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Lateral Mosfets Double Die TO-3 ESP P101
Lateral Mosfets Double Die TO-3 ESP P101
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Old 14th March 2019, 05:16 PM   #31
a1095us is offline a1095us  United States
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Default P101 Build Relay Contact Issue

So I purchased and installed the pictured Ebay (Chinese) speaker Relay assembly with Omron G2R-2 relays. Dual relay contacts ea. rated at 5A or 10A per channel. The problem did not shown up due to high output failure but low level test tone level tests especially in the 80-100 Hz range. The sound became raspy and distorted like a dirty preamp monitor switch (both channels). If I turned up the volume, the symptoms cleared up. I verified that it was the relay contacts when I bypassed the relays with clip leads. Clean output.
Not sure if this is common issue with relays and low levels or if they are just faulty. Looking into other boards or options. Replace the current Omron relays or go with a different relay board with beefier relays?
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Old 15th March 2019, 01:35 AM   #32
Ian Finch is offline Ian Finch  Australia
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Relay contacts certainly give problems with low level audio but that's after many years, due to contamination from accumulated arcing debris, airborne dust, sulphation from automotive and industrial pollution etc. For new relays to have this problem, it says fake or bad quality control to me. G2R relays have been very popular for decades but they've been assembled in China and elsewhere in SE Asia for many years now and many design details have changed significantly. What you get now isn't the same as the original type used in so many high quality Japanese amplifiers up to 20 or so years ago.

The relays need to have a a high DC contact rating, at least 30V, to reduce the chance of the contacts welding together or suffering arcing damage when they try to open under a fault condition. Many cheap relays I've seen in recent times are obviously not suitable because the clearance and spring force isn't sufficient but we buy on price and low-res pics from Ebay stores which isn't a good way to buy anything that needs to perform reliably for safety, just sayin'.

I don't know if you have experimented with bias but 30mA is way too low for any power mosfet anyway. Early lateral mosfet DIY designs usually suffered from too low a bias current spec. and soon gained a bad rep for harsh sound. They were popular for stage and pro. applications where high power more or less obscured the distortion problem. 100mA bias current per output pair is recommended and typical of most class AB Mosfet audio amplifiers for home use.
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Old 15th March 2019, 03:59 AM   #33
stocktrader200 is offline stocktrader200  Canada
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57v rails seems high for single pair output AND 4 ohm load. I am using single pair of IRFp9140, 9240 at 40v and they seem to be fine. The LatFETS are tougher tho.
if you have a low open loop gain amplifier or a unstable design the bias current matters. If you have a stable, high bandwidth amplifier crossover components become visible under load when the bias is 2 -3 volts low at 20khz. I can't hear an obvious difference with the bias dropped from 7.8v ( 70ma) to 4.5v while playing music ( 1 -5 w) , it does show up on the scope. 0v still sounds good. It is one of the tests my amp must pass.

Last edited by stocktrader200; 15th March 2019 at 04:16 AM.
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Old 15th March 2019, 02:56 PM   #34
a1095us is offline a1095us  United States
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[QUOTE=Ian Finch;
I don't know if you have experimented with bias but 30mA is way too low for any power mosfet anyway. Early lateral mosfet DIY designs usually suffered from too low a bias current spec. and soon gained a bad rep for harsh sound. They were popular for stage and pro. applications where high power more or less obscured the distortion problem. 100mA bias current per output pair is recommended and typical of most class AB Mosfet audio amplifiers for home use.[/QUOTE]

This is the bias (actually 20mA) recommended on the ESP Rod Elliot website. Not sure how double die To3 mosfets would work out in this case but I will try his max. recommended 50mA. Maybe move up gradually if it does not become a thermal issue.
I did the contact cleaning procedure with glossy print paper and Caig Deoxit and has seemed to work. I still plan on ordering some Omron relays from Digikey or Mouser as backups.
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Old 15th March 2019, 02:58 PM   #35
a1095us is offline a1095us  United States
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[QUOTE=stocktrader200;5729914]57v rails seems high for single pair output AND 4 ohm load. I am using single pair of IRFp9140, 9240 at 40v and they seem to be fine. The LatFETS are tougher tho.

I'm using Exicon To3 double die outputs. The heat sink assembly is very robust.
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Old 15th March 2019, 04:28 PM   #36
NMOS is offline NMOS  Germany
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[QUOTE=a1095us;5730363]
Quote:
Originally Posted by stocktrader200 View Post
57v rails seems high for single pair output AND 4 ohm load. I am using single pair of IRFp9140, 9240 at 40v and they seem to be fine. The LatFETS are tougher tho.

I'm using Exicon To3 double die outputs. The heat sink assembly is very robust.

Class AB circuit with additional Class TD circuit Latfets efficiency will increase and heatsink size reduce - 50 %

with 4 pair latfet output devices up to 1500 W is possiile

Last edited by NMOS; 15th March 2019 at 04:30 PM.
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Old 15th March 2019, 06:32 PM   #37
a1095us is offline a1095us  United States
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Default Complex vs Simple Driver Section

Just a curious note about complexity vs simple design. Here is the original drive circuit for the Tandberg 3012A driving a pair of mosfets per ch. (57V Rails, 2sK175 and2sJ55).
The second pic is obviously The P101 schematic.
Iíve resorted to double dies due to high rail V+/- and Tandberg thought 8A 100V devices could be adequate. The Tandberg power amp. section never failed in the 20+ years I used it. Switches and preamp section were its demise.
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File Type: gif p101 Double Die.gif (14.5 KB, 58 views)
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