Guys,
If I put fuses on the PSU after the filter capacitors, what safe value should
I choose? Sorry kinda' too lazy to work with the calculations and my net access is crawling
In the PC board it uses 2 fuses, the - + rail and thats x2 for a stereo but on the PSU I will only be using 2 fuses right?
If I put fuses on the PSU after the filter capacitors, what safe value should
I choose? Sorry kinda' too lazy to work with the calculations and my net access is crawling
In the PC board it uses 2 fuses, the - + rail and thats x2 for a stereo but on the PSU I will only be using 2 fuses right?
If you use only one pair of fuses for both amplifiers, you will not protect anything correctly (other than the power supply). The two pairs of 3A fuses can be positioned on the PSU or the amplifiers but you should use a separate pair for each amplifier as the schematic suggests by including the fuses on the amplifier schematic. 60-80W Power Amplifier
My build is pretty compact onboard fuses are omitted, I currently have one fuse located at the AC mains but I was thinking of installing a crowbar dc fault protect. I know its not a wise thing to do because of its possibility to destroy other components right on its path when it triggers. (hopefully it won't happen)
I like this circuit for its dormant state (passive) no power is required and does not seem to intervene with the circuitry unless called for action (only in the event of a DC fault).
I do not want to put relays at the moment because it will be needing add'l external PSU and the board is somewhat larger. I have read that fuses is a must when implementing crowbar circuit.
Any thoughts on the matter?
I like this circuit for its dormant state (passive) no power is required and does not seem to intervene with the circuitry unless called for action (only in the event of a DC fault).
I do not want to put relays at the moment because it will be needing add'l external PSU and the board is somewhat larger. I have read that fuses is a must when implementing crowbar circuit.
Any thoughts on the matter?
Attachments
Member
Joined 2009
Paid Member
Yes, you can mount the fuses anywhere you find convenient and safe. Even in-line fuseholders for automotive/solar 12V systems will be fine. However, crowbar protection for small amplifiers is a waste of resources, in my experience, You will likely find that for every time it protects your amplifier, even a carefully set crowbar trigger will just as soon cause the destruction of both amplifier and fuses.
It seems to be a more reliable protection system in very large amplifiers, though they can suffer occasional disasters too. Try the fuses alone and see if you have problems first. If so, fit a universal DC/current limiter chip such as the clones of uPC1237 etc. Despite the apparent advantages for audio amplifiers, I think the crowbar is a last resort technique myself and you soon tire of needless replacements.
It seems to be a more reliable protection system in very large amplifiers, though they can suffer occasional disasters too. Try the fuses alone and see if you have problems first. If so, fit a universal DC/current limiter chip such as the clones of uPC1237 etc. Despite the apparent advantages for audio amplifiers, I think the crowbar is a last resort technique myself and you soon tire of needless replacements.
Member
Joined 2009
Paid Member
For peace of mind I designed a dc speaker protection circuit with solid state 'relay' into my advanced version of this amplifier that runs off the same power rails as the amplifier itself and it works well so I would be happy to recommend a similar approach for speaker protection.
Details somewhere here: http://www.diyaudio.com/forums/solid-state/245619-tgm8-amplifier-based-rod-elliot-p3a.html
Details somewhere here: http://www.diyaudio.com/forums/solid-state/245619-tgm8-amplifier-based-rod-elliot-p3a.html
Ok...new thread open... http://www.diyaudio.com/forums/solid-state/279804-p3a-pcb.html#post4451459
Thread is long lived and bits of this and that is getting added once in a while...
As said there is always a P3A amplifier in the shop made as standalone or integrated probably made with previous versions of PCΒ or with /without the latest refinements .
Usually these amplifiers we give away as a replacement amplifier to customers that dont want to run out of music while their amplifier is under repair ...
I will have to compose a list of amplifiers that was outperformed by the P3A stand alone or combo at least according to the customer ..
As said there is always a P3A amplifier in the shop made as standalone or integrated probably made with previous versions of PCΒ or with /without the latest refinements .
Usually these amplifiers we give away as a replacement amplifier to customers that dont want to run out of music while their amplifier is under repair ...
I will have to compose a list of amplifiers that was outperformed by the P3A stand alone or combo at least according to the customer ..
Before using some driver transistors in my LATFET amp projects, I tried to put them in the running P3A. I changed Toshiba metal 2SB/2SD (I think B543 or something) into A1531D/C3951D and even tho there was a reduction in THD I didn't like the sound. But it was a nice surprise (improvement) when today I changed into A1538E/C3953D...
A1358/C3421 is a better transistors spec-wise, but I forgot where I put them after I used them in VSSA projects.
How would you describe improvement in sound with Sanken power transistors compared to Toshibas?
Member
Joined 2009
Paid Member
it would be interesting to look at the hfe curves to see how these parts are different in that regard. My version of this amp (TGM8) is a bit more complex, it uses BJT output like P3a but also a pair of MOSFETs in class C that turn on when the hfe of the BJT falls - the bass performance is simply phenomenal.
Bigun, it is a smart decision conceptually, is there any weaknesses of the V2 compared to V1?
I found trade-off between "drive" and distortion. I want the lowest distortion where minimum "drive" is achieved. Because without this "drive", low distortion is useless (boring and not musical). But unfortunately this depends on the speaker used...
And the output plus the driver should be seen as a "combo". If the output is "high drive" it is usually better to have "low drive" driver for lower distortion. And vise versa...
BD139/140 is poor but "high drive" type. Toshiba is "low drive" type and Sanken is "high drive". And in general CFP is "low drive", better at HF but poor at LF...
So, BD139 should be matched with Toshiba, and better driver (Cob less than 2pF) should be matched with Sanken. And when low Cob driver can be made to work with low Cob output (Toshiba), meaning that the minimum "drive" is achieved, it is usually my preference. (The "drive" brings musicality and low Cob brings naturalness and low distortion sound-wise)