Being my first post, I though a brief introduction is in order. in the early 1970s while in College, I built a Dynaco ST150-from a kit, partially just to do it, and partially because I needed an amplifier. The only bad part of all of this is that I sold a perfectly function pair of Dynaco 70 monoblocks (grrrrr). Oh well...
Anyway, about 20 years ago, most of my stereo was upgraded to Audio Research SP-8 preamp, ModSquad CD player, and Martin Logan CLS speakers. The CLSs were further upgraded to CLS-IIs revZ in 1996.
Well, after 35 years of nose to the grindstone work regimine, I found myself with some free time, so I decided to look insides the ST-150. This lead to several wires breaking simply from taking that look--(oh well). While attending to the broken wires, I disabled the (never used) dual/mono operation and added a couple more ground wires from the power supply to the audio board. This ended up getting rid of a lot of the hum (which was barely noticible) as a side benefit.
Now that I have been successful in this matter, I though I might try a couple other mods. I would like any feedback anyone cares to throw in my direction.
Mod 1) beefier power path wiring. I was thinking that by using larger wires for the main power supply caps (75,000 µF 75V) to the output transistors and to the outputs themselves. If one goes to :
http://home.insightbb.com/~dunn.greg/ST150/ST150sch1.jpg
a) I am talking about bypassing the 2->3 (24->25) and 11->10 (17->16) wires with larger wire. The current wire is approximately 18 gauge and I am thinking that heavy speaker wire 8-10 gauge wold be more appropriate.
b) I would also like to jump from the common output point (.33 ohm resistors near teh output transistors to the L1 inductor with bigger wire (points 5,22) and get from the L1 inductor to the speaker terminals with the larger wire (points 4,23)
what I do not know is whether leaving the audio board wires with the thin wire and passing big wires directly to the output transistors would enable some strange current loops that could contribute to instability? or whether this is not necessary because "these wires (resistance) are inside the feedback loop"?
MOD 2) I am thining about reducing the global feedback by placing two small emitter resistors (approx 30 ohm) in the common path of the differential amplifier, linearizing this section decreasing the global feedback. I found this trick several places--mainly in reference to transient intermodulational distortion and amelioration thereof.
BUT the places that mention this typically use a darlington on the Voltage Gain Stage. Can I get by with the emitter resistors and skip the darlington. Or is the darlington the more valuable of the two?
MOD 3) changing out all the 35 year old electrolytic caps. Does anyone have a suggestion as to the most audio appropriate brands to use as replacements?
MOD 4) In mono mode, the power supply delivers +/-65V instead of the more normal +/-55V. Thus it seems clear the outputs (and audio board) can handle the voltage, but probably not maintain the safe operating area when used thusly over any condition. I understand that maximum power disipation in the outputs occurs around 30% max unclipped voltage swings.
I don't listen to this amp "all that loud" (due to other people in this house with auditory voting rights). So it is seldom that the heat sinks are noticibly above room temp (no fan).
So my question is: can I buy a little more headroom "safely" by switching the transformer leads at the power supply if I promise not to use too much continuous power from the amp? Or am I just looking for troble with little payback, here?
Thanks for any help
Mitch
Anyway, about 20 years ago, most of my stereo was upgraded to Audio Research SP-8 preamp, ModSquad CD player, and Martin Logan CLS speakers. The CLSs were further upgraded to CLS-IIs revZ in 1996.
Well, after 35 years of nose to the grindstone work regimine, I found myself with some free time, so I decided to look insides the ST-150. This lead to several wires breaking simply from taking that look--(oh well). While attending to the broken wires, I disabled the (never used) dual/mono operation and added a couple more ground wires from the power supply to the audio board. This ended up getting rid of a lot of the hum (which was barely noticible) as a side benefit.
Now that I have been successful in this matter, I though I might try a couple other mods. I would like any feedback anyone cares to throw in my direction.
Mod 1) beefier power path wiring. I was thinking that by using larger wires for the main power supply caps (75,000 µF 75V) to the output transistors and to the outputs themselves. If one goes to :
http://home.insightbb.com/~dunn.greg/ST150/ST150sch1.jpg
a) I am talking about bypassing the 2->3 (24->25) and 11->10 (17->16) wires with larger wire. The current wire is approximately 18 gauge and I am thinking that heavy speaker wire 8-10 gauge wold be more appropriate.
b) I would also like to jump from the common output point (.33 ohm resistors near teh output transistors to the L1 inductor with bigger wire (points 5,22) and get from the L1 inductor to the speaker terminals with the larger wire (points 4,23)
what I do not know is whether leaving the audio board wires with the thin wire and passing big wires directly to the output transistors would enable some strange current loops that could contribute to instability? or whether this is not necessary because "these wires (resistance) are inside the feedback loop"?
MOD 2) I am thining about reducing the global feedback by placing two small emitter resistors (approx 30 ohm) in the common path of the differential amplifier, linearizing this section decreasing the global feedback. I found this trick several places--mainly in reference to transient intermodulational distortion and amelioration thereof.
BUT the places that mention this typically use a darlington on the Voltage Gain Stage. Can I get by with the emitter resistors and skip the darlington. Or is the darlington the more valuable of the two?
MOD 3) changing out all the 35 year old electrolytic caps. Does anyone have a suggestion as to the most audio appropriate brands to use as replacements?
MOD 4) In mono mode, the power supply delivers +/-65V instead of the more normal +/-55V. Thus it seems clear the outputs (and audio board) can handle the voltage, but probably not maintain the safe operating area when used thusly over any condition. I understand that maximum power disipation in the outputs occurs around 30% max unclipped voltage swings.
I don't listen to this amp "all that loud" (due to other people in this house with auditory voting rights). So it is seldom that the heat sinks are noticibly above room temp (no fan).
So my question is: can I buy a little more headroom "safely" by switching the transformer leads at the power supply if I promise not to use too much continuous power from the amp? Or am I just looking for troble with little payback, here?
Thanks for any help
Mitch
Audio Amateur had some extensive mods including adding the Boak Regulators....I think it may have been part of the Pooge series although I am not certain. I have two of these things and someday I want to get back to them. Can't remember the dates when the articles appeared.
rt
rt
Dynaco ST 150
Hi
Can you tell me if there is possible to connect this amp for 230 volt.
I am going to buy one here in Sweden.
But i is set up for 110 volt.
Hi
Can you tell me if there is possible to connect this amp for 230 volt.
I am going to buy one here in Sweden.
But i is set up for 110 volt.
There are two windings of 120V on the primary side of transformer. Serie conected for 240V.
Power supply
But there can be some different models?
Dynaco 150
Power supply
But there can be some different models?
Dynaco 150
some long time ago
there was a greek made amp used to sell a lot of pcs mostly used for 100v amplifiers and thousands of modules were installed in hotels banks and hospitals ....
this amplifier prooved to be a monster of durability and reliability ....for yeras i was wondering who stolen it and from where ...
thanks to the above thread now i know ....he he he
there was a greek made amp used to sell a lot of pcs mostly used for 100v amplifiers and thousands of modules were installed in hotels banks and hospitals ....
this amplifier prooved to be a monster of durability and reliability ....for yeras i was wondering who stolen it and from where ...
thanks to the above thread now i know ....he he he
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