equivalent to metal oxide.
The only resistor type better than thin film is solid metal in either strip, or wire.
thick film smd are equivalent to metal oxide.
The only resistor type better than thin film is solid metal in either strip, or wire.
I'm not going to use any expensive boutique resistors, the problem is that Mouser doesn't carry 1% thin film, only 1% thick film or 0.1% thin film. The thin film are much more expensive because they are 0.1% and 0.5W even more expensive. So I thought I could use thick film for the less important parts and thin film for the more important. The resistors from the BOM are the best of both worlds - they are thin film and 1%, so quality resistors but not expensive. I can't get them.
Of course, I can't order from Digikey because of the 'hidden' handling fees that the shipping company charges at delivery, something like 100 € or more, and I'm not talking about customs duties, with Mouser there are no hidden fees and duties are pre payed, so there are no 'surprises' at delivery.
Last edited:
Edit: I found some 1% thin film at Mouser but only rated at 250mW. I'm tempted to buy these. Should I?
Do it.
R14 and R18 will need to be higher as I explained above, but the other values with unspecified wattages should be fine with 250mW.
R14 and R18 will need to be higher as I explained above, but the other values with unspecified wattages should be fine with 250mW.
Member
Joined 2009
Paid Member
I'm not even sure that you need 1%, most likely 5% is fine. The resistors that set the gain would benefit from 1% matching, maybe, but otherwise there isn't much need for the higher tolerance parts. I used 1% because they were so easily available from digikey.
If you get stuck, I can order parts from Digikey and mail them to you 🙂
If you get stuck, I can order parts from Digikey and mail them to you 🙂