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I have a $180 sub amp that I purchased from Steve at DecWare. It is one of the amps that Parts Express sells. It powers my DIY sub with inputs fed directly from the 8 ohm speaker lugs from my Jolida Tube amp.QUESTION: Is it worth tweaking this amp by adding larger/more filter caps to the power supply and upgrading bridge rectifier to HEXFREDs? I was thinking of spending a conservative amount of money on the mod, but I thought that more filtering and HEXFREDs could really improve the bass response by reducing noise and PS impedance.
Any thoughts/opinions on this matter would be greatly appreciated.
Dan W.
First, does the amp have a power supply regulator? Anyway,Diodes: what is good for tube amp is not good for SS one. Shottkies should be much better than HEXFREDs in this case. You may use significantly underrated ones for lower PSU impedance, just keep in mind their very high reverse current.
Caps: Not a simple question. Increasing the capasitance has some drawbacks, first, higher start-up current and second, higher current peaks in the power transformer and further in the power lines.
Also: I don't think using the output of a tube amp loaded with a speaker is a good idea. Especially if you remove NFB.
Lesha
Lesha, I appreciate the input, but you are talking a bit above my head in some cases. I am not too familiar with shotke diodes. Why is reverse current a problem?Why is loading the amp from the ouputs from the tube amp a problem? The amp is seen as nearly a zero load by the amp, as I understand it. And don't worry, I like my NFB, you should know that :)
Your comments about cap size are also a bit baffling. I guess my tweakings have been entirely in the tube domain until now, so I am fishing in dark waters.
Further input would be greatly appreciated.
Dan W
Diodes: Shottky diodes have very low forward voltage drop and very fast and smooth recovery. However they suffer from two things: low breakdown voltages and high reverse current. I was trying to warn you against using the highest current rated diodes that fit. I don't know the voltage and current of your power supply so I can't say more.Sub connection: the impedance curve of the speaker is not very flat at low frequencies especially if they are placed in a real room and with relatively high output impedance of the tube amp it may give a frequency response that is not very flat as well.
Caps: Of course you may try to calculate the capasitance you need, then simulate the rectifier and calculate if power transformer core would saturate. But I think you'd better double the present capasitance and see if it makes things better.
Lesha
NT
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It is not class 'D', I believe it is said to run in class A-B mode...It does produce good sound, but I am looking for input into how to make it sound even better. Any comments would still be helpful.Dan
I have two parts express 100 watt/8, 150 watt/4 sub amps. I use the low level inputs. There were small square film caps on the link to the low level out. I removed them and cut out the stock rca jack assembly and replaced them with individual gold plated units wired directly to the pc board with silver wire. There is also a large bass boost on the amp circuit that when removed improves the sound and the sensitivity of the controls. The HexFreds sound like a good idea. I have used them in a number of applications with good sonic effect.
That is an excellent idea, but I am running the full range signal from my speaker terminal outputs and am relying on the crossover network in the amp. I have considered simply installing a 24db(?) crossover (actually just a coil) set for my usual listening point of 60db. Outside of using an electronic crossover, I don't see any other way of going about it. I have considered trying to tie the low level inputs into the crossover network and thus not have to use the cheesy binding posts on the amp.I am also still using the cheap hookup wire and clips to connect the amp to the subwoofer cable. I have the amp sitting in a box with binding posts on the outside where I connect my sub cable to. The subwoofer cable is made of three runs of cat five plenum rated cable, braided (3 whole cable braided, not individual twisted pairs) and then I have the cable hard-soldered to my sub. I figure that I could probably get some improvement from replacing stock hookup wire with something beefier and directly soldering it to the posts on the PCB.
Dan W
I hav my amps in seperate boxes as well. I replaced the hookup wire with 12 guage. The built in X-over only filters the woofer from the X-over frequency selected by the pot control. Both high and low level outputs are full frequency.
I don't quite understand what you mean when you say that both high and low ouputs are full frequency. I thought that the low level inputs bypassed the integral amp crossover thus sending a full range signal to the sub. I understood this to be used if you have a receiver, etc. which has already filtered the sub out signal. Could you please explain again, sorry, confused. Thanks in advance,Dan
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